Find answers to Frequently Asked Questions for First Generation Firebirds that have been asked and answered on FGF. Special thanks needs to be given to all the FGF members who took the time to respond to other member's questions.
Wheels, Brakes, and Axle - Axle
Q: Traction Bars for 1967 and 1968
I was recently browsing the archives and seen information about what firebirds came with traction bars. I am confused to what models got what type of traction bar.
I have a 1967 Firebird convertible with a 326 two barrel but I have two traction bars. This car is not a high output model. And to my knowledge this car is original.
A: 68s didnt have traction bars.
1967s breakdown:
-
OHC-6 1bbl auto. none (exception is rear end ratio 323 or higher) OHC-6 1bbl man. RH side
-
OHC-6 4bbl. auto. RH side
-
OHC-6 4bbl. man. both sides
-
V-8 2&4bbl. auto. RH side
-
V-8 2&4bbl. man. both
I also found that the rear end ratio or type in this case determined the option of one or two bars or radius rods. i.e. if a car has a 4 pinion rear end it will have both bars. this is for posi and open 4 pinion rears.
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Content last modified: January 22, 2014 at 10:17 am
Q: Axle Codes for 1967 and 1968
How do I identify the Sales Code for the axle ratio that is shown on the Billing History cards.
A: In 1967, the ratio will be shown in the box marked 74 and in 1968, it will be shown in box 37. In both instances, the codes used to identify the axle ratio will be the same and they are as follows:
C = 2.56:1
D = 2.78:1
E = 2.93:1
F = 3.08:1
G = 3.23:1
H = 3.36:1
K = 3:55:1
P = 3.90:1
S = 4.33:1
Note: Do not confuse these Sales Codes with the two-digit code that is stamped on the axle tube.
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Content last modified: January 24, 2014 at 9:50 pm
Q: Rear End Code Facts
I am confused by the codes found on the rear end.
A: After reading all the comments, I thought I’d better give some facts. The 1967 Firebird axle housings have the loops (where control arm bushings would mount) on top of the center chunk as if they were getting A-body control arms, but they also have the spring perches for leaf springs, and the brackets for the factory style “traction bars”. There should also be a date code cast into the center section somewhere. In 1968 they left off the control arm bushing loops and the traction bar mounts, but seemed to use the same codes as 1967. In 1969 the date code position moved from one side of the center section to the other, but I can’t get to my rearend housings to see which are which. Another change from 1968 to 1969 was the addition of flattened spots on top of the axle tubes where the snubbers meet the housing, 1967 and 1968 did NOT have the flat spots. Again, check your cast date codes if at all readable.
Also, all 3 years had the 2-letter stamped code in roughly the same position, about 3-5 inches to the LEFT of the center section, on the rear of the left axle tube (left being the driver’s side of the car). Many times it is obscured by the steel brake line – you’ll need to loosen the clip welded to the axle tube and raise the brake line a bit to see it.
The 1969 codes were different. Here’s the list (first the open ratio, then the posi):
1967, 1968, and 1969 Axle Identification Codes |
|||||||
---|---|---|---|---|---|---|---|
Ratio |
1967 |
1968 |
1969 |
||||
Std. Diff. Code |
Lock Diff. Code |
Std. Diff. Code |
Lock Diff. Code |
Std. Diff. Code |
Lock Diff. Code |
||
2.56 |
XB |
UN |
XB |
UN |
YB |
ZB |
|
2.78 |
XC |
UP |
XC |
UP |
YC |
ZC |
|
2.93 |
XD |
UR |
XD |
UR |
YD |
ZD |
|
3.08 |
XE |
US |
XE |
US |
YE |
ZE |
|
3.23 |
XF |
UT |
XF |
UT |
YF |
ZF |
|
3.36 |
XG |
UV |
XG |
UV |
YG |
ZG |
|
3.55 |
XH |
UW |
XH |
UW |
YH |
ZH |
|
3.90 |
– |
UX |
– |
ZP |
– |
ZK |
|
4.33 |
– |
UY |
– |
ZR |
– |
ZM |
I hope this clears up some confusion and misinformation. Whenever possible, ask about date codes (same style of codes as engine parts), axle codes (rear of left tube), spring perch depth (67 Monoplates are shallow), whether it has the extra brackets for traction bars (67 only), or if there are flattened spots on top (69 only).
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Content last modified: December 8, 2017 at 4:11 pm
Q: Rear Axle Code Location
On a safe t track rear axle where is the two letter code stamped?
A: Axle code should be on the left (drivers) side of the axle housing about 6 inches give or take from diff. cover.
A: The code is stamped on the drivers side axle tube facing the rear. This code took me forever to find it is to the left of the brake clip. You must do a lot of sanding to find it.
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Content last modified: January 21, 2014 at 9:26 pm
Q: Axle Codes 1967-1968
I received a note concerning axles and how to identify the Sales Code for the axle ratio that is shown on the Billing History cards.
A: In 1967, the ratio will be shown in the box marked 74 and in 1968, it will be shown in box 37. In both instances, the codes used to identify the axle ratio will be the same and they are as follows:
C = 2.56:1
D = 2.78:1
E = 2.93:1
F = 3.08:1
G = 3.23:1
H = 3.36:1
K = 3:55:1
P = 3.90:1
S = 4.33:1
Note: Do not confuse these Sales Codes with the two-digit code that is stamped on the axle tube.
I hope that this information helps answer most axle ratio related questions.
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Content last modified: January 21, 2014 at 9:27 pm
Q: Rearend Decode 1967
I would like to know how to tell if the rearend of my 1967 car is original to this particular model year, what can i look for on the housing that will help me identify the original numbers’s matching rear.
A: From the 1967 Firebird Supplement to the 1967 Pontiac service manual:
“Eight different axle ratios are available from the Firebird models. They can be identified by the two-letter code stamped on the rear of the L.H. axle tube”.
Here are the codes:
XB – 2.56 open
XC – 2.78 open
XD – 2.93 open
XE – 3.08 open
XF – 3.23 open
XG – 3.36 open
XH – 3.55 open
UN – 2.56 limited slip
UP – 2.78 limited slip
UR – 2.93 limited slip
US – 3.08 limited slip
UT – 3.23 limited slip
UV – 3.36 limited slip
UW – 3.55 limited slip
UX – 3.90 limited slip
If the rear end is original, the two letter code will tell you what axel ratio you have and whether it is an open or limited slip rear end.
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Content last modified: January 21, 2014 at 9:36 pm
Q: Find the Rearend Gear Ratio
Does anyone know how to find the rearend gear ratio on a 1967 firebird. (Besides pulling the cover off and counting teeth.) Any help is appreciated.
A: Take a piece of chalk and mark a line from the driveshaft yoke up to and on the differential housing. without moving the tire pick a reference spot on the car body near the rear tire (a screw or bolt, etc.) and mark the tire at this reference spot. Now, slowly rotate the tire while counting the number of times the drive shaft rotates past its’ reference mark. The rear gear ratio is the number of times the drive shaft rotates divided by the number of rotations the wheel rotates. example: drive shaft: 17, tire: 5… 17/5=3.4 so the rear gear ratio is 3.4:1. Good luck.
A: Look on the rear facing side of the left hand (driver’s side) half of the rear axle, about half way between the drum and the pumpkin. There should be a two letter code there. You may need a wire brush to clean it off to see it. Here is how you decode:
POSI CODES OPEN CODES
UN 2.56 XB
UP 2.78 XC
UR 2.93 XD
US 3.08 XE
UT 3.23 XF
UV 3.36 XG
UW 3.55 XH
UX 3.90
UY 4.33
Also, Here are the gear ratios for TH400 and Powerglide:
Power Glide 1st = 1.76 2nd = 1.00 Rev = 1.76
TH400 1st = 2.48 2nd = 1.48 3rd = 1.00 Rev = 2.00
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Content last modified: January 21, 2014 at 10:00 pm
Q: Gear Ratio Calculations
I was trying to figure out my differential gear ratio. So I did as suggested and marked the axle and the tire and counted revolutions. I came up with two sets of numbers where the marks both came back to the starting point at the same time.
Axle revolutions = 26
Tire revolutions = 19
Axle revolutions = 41
Tire revolutions = 30
If I did the math right the ratio is 1.37.?
What is this? How can it be so low(numerically). No wonder the car seems to be a bit of a dog out of the hole. Did I do this right? Can anyone explain why someone would knowingly do this to a 400?
Note: 1968 Firebird, 400, auto. Not the original rear-end (from external observations, specifically no code where everyone says there should be a two letter code)
A: If this is a non-posi rear (must be) then you should have seen the other tire turning the opposite direction to the one you were turning. In this case, the number you got is 1/2 of the numeric gear ratio, making yours not 1.37 but 2.74 which means it is probably 2.78 which is a standard Pontiac Ratio.
Why would someone do this? High top Speed? Good Mileage? Who knows?
A: First you need to 1 (spin the axel and count the yoke revolutions) and not 2 (axel and tire) if you ment the first sorry. But sounds like you looked at the second and that is why you got the reading you did….
A: Are you sure that the yoke and wheels came back to the “exact” mark? In this case, close doesn’t count. If it is a non-posi unit, did you block one side so it would not spin? Take another look.
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Content last modified: January 22, 2014 at 9:23 am
Q: Choosing the Right Gear Ratio – Revisited
I’m looking for recommendations for the optimum gearing on my differential. I have a 1968 firebird convertible with a 350. Non-stock changes are – TH400, transmission, Rochester Q-jet, headers, P22560 tires and cast iron Pontiac intake. I presently have 2.78 gears and the car is pretty doggy.
I don’t really want to modify the engine or put in a higher stall converter. I am thinking of putting in either 3.23 or 3.55 gears. I do mostly around town driving but occasionally go out on the highway at 60-70 MPH. Does anyone have any suggestions on what is a good ratio?
A: I just went through the same thing with a 2.56 rear and picked 3.23 as a good all around ratio. Should run around 2600-2700 RPM at 60 MPH where a 3.55 would run 2900-3000 or so (ballpark numbers).
Also, keep in mind that if you are simply planning on changing gears that you can’t go any higher than 3.23 without changing the housing, or so I’ve read.
If you are planning a whole rear end swap, you might want to consider using a rear out of a 2nd gen car. The overall width is about 1″ wider, and you will have to have the spring perches cut and re-welded but the 8.5 inch rear and the posi unit are much stronger. Also, these rears are more common and Cheaper than 1st gen rear ends.
