how can one tell the difference between a high, middle, or low gear posi carrier without the ring and pinion atttached?

Wow, I would think the only option would be to go by the part number cast on the pumpkin.

That would only work if it was the original carrier. I think there are two sizes. I would try a ring gear and see which one it is.
Jim

can't get a ring to check it out but i understood there were three types, will open gears fit on an original posi bop?

You can change them back and forth between posi and non posi carriers. I think Salmon was right about the pumkin numbers. I think the housing will only accept the gear ratio range carrier it was built for.
Jim

It's my understanding the housing/pumpkin doesn't matter unless you go with a different size ring gear....ie. 8.2 vs. 8.5 vs. 7 3/4. The Posi CARRIER I believe should have a casting number on it of some kind identifying it as a 2,3, or 4, I believe, but don't quote me on that part.

Er, that's what I actually meant. There should be a part number on the CARRIER.

the responses are vague, i do understand that i must use an 8.2 ring gear however what stamp on the carrier(pumpkin) signifies it is a low, medium or high gear ratio unit? and what makes each one different if there is any?

I know that some housings will not take a carrier with with the larger ring gears. For example; You can't put a carrier with a 4.11 into a housing that was built for a 2.70 gear. That's where the code will help. If you find the axle code(on the axle tube) you will know what range of gear ratios you can use. The only other way is to try the carrier with the ring gear in the housing and see if it fits. If it fits then you can set up your pinion.
Jim

The housings are the same, regardless of ratio. The carriers are different. The ring gear bolts to the carrier.

Salmon is right: The carriers are identified by their casting numbers. The carriers are specific to a range of gear ratios. 3.36 is the break point. Below 3.36 a "2-series" carrier is required. For 3.36 and above, a "3-series" carrier is required.

You can use a "3-series" posi or non-posi carrier with the same gear set, in any housing.

I do not have the casting numbers handy for the Firebird 10-bolt carriers, and I do not know if they are different than the "A" body carriers, of which I have one of each.

Q

OK. Thanks for all the info. I'm currently using a 2.56 open so if i bought a 2 series posi carrier i should be able to use up to a 3.23 ring and pinion. I heard there were three carrier sizes.

I've heard that too, but I've only ever seen two. I know that all of the aftermarket have only two.

There are also four-pinion and two-pinion posi carriers ... that might have something to do with it. (This has to do with the smaller "spider" pinion gears.)

Q

wouldn't a 2.56 be a 1 series? that's highway gears to the extreme. ick.

seies 1 is for 2.76 and down, or thereabouts. i think those 1 series are rare. (because nobody want's them unless they're making huge amounts of torque and hp i guess.)

Sorry about the wrong info on the housings. Q is right about the carrier determines the gear ratio range you can use. So, buy the carrier that fits your housing and uses the gears that range in the ratios you would like to run.
Jim

No probelm. It's often a terminolgy problem rather than an information problem. I just wanted to clarify that what we call the carrier is the internal component. Some other companies call that the housing, and they call the housing the carrier.

I was merely clarifying.

Q

Found this on the web...not sure if it will help you at all? but go to this and there is casting info on the rears. maybe it will help you with what you have and or what to look for.
http://www.teufert.net/pontiac/rears.htm

I know how you feel... everytime I start gathering info on this, I get conflicting info, and conflicting terms being used... Doh!

As Q has so eloquently explained is how I was understanding the whole scenario...

As in my case also, eventually, I plan on switching my gearing from 2:56 (posi) to (again, from what I've been told) a 3:08 or 3:23 (Posi) preferably and I should be able to use my carrier (the part that's installed into the housing) to put the new gears (ring and Pinion that bolts into the carrier) into.

From some of the info (nothing difinitive yet?) I should be able to go up to at least a 3:08 ring and pinion, and as Q mentions possibly a 3:23 before having to switch carriers if I wanted to go to a better gear combo than that.

So this tread is a great one to help spell things out a little better!

Thanks again guys!

Brett - 67 Drop Top 455!

I quote from the '67 Firebird Service Manual Supplement, Page 4B-1, paragraph 5:

"Three differential cases are used on the 1967 locking differential Firebird models: one for the 2.56 and 2.78 axle ratios, one for the 2.93, 3.08, and 3.23 ratios and one for the 3.36, 3.55, and 3.90 ratios"

what we call the 'carrier', the service manual calls the 'case'. this is the part of which there are three series'. this is the part that the ring gear bolts to.

what we call the 'housing', or 'case', the service manual calls the 'carrier'. this is the outside cast iron part the axle tubes go in, and everything else fits inside. it is a 1 size fits all.

in other words, the service manual vs. most of the rest of the world use opposite terminology. if you try to go by the book, you will be told you are wrong, and everyone will be confused. feelings will be hurt, and children go to bed hungry.

pictures and part names

in other words, in most of the real world, the case encases the carrier, or the housing houses the carrier, and in the manual, the carrier carries the case. confused? i am.

Scott -

I'm glad you're on the case. We needed someone to carry the flag, and it looks like you're geared up. They should have known we'd send in a ringer.

