Loose Jag IRS Diff Bolts(?)

Typically it is the bolts that hold the inner fulcrum brackets to the diff that get loose. There are shims between the bracket and the dif, and if a bolt is slightly loose, the shims creep out, leaving a gap and a very loose bolt.

This then throws a lot of extra stress on the bolts at the top of the diff, sometimes causing metal fatigue and cracking of the subframe around the top bolts.

If all 8 of the diff mounting bolts are tight, then your problem is elsewhere. Replacing the bolts is a waste of time, as they don't wear out. BTW, the classic symptom of a loose jaguar diff is rear-end steering if you suddenly accelerate or decelerate at speed.

Other things to look for are axial play on the diff output shafts (have just fixed one where this was caused by a manufacturing defect in the tab washer that locks the nut on the inner end of the output shaft. The tab broke off, allowing the nut to come undone, leaving the output shaft constrained only by the brake disk in the caliper).

A clunk when changing into reverse could also be caused by low oil level in the diff.

Check for loose U/Js (bolts and play in the joint).

Also (but less likely to cause a problem at idle) clunks can be caused by deteriorated subframe mounts or radius arm bushes.

For next time, you should really have got under the back of the car to check for movement of verythin before dismantling.

regards, Mike

Avian 'Flu ? :-)

Thanks very much Mike, your reply has been really helpful.

I was thrown a bit because the previous owner had said the oil level was topped up but I think that low oil level is most likely the problem

- as when manually rotating the input shaft it travels freely for about

45degrees before engaging which seems to tally with the clunk. Based on the amount of oil that I got on me when disconnecting the prop shaft I am thinking that the pinion oil seal is perhaps failing or would just disturbing it cause it to leak like this? Is it worth replacing the pinion oil seal anyway?

Any thoughts or suggestions greatly appreciated,

Jonathan

That seems rather excessive. I sould expect the backlash to be only a few degrees.

The pinion seal should not leak, but until some time in the mid 70s, the differential seals were made of leather not rubber, and the leather seals are inclined to leak if they are ever left to dry out, or disturbed. Sometimes the leather swells again, but sometimes it doesn't.

The pinion seal is not too difficult to change, but you MUST follow the correct procedure for torquing up the nut on the drive flange, or you will ruin the diff (assuming it is not ruined already). The problem is that normally when assembling the diff, you are compressing a crush spacer when torquing up the input flange, but if you are just replacing the seal, the spacer is already crushed.

The Jaguar service manual does give a procedure for re-torquing the pinion nut, but it involves measuring the torque required to turn the pinion through its backlash BEFORE loosening the nut, and this requires a torque screwdriver (a torque wrench for measuring very small loads).

There is another unapproved procedure for retorquing the input flange which just involves marking the nut before removal and then retightening it to EXACTLY the same place. I can't see anything wrong with this, but I tried it on my e-type, and the diff afterwards seemed to have a vibration at high speed, but I don't know if was related.

All in all, it is attractive to find a second hand diff without leaks.

BTW, unless you are sure that your diff has synthetic seals, you must not use synthetic oil in it, as this will destroy the leather seals. (maybe this has already happened).

Good luck! Mike

Hmmm, right well I guess I'll refill it with oil and see how it behaves (didn't have chance this weekend). If it fixes it I'll run it and see if there is oil depletion. If I fill it with oil and it still has the excess backlash, replacement diff time.... doh....!

B.t.w. as it's an '84 model I'll assume they're rubber seals.

Thanks very much for your help.

Jonathan.