FYI…the code PX was used from 1976 to 1981 (or something like that) for a 3.23 Posi.
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Content last modified: January 22, 2014 at 9:27 am
Q: Rear Axle Gear Swaps 1968
Now for a question. I have 2:56 gears in my 1968 does anyone know what ratios I can go to without changing the differential? Is 3:23 or 3:73 a possibility?
A: Not with your differential case! Break out your trusty 1968 Factory Service Manual, and turn to the pages on rear axles. They have descriptions of the available axles, and a chart for how the cars were equipped with each ratio with the 2-letter codes stamped on the axle tubes. Mine (for 1969, same parts, different 2-letter codes) states that there were 3 differential cases (by ring gear mounting dimension, plus others for posi/non-posi), the first is for 2.56 and 2.78, the second is for 2.93, 3.08, and 3.23, then the third is for 3.36, 3.55, 3.90 and 4.33 ratios. This is for using original gears. The 3.90 and 4.33 used ONLY the 4-pinion locking diff case, the 3.36 and 3.55 posi used a 2-pinion case, or could be had in a non-posi type also. The 3.08 and 3.23 axles are not too uncommon, so you may want to look for one of those. I probably have a couple non-posi units kicking around here. Another choice is to see what the aftermarket offers, maybe Richmond Gear has something that would work with your differential case, although it might not go higher than 3.23.
Here I go again suggesting everybody get as much factory information as you can get your hands on! The factory service manuals are available in reprint, you can’t tell it from an original. Get it while you can!
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Content last modified: January 22, 2014 at 9:28 am
Q: Rear End Gears Swap
1) I want to be able to change to “highway” gears when I plan a long road trip, and then put the others back in when we get home. Is this possable?
2) If the rear ends from those other Pontiac models are a direct bolt-in, will the gears out of them swap into my rear as well?
A: Have you done this before? Gear swaps require some considerable skill to perform. Getting the lash and tooth engagement correct are probably the toughest part. A dial indicator would be among some of the specialized tools you would need. So, figure on $250 for gears, another $100 for tools, or $250 to get a shop to do the install. Going from 3:23 to 3:08 or even 2:73 shouldn’t require a different carrier. Figure a weekend to do it yourself, for the 1st time, and then half a day once you get the process down.
Excessive gear noise, and overheated fluid are common signs that a mistake was made.
As you want to hang onto you lower gearset, my suggestion would be to either get a second rear end (replacing the rear ends would probably consume less time than changing gears), or consider some type of overdrive. You didn’t mention whether you had a stick shift or an automatic. You could replace the automatic with a 200R, or the stick trans with a T5 or Tremec. Either will get you an overdrive, reducing your highway RPMs. Of course, this would be more costly at first, but consider the cost of 3 or 4 gear changes.
My buddy, who has 3:73 gears in his 65 El Camino, uses a taller tire (235/70s) mounted on a spare set of wheels for the roadtrips. He carries his cruising wheels and tires (225/55) in the bed, and we swap them when we get to our destination. This gets him what amounts to a taller gear that makes the RPMs at highway speed (2700-3000) a bit more liveable.
2)The 1st generation Firebirds use an 8.20″ 10 bolt unit that was unique to the Pontiac and Buick cars. There is a corporate 8.20 whose gears will not interchange, used in Chevys. In 1970, GM went to one 8.50 10 bolt carrier across the board. This unit can be found in Novas, Apolos, Omegas, and Venturas, 1970 thru 74, and 2nd generation Firebirds and Camaros. The second generation F body rears will fit under your car, but you will need to relocate and replace the spring perches, and use a unique rear u-joint.
Luckily, tall gears are plentiful in these cars.
There are 2 other 10 bolts, a 7.50″ used in late 70s and 80s cars, and a 8.875″ unit used in trucks. So when presented by someone selling you a 10 bolt gearset, be very careful about what you’re buying.
Don’t forget to correct your speedo gear, whatever choice you make.
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Content last modified: January 22, 2014 at 9:33 am
Q: Limited slip vs. Positraction vs. Safe-T-Track
What is the difference berween a limited slip rear end and a posi? Or are they one and the same? If they are different, were they both available in 1st gen birds? How do you tell the difference.
A: It’s my understanding (someone please correct me if I’m wrong) that they are one and the same. Dealer literature called them “limited slip” while the users called them “posi”. If could also have been the used by two different car builders (i.e., Pontiac/GM called them limited slip while Chrysler called them posi-traction). That’s my guess.
A: There isn’t any difference. Each GM division had its own name for it, and probably a slight variation on the design too. Pontiac’s was actually called Safe-T-Track, Chevy was Positraction, they are both “limited slip” type rear ends.
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Content last modified: January 22, 2014 at 9:34 am
Q: Safe-T-Track Clicking
I just installed a 3.23:1 safe-t-track (2-pinion) carrier into my firebird. The backlash is about .008″ and the pattern looks good. No howling at any speed. The problem is when I was pulling into my garage (tight right turn) that I noticed this “clicking” sound coming from my drivers side rear tire/axle.
Is this normal? Are the spider gears/cones disengaging as I make a slow turn? At higher speed turns (+15-20) I do not notice it. The center section was rebuilt with new machined and shimmed cone seats. It is very tight. Any old school mechanics out there? Thanks in advance.
