Rear end differential work advise

I just lowered my rear end for brakes so I was looking to see what I’d done with it I’m happy I didn’t get sucked in years ago and installed the donuts stock

Now Dennis has got me thinking about that differential while it’s out
He suggested some preventative maintenance which I should have thought about
The parts are cheap and apparently available
The Jag manual lists a bunch of special tools :toolbox:
Change the three outer seals I don’t think I need anything for the drive but the pinion has something for installation
Who’s done the job any thing special ,tricks it looks easy

How about changing gear ratio … some buddies want to smack me
And a suggestion was to just add a gear oil with seal conditioner
There’s no right or wrong answers…risk management

I’m not looking for work after having worked on it everyday for months ,the whole front end has been off and on frames too, long long story

Now I drove the car 200 yards the other day for the first time in years
The fuel pump quit, expected after years in storage
The carbs started leaking what took so long ,stop laughing and I’m doing the rear brake cylinders now so my PTSD is rather pronounced
So what do you guys think

Some of what you ask (especially the diff ratio) depends on how you expect to use the car.

There is nothing inherently wrong with the 3.54 ratio though if a lot of long-distance driving is in your future something taller (like a 3.07) might be appreciated.

Lots of future miles also makes the case for preventive maintenance but going down that rabbit hole will take some time.

I did the brakes and stopped there. Then two years later dropped it again to change the diff ratio then 6 years later had to do the bearings on one side (though that does not require an IRS drop). But I got in a lot of driving between those intervals.

1 Like

I’m kinda taking a similar approach. I dropped the IRS primarily for the rear brakes. In the process I’ve cleaned and painted/powder-coated most of the IRS items. New shocks. Replacing the inner fulcrum bearings and races (the ones in there were shot). The inner and outer u-joints felt good and purged grease well, so I just cleaned and greased them. The rear hubs and outer fulcrums felt ok, so I’m going to assume they are for now - I just cleaned things up, including the driveshafts (no paint or powdercoat). I’ve cleaned the diff inside-and-out and I’m going to assume the seals are good for now. That’s probably a bad assumption but I want to drive it with the 3.54 that’re in there and see if I like them, rather than reseal/rebuild it now just to do it again if I want to change.

While my approach has wandered, I’m kinda trying to walk the line of “make it good enough” and “make it great”. I just want to drive it a little bit. I’ve got the rest of my life to spend “making it great”.

And the good news is that the 2nd time you remove the IRS the job goes faster.

Haven’t done it the 3rd time yet, but expect that to be really quick.


Actually the third time it’s done before you do it! 😵‍💫

1 Like

Now, I could’ve sworn I responded to this post, but for the life of me I can’t find it.
gear ratio? that all depends on the gearbox, and how you feel about the cars drivability. 2.81 on the '83 and onward Xj’s is a bit too tall especially for the limp wristed Federal Jags. Non of which is probably applicable to your situation. 3.07 with a manual gearbox I would think it would make for a quick shift from 1st to 2nd. 3.54 is perfect for an auto gearbox.
but it’s really up to you and how you drive; and how you like the way the car performs.

I’m gonna look for that post - I may have posted on the wrong thread… idk…


2.88 may be a little high for the 1800kg XJ but 3.54 is way low with the auto - maybe okay with the overdrive - the E is much lighter so it will take a lower ratio. The 3.54 is too low! (Unless you live in a little village in Switzerland).

Actually, most autoboxes use a high rear end ratio, due to the torque multiplication action of the torque converter.

1 Like

Thks for the reply’s guys keep them coming
I remember years ago driving my car thinking :thinking: that it needed a overdrive on the highway. Latter I worked with a fellow who lived in Germany in the sixties-seventies he returned to Canada with an e type and he told me that they wouldn’t allow him to import a car with the high speed gear ratios in.
I always thought it was marketing to compete with corvettes etc.
Interesting to hear from people familiar with the changes

So I dumped this out of my car and found the diff tags with these numbers
Housing has A 66
One tag has the gear ratio
And a second tag. 8P-L
Anyone know what they refer too

A buddy came by couldn’t believe I was just working on the brakes

Thks to all who have responded to my plethora of questions
Cheers Jim

The ratio is usually expressed as a fraction, e.g. a 3.54:1 is shown as:

I think the number is stamped into the case and may also indicate whether a crush washer ‘C’ or shims were used:

The PL would refer to Power-Lock (LSD).

Here is someone’s pumpkin (not mine) that show all three:

Frankly, for all but a pad change, I found it easier and far less stress to just drop the IRS.

1 Like

Look a little closer and I think maybe you’ll find that the “8” is a “B”. I’ve dubbed “BP-L” to mean British Power-Lock. I don’t know if I read that somewhere, or if I made it up! :rofl:

Ya in the manual they call it a Thornton Power -Lok 8 was my best guess B makes more sense I’ll go with that
The tag for the gears shows 13 that’s the pinion
And 54 that’s the crown which is 3.54/1
I see you can just change the crown gear and get 3:31. Cheers. Jim

I have never heard that before. Generally it is accepted that crown and pinion are a matched set and are installed as such.

That could be the factory manual just shows the same pinion 13 with two different crowns
of course the guy selling parts would tell you that
They’d be matched soon enough
Cheers jim

You are correct John. Matched set.

I found the source of my information. Looks like I read it on JL -

The Crown Wheel and Pinion gears are lapped together to form a matched set. After running unmatched gears in a differential for a year of Sundays, they still wouldn’t be matched, unless by a fluke of nature, they just happened to be to be a good match after random selection.


Maybe he meant, “they’d be machined soon enough,” into rotary razor blades…:stuck_out_tongue_closed_eyes: