7/13/23

On the bench this week is a 63 differential that came to me in various pieces. Since this is going into a very nice FI SWC, it will not have a drain plug fit.



A core diff was shipped as well and it has a cracked posi case. The original 63 posi is a DANA and they were bad, the gears were also bad.



This will get a 411 thick US Gear set, new Eaton posi, used 10-17x17’s, solid steels, ARP RG bolts, full polish and tune. The axles will be thru hardened and cryo treated GM-non rebuilt, not new imported, but quality solid axles fit to 005-007” endplay. The result will be an original appearing diff that is much stouter than the DANA ever was.



The first thing I did was pull the new posi out of the box and check the axles in it. I wanted to see where the endplay was in this stock built unit. I knew where the axle face wear was so I should have seen about 015- 020” endplay. That is not good and I don’t consider even close to where it should be as stated above, but in the 015-020 range I know I can get dialed in. What I found in both is 045-050” which is lousy.



Next, I took the new Eaton apart for inspection. With the spring pack out, I could move the side gears 030”- lousy. That didn’t bother me because I am going to use new internals and not the new fiber clutches.



I started to blend the bare housing and found a good size casting hole in it. Looked like someone spotted it with a ¼” drill bit. This case was then reassembled and shipped back to Summit for a replacement.



So, if you just bought a new posi, doesn’t matter what brand, you might want to check it close. If you paid someone to rebuild your diff or you bought an exchange diff with a new posi case, good luck.



The pin hole is not common, the sloppy setup I have seen plenty of times. Once assembled it will work, smudging away the clutches at every turn. The oil will be black in 100 miles.

 

So much for buying USA over Chinese 'junk' I guess. Pathetic that QA is so poor anymore.

 

Eaton and Yukon posi are imported.
The Eaton cases are Chinese cast and machined and the machine work as been better than original GM/Eaton- cnc's make the difference. The new Eaton spiders are USA made and not bad but I will use original 10-17's. The clutches, fiber, no way. No spring pack. They are assembled in Mexico and this case should have been rejected.

 

It is a shame that so many manufacturers of so many goods would rather replace a few bad parts under warranty rather than just have good quality control in the first place.
The warranty replacement costs on replacing a few units are less than cranking up the QC on all the units.
That's the business school model, optimize the money.
But it ignores the effect on customer goodwill and brand reputation.
It is just too bad the almighty dollar rules so many decisions.

 

New case opened, checked, polished and tuned. No lash, no endplay, no binding, requires grinding shims to size and correct knowledge on how to do it. Action is smooth and quiet. Balanced between the sides.
Note.
I did not invent this procedure, it has been around for 60 years or more. Done correctly it works better than a spring pack setup. Done incorrectly and it will act like an open diff or bind and break the spiders.

 

For countless hours now I've been stalking your posts and rebuild posts from those members you have helped. Thank you again for the succinct and extremely helpful write-up.

 

Thank you, hope I was able to answer your questions. That posi is in the completed diff and on the way to the car now.