Rear End Gears

[Qdub24]

I have an '85 Cutlass Supreme that came w/a Buick 231 V6 and 200-R trans. I plan on dropping in a rebuilt '71 Buick 455 and a rebuilt TH-350 trans w/shift kit, as well as running some 22x9.5 chrome wheels with 265/35/22 tires. 8) It still has the stock non-posi rear end. I would like to know if I need to change my rear end gears? If so, to what gear ratio? :?:

 

[85 Cutlass Brougham]

I wouldn't run wheels and tires that big. It will put too much strain on the stock drivetrain, not to mention the wheel bearings, etc. But, if you insist on making the car look silly, you will definitely not want to have the stock 2.41 or 3.23 gears. For advice, look at Jeep and 4x4 oriented vehicles and magazines as to what gearing works with your tire height. You will probably want at least a 4.10 gear, if not something even shorter. Even so, the stock rearend will not hold up to the combination of the 455's torque, the added rolling resistance of the taller tires, the rotating mass and inertia of the wheels and the weight of the vehicle. All of these factors add to the shock loading of the drivetrain, and the added ride height will likely cause excessive driveshaft angles and kill your U joints on a regular basis.Not to mention, all of that rotating mass will make the car much harder to stop using brakes that are not adequate for a more normal 25 inch tall wheel and tire combo used in a performance application. Just remember that the GM 7.5 axle was originally designed for the Monza/Sunbird/Starfire/Skyhawk RWD subcompacts of the later 1970's, and will not hold up too well with what you are suggesting. Not that it can't take some abuse on occasion ( I have 350hp/420 ft lbs of torque going to mine), but extreme applications are not going to make it last long.

 

[Qdub24]

Okay, thanks. I know a lot of people with similar set-ups, and I hear a lot of talk about using a 3.73 gear ratio. Do you think I could get away with using that? I'm from Columbus, Ga and I'm 21; just about every young dude down here w/one of these cars (any car now) is at least sitting on some 20's. I've got black 22's with 265/35/22 tires on my 94 Impala. I know the stock rear end could work (at least temporarily); my cousin has a '78 Regal w/22's on it and a Buick 350 and 350 turbo trans (same rearend as mine). But I want the satisfaction of knowing that my rearend will hold up to all of my demands. And if it makes any kind of difference, my car has a 3 inch lift kit on it (not much, just enough to sit over the tires).

 

[pontiacgp]

265/35/22 tires

I guess that size is ok as long as you don't really want to drive the car.... :?

 

[85 Cutlass Brougham]

My car is lowered 2 inches in front, and about an inch in back and sits on 16x8's I've had on the car since I was 20. My AMC is also lowered, and I am thinking about lowering my Nissan Frontier too.I plan on either 17's or 18's in the future so long as they don't rub or raise the car. 275 35 or 40's on the back, 245 40's or 35's front. I would lower it even more but I need a little ground clearance on bad roads, plus I don't want to hit the bumpstops cornering. It's being set up as a BMW killer.

 

[pontiacgp]

The problem I have with 35 or 40 series tire there's no sidewall.....part of the suspension on G bodies are the give from the tires and without that you'll end up vibrating the car apart..I run eibach springs and 60 series tires, 255 on the back and 245 in the front, which gives me a nice solid ride and I can chase rice burners around corners if I'm in the mood....it's a choice I guess but I'd rather have a nice driver than something to be looked at...I don't put anything on my car if it's not functional...

 

[Qdub24]

I'm probably only going to drive the car on weekends. I keep it locked up all week anyway because my first Cutlass, which was all original, was stolen out of the front yard a year and a half ago. 😢 But I do drive my SS everyday, all day. I have the exact same size wheels and tires on my Impala and I can still outrun anybody I choose. And the lift kit I used makes the car's suspension ride like a new Cadillac because it was custom made just for my car and installed by a suspension expert, Robert Battle, here in Columbus.

But back to the question at hand, will a 3.08 (like the Impala) or a 3.73 gear ratio work well with my car's setup? :?:

 

[87MonteSS]

3.73 with a TH350 trans means not much highway driving and it would be totally out of the question with 4.10/4.11 gearing. I'd stick with 3.08 for overall driveability. The big block will have enough snort to get you moving fairly quickly anyway.

 

[85 Cutlass Brougham]

What is the overall height of the tire/wheel combination you have? 30 or 31 inches? If so, the 3.73's are the ones to choose. I have 3.23's with a 25.5 in tall tire for reference and it is fine on the highway. I also have an overdriven 4th with a .67 ratio that drops it to a 2.16 in OD, but out of OD it's around 2500 rpm. Many Jeeps leave the factory with 31 in tall tires and have 3.73's or 4.10's from the factory to compensate.

 

[c_unit productions]

whats up man? im from da south and we got a monte carlo on 22's and we got 3.73 and the only bad part is highway use we run around 3000 rpms at 65 mph. we got a 350 in it now and we run it at the track too. we got a regal on some 26's and we run the same gear but we dont really drive it much in fact the wheels r for sell looking for some floaters. check out my pics and ull see the cars. holla at me if u need some help.