A: Mine does it. The posi unit might be worn. I think the nosie comes from when one of the cone slips and then this sudden slip is translates to you drive shaft making a tinging noise. My friend 78 Z28 did the same thing. Check your transmission output shaft bushing too. If its a 4 speed car the bushing only last about 40,000 miles under hard use.
A: This is pretty common on GM posi units. If you add 2 bottles of GM posi additive( use GM not brand X) and it still does it , try changing the gear oil and add 2 more. You must do some sharp right and left turns, back up etc to get the additive circulated real good before giving up and changing lube again.
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Content last modified: January 22, 2014 at 9:36 am
Q: Possi. Traction Rear End 1967
I have a question that no one out here seems to be able to answer! Did the 1967 Firebird come stock with a 323 possi. traction rear end with traction bar brackets and tortion bar eyes on the top of the punkin? If so were these able to fit a 68? The reason is from backing plate to backing plate is the same length as on my 68? Why are there eyes on the punkin? Thanks for any information you can give me?
A: I think I can answer questions on rear ends. All 67s had the eyelets on top of pumpkin because they used the A body rear (Tempest,GTO) 1967. Cars that had traction bars were any that had a Heavy duty rear end whether it was 326 HO or 400. I have had several 1967 Sprints with traction bar rears. As a matter of fact ALL Sprint Firebirds for 1967 came with factory traction bars. These could be adapted to the 1968 but then I pose the question WHY… with staggered shocks and multileaf springs the 1968 was a better setup. just try going over a washboard road and youll experience this. All posis were an extra cost item, until the Trans AM. Some models it was required tho. On the trim #s I think John boo booed and that was 250 and 270 dk. blue standard buckets and dk.blue bench.
A: There has been a ton of speculation on this issue, but no one has ever come down with an authoriatative answer. However, it has been my experience that as a rule, Firebirds with open rear-ends got one traction bar on the right, while cars with limited-slip rear ends got traction bars on both the right and left.
IF there were, (and that is a big IF), cars which had none, I’d bet it had to do with the ring and pinion ratio. The rear end codes on the third members were independent of the engine/trans installed in the car.It is my guess the traction bars were an after thought to make up for excessive wheel hop due to the mono-leaf springs.
A: I have a 1967 that came with sprint 6 and it has both traction bars…hope this helps …
A: In the past, there have been a couple of threads concerning the factory traction bars on 1967 Firebirds, in particuliar, the rules governing the hows & whys of whether you got none, one or two of them.
While researching differentials and available axle ratios, I came across what I believe is the definitive answer to those discussions. In the Firebird supplement to the 1967 Pontiac Service Manual, it has a section on the rear suspension, propeler shaft and differential. (Section 4 for those who have a copy of this supplement). First, these tranction bars are refered to as Radius Rods in the supplement. Here is the chart, (reproduced here in ascii text), which shows how many radius rods were on the car, based on engine size, transmission type, and in one case, axle ratio:
RADIUS RODS USED | 6-cyl. 1-Bbl. | 6-cyl. 4-Bbl. | V-8 2 / 4 Bbl. |
---|---|---|---|
None | *Auto Trans. | ||
One on R.H. Side | Man. Trans. | Auto Trans. | Auto Trans. |
Two | Man. Trans. | Man. Trans. |
*One rod is used if ratio is 3.23:1
I hope this information sheds some informative light on the subject.
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Content last modified: January 26, 2014 at 4:30 pm
Q: Saf-T-Track Axle on Ram Air
Was the Saf-T-Track Axle part of the Ram Air package?
A: …According to 1967-1968 Firebird Sales Literature, when you ordered the Ram Air engine, it was mandatory to get code 361 (Saf-T-Track Axle). However, I don’t see this prerequisite for 1969 on either the Trans Am or 400 H.O. option (with or w/o the Ram Air Hood Option). So, if your documentation does not show code 361 Saf-T-Track then that’s how it is in 1969. 🙂 Anyone have something that says otherwise ?
A: T/As came standard with posi rears ,all 1969 T/As had R/A engines . other items were of course… variable ratio p/s,power discs,1″sway bar etc.
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Content last modified: January 22, 2014 at 10:01 am
Q: Rearend Swap 1967
Does anybody know if a 1969 Lemans rearend will fit in a 1967 Firebird?? Any modifications needed?
A: A body cars use _coil_ springs in the rear, whereas F bodies use leaf springs.
The A body housing will be wider than the stock Firebird piece, and will require narrowing, or special offset wheels. You can cut off the perches and mounts from the Lemans rear, and weld on perches for the leaf springs. But this is a lot of bother for a 10 bolt.
I’ve read that some 1st gen owners use the 2nd gen rear, which is a bit stronger. But this rear is still wider than your 1967 rear. I don’t know how much wider, or if the spring perches have the correct spacing.
A: I just bought a 1977 Firebird 3.23 Posi (Code PX) Rear for a 1969 Firebird. I too was told that these are wider than the 1st gen rears. However, I have measured both rears, more than once, and in more than one way, and could not find any difference in the OVERALL width.
