Rear Gear question

[85Caballero350]

Im trying to figure out what gearing came in a 85 Caballero with a 305.Im hoping that I dont have to take the cover off and count teeth by teeth lol.Does any one have the slightest clue of what gearing the v8 Elky's and Caballero's had?The tag on the rear is gone 🙁 One day i'll swap out the gears but there is a ton of other stuff that needs to be done first.

 

[87MonteSS]

My best guess is 3.08 but I could be wrong.

Block up the back end and count the turns of the driveshaft required to make the rear wheels go around once. Round it to the nearest ratio available.

 

[85Caballero350]

Thanks for the tip.

 

[clean8485]

If the vehicle still has the original service parts identification label on it, then you should be able to determine the rear axle ratio by decoding the RPO code for the rear axle. Rear axle RPO codes usually start with the letter G, then a 2 digit number after it.

 

[8GPLE7]

I just left this link in another thread. Very useful if you have the RPO codes.

http://www.drivetrain.com/GMtrkratio_posidata.html

Cj

 

[85 Cutlass Brougham]

My best guess would be a 2.29 (GH2 code) axle as 305 cars tended to have awful gearing. What transmission does it have? 3 or 4 speed automatic? Other possibilities I can think of would be a 2.56(GM8), 2.73 (GU2), 2.41(GU1), 3.08 ( GU4), 2.14(G72), 3.23 ( GU5-used in V6 high altitude cars), 3.73 ( GT4). Those are all of the codes off the GM data sticker decoder I have in my 1985 Oldsmobile Factory Service Manual set, Chevy should be the same. Oh, and the code for a limited slip diff is G80. If you need any other codes translated, let me know and I'll look it up. One more thing: The 3.23 gear is a cheap upgrade as you can pull the whole axle and do the swap for under $100-including a brake rebuild. that's what I did on my 2.41 geared car and it made a dramatic difference, quicker and better on gas than the 2.41.

 

[85Caballero350]

My best guess would be a 2.29 (GH2 code) axle as 305 cars tended to have awful gearing. What transmission does it have? 3 or 4 speed automatic? Other possibilities I can think of would be a 2.56(GM8), 2.73 (GU2), 2.41(GU1), 3.08 ( GU4), 2.14(G72), 3.23 ( GU5-used in V6 high altitude cars), 3.73 ( GT4). Those are all of the codes off the GM data sticker decoder I have in my 1985 Oldsmobile Factory Service Manual set, Chevy should be the same. Oh, and the code for a limited slip diff is G80. If you need any other codes translated, let me know and I'll look it up. One more thing: The 3.23 gear is a cheap upgrade as you can pull the whole axle and do the swap for under $100-including a brake rebuild. that's what I did on my 2.41 geared car and it made a dramatic difference, quicker and better on gas than the 2.41.

Well now the car has a th350 trans.Im assuming it had the 200r originally? I guess i'll look for the RPO list later tonight.Thanks fellows

 

[kyhunter89]

Pulling the cover off isn't that hard. jack car up-put on jackstands- Remove the oil fill plug on the front of the rear end assembly (do this now to make sure you can get it out) remove 10 bolts- catch oil- spray inside with carb cleaner- turn gears and look for ratio stamped on ring gear (for example 15-41 for my car, done this yesterday), get all oil and cleaner out of the rear- check for wear- scrub the cover inside and out- paint out side of cover- put a healthy amount of silicon on the cover's surfaces- hold in place- start top bolt- then bottom- then hand tighten every bolt- torqued all bolts donw in a star pattern- take three bottles of gear oil and buy the hose that screws in place of the stock cap, put oil in until in over fills- screw oil fill back in.

 

[Pit_Boss]

Any body know where I can get my hands on a 2.56 ring and pinion?

 

[85MonteCarlo305]

I've got an old rear end I just ripped out of my Monte Carlo. I don't know what gears are in there but they should be pretty close. I'll sell it to you for 75 bucks.