[83_Chevy]

Hey guys I have a question I just bought an 83 chevy 1/2 ton P.U. with a 3/4 rearend my question is my other truck is a 74 3/4 ton with the same motor not sure about the transmission but the 74 picks up alot quicker than the 83 and I was wondering if it's the transmission that makes it pick up faster or is it in the rearend?

[curtis73]

It could be one of a thousand factors. First of all, the transmissions have very similar gear ratios regardless of what tranny is in there, so I doubt it would make a huge change in your perception. Tire size, rear axle ratio, and engine power are the big ones, and if you are trying to compare the engine output of a 74 to an 83, its a tough comparison. Smog equipment, cam changes, technology, everything is vastly different between them. Literally night and day. Also, rear end ratios can vary between 2.73:1 all the way up to 4.56:1. That could mean a difference of 67% in the amount of torque that makes it from the engine to the wheels between the economy gears and the performance gears.

[83_Chevy]

ok I see, the engine in the 74 is an 80-85 block not sure if that makes a difference and the tire size is the same on both trucks.

[M&M CUSTOM]

What transmission is in each one?
You can look in the knowledge base for my transmission information thread for identification purposes.
The rear axle gears are definitely going to be different too. (This will make a HUGE difference).

[83_Chevy]

both trannys are th400's but i'm guessing the rearends are different the 74 tranny shifts harder more torque than the other.

[M&M CUSTOM]

I'd say you have different gear ratio's in those axles.

Only way for sure to tell what you have is to remove the covers from both, and chechk the ratio's.

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[83_Chevy]

ok i'm gonna look at the gears in the rear end. How do i know which ones are there count the teeth? and if they are different how hard would it be to swap gears?

[curtis73]

You can count the teeth, but 9 times out of 10 there are numbers stamped in the ring gear. Rotate it around until you find them and it will say something like 41/10 which is the number or ring and pinion teeth. Just divide those two (which equals 4.10) to get your ratio. If those numbers aren't stamped, you'll have to count the teeth yourself and then divide.

You can also get close by jacking it up, turning a wheel once and counting how many times the driveshaft spins. If you have a posi it will be easy. If you don't have a posi, only jack up one wheel, then you'll have to double the number of driveshaft spins. Its only a guess though. If you get 4 turns of the driveshaft it could be 3.90, 3.92, 4.10... but it would probably get you close enough without having to drain the rear lube