Pictorial - Rear end rebuild Part 3 - Pinion seal replacement.

[WGB]

This relatively simple procedure is fraught with problems as it involves potentially moving the pinion position and causing my nice quiet diff to become a howler.

I would have preferred to leave well alone but as it had a weep it could not be ignored.

The manual calls for initial measurement of pinion bearing preload followed by replacement of the pinion nut with a newer type of nut but I have stuck with the original old nut for a number of reasons which I will attempt to explain.

Here is a view of the slotted pinion nut with it's locking point peened into an eccentric in the shaft. You will notice there is another unused eccentric on the opposite side of the pinion shaft with a pristine piece of nut adjacent to it.



Here is a picture of the socket required for this style of slotted nut.



I cobbled up a pinion pre-load measuring device using a 1/4 inch torque wrench but essentially the preload was zero so it was not a lot of use.



On advice from Koan that the nut should be replaced back in it's initial position and advice from S class that there are two locking points I decided to re-use the old nut and use the old locking point as a marker and the opposite side of the shaft to actually lock it.

The nut must first be loosened and to do this the pinion must be locked from turning. The manual calls for another special tool  but I am very over special tools and a large phillips head screwdriver inserted through one hole in the flange will lock it quite successfully. This photo shows the screwdriver in position for tightening the pinion nut - opposite side is used to unscrew it obviously.



Once the pinion nut is unscrewed and removed the yoke can then be tapped gently from behind to remove it from it's splines and then the seal is exposed. This must then be prised out with a screwdriver and a new seal is lubricated and tapped into position.

Here is a picture of the old seal before removal.



Because I was re-using the old nut it was easy to return it to it's original position but the torque required to get there was very low so I torqued it to the recommended 180Nm and here is a picture of the final position showing the nut has been turned 3 or 4 mm further than  it's original position.



I could find no perceptible change in pre-load torque on turning the pinion so now we will have to wait and see what it sounds like.

Bill

[TJ 450]

So, if I read correctly, there was no preload anymore.

I'm pretty sure that there's a special crush washer that needs to be replaced to reset the preload. No doubt you have read up on this though.

Anyhow, fingers crossed you will still have a quiet diff... worst case, you would be able to rectify that in-situ anyway.

Tim

[WGB]

I am sure it must have more preload now than before but time will tell and I will get the Star Shop to do it again if I am not happy with it.

Bill

[oscar]

Very interesting WGB.
Just wondering, I'm a novice with diffs, but by tightening that nut 3-4mm further than it was, wouldn't the pinion be pulled away from the ring gear?  Wouldn't it be better to wind the nut back to the original position?

[TJ 450]

Correct, and it would mean that the teeth are going to mesh with less clearance (more preload). However, this may not be a problem, and it might be better than a pinion that is left to decide where it wants to be, which would be the case if the nut was loose.

The latter issue pertains to the diff in my 6.9, and it can be quite noisy.

Only time will deliver the verdict.

Tim

[koan]

The engagement of crown wheel and pinion is set by two things, shims under the side bearing caps and a selected thickness "compensating" washer on the pinion shaft, don't believe the pinion bearing preload is relevant to meshing of gears and noise.

Think what you've done WGB should be OK, the preload on used pinion bearings is 50-100 Ncm, not much at all, so taking up the slack plus a bit more is probably about right.

Would have been good to fit a new crush sleeve and get the rotational torque correct but that involves removing the diff centre section, all too hard.

koan 

[WGB]

Thanks for the words of encouragement Koan.

If a new nut had been used it's exact final position would not have been known except by the preload torque anyway.

Bill