Q

ouch! my rearend!

That's just one man's pinion, others may diff. :p

I'm positive

I don't think it has any bearing on the case.

I'm gonna bolt now before i get the shaft.

And here I thought I was king of the puns! Guess the yoke's on me (grammar-wise, that was a limited slip) and someone else will get the crown. I see that most of the puns were by two others, so can I join the club as the third member? Or should I just stop the chatter? Do I really need to axle you guys what to do? Did I make a mesh of things again? (I think I see a pattern here.)

So , if I'm getting(sort of) this, and I wanted to change my 3.23 open to a 3.55 posi I have would have to totally gut my rearend and replace everything on the inside with different stuff.(Ouch that's gonna hurt) Better off staying with the 3.23s and adding a posi unit?

Robert

Will a 2.56 posi guts fit with my 3.23 gear set? I just want to make mine into a two burner.

Robert

Eaton makes a reasonably priced new posi unit that alot of guys posting here like. I put nearly a grand in the posi I built last year for my '68, so be ready to burn some dough setting it up, but would be well worth it in the long run. Your 3.23's would be a nice street gear, especially with a 455! 3.55's would be great with a 400. I would use a Richmond gear if replacing old set. Just my .02

Steve

Well I ask because I have found a 2.56 posi and gearset for a good price and I would like to use the posi unit to upgrade my one legger 3.23 to limited slip. Anybody know if this is a direct bolt in?

Robert

Yes, it should be a direct bolt in. But please give me hell if it turns out it isn't.

Q

i'll take that bet, Q. i dont really want to give you hell, but i s'pose i must. at least we got the puns out of the way.

the 2.56 is a 1-series, and the 3.23 is a 2-series. i'd have to say you can only go up to a 2.78 from a 2.56.

the 2.56 and 2.78 use one bolt pattern
2.93, 3.08, 2.93 use a second pattern
and the 3.36, 3.55, 3.90, and 4.33 use a third.

at least according to-
axle ratios, tempest and firebird
i cross referenced some part numbers using that site, and it is consistant within the book. this is also basically the same as what salmon38 quoted earlier, just from a different book.

of course, there's nothing like real world experience to prove a book right or wrong....

and if you have a corporate c-clip rear, such as out of a camaro or nova, the splits are different.

Well, I think I could resolve this because I have an old 2.54 gear set that I could match up to my 3.23 if I want to pull the cover. Hmmmm. I probably will before I spend $$$ on another posi set. I'll keep you all posted.

Robert

Scott / Bob -

I thought the 2.56 was the lowest ratio in the series 2. I guess I learned something new today. (I like it when that happens first thing in the morning, because it means I can take the rest of the day off!)

Bob, take Scott's advice. It sounds like he's got more up-to-date experience in this matter than I do.

Q

Q, dont take the rest of the day off.....

I think maybe FireBob got up a little early (not awake yet?) , I think you are right , its a 2.56 not 2.54 , prob. a "fat finger thing"...

OK ... I did my own homework. I am wrong.

Here's a page from Randy's Ring and Pinion. They have a pretty good reputation in the industry.

http://www.ring-pinion.com/tech/techg1199.html

According to them, the 2.56 is a series 1 (Scott, take a bow) and the 3.23 are in series 2. 3.55 are in series 3.

Now, can I please go home?

Q

i dunno if i'd call reading a 1972 service manual as "up to date experience". i'd really like to know for sure too. books only have words and pictures, and they're drawn and written by second or third hand knowledge by artists and writers, not by mechanics or engineers.

you're talkin' to a guy who's trying to get an s10 rear to fit because it's cheap. i dunno if i can do that either. it's pretty narrow.

ps i prefer pop-up books

I don't see what all the confusion is. If you page up, you'll see that I provided the carrier break info that you have been digging to find from the Service Manual.

And the manual also points out the breaks are different between a posi and a non-posi. None of those other sources talk about that.

no bow for me. salmon38 said it first. (i did give credit in my post earlier)

but the online manual says the safe-t-track is interchangeable with the standard. so the break points should be the same.

the corporate rear and the BOP have different break points. so as far as i can tell, you can use the same ring and pinion on a posi, as long as it is the same seies, and you're not trying to bolt a BOP bolt pattern ring on a GM corporate unit.

i think most of the chevy corporate rears (8.2, 8.5, 7.5, etc..) all have the same break points as each other... also whether or not they are posi. they are listed in the first column of the link i gave.

To make matters worse, though the BOP is supposed to be B-O-P, some of it does not apply to Our Birds, because there were no "B" and "O" F-bodies. I have read stuff about Olds 10 bolt rear ends that might be true about Olds, but are wrong when applied to Pontiac. (Don't even get me started about the Olds 12 bolt 10 bolt rear end.)

And, Salmon - you are right. Your information is probably the most accurate. I was trying to find a back-up source. Of course, as you and Scott also correctly point out, unless you have "real" experience, the information in the books might not be worth the paper it's printed on.

Q