Samps, I know this doesn't apply to your situation, but another option for those looking for a similar result, swap in a 12A or a 13B trans from an FB. You'll probably trip over a 100 of them in a junkyard before you find a GTUs diff. Cheap too. With a 5th gear of between .807 - .825 depending on year, and the stock 4.10 rear of a 5 spd FC, you'll get around 3800 rpm @ 80 mph. 1st equates to around a 4.30 diff, 2nd to a 4.50, 3rd to a 4.30, but 4th is still 4.10.

Curtis
'86 GXL autox'r

 

Would that be a simple bolt in? If so, then that is deffinitely a worth while option.

I wonder why some manufacturers choose to vary ring and pinions and some change tranny ratios? There must be pros and cons of either one.

 

so if you get smaller rear wheels say like 14in on a TII diff you'd prolly be running close to a 4.30 right?

 

Wheel diameters will due basicall the same thing. Only problem is calibration. You will need to figure out the rolling distance difference and either live with a wrong speedo or have it calibrated. I for one, will not drive a car that I do not know how fast it is moving.

 

akageals,

When you installed the bushings into the rear control arms, did you pull out the steel sleeves? The reason I ask is because I installed poly bushings about 5 years ago. I worked all night trying to get the rear bushings in. I could force them in but then they would pop out.
I called energy suspension and turns out their directions and diagrams left out the instructions for removing the sleeves that are left in the control arms once your get the old bushings out. I went back to my shop and pulled out the sleeves, and "thank the Lord" the new poly bushings actually fit!! It was a good snug fit not too tight.
If you did not remove these sleeves your bushings may not operate properly. they may feel ok, but they will wear out very quickly being that they are in a constant bind. Just a thought.
Also anyone else thinking of doing this job, its not too bad. I completely swapped my gxl suspension with all turbo suspension and added the bushings in only a couple of days.

 

Yes, I forgot to remove those sleeves at first. After watching the bushing pop back out about 20 times I re-read the directions. The directions do say to remove the sleeves but they do not use that terminology. I forget what it says, but it is mentioned.

 

I just ment for drag racing.....