I have a 70 Olds 442 W-30, 455 worked nicely. 400 tranny. 12 bolt rear; only one tire spins. Original rear from 70 Cutlass 455. I know nothing abut rear-ends. I want to change my gear to a 3.90 (maybe); daily driver- so I like the idea of limited slip. Can someone teach the ins and outs of a rear and my options. TIA

The rule of thumb is that 3.55 gears are the numerically highest you should go on a street car. Even then, if you do a lot of freeway driving then you may want something numerically lower. A good compromise would be 3.23 or 3.31 gears. The absolute best setup would be to run an overdrive transmission with a 3.73-4.10 rear end. This gives you acceleration and low crusing RPM.<P>To calculate what gear ratio you have right now jack the rear of the car up and put a chalk mark on the driveshaft and one on the tire. Turn the wheel one revolution and count how many times the driveshaft turns around. For instance if it turns about 3 and 1/4 times for every tire revolution then your rear-end ratio would likely be 3.23.

I recently went through the same ordeal of trying to identify and investigate options for an Olds 12 bolt I acquired. A great website with a wealth of information is <A HREF="http://www.442.com" TARGET=_blank>www.442.com</A> The frequently asked questions section has a great deal of useful information on differentials as a whole and gives some useful information on the Olds 12 bolt. Good luck. <BR>Kevin.