Since I had heard so much of this “the 2nd gen rears are wider” stuff I still couldn’t believe my measurements so I checked my AMA spec for Track Width Rear and the number is 60 inches, same goes for 1968’s. I didn’t have a 2nd gen spec but thankfully one of you on this list did and guess what? The number is 60 inches for 6″ rims and 60.3 for 7 inch rims. I’m now convinced that the 2nd gen rears are NOT wider. I’d be glad to hear anyone else’s 1st hand experience.
As far as the Spring “perch” or mount that is welded onto the axle tube, they ARE indeed wider on the 2nd Gen by about 2 3/4 inches. I will have to have these cut and re-welded.
Last thing, 1968-1969’s and 2nd Gen’s all used multi-leaf springs so if you get a 2nd gen rear for a 1967 you’ll either have to convert to multi-leaf of use “perches” from your old rear because the depth is different.
A: I have used a 2nd generation rearend in a 1968. It’s only about 1/2 wider on each side. The existing spring perches must be removed and new one welded closer to the differential. Care should be taken to properly align the pinion angle. The drive shaft will have to be shortened. If you use a rearend from a 400 transmission car you’ll need a big-and-little U-joint as well. Aside from the cost of the rearend itself, The costs were as follows: new perches $25; drive shaft work $35; U-joint $18. Good luck.
A: I’ve got a gto rear in my 1967. had to add spring perches, and clean up the coil spring stuff. not many 12 bolt rears around, so its worth the work for a 12 bolt.
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Content last modified: January 22, 2014 at 10:02 am
Q: Rearend Swap 1968
Does anybody know the particulars on swapping a second gen. rear end in to a first gen firebird? I have heard that the second gen. is wider but not by much and that you have to cut off the spring mounts and weld on new spring mounts. Any first hand knowledge out there?
A: The swap you are researching is rather straight forward. I completed a successful swap of this type on a 1968 Camaro. The posi was a lot cheaper and the breaks are the same. Some things you’ll have to do or look out for:
-You will have to relocate the spring perches. either cut these off of the old rear end or by some weld in units from your local speed shop. – When choosing a rear end, look for a transmission match (i.e., if you have a power glide or 350 turbo, get rear from a 350 turbo car or 400 turbo from a 400 turbo car. 350 and 400 turbo use a different size U-joint. -Be sure to match the pinion angle of the old rear end with the new (i.e., the relation of the pinion angle to the pads is critical fro long life. – You’ll may also have to shorten your drive shaft.
A: First, why would you want to put a 2nd Gen Rear in a 1st Gen Car? Well, they’re more readily available, which also means cheaper.On top of that, the 8.5 inch rear is much stronger than 8.2 inch. Of course, there are some mods you’ll have to do so that’s something you have to weigh out to see whether it’s worth it to you.
Now for some short disclaimers. The car I was putting the Rear into was a 1969 Firebird which originally had a 2.56 open Rear and multi-leaf springs. The new Rear was a PX code 3.23 Posi with a casting date of C187, from a 1977 car. I know there are some minor difference between the early 2nd Gen cars (1970-1975 or 76) and the later ones (1976 or 77-1981) with respect to U-Joints and Brake parts so I can’t be sure that everything that worked on mine will work on yours.
Here we go…..
OVERALL WIDTH – I had read many times that the 2nd Gen Rears were anywhere from 1-2 inches wider overall than the 1st Gen Rears. Well, I took many, many measurements to be sure I wasn’t fooling myself and found that the 2nd Gen Rear is only 1/4 inch wider overall (1/8 per side) than the 1st Gen. This measurement was taken on the outside of the ends of the axles where the lugs are pressed in.
MULTI VS MONO LEAF – As I understand it 1967 models will have mono-leaf springs. 1968-1981 are all multi-leaf. I don’t know too much about mono to multi leaf conversion, I’m going to assume that you are swapping into a 68-69 car. If you want to put one in a 1967 car, I would guess you’ll either have to use your original mono-leaf mounts/perches or convert to multi-leaf. Let’s just say that you will have to work out all those further complications.
SPRING MOUNTS (OR PERCHES) – There are some very important things to remember here. First, if you haven’t figured it out yet, the 2nd Gen mounts are much further out (about 2 3/4 inches) from the center than the 1st Gen mounts, you will have to cut them off and weld different ones on. Why not just re-weld the ones you cut off, but in the new location? Well, the first gen mounts have a built in angle such that the springs are further apart at the rear of the car (by the shackles) than at the front. The 2nd Gen does NOT have this angle. I didn’t know this and simply cut and moved the mounts on the 2nd Gen Rear. It turned out there was enough play between the spring and the mount that I could still cock them a little and they would fit but I would recommend to anyone doing this to either cut and use your old 1st Gen mounts or get a set from another 1st Gen Rear end. Another good reason to do this is that the 2nd Gen mount is about 1/2 inch “taller” than the 1st gen which lowers the spring (and the car) off the axle by that extra 1/2 inch. The last thing you should take care about is the pinion angle. This is the angle between the Rear End pinion and the drive shaft. If you screw up the mounting of the perches you will mess this up. I took measurements of the angle between the pinion and the spring mounts on both Rears and found them to be the same, so I just cut off one perch and moved it to it’s new location (you should be using a new perch here), made sure it was level with the other one, and re-welded it. A different (or better) way would be to place the Rear under the car and put the car’s weight on the springs. Then set the angle to what you want it and tack weld the spring mount. Remove the rear and finish the welding. I couldn’t do it this way because I didn’t have any welding tools and the car was in my garage. By the way, this didn’t cost me anything because I did the cutting and welding at a friends house, but it did take a few hours. MAKE SURE you have your measurements correct, you don’t want to have to do this twice!
