Differential Yoke

[Walter R.]

I have my 66 on frame stands and can see a seperation between the left side yoke seal and differential. The seal pulls out about 1/8". I wouldn't think this is normal and see no seperation on right side. Possibly missing side yoke "C" clip?

[Gene M.]

Re: Differential Yoke

Walter, right, the slop is a bit much. 1/32" or less is better. This has been covered previous on this site. Check the search for more.

[Dick W.]

Re: Differential Yoke

1/8" is not uncommon, but seal should be seated in the differential housing. If the clip comes off, all it does is allow the yoke to slide out, it will not pull the seal out.

[Gary R.]

Re: Differential Yoke

If indeed the side yoke seal is moving then you have a seal/bore issue. If you're referring to the yoke itself coming out .125 then as the others said that is too much and the snap ring is missing. Typically the snap ring groove is .180-.200 from the face of the yoke. Common endplay can be between 020-040". 050" is about where I would start to get concerned.

Now since many of these cars haven been worked on and changed over the years the question is do you still have the original '66 diff and yokes or were they changed? The reason I ask is because many of the 63 up to about 72 original yokes are in good shape 40 years later. I have seen some diff's of this era with over 100k miles and still have good yokes. Now the 73-79's are a different story, since they were not hardened running up against the cross shaft which is hardened wore them out.

Yoke endplay is caused by a few things,
1- worn side yoke faces
2- sloppy stock type posi build
3- enlongated posi case side holes

If you have the diff out of the car and on a stand then I would recommend you remove the rear cover and take a look. You will see where the problem is if you know where to look. Also look to see if you have the original '66 posi case with the postage stamp window, if so you should check it for cracks. Use some brake cleaner and spray small areas of the posi case, then apply light air pressure. If there is a crack there it will stay wet and then you have to address the posi. Replacement is the way to go, welding is not an option.

To help you I posted some pictures of a posi case and yokes, these are from a 66 in fact.

Yokes fit in posi case. NOTE this is a custom case yours will have springs and a rough casting.


Endplay in yoke



Yoke and ring


65-68 Eaton 1 st design case- very prone to cracking


Good luck, hope you don't find anything bad.