LOL> While cleaning out my rear end, checking all the bearings and gears and changing fluids, I noticed someone has put 2.73 gears in my rear end. There should have been 3.36 gears in my ZM axle.

Is this a big difference in ratio and how will it effect the performance?

Switching back to at least the OE gears will make it a whole lot faster.

It will surely give you better gas mileage and run better on the highway.

But you won't be as quick off the line.

I had about five different comments about the heading of this thread, but decided to just be quiet.

2.73 are great highway gears. Not very good for low end punch
Not recommended for 4 speeds as you will probably be slipping your clutch in 1st more. I had 2.73 in my stock coupe /w 350 2 bbl and 2 sp PG. Could not spin my tires unless sand on the street !

IMHO

I was trying to get some laughs out there.

I guess it's pretty complicated to switch them out and I guarantee I can not find someone local to do it.

I have an almost brand new set of 3.70 gears out of my 400 coupe. I swapped them out for a set of 3.08's when I had my rearend rebuilt. I think they had less than 500 miles on them.

If interested, let me know.

Not mentioned yet was checking the speedo gear in the transmission to see if it was also changed to match. If not, your speedo accuracy will be way off.

Almost spit my ice tea all over the keyboard when I read this.

DAYUM.

I`m not going to comment on what I thought,.... but re the rear end of the car...I have 2.56 rear gears, better for gas mileage.....and highway RPMs,...and I get pretty quick starts...but IF you are going to RACE the car ,yes get the other gears back...BUT I can just tell you that if you drive 10 miles or more, you will get there as fast as the others...I usually get there BEFORE the others , no matter my 2.56 gears! 'some' of them get to a 50 yd line before I do, but we usually drive further than that...lol

I guess I'll get the car back together and see how it performs. Then go from there.

2:73 gears: Don't rev your engine at a stop light challenging the car next to you to a short race...LOL

But, you'll get better gas mileage and likely more comfort at highway speed...

If you are rebuilding an HO and are being so specific with your restoration, the change to the original 3.36 gearing is a no brainer.

Most HO's came with 3.55 gearing for manuals and 3.36 for autos.

Will it affect? You will NOT be happy with 2.73 gearing in your HO. 2.73 gears are a dog.

Had a 68 400 manual (numbers matching, engine rebuilt to spec) with 3.36 gearing and was awesome. If you plan on a lower compression engine with a hp decrease, go with a 3.08....but to each his own.

maybe not against another Pontiac , but against most other cars your initial torque will out operform them at redlights

I would add Buicks to that short list.

Not sure your intended use after this car is done. Trailer queen? Gears don't matter. If you actually intend to do any substantial "fun" driving at all I can promise that you are going to HATE 2.73 gears behind a 400 HO 4 speed. That is a drastic mismatch that will have truly dismal and inconsistent holeshot from a standing start unless you consistently and completely SMOKE your clutch every time you take off.

Agree you might as well drive it first and get an idea of what you might want. But starting thinking right now, because you will absolutely want different gears in this car unless you are truly gonna granny-drive it.

LOL, I dont "granny drive" mine for sure...and I love it with 2.56 gears....smoking tires and all...its not just the power of the engine when you drive ,you also need to know "how to"....unless qtr mile racing...it really doesnt matter much....to "get thru' traffic , driving right....of course just my humble opinion...but IF you are going to drive it 'hard' be sure to add the chin spoiler (Camaro part!) to keep the front wheels on the ground....I did add it , as it get really swayee after 80 mph without it...

Looks like my whole insides have been molested. My posi unit is gone as well as my gears. I'll need to find a posi carrier and gears now.

Should I think about a new posi unit like eaton or Yukon with 3.55 or 3.36 gears?

Thought I would update this thread....
The 2.73 gears are a dog on takeoff with the M20 Muncie. We live in the mountains and pulling off on a hill was really hard on the clutch.

I tracked down a date correct ZM axle with the correct 3.36 posi earlier this year. It was really clean and looked like the axle bearings had been replaced but I media blasted, painted and changed the fluids. I was finally ready for a axle swap.

This past Sunday I swapped them and it went pretty easy. Since the new rear axle has the correct 3R pinion yoke, I had to change the universal joint back from the 1310 -3R combo joint. The swap was straight forward. I jacked it up on stands. Dropped the driveshaft. Disconnected emergency brake cables, disconnect brake line at piston and removed top holding bracket from top of cover, unbolted lower shock bolt, unbolted the u bolts and t bolts from lower shock mount to axle, unbolted front spring cup and lowered front of spring to ground and slid out axle.

After putting the new axle in in reverse order, I changed over the brake components to new axle.

I have not test drove it yet and I hope to finish up some small items like add friction modifier additive, torque some bolts and bleed the brakes. I then hope to test it out this weekend. I am hoping to see a big difference in take off as well as my speedometer calibrated correctly.

My plans now is to try out the 3.36 and see how I like it. Then have my original rear end completely rebuilt with a new posi carrier, bearings and either 3.55 or 3.36 depending how these go.

IMG_0570 by Silver - Bullet, on Flickr
IMG_3721 by Silver - Bullet, on Flickr
IMG_3987 by Silver - Bullet, on Flickr
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IMG_3999 by Silver - Bullet, on Flickr

IMG_4007 by Silver - Bullet, on Flickr
IMG_4008 by Silver - Bullet, on Flickr
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IMG_4012 by Silver - Bullet, on Flickr
IMG_0764 by Silver - Bullet, on Flickr

The original 3:36 ratio for your car would be in the nice "happy medium" in gear ratio. Not the best on mileage, but certainly better than feeling like your car has no pep. My car has a 3:55 axle, you can definitely feel it has some gear behind it.

I tested out the 3.36 gears and it is like night to day difference. Pulling out is a lot better and you can easily light up the tires. I am so pleased with the change. My speedometer is now correct too. Awesome.

I just can't belive someone would change out these gears to 2.73 and leave it that way. Unbelievable.

Just to update the thread,

I found a Pontiac 68 4 pinion posi carrier with 3.36 gears last month. I had it shipped to J D Race and Restoration - Jim Mitschke to have it rebuild. I also shipped him my original rear axle so he can install the posi and set up the 3.36 gears. He installed all new bearings. The posi and rear is all with in spec and will be ready to hit the road soon.

Jim made it so easy to ship the rear axle to him and the cost for all the service and the shipping was very reasonable.

Did you do all that to have an extra set up? Jim is good people and does very good work and is very resonable. He put together an 8.5 rearend for me with eaton posi and 3:73 gearing... and I love it. Good luck on it!

I will put this original one back in the car and sale the extra one I have. There is several people looking for a 68 nodular rear axle. So I might as well make some one happy.

Are you trying to find out if someone had a similar experience? https://firstgenfirebird.org/forums/images/icons/default/crazy.gif
BTW: This is not a dating site!

I got the rear axle back from Jim a couple weeks ago. I just installed it and went for a little test ride. It sure rode nice. No vibrations, noises, roaring. Seems to even feel smoother at 75 then it did before.

Jim did a great job on the setup. I give him a A++

I have been talking with Jim about a rebuilt axle for my sons chevelle. Great guy and easy to work with.

Was it a date rape drug?


Laugh every time I see the title...

Somebody put those gears in my rear end they going to get [censored] up good!