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final drive gear swap

R

rbob900

New member
I have a 99 Pontiac Grand Prix GT n/a that is starting to have slight transmission issues. I talked to my local transmission mechanic (who is the only transmission mechanic I will have work on my car) about the issues and a possible rebuild but with a change in the final drive ratio from the 3.29 to the 3.05. He wasn't sure if it was possible and what, if any, computer issues that might cause. I guess what I am wondering is if it can be done and what all it involves. Anyone with any idea?
 
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Final drive? You mean changing your differential and you only have 3.29 gears if you have a comp G or GXP
 
I thought the 97-03 GP GT's had 3.29 gears, while the GTP has 2.93?

If you change the gear ratio you would have to tune for it I would think or it would confuse the PCM and cause strange shift points and whatnot.
 
You'd definitely need a tune but no only the comp G and GXP came with 3.29 gears all other cars came with 2.93 and trim level (SE, GT, GTP)
 




The link is to 4T60, 98+ all had a 4T65. Gear ratio's were close, not exact.

asite: I dunno what goofy thing or factory ordered car your Grammy had, 2.93 was only used in SC cars, on any GM 3800 platform from 97 up.

GT would be 3.29
Regal could be found as a 3.05
Bonneville, Park Ave, Riviera, LeSabre etc could be found as 3.05 in an NA version. Most of them could also be found as a 2.86 (or was is 2.85).

I've seen swaps where it didn't confuse the pcm. If you found issues/TCC lockup acting funny then you could reprogram. Or reprogram from the start. IMO you need to reprogram because your shifts will happen too soon based on the 3.29 points. So the 3.05 is likely to be boggy.
 
You have to click on the 4t65e once you get into the link. 4t60 isn't a whole lot different then the 4t65 which is why they are combined into one page.
 
No problem. Only thing about that page is its showing the gxp with the 2.93 and everyone else is saying it is a 3.29. The comp g is listed with the 3.29 though.
 


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