Eaton Posi Diff. pinion shaft lock screw torque

[Wayne M.]

This lock pin screw is 1/4" dia. with 20 threads/inch and is to be torqued to 20 ft.lbs [ie. 240 inch-lbs], per the 1966 Chassis Overhaul Manual. The hex head is 7/16". I'm afraid that it might shear at this high spec.

With the internal-tooth lock washer, it snugs into the case after 8_1/2 turns.

Referencing other 1/4_20 screws (from engine torque table) show 80 inch-lbs (oil pump cover; oil filter by-pass; timing chain cover); a little less for rocker arm cover (50-55).

Any thoughts, recommendations ? These puppies are hard to come by.

[Gary R.]

Re: Eaton Posi Diff. pinion shaft lock screw torque

Wayne,
You may very well shear the head off if you try to torque it to 20 ft/lb. I use a small 7/16 combo wrench to tighten the bolt but I do not use a TW on that bolt. I may add a drop of #242 loctite but the combo wrench works good, you will get it tight but it should be enough to over come it.

You may want to check the depth of the bolt through the shaft into the case. Many times the bolt is shallow and I have seen them break there at the bolt or even break out the side of the posi case. I set them up in a Bridgeport and mill the pad .100", chase the tapped hole and test fit the bolt. Just a little BP trick.
Be sure to check that case for cracks as well.

Gary

[Joe L.]

Re: Eaton Posi Diff. pinion shaft lock screw torque

This lock pin screw is 1/4" dia. with 20 threads/inch and is to be torqued to 20 ft.lbs [ie. 240 inch-lbs], per the 1966 Chassis Overhaul Manual. The hex head is 7/16". I'm afraid that it might shear at this high spec.

With the internal-tooth lock washer, it snugs into the case after 8_1/2 turns.

Referencing other 1/4_20 screws (from engine torque table) show 80 inch-lbs (oil pump cover; oil filter by-pass; timing chain cover); a little less for rocker arm cover (50-55).

Any thoughts, recommendations ? These puppies are hard to come by.

Wayne------


Yes, they are hard to come by and if you do find any be prepared to spend some bucks for them (unless you find someone that does not know what he has). They are GM discontinued and when they were last available they carried a GM list price of $28.04! They might be cheaper if you could still get them from Eaton.

By the way, the pinion shaft is still available and GM lists for $35.51, so the screw costs almost as much as the shaft!


DSCN2747.jpg

[Clem Z.]

Re: Eaton Posi Diff. pinion shaft lock screw torque

any good machine shop should be able to fabricate it if you can't buy one.

[Gary R.]

Re: Eaton Posi Diff. pinion shaft lock screw torque

I have some of the Eatons and they are ok. Some of the aftermarket ones have a plain head, I would not use them I had one shear off setting up a posi. I got out the screw but stick with the originals or the better aftermarket ones. They were over $20 the last I recall too.

[Glen C.]

Re: Eaton Posi Diff. pinion shaft lock screw torque

Glad I read this thread! Sorry for jumping in here. But, I'm in the process of changing out my diff & putting the BB yokes on the replacement. The bolt I removed is as described above with head markings F-C and 4 lines. Not a grade 5 or 8. what is it? Is this an original diff pinion lock bolt?

[Gary R.]

Re: Eaton Posi Diff. pinion shaft lock screw torque

That is an original bolt

[Glen C.]

Re: Eaton Posi Diff. pinion shaft lock screw torque

Thanks, Gary.

[Gary R.]

Re: Eaton Posi Diff. pinion shaft lock screw torque

Wayne
Here are some pictures of what I referenced above, the bolt through the case. I find this a lot and mill most of the cases I build. In fact I'm building a new case now and had to mill it.








Here is one I opened up and found the case broken out.

[Wayne M.]

Re: Eaton Posi Diff. pinion shaft lock screw torque

Wayne
Here are some pictures of what I referenced above, the bolt through the case. I find this a lot and mill most of the cases I build. In fact I'm building a new case now and had to mill it.
I opened (one) up and found the case broken out.

Gary -- great pics. I agree with the milling operation you perform. Checked a case of mine that I have on the bench, and to my surprise, the screw/pin only inserts 50 thou into the hole (on the right in my photo), finger tight with the internal tooth lock washer in place. The hole itself is 290 thou deep, so much contact insertion is wasted.

In the pic I show the pin just as it enters the hole at full diameter; you can see the 50 thou gap between the bolt head and the washer; translates into one turn to finger tight, or, if the washer is removed, 1.5 turns. Not a great design !

[Gary R.]

Re: Eaton Posi Diff. pinion shaft lock screw torque

Wayne I would address that case before you use it, 050 isn't much. This is pretty typical too, I'd say I have to mill most of them. Is that an square window case from '65-'68? If so I wouldn't even use it since they are very prone to cracking.