View Full Version : Rebuilding rear.

03-10-13, 05:13 PM
Does anyone have any info on replacing all of the seals and internals of our Getrag 645 rears? I just pulled my and would like to rebuild it myself rather than have someone do it.

03-10-13, 07:23 PM
The attachments are all I have on it. The full Service Manual (available from Helm, Inc.) has several pages on the removal, inspection, installation, and clearance adjustments for the internal components. Before getting too deep into the project I would find a good GM parts person and check for the availabilty of the various internal components. The online GM Parts suppliers do not list internal components for the differential and most dealers reportedly do not rebuild these units so I am unable to verify that parts (other than the ring and pinion gears which are shared with other models) are available.

03-11-13, 10:40 AM
I had mused about doing this at one time and even started a thread on it. But, from what darkman says about the possible inavailability of parts it might be mission impossible.

If you do decide to take it on, take lots of pics and record your sources with links and by posting that all up here you'll be a hero to many.

03-11-13, 11:46 AM
I might just end up replacing it with a newer diff. How can I tell what generation different riffs are?

03-11-13, 12:15 PM
I think the latest Generation 4 differential is part number 25873498.

03-11-13, 12:32 PM
There is also a thread on here you can search for that shows pics from the back of all 4 diffs. Each diff has a different back casing design (fins differ). IIRC, the serial number is on the top of the diff, making it impossible to get the number unless you take it out of the car.

03-11-13, 01:29 PM
I think I will just open her up myself. Check all the tolerances, bearing things of that nature then put it back together will all new seals. I never had any problems with it other than the drivers axle seal leaking. I would convert it to an 8.8 but I don't have money for it now. I don't think it's that hard of a job to pull the rear.