AXLE REMOVAL – You will have to remove the axles and break backing plates to be able to cut the mounts very well. Be sure to understand how to do this before you start, it’s pretty easy.
BRAKES – The brakes parts are pretty much the same for both. I bought all the new brakes parts by asking for the 1977 parts, used the 1977 backing plates and drums. As far as brake lines, if you are getting new ones, buy the ones for the original 1st gen year. This way you don’t have to re-route the line coming back from the front of the car. On mine there was a bracket that mounts to the top rear end cover bolt. This holds the fitting at the end of the flexible hose that the two brake lines thread into. Make sure you get this off the old rear and put it on the new one BEFORE you get the rear up under the car or it might be hard to put on. Plus you’d hate to have to remove a cover bolt after you have your gasket sealed well.
SEALS and BEARINGS – Seals are cheap, so replace them. Don’t buy them from the repro companies, they charge a lot. Get a decent brand from a local parts store, they should only be about $1-$2 a piece. As far as bearing, they are more difficult to replace and more expensive but you should at least check the old ones for wear and replace if necessary.
AXLE to U-JOINT DISTANCE – By my measurements the 2nd gen rear is longer from the axle to the u-joint mount by 1 inch. Unless you have a lot of play up at the transmission end, you will need to have your drive shaft shortened or fabricate a new one. While you’re at it, replace the u-joints if they’re still the original 30 year old ones. My cost $65 for cut, balance, and install 2 u-joints. They wanted about $125-$150 to fabricate a new shaft from scratch. While you have the drive shaft out, why not replace the output shaft seal on the trans too, again very cheap. Oh, and I was able to get my driveshaft out without removing either exhaust pipe but you might not be so lucky, be prepared to have to unbolt one at the manifold or header in order to get the drive shaft out.
U-JOINTS – Make sure when you get the Rear, you get the hardware to strap the U-Joint to the Rear End. The hardware was different on the two Rears for my swap. It may be the same for you but it’s better to have it to be sure. Also, depending on the donor car you may need to get a “Big/Little” U-Joint to adapt pontiac type to Chevy type.
SPEEDO – If you changed ratios you’ll need to recalibrate you’re speedo, I know you already know this but for some good info about doing this with Auto Trans try http://www.classicalpontiac.com, go to the Q and A, go to Archive #5, and look at Topic #1162. By the way, I haven’t done this yet. It’s weird to cruise to work at 90 MPH…
GAS TANK – Probably a good idea to remove the gas tank as a precaution. Definitely do this if you are also replacing the springs as you will probably need to use a torch or grinder to remove some bolts! While you have it out, why not clean it out and get it painted nice. I found all sorts of junk in mine…yuk!
SPRINGS – As far as leaf spring replacement goes, just a few comments. If they’ve been on for 30 years you WILL need to cut or torch the bolts off. (Again, remove the gas tank!) Even then the rubber bushing are a pain to get out, be patient. You will probably also have to scrape the rust out of the body slot before you will fit the new bushings in. Also see “Parts To Buy” below.
PARTS TO BUY – I’d recommend having the following new parts ready when you start:
- FOR THE REAR END
-
—————
-
Seals
-
Bearings (If You Choose)
-
Brake Lines
-
Brake Parts
-
New Posi Tag
-
Gear Oil and Limited Slip Additive
-
Cover Gasket
-
Housing to Break Backing Plate Bolts/Nuts (if you break ’em)
- FOR THE SWAP
-
—————
-
U-Bolts and Nuts (May Break ’em)
-
T-Bolts and Nuts (May Break ’em)
-
Upper and Lower Pads
-
Trans Output Shaft Seal
- FOR NEW SPRINGS
-
—————
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Front Eye Bushings (If they don’t come with the springs)
-
Front Bracket Bolts and Clip Nuts
-
AMES carries these, others only have the clip nuts
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If these haven’t been replaced very recently,
-
you will probably break the clip nuts
-
Front Eye Bushing Bolt/Nut
-
Shackles/Bolts/Nuts
-
Rear Shackle Bushings
- GAS TANK
-
—————
-
Tank Straps
-
Attaching Bolt Kit
-
Tank to Body “Anti-Squeak” Kit
Hope this turns out to be helpful to someone. Good Luck. And if anyone else does this swap and has some feedback, let me know.
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Content last modified: January 22, 2014 at 10:04 am
Q: Rear End Swap
A: Classical Pontiac a good reference sheet in their restoration section on putting a second generation diff into a first generation. There are some mods to be made, but it is possible, and I think worthwhile. I am planning on replacing my 256 open diff with a 373 posi unit from a 74 f body. I am counting on the info from that site to be accurate, and the change to be not too difficult
A: I did this swap this last summer, and in reading Geebgens report, posted both on his own website:
http://www.angelfire.com/on/geebjen/rearswap.html
(geebjen is a member of this list and has an excellent site with tons of useful info)
…and on the Classical Pontiac site:
http://www.classicalpontiac.com/
(click the restoration link)
…I found that it is pretty much spot on with the description of the rear swap. The only thing I could add to this would be that I found that I needed to keep the parking brake cables and the approriate bracket from the 1st gen. rear end. The 2nd gen cables wouldn’t work.
