HD Diff???

[05grndprix]

Ok i have a 05 base model grand prix and i got a HD Diff from what i think was a 99 or so SSEI i cant remember the year but it is the 4T65... should i have any problems putting this in is anything diffrent between them except the strength


looked threw the whole fourm found nothin really on HD diffs

[05grndprix]

oh and if it dont work oh well i got it off a friend for like nothing lol

[Trannyman95]

The HD diff will require a matching output shaft, diff cover, outer shim and bearing, and passanger side axle from a supercharged car.

[05grndprix]

ok not that bad i figured everything you said and priced it except...but the output shaft... are they exspensive?

[Sabrewings]

What is your current final drive ratio, do you know? Going to an HD diff will give you 3.29 final drive. If you don't already have 3.29 then you will need to have your PCM adjusted for the gear change.

[05grndprix]

yea i donno i dont think its different if it changed that would probably mean the ring gear is different and i know thats not different but i could be wrong

[Scimmia]

I believe all 3800 GPs used a 3.29 diff. I could be wrong there, but the ring gear is the same on all of the different ratios, so that doesn't tell you anything. You have to count the teeth on the sun gear, but I don't have the numbers in front of me.

[Sabrewings]

yea i donno i dont think its different if it changed that would probably mean the ring gear is different and i know thats not different but i could be wrong

Ring gear is the same in all 4T65Es, and there are three possible differential ratios from GM. Just because it didn't change doesn't mean the ratio didn't change. What does change the ratio is the size of the sun gear and likewise the size of the planetaries.

May want to make sure before you go slapping it in.

I believe all 3800 GPs used a 3.29 diff.

Up to 03, I'm pretty sure that's the case. But 04+ I don't have any info on, so that's why I figured he should check it out.

[Scimmia]

Sun gear info:

42 Teeth = 2.86 Ratio
38 Teeth = 3.05 Ratio
34 Teeth = 3.29 Ratio

[05grndprix]

ok did a little bit of research and i cant find a 05 grand prix but i did find 04 and its a 3.29 diff ratio

http://home.att.net/~subzero350/2004_4T65-E.pdf

and the HD diff is from a 99 bonneville ssei which seems if im reading right is also 3.29

http://home.att.net/~subzero350/1999_4T65-E.pdf

[Scimmia]

ok did a little bit of research and i cant find a 05 grand prix but i did find 04 and its a 3.29 diff ratio

http://home.att.net/~subzero350/2004_4T65-E.pdf

That chart is from the ATSG manual, I checked that last night. Notice that it does list 4LBB as going into a 3800 Pontiac W Body, with a 3.05 diff. Makes it tough to say just what you've got.