Rear diff - how to check off the car?

I am rebuilding an xj6 base for a project the car was taken apart 18 years ago - any thoughts as to how I can check the diff off the car before I reassemble (I don’t fancy taking it off again once the car is built up!) Many thanks.

What type diff is it?
Do you know it’s history?
Any signs of leakage?

Measuring overall backlash might be an indicator.
On an unknown diff I would definitely change all the seals and the output shaft bearings.
You should also check the crown and pinion gear mesh and backlash.

Considering the amount of work involved to take it out again I believe it’s a worthwhile investment.

It’s a 75 xj6 3.4, was as bout a 70k car it’s been drained and u fortunately that’s all I know😕

Definitely take it appart.
Good luck.

I would just check the backlash, and if no leaks from the pinion or drive shafts just box it up a fit to the car. You will find that once you have cleaned and rebuilt the rear end once, it is dead easy to remove it a second time if needed. I had to pull mine out after I had fitted it and driven the car for a couple of weeks. Turned out I had not correctly installed the hand brake mechanism. I had the whole rear end in and out within the day.

At the very least, take off the back cover. Inspect the gear teeth. Check to lube if any for metal particles. Feel the lash by turning the pinion. Is it limited slip? turns smooth or “notchy”.

My guess is that the worst thing if any will be a leaky seal or more.


Easy yes, but time consuming.
Besides having to remove the cage, remember that on assembly the diff is the first thing to be mounted on the IRS. So to get there everything else has to get disassembled, hubs, wishbones calliper brackets, safety wires, etc etc.
At 70K the output shaft seals are most probably cooked from the brakes and at the end of their life.
These seals are now 35 years old. And en plus it sat dry for 18 years… I see very minimum chances of success.

Unfortunately it’s been stored with the out put shafts removed so I’ve ordered a dial gauge and some engineers marker to check it over, the splines on the output are a bit rusty so i am hoping they will clean up!