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What was the "standard," or most common, gear ratio in 1971 Cutlass Supremes? Is there any way to tell what gear ratio you have short of taking the diff cover off and counting the teeth on the ring and pinion?
You can crawl under the car and find the differential code letters stamped on the right front inboard side of the axle housing tube. The first two letters designate the ratio code. The letters are ~1/4" high. You may have to wire brush the axle tube to remove the grime. Picture below is of mine. R2 = 2:56
I don't know the answer to your question regarding the standard or most common; but, I suspect a standard or most common gear ratio would be of the particular "SERIES" of vehicle. Once you find the differential code letters, post them and we can provide the differential gear ratio.
Mine is a 1971 CS Convertible sbo.
Here is a post I created w/ several other members providing useful information regarding gear ratio which may assist you. I did the wheel rotation/drive shaft spin count to confirm the gear ratio.
Thanks. Next time I have the car on a lift I'll look for the code. Reading your reply and other responses I received, I'm pretty sure mine is also a 2.56:1, which is fine with me. My car is a standard run-of-the-mill '71 CS convertible, nothing fancy, but a very nice 75,000 mile survivor with no rust, no repairs and no dings.
What was the "standard," or most common, gear ratio in 1971 Cutlass Supremes?
My experience since around 1980 with my cars and friends cars is that 2.56 is the most common ratio as that was the standard, no cost ratio. Others were available as options at an additional cost.
Originally Posted by rockdr
Is there any way to tell what gear ratio you have short of taking the diff cover off and counting the teeth on the ring and pinion?
Yes, you can use an online RPM calculator. Input the MPH, RPM, and tire height and it will give you the gear ratio.
You can also raise the rear tires off the ground (or just one with an open diff) with the trans in neutral, rotate the tire(s) and count the driveshaft revolutions. With the open diff, the turns will be off by a factor of 2 due to the differential action.
Some of the info from that automobile catalog website is incorrect, or at best confusing, which is why you should only use factory literature for info like this. Here's the actual factory information on standard and optional gear ratios with each engine and trans package in every Olds car line for 1971. The short answer is that with any engine, 2.56 was the standard ratio with AT and 3.23 was the standard ratio with MT. Of course, that means nothing since there were several optional ratios.
Addressing your original question & a follow-up to Post #2, once you have determined the differential code letters stamped on the right front inboard side of the axle housing tube, look them up on the below chart (pg. 0-6; Fig. 10A - Differential Identification Code; 1971 Oldsmobile CSM).
FYI, this is the code on my 1971 rear with 2.56 gears. Note that this rear has been wire brushed to remove rust, dirt, crud and has been painted. The stamping is difficult to see on a rear that hasn't been cleaned up.
Well I have Parted out tons of Muscle car rears over the years and most common ratio I see is 2.56 and Chevy 2.73. That is just from thousands of rears in the Ohio area.
Remember most B O P vehicles had V8 power plants and that ratio was just the best for fuel mileage on a standard off the lot car.
Remember not all these cars were MUSCLE CARS - the were standard A-B cars drivers.
