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True Trac into M80

losh1971

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Got a pic, you've got me here.

I'll be honest, I put in a new truetac center so I just pressed the new bearings straight onto it. I don't remember seeing any shims on the old LSD centre that came out.

We are talking about the M80 (or m75/76/78) here.
I would have Sunday night, but I sent the housing and centre to Adelaide for a rebuild just yesterday. The shims on the ZF fit on the outside of the carrier bearings, not underneath. The diff tech said make sure I send those as he will need them to set up the new centre.

I'm not sure they just set the centre in the right spot or if they add preload to the tapered bearings.
 

Jolls

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Nothing of substance and my research indicates that Dana don't mark them. Here is what I got.

The engraving reads 94 002 there is a T as 10 O'clock and a 6 at 3.
Dana 3.9 Pinion.jpg
 

Jolls

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I ratted through the diff box and found nothing but the bolts for the cover and the pinion yoke, which needs to be changed to a 4 bolt (VT I think) to match up with the solid centre drive shaft that came with the setup. The old pinion and centre were turfed by the pervious owner so I don't have a pinion shim to do the initial set up. I will ask a couple of questions at the local diff shop today and see what I come up with.

So the plan at this stage is to purchase a diff rebuild kit from the local shop along with some new crown wheel bolts and a second set of pinion bearings. I will oversize one set of pinion bearings using a dremmel and, based on the advice from the diff shop, do a first fit of the pinion and lap the crown wheel and pinion to get a feel for it and shim it from there to get the right pattern. Once I have that done I will replace the bearings with the unadulterated set and put her together from there.

It is so easy to type this in - not sure the practical application will be as smooth but what have we got to lose? This is probably a good DIY subject.

Cheers n Beers
Jolls
 

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My new 4.11 Spicer gear set is the same, no markings.

Does the diff housing still have the bearing cup fitted? If there is a shim it should be under there.

I would have Sunday night, but I sent the housing and centre to Adelaide for a rebuild just yesterday. The shims on the ZF fit on the outside of the carrier bearings, not underneath. The diff tech said make sure I send those as he will need them to set up the new centre.

I'm not sure they just set the centre in the right spot or if they add preload to the tapered bearings.

ZF is different to M80, different design so different bits inside. Not comparable in how they are set up.
 

Jolls

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My new 4.11 Spicer gear set is the same, no markings.

Does the diff housing still have the bearing cup fitted? If there is a shim it should be under there.



ZF is different to M80, different design so different bits inside. Not comparable in how they are set up.
No such luck.

I tried to get parts from the two local diff repairers and they weren't interested in supplying parts on the grounds that they get blamed if it all goes to poo. Wouldn't even sell me pinion shims. I rang around the spare parts places and they could provide shims but the smallest was 1mm and they went up from there.

I finally got onto a mob in SA, Autotranz and Diff Parts, they were very helpful and I purchased a diff rebuild kit and an M78/M80 pinion shim kit. Not sure what is in the pinion shim kit but I expect I will be able to get the job done with the components. What I don't use I will offer on here to those who may need them.

What I don't have now is the crown wheel bolts and a VT flange/yoke so I can match up the solid centre tailshaft. The search continues.
 
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Jolls

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The diff rebuild and pinion shim kit arrived today. Not exactly what I was expecting.

The rebuild kit does not contain the pinion crush spacer so I will need to find one of those first. The pinion shims do not match the bearing cup; however, they do match the bearing cone. This is the opposite of what is shown in the manual (and what I expected to receive).

Is there a problem with the shim being on the bearing cone side as opposed to the cup side? Theoretically it makes no difference - just not sure if the stress factors change.

It also stuffs up my preparation as I sourced a bearing cup and turned it down slightly so I could dummy it all up. I will now have to search for an old cone that I can oversize to get it to work.

One step forward at least.

I look forward to the wisdom of the experienced on this development. Taking it to a professional would be have certainly been easier. I am determined to get it done now that I have forked out the $ on parts.

Cheers n Beers
Jolls

Edit: Found the crush washer in the blister pack - it was inside the pinion seal. One less thing to find - what I did not pick up on initially is that the kit does not include the pinion flange nut. So still one more thing to find.
 
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Jolls

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The diff rebuild and pinion shim kit arrived today. Not exactly what I was expecting.

The rebuild kit does not contain the pinion crush spacer so I will need to find one of those first. The pinion shims do not match the bearing cup; however, they do match the bearing cone. This is the opposite of what is shown in the manual (and what I expected to receive).

Is there a problem with the shim being on the bearing cone side as opposed to the cup side? Theoretically it makes no difference - just not sure if the stress factors change.

It also stuffs up my preparation as I sourced a bearing cup and turned it down slightly so I could dummy it all up. I will now have to search for an old cone that I can oversize to get it to work.

One step forward at least.

I look forward to the wisdom of the experienced on this development. Taking it to a professional would be have certainly been easier. I am determined to get it done now that I have forked out the $ on parts.

Cheers n Beers
Jolls
Hi Team

Found a couple of vids on the interweb that talk about shims being applied to either side of the pinion bearing to achieve the correct depth. It does not appear to matter which side of the bearing they go as long as the end result is a pattern in the centre of the ring gear.

Cheers n Beers
Jolls
 

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I don't think it matters either, all the early Commodore diffs I've seen have the shim under the pinion bearing and as far as I'm aware they only changed to putting it under the pinion bearing cup for the M80 diffs. I don't know why they changed it. The only reason I can possibly for see is that it is a lot easier to R&R the cup in the housing rather than the R&R the bearing on the pinion. I don't know if it was my aftermarket gear set but the bearing seemed a lot tighter on the pinion when I pressed it on than when I removed the bearing from an old pinion to recover the shim.

Diff rebuild kits I have purchased here in NZ have had everything required except pinion bearing shims.
 

Immortality

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This should assist with the rebuild. It's to suit VT but should have all you need.

I'll move this thread to the transmission section too.
 

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  • sect-4b Final Drive and Drive Shafts.pdf
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Jolls

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This should assist with the rebuild. It's to suit VT but should have all you need.

I'll move this thread to the transmission section too.
Thanks.

I have the manual - that's where the confusion arose - the two different pictures. One showing four bolts and one showing six holes.

Cheers
Jolls
 
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