Pricing varies from area to area. I paid $75.00 to get the spring perches done. I didn’t realize until too late that they had used a generic perch that required 2 ubolts per axle, compared to the single ubolt that is stock. The original perch has a pocket or recessed area for the spring to seat, while the replacement perch is flat.
Another gotchya was that they welded the perches about 1/2 to 1″ too far apart. I had to muscle the springs into place, and this placed the shock mount in contact with my passenger side wheel rim.
My rear wheels are 8″ wide, w/ 4.74″ back spacing.
I also paid $110 to have my drive shaft shortened and balanced.
Check the ratio on any second gen. rear you think about buying. While 3.23 and 3.42 ratios are fairly common, you can still run into Posi rears with 2.73 and taller gears. Not optimal ratios.
A: I made this swap last winter and found out that replacing the perches was not necessary. The first gen. perches are slightly angled versus the second gen. which is straight. The leaf springs are further apart in one end than the other on our cars. Still the sec gen. perch is wide enough to accommodate the angled springs. Therefore I just grind the perches off the sec gen. rear end and moved them closer together. I did not buy any new perches and I did not remove the old perches from the original rear end. Only thing to remember is the sec gen. perches are about 10 mm higher which LOWERS your car by the same amount. ( oh sorry, 3/8″ )
How to get the correct position: I took lots and lots of measurements of the rear ends and also the distance between the leaf springs under the car. I then drilled two holes with the correct distance in a wood plank and bolted the front spring brackets to it. When I had this assembly (springs, plank, perches) clamped to the rear end with the U-bolts I could measure that everything was correct and weld the perches.
The only parameter I couldn’t measure and had to use my eye was the angle of the yoke to the horizontal plane. The only way to do this in a better way, that I can think of, is to have the rear end mounted in the car with the prop shaft attached and weld the perches in place when the cars weight is on the springs.
Regarding prop shaft length. Don’t go wasting your money to get it shortened before you have searched your junk yard. You will be surprised how many different lengths there are. I managed to find one that bolted right in.
A: Niklas, your input on the 2nd gen. perches is useful. I’d read in another write-up that the user had not accounted for the perch angle and had a minor problem due to that. If I had it to do over again, I’d probably stick with either the 1st or 2nd gen perches.
Regarding prop shaft length. Don’t go wasting your money to get it shortened before you have searched your junk yard. You will be surprised how many different lengths there are. I managed to find one that bolted right in.
Interesting, though I might add that a junk yard prop. shaft is an unkown factor. After hunting for the right length, yoke and u-joint types, I might still end up with a unit that is either bent (causing severe vibration) or with bad u-joints that could fail shortly after installation. As my car has some modifications that enhance it’s power output, I didn’t want to go too cheap on this critical link. I’ve had 1st hand experience in drive shaft failures, and want to avoid them whenever possible.
The 1st time was when the rear joint in my 1969 Chevelle gave way while driving down Colfax Ave in 1976 in Denver. While resulting in a lot of noise and a loss of power to the rear wheels, I lucked out and coasted to the side of the road. The second time was when I was following some friends at Lake Tahoe in California in 1980. They had piled into thier freshly painted 1968 Camaro Ralley Sport. The front u-joint on the Camaro failed at about 45 mph. The drive shaft dropped to the ground and immediately pole vaulted the Camaro’s rear into the air. The rear axle assembly tore loose from the leaf springs and was thrust up into the fuel tank, spilling gas everywhere.
The occupants got lucky in that the car didn’t end up on it’s roof, and further lucky in that aside from some bad bruises, no one was seriously hurt. That wasn’t the case for the car. Sadly, the wounds were mortal and the car ended up in the junk heap. We salvaged what parts weren’t bent up, and that was the end of that car.
From my perspective, the money I spent on the cutting, balanc- ing, and new joints was a good investment. But I do see your point when trying to keep the budget under control.
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Content last modified: January 22, 2014 at 10:07 am
Q: 8.2 vs 8.5 10 Bolt Rear
What is the difference in the two 10 bolts in ’67? Was the 8.5 the posi? I haven’t been able to find an explanation anywhere.
A: As far as firebirds go, all 1967, 1968, and 1969 firebirds had the 8.2 inch rear end. It has nothing to do with whether or not they were posi. The 8.2 inch rear (at least in firebirds) is considered a BOP rear (Buick-Olds-Pontiac). Starting at least partly in 1970 and then from 1971 on (I think) the firebirds all used the Corporate (Chevy) rear end which is 8.5 inch. Again, nothing to do with whether or not it is posi.
Aside from size of the ring gear, 8.2 inch rears also used a different posi unit (cone-type vs clutch-type) which is considered weaker, they attached somehow at the end of the axle near the bearing (haven’t taken the time to figure exactly how yet) vs the 8.5 which use c-clips inside the carrier, plus other differences.
