ZR1 Dana44 Diff rebuild

Sun 07 Feb 10 16:14

Re: ZR1 Dana44 Diff rebuild

theo how much play is acceptable(in and out)in the side yolks in 71 cast iron diff.thanx chris

--------------------
i just cant wait to get on the road again

Sun 07 Feb 10 16:28

Re: ZR1 Dana44 Diff rebuild

Hey Chris,


Well, to my knowledge GM never actually published a spec for that play. BUT, in a newly (and correctly) set up posi unit with new yokes it should be pretty minimal, like a few thou. You would maybe just be able to "feel" it. Many vettes survive with more than that, but you must bear in mind that
1) The side yoke is a suspension member in the vette IRS system, so if it wears too much here you will end up with excessive wheel camber, so much so that it can't be adjusted back with the normal travel of the camber rods, and

2) If they wear down too far, the yoke's seal guard will machine itself into the diff casing!

Cheers

Sun 07 Feb 10 17:33

Re: ZR1 Dana44 Diff rebuild

ive more than a few thou,would excessive play result in leaks,diff doesnt leak .cant the play be shimmed out chris

--------------------
i just cant wait to get on the road again

Sun 07 Feb 10 18:40

Re: ZR1 Dana44 Diff rebuild

Nice job Theo, The more I see those diff's the less I like them, but I'm an old school c2 & C3 guy.

I'm rebuilding a 69 BB diff now and reusing the same gears. The pattern on them was pretty good, Full equal drive and equal coat center to toe. I ran with the same pinion shim and lash as they had before, 032 & 010-012.

Keep them running over there!

Note on the C2 & C3 side yoke endplay. Many of the rebuilders over here push the jobs out fast and cheap to make a buck. They endplay on those types of jobs can be from 020-.120" - all bad. One vendor told a customer that the 120 endplay he had in his new rebuilt c3 diff was normal. That is true in the sense the rebuilder does lousy work! The endplay should be set to 005-009" At least that's where I set mine to. If the posi is correctly setup then using the origninal or rebuilt yokes usually requires grinding to fit. The spec for checking the yokes is .180-.190 from the face to the snap ring. Sorry for the long answer, didn't mean to move beyond this thread. You can find more info on the c3 forum or pm and I'll be glad to help.

--------------------
Gary R
69 'Vert 350 4 spd 373's
72 Coupe 350 TH400 336
75 Coupe 350(400hp)4 spd 373 12bolt,3.5" shafts, 31 spline outer axles.
Building vettes the past 30 years!!!!!

Sun 07 Feb 10 20:40

Re: ZR1 Dana44 Diff rebuild

v8vette wrote (View Post):ive more than a few thou,would excessive play result in leaks,diff doesnt leak .cant the play be shimmed out chris

Leaks are possible, specially if the yoke's stone guards start grinding into the casing and/or seals. But if yours isn't leaking now.. well, that's obviously not a problem yet, which is a good thing.


The play can't really be shimmed out as it happens as a result of the stub axles' inner tips wearing away, and you can't "shim back" the worn out material!

Gary's pretty much summed it up in his answer too.

If it wears excessively, the circlip can drop off the end of the yoke into the diff and then in theory there's nothing stopping the yoke popping out of the diff. I say "in theory" because in reality the rest of the suspension arms should prevent it, but with the car up on a ramp and the weight off the back wheels, you would be able to grab hold of the wheel and pull it in an out a cm or two - so any MOT man worth his salt would fail it. How much play have you got in yours?

Gary, you've got it easy mate, the old shim AND the old B/L measurement - luxury!

And don't apologise for "moving beyond the thread" - it's all about rebuilding diffs and your comments answer Chris' question too!

Mon 08 Feb 10 14:36

Re: ZR1 Dana44 Diff rebuild

theo thanx for the info.measured the end play about 3mm on one side and 2mm on the other.when i bought the car some years ago the diff was low on oil so that would explain a lot of the wear.no play at the yolk at the front of the diff but there is a bit of backlash in the diff.is it possible to replace the side yolks with new/reconditioned yolks without stripping the whole unit or should i bite the bullet and rebuild the lot.what is a full rebuild likley to cost chris

--------------------
i just cant wait to get on the road again

Mon 08 Feb 10 19:57

Re: ZR1 Dana44 Diff rebuild

Hi Chris,

Yes you can replace the yokes without tearing the diff down majorly - you only need to have the back cover off. But this does require it to be out of the car.

As long as you didn't find any other problems when you had it apart, that would definitely improve your play. If the Posi clutches are worn then even new yokes would not completely get rid of it, but would certainly improve it.


I've dropped you a pm with some more info about rebuilding.


Cheers

Wed 10 Feb 10 08:57

Theo - great post - and good to hear some of the other comments on here.

Since I'm taking notes (and scaring myself about a diff rebuild)

If you have the shims, should fitting new bearings and using the old shims, then checking the tooth contact a la the method shown, have a high likelihood of success?

My diff stopped locking up a few years ago (probably doing too many takeoffs from T-junctions in the way you do/did in Melton Mowbray with your '80!), I'm guessing posi wear is the culprit (I have heard replacing the old oil with new, and of course the GM slipper additive does sort some out) - what's the damage on a new set of clutches? Are these a pain to fit?

Hope you're keeping well. I take it when you referred to your 'village' you no longer live in Nottingham, where of course a killing spree would be seen as regular everyday behaviour...

--------------------
1986 Corvette Z51 Coupe
1990 Japanese thingy

Fri 12 Feb 10 17:27

Re: ZR1 Dana44 Diff rebuild

Hi mate,

Using the old shims when re-fitting the old ring gear should get you pretty damn close, or even bang-on. However, be aware that IF there is any variation in the lengths of the new bearings as compared to the old (and there can be) then this method may not get you back to exactly where you were. It's unlikely to be miles out but it would certainly be wise to compare lengths of old vs new bearings just to make sure - although this might be tricky without the sort of tool I made up and showed above, that will reliably give you a measurement of the SEATED bearing, accurate to the 0.001".
I'm sure you could come up with something though.

Basically, as long as you measure the pinion depth (this doesn't have to be the "actual" depth, just a reference distance from a repeatable location) and the backlash in various places, and also take a good pattern on coast and drive, you've always got a fixed point to come back to.

The thing that makes these diffs tricky(er) is the fact that the carrier bearings are pressed on AFTER the adjustment shims. On the older units you can swap and change carrier shims as much as you like to get it right.



Regarding the posi, you need special tools to get this apart. A quick look at Zip corvette's site brings up the price of about $95. Not too bad:
Posi clutches

Gimme a shout if you need assistance with the tools...

Cheers