I have an '88 TA w/ the 305 TBI. The car has a severe high speed vibration that I've spent a lot of time chasing down. I'm almost to the pt where the only thing left is to replace the rear end.

If I do this, what rear end should I put in? I'd like to upgrade if it isn't too much of a hassle or too expensive. So should I do a direct replacement? Are the rear ends from the cars w/ the 350 engine bigger/better/stronger? Is the gear ratio the same? What about posi? And what about getting a rear end w/ disc brakes?

As u can tell, I'm confused about the options that are available. I've done a lot of searching, but I keep finding conflicting info. So can someone plainly lay this out for me?

 

9 bolt would be you're cheapest and easiest way to go and have posi, disk, and more strength. ratio would be differant, might have to get differant wheels for the disk.

 

Checked the driveshaft? Might want to get an LS1 ds.

 

or if you dont want to go to a new drive shaft i have a stock one out of a 91 camaro

 

to answer your question about rear ends, not all 350 cars had stronger ones. I'm not sure exactly which years it was available, but in the late 80's, some higher model cars came with a 9 bolt rear which was stronger than the more common 10 bolt. I'm guessing your car has a 10 bolt with 2.73's since it's an L03 700r4 car (you can check by running your rpo codes), so you'll just about be guaranteed to be getting a better gear ratio with a new rear end. Check the tech data section of this site.. it has information regarding what gears came in differently optioned cars.

 

I checked it out, but it looks like the speedo will be way off if I change gear ratios. The tech section talks about changing the speedo gears, but it doesn't say anything about how this is done. The lower ratio doesn't really appeal to me that much anyway... this car sees about 90% highway miles. What are RPO codes?

 

rpo codes are codes printed on a sheet that stand for every option on your car; for example, your car has a tbi 305, or an "LO3". Since your car is an 88, it should be in your center console compartment. Write those suckers down and type them into the rpo decoder in the tech section.

 

Except for the few cars that got the 9 bolt in the late 80's, GM installed the same 10 bolt in all the third gens no matter what engine was in the car. The only differences were gear ratios and if it had a posi or not. Some also had disk brakes and most were drum brakes.

Around 1986 they upgraded the ring gear size from 7-1/2 to 7-5/8" The larger ring gear still fits on the 7.5" carrier so we still call it a 7.5" diff.

In 1990 all the cars were upgraded from 26 spline axles to 28 spline. There may be a few late in the year 1989's with 28 spline.

Other than that, finding a 10 bolt in a 350 car is no different than finding a 10 bolt in a V6 car.