Grizzlybear226

I've got a nice stout 350 bored.40 over ready to go into my 88 trans. I've been wanting to beef up the rear with higher ratio gear but am confused as to picking out the right one. I need to know what rear is in my car; such as the axle model, ring gear bolts, spline count and even diamater. Anything that would help me choose the correct one. It's a 88 Pontiac trans am, 305, 700r4, 2:73 ration and a open carrier. I was thinking either 373 or 390s for the car when it's finished. Thankyou

Tobias05

do yourself a favor and skip throwing money at a ten bolt and just buy a nine inch or S60. I wish I did.

however, in your 88 you have a 7.625 10-bolt. late model year cars received 28 spline axles.

I've seen budget 10 bolt builds run about 800 dollars on the cheaper end. Mine cost me 2500...

whatever flavor you decide I'd go with 3.42 gears. I cross the line in the 1/4 at about 5200 RPM with my 700r4 and 3.42s. 3.73s at the MAX with a 700r4.

what kind of stall do you have?

Grizzlybear226

I'll be putting in a b&m 2400 torkmaster. I found a posi rear on craigslist last night out of a 86 iroc for 150 so I may just buy that, take our the carrier and throw it in mine with the new gears cause I just redid every part on the rear drums and don't want to throw away money. Alot of people on the site say they run 342. Is there something about the 700s that can't take higher gears?

84 z28

700r4 has a low 1st gear. The higher the gear the more useless 1st gear is and the more tire spin you will have unless the car is setup right. Before you go picking out gears whats you motor specs ? Cam,heads and so on. Depending on your motor you should pick the stall and gearing. A higher reving motor can get away with a higher stall and more gearing.

big gear head

You can't just take out the carrier and stick it in another rear end. There are 2 series and 3 series carriers, which must be matched to the gears that you have. If you have a 3.08 to 2.14 then you need a 2 series. If you have a 3.23 to 4.10 then you need a 3 series. There are also different splines on the axles. Up to '90 they had 26 splines. From '90 and up they had 28 splines. Even if you get the right series and splines you still must set the backlash and bearing preload. This is done with shims and must be done correctly.

Grizzlybear226

Thanks alot for all the information big gear head I had no idea it got that complicated when building rear. I think I'm just gonna sop round and find a place to do the gear swap for me or a rear that's already done and just swap over the brakes.

JamesC

iTrader: (5)

Some other considerations:

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC

Tobias05

how about a 4th gen rear? even opens the door to alot better wheel options, such as my 17x11 zr1s.

Grizzlybear226

How difficult is a switch to a fourth gen rear?

JamesC

iTrader: (5)

One out, one in. But there are other considerations:

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC