What rear end gears go with a TH 400 automatic trans..I have a rear end from a 86 chevy El Camino, not sure what gears,came off automatic car.
what kind of car is it going in? how are you going to use it? (drag race, street drive, around town, freeway) what is the engine? so many questions....
If you still have access to the original car you can look up the rpo code. (Google gm axle codes) or decide the vin Does the rear have a tag? If not toe gonna have to count revolutions between the pinion and axle or remove the cover and count teeth https://tuning.americanmuscle.com/h...60743-How-do-I-verify-my-rear-end-gear-ratio- maybe this can help
No matter what gears in the rear you use, you'll always be 1:1 in drive. Maybe look at the RPMs you want at the speed you will drive, then work backwards?
Here is a tire size/speed chart http://myjeeptj.com/wrangler-write-ups/gear-ratio-to-tire-size-chart/ You need to know rear end gear and overall tire diameter. Unless you are running an overdrive (a th400 isn’t) you have a final drive of 1:1. This chart will help you determine engine rpm at a certain speed
I have 2:73 behind my stock 454/th400 and they are perfect... It depends on the engine size and cam selection..
If that '86 El Camino had the fuel injected V6 you have either a 2.56 or a 2.73 rear gear. If it was the 305 V8 it's either a 2.41 or a 3.08. Most likely a 2.41 if it was an automatic. Both were a 7.5 inch ring gear (ie, weak). Buick Grand National and Olds 442 of the same era will bolt in, and will be an 8.5 inch ring gear, and much more likely to be a limited slip differential. I happen to have an '86 El Camino with a 305, 2004R transmission and 2.41 rear axle ratio. It runs 1600 RPM at 65 MPH.
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