Mystery Differential oil leak Finally resolved !

[44DHR]

I have had a mystery oil leak from my rear differential and now finally found it. I did a previous post back in 2017, when I failed to admit it was actually on my car - and it turns out now that my hunch in my first comment was actually correct.

http://forum.etypeuk.com/viewtopic.php? ... 942#p89942

I have been working on Jaguar 4HA Powr-Lok differentials for over 40 years - from my Hot Rod and Custom days - to working on many E-Type differentials, both building up the Powr-Loks to fitting XJS 2.88:1 diffs into E-Types, where I had to fit and shim the corresponding E-Type Inner fulcrum mounting brackets to the axle mounting cage. I have been embarrassed to say I have had a minor drip from my Diff for many years and despite taking out the back axle in 2013 to replace the Pinion oil seal and again in 2016 to fit a new rear cover, I still had the odd drip from below the tie plate on the nearside.

I resigned myself to it coming from the nearside output drive shaft oil seal leaking out through the “special” holes in the bearing housings - as detailed in the previous posting above - with oil tracking down the Diff casing, avoiding the discs, then dropping onto the tie plate and then from the plate onto the garage floor. Having ordered my required parts - I decided that I might as well do both sides and replace the bearings if the axle is coming out again - the oil seals, O rings, bearings - and perhaps the very last 11108 tab washer sourced as NOS from a California garage, I was ready to begin as a Lockdown project to keep me busy.

I dropped the axle out and left the oil inside the Diff. On removing the brakes and discs - no oil leak under the bearing housings. It turns out that my Diff is the earlier type without the additional holes to permit oil to pass out the casing after going past the oil seals. So where was the oil coming from - the tapped thread into the axle casing to secure the Inner fulcrum mounting brackets ! There was adjusting shim between the casing and the bracket with the bolt being securely tightened, yet the oil had still slowly seeped out. Most peculiar and I have never seen this before.

Perhaps of use to know of this potential oil passageway and apply a sealant to the threads when fitting these mounting bolts !











Stay Safe !
Cheers,
Dave

[mgcjag]

Hi Dave.....nice find...just a tad too late...iv recently refitted 2 leaky diffs......if id known about this potential leak area i would have sealed them ..will find out on a run after lockdown......i wonder if all the mount holes go right through....i have an emply body will check it tomorrow. ....Steve

[44DHR]

Steve,
That would be most interesting to see if with an empty case if the threads do just punch through - even if it is just a small amount of the drilling. It’s hard to see that area with the Crownwheel in place over the leaky mounting area.
Interestingly, my Diff is presently full of oil, just I’m leaving it to see how much drips out overnight. I wouldn’t normally have seen this as when I build up the diffs, the casing would be empty of oil and I fill them with oil once the whole back axle is assembled ready to go back into the car.
I will empty the Diff later on to flush the case out and see if I can get any lighter weight fluid to flush out the thread.
Cheers,
Dave

[abowie]

You have to wonder whether variations in castings and machining sometimes allow this hole to accidentally penetrate the casing.

You could imagine that if the raw casting isn't loaded into the mill exactly centred more material could be removed from one side rather than another resulting in a thinner wall.

I can't imagine that it's beneficial.

[mgcjag]

Hi Dave....just looked at at my spare diff case....its from a later S2.......there looks to me only one threaded mount hole that if drilled too deep could go through into the oil chamber and thats the front left....mine are ok....i think from looking yours is also front left........front right is a moulded boss lower i think than the chamber and the 2 rear are more on the rear flange......well spotted and a great find.....Steve