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Differential COMPLETED!!

JCGT

JCGT

New member
I finally was able to finish my differential install tonight. I had to put it off for a few days because of the snow we recently had in NJ. Taking that break was probably the best thing I could have done. Everything literally FELL into place tonight. I spent the last few days pretty much strategizing and trying to figure out what was wrong. I have to thank David Norris again because his writeup helped me in the end. MAKE SURE YOU HAVE THE OUTPUT SHAFT IN CORRECTLY. I had the wrong splines on the wrong sides which was not allowing my differential to seat completely. Needless to say, I pulled it apart and had everything back in and the wheel on in two hours. I could probably complete the job again in about 3 hours if I had to. Most of the time was spent disassembling it for the first time and figuring out which angles to use to approach things. It's not that bad of a job at all with the trans in the car, and I didn't lower the cradle at all. Just follow Dave's writeup step by step and you'll be fine.

It's very important to hold the driver side axle from underneath as you're tapping the differential into place. It'll be hard to get it to lock otherwise, as the CV will act like a spring. It's so cool to have completed this in the driveway, I'm too used to having the conveniences of a shop and forklifts. All I needed were 13mm, 15mm, 22mm, and a 36mm socket for the axle nut. It's not that hard of a job at all. THANK GOD IT'S OVER, I'm becoming all too familiar with the internals of my transmission.

Much love for all you GP guys and Trannyman95.

** On a separate note, if your differential housing literally doesn't slip right into place, something is wrong internally. Initially I had a 1/4 inch gap between the diff housing and the trans. As I mentioned above, the output shaft was in the wrong way. OOOPS. DO NOT TIGHTEN DOWN the housing unless it is seated flush against the transmission!!! **
 
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Just got back from the test drive, everything is smooth as silk. Just in time for opening day of race season too! March 8th is when us Jersey GM guys are heading down to Atco Raceway to see how all the off season modding worked out. I put my GT2 cam in back in November and haven't had a chance to run it and see the new numbers. Thanks to this new differential, I'll be in good shape for a new personal best.

** Just so you know, no more one wheel burnouts for me. **

Completion!:
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I'm a newcomer to the grandprix owner world, and I see you guys speaking of this hd diff a lot. What is this heavy duty diff you are reffering to? Does it change the final drive gear ratio?
 
The HD stands for Heavy Duty and was used in the supercharged cars. Basically the only differences where a larger more durable torque converter and a larger differential to withstand the extra power and handle more stressful driving conditions. The HD diffs came in a 3.29 ratio and will interchange with a non-HD differential by changing a few other parts to make it work. Most of the gear changes in these transmissions are made by means of a different drive and driven chain sprocket arrangement. The stock HD transmissions, except the Comp G performance package, all had a 2.93 overall ratio and this was accomplished with a 37 drive and 33 driven sprocket setup with a 3.29 final drive/ differential. 37/33 = 1.121 x 3.29 = 2.93 . The GT or most all NA non-HD 3800 had a 35/35 setup which = 1.00 x 3.29 giving you a 3.29 overall ratio. I hope this helps you out and answers your question about the differences. There are other ratios available but are non HD final drives and the 3.29 is the most common
 
I've never attempted to mess with the gear ratios, because I always thought it would set a code. Is it possible to change the diff ratio and the drive sprocket driven sprocket to obtaitn a higher overall gear ratio without setting a gear ratio error code?
 


No changes can be made to the ratios without tuning or using aftermarket reluctor wheels and a speedo recalibrator or you will set an incorrect gear ratio code and make the trans work horrible and can cause damage.
 
They are a larger diameter, have larger spider gears and cross shaft, and the diff carrier itself has a lot more meet on it. Here is a link to my parts page of my website and there is a pic of a non HD and a HD diff so you can see the difference.
4T65E Parts
 
I see, so it is just a strenghtend housing then? On a stock supercharged grand prix should you worry about the diff, or is it okay to use the original diff if it's in good shape?
 
The original diff in a supercharged car is an HD diff, there is really nothing better out there unless you look into the aftermarket and those options often caues more problems than they are worth. The HD diffs do still fail but do handle a bit more abuse than the standard non HD diff will.
 


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