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Content last modified: January 22, 2014 at 10:09 am
Q: Drive Shaft Yoke Seal Leaks
Question about the drive shaft yoke that goes into the tail of the trans. Gear oil leaks out the tail of the trans so I replaced the seal. No biggy. What my problem is .. I slid the drive shaft out and you look at the yoke to find that the about an inch of the outter yoke seems to be worn badly.I think this surface should have a machined finish to it. My brother looked at it and seems to think the drive shaft is to long. I drained the oil and didn’t find any big pieces off metal. The magnet on the plug had a finger tip size of sludge and some small fillings on it.
A) Is this normal wear? 30years +
B) Is drive shaft to long? How do you measure?
C) Is it the wrong yoke?
D) Can you cut an inch off the yoke?
A: If the yoke is that worn chances are that a new one isnt going to fix it. I think the inner tailshaft bushing is severly worn. You must remove the tailshaft to remove /and replace this bushing. It is pressed into the housing and is about 2 in long. This is a softer material than the yoke so it is sacrificial.
A: Sounds like normal wear for a 30 year old drive shaft. The yoke can be replaced fairly inexpensively. Your obvious choices are new or used. Check with your local parts dealer or dealer parts counter for the price. The other choice is to check with the local junk-yards for a good used one. The yokes are common to almost any brand of GM car with similar transmission.
As far as length, in the normal weighted condition you should have about 3/4 to 1 1/4 inch sticking out of the tailshaft.
A: Your drive shaft seems to be in pretty normal condition to me. The part of the yoke that sticks out of the tranny always looks pretty bad. The question is what does the yokes surface area look like that is inside the tranny. It should be clean due to constant contact with oil. And most importantly, what does the yoke look like where it comes in contact with the seal. My bet is that the seal has worn into the yoke. Again, that is normal for a 30 year old car. The problem is that if there is too deep a groove from the old seal, a new seal will still leak. I would first replace the seal in the tranny and replace the driveshaft. Sounds like you have already decided to replace the gear oil. Good move! If after new oil and a new seal it still leaks, replace the yoke. Fortunately, none of this work is rocket science, so go for it!
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Content last modified: January 22, 2014 at 10:10 am
Q: Rear Seal Replacement
I intend to replace the rope rear main seal in my 1968, 350, with an original type rope seal. All the information I could find on the cheveron/lip type Cadillac seal required pulling the engine and crankshaft to properly install it.
The engine is still in the car and at this time that is where I would like it to stay. My question: Is it possible to drop the pan with the engine in place? I am worried that there may not be enough clearance between the front crossmember and the pan to allow the pan to clear the crankshaft and be removed.
If so are there any tips or procedures that make this possible or easier? The bellhousing and flywheel are removed at this time.
Any advice would be appreciated.
A: The rear seal (upper half) can be changed without dropping the crank by using the new seal and turn the crank by hand. The seal can be rotated out of it’s position, and the new rotated in. But, the hassle you’ll have just getting the pan off isn’t worth it. It’s best to pull the engine and do it right. With the engine out, it’s a lot easier and you can do some other things while you’re in there. Like change all the bearings. These can also be turned out by using a bent cotter pin. Just bend the cotter pin to look like a “T” and put the bottom of the “T” into the oil journal. Then, you can turn the crank and the bearing will turn out with it. Put the new one in this same way. This way you don’t have to remove the crank. Just remember to use engine build lube. This is also a good time to replace that 30 year old oil pump, the heart of your engine (it stops, you stop). I’ve tried removing the pan and doing this on a Camaro with a 350, and I had to drop the steering idler arm, and lift the engine a couple inches just to get the pan off. Even then, things were tight and made changing parts very hard. I finally pulled the engine and finished it right.
A: I can tell you this much…. Yanking the engine at this point would be pretty simple… especially if you can easily disconnect the exhaust system. My guess is that you can yank the engine with about 4 hours of work and two sets of hands at this point. Swapping the seal once the engine is out is only an hour or two (plus whatever else you want to do). If you do it, keep in mind that you can also reinstall your clutch with the engine out and avoid the pain in the butt of remounting and aligning the clutch assembly from the underside of the car. All said, you’re probably about even, or ahead time wise (removing the engine vs not removing the engine)….. And that assumes that you would have had no problems if you did all the work from the underside. If you consider the skinned knuckles, oil in your hair and @#!%$@@ words that go with under car work, I would certainly remove the engine…. But that’s just me. Now that I’m a member of the 40+ gang, (who has false teeth do to hitting himself with a misguided wrench) I try to stay on the top side of the car as much as possible.
A: would go one step further. replace your rod and main bearings along with the oil pump while you have it down. It has been my experience that seals dont start leaking for no reason ….. there is wear there that is allowing the componemt to move and cause the seal to leak.
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Content last modified: January 22, 2014 at 10:11 am
Q: Thumping at Low Speeds
I have had a problem with thumping noise coming from the rear passenger side of the car since i got it. I have replaced the bearings and no difference. What could this be. The sound dissappears at high speed (or just becomes one noise) so I am pretty sure it has something to due with the tire. ITs new and the same size all aroud. Could it be out of balance?
A:
1-Check for broken spring
2-check for loose or broken U-bolts
3-Check and replace U-joints
4-This you do not want to read , worn carrier bearings causing the pinion and ring gear teeth to hit , but at high speeds the carrier goes back into place .
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Content last modified: January 22, 2014 at 10:12 am
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