changing rear diff. fluid
 

Took my recently required 2004 xk8r convertible to my local garagetell me 7hours labor to drop unitl to my LOCAL garage for rear diff fluid change ,they tell me 7 hours labor y drop the unit or drill a hole in the trunk to access plug. Can someone who knows better please advice. Thank you=Ed

Hi edwood
Sorry to be a profit of doom but I tried and failed to change the diff oil in my XK8. I found access from underneath to be just about impossible although I was lying on my back. No doubt it's easier if you have a garage type ramp. Next I drilled a 2" hole in the trunk using measurements from one of the forums. Even with the suspension tie bars removed access is very difficult. Then you have to suck out the old oil with a syringe and I'm not sure how much you would get out so I talked myself out of the job.
I made a removable plate to blank off the hole I had made while mutilating my spare wheel well and decided to leave it till one of the seals leaks and the unit has to come out.
It's one of those things that I think about every now and then and convince myself that I gave up too easily. Out come the Jacks axle stands and crawling board and I get underneath and after a few minutes say "Naaa"

Hope you have more luck than I did and I'll watch this post with interest.
Cheers
Pete

I cut a piece of 1/2"sq stock which will slide in while holding a 15mm ( I think) ratchet wrench in place. The hard part is breaking the plug loose with so little space.

Bad access for the convertible
 

There are a few previous threads on this subject, if you use the search function. Do-able from underneath, if you have the hard top model, but access is much worst if you have the convertible. Some members have done it though DIY. Seemed very fiddly though.

Drilling a a hole in the front wall of the trunk for access is actually a Youtube video. Hole is hidden and can be covered but it’s next to the high power bus panel. Even covered I’m not sure I want this potential problem.

Someone else even drilled a hole in the bottom of the diff unit and fitted a threaded plug. Diff Grease is really thick and usual pumps won’t be up to it.

Unless you actually have other work on the rear, dropping the actual subframe, for this one job, seems overkill.

Do you actually have a problem? Bad whine? Are you paying a garage for the job? Maybe better to just wait

Its been my experience over many years (50), that often, shortly after I change diff fluid, I lose the diff bearings. I cant explain why but this has happened four times.

If the diff is not whining or leaking, concentrate elsewhere for something to change. The typical life of one of these diffs, based on many forums, is around 120K miles.

Getting the plug out is a matter of making up a tool that will do the job, basically a piece of 1/2" square stock and a flat wrench with a ratchet on the end that the stock will fit into.

I recall reading here that the convertible has bracing which makes the job of changing the differential fluid much harder than it is on the coupes. On my '02 coupe it was not too difficult, As with all rear ends, keeping the stuff from touching you is most important. Once that stink is on your skin, your social activities will be limited to staying downwind of others.

Once the old fluid had been sucked out as much as possible, consider using a good synthetic synthetic lube. It will handle the heat better, and your gears and bearings will last longer. a 75w-140 fluid is more costly than the 75w-90, but worth it.

Z

PS the mileage on my car, and the differential, is about 138,600. I changed the fluid at 124,500 miles, replacing it with 75w-140 Mobil 1 . So far so good.

Did mine from underneath. A struggle but doable. Pumped mine out with a cheap pump off ebay £10 English pounds. Into a measuring jug. Then put the same amount back plus a little more till it started coming out of the hole. Enjoy!

Changing rear diff fluid
 

I can assert that with my 98 xk8 convertible, it was simply not possible to loosen the level plug from underneath. I eventually cut a 2” hole in the trunk. I was able to loosen the plug with a 1/2” wobbly extension thru the hole. There’s a bleeping cross brace in there for the vert that isn’t there for the coupe.

ltd

If the only options are to drill a hole in the trunk or remove the whole diff I would just take a chance and keep running the old oil.

I did quite painlessly, cut a hole in the boot big enough to get my hand through with a vibrating saw. Put the extension 1/2" direct onto the plug, no wobble bit, undid it, used a metal heavy duty oil syringe which took a pint at a time. Put the tube directly in the diff and filled it up, then put my hand through the hole with the plug on the end of a bit of 1/2" by 1", and just managed to get it screwed on. Took about an hour.

View of plug through hole.
https://drive.google.com/file/d/1GkG...ew?usp=sharing

How did you seal the hole afterwards? Any noticeable increase in road noise?

Been following the thread closely and not a lot of options. My 1998 XK8 convertible has 35,000 miles on it and has been garaged kept from the beginning. I think I will let her ride for awhile since it will probably out live me. :icon_cool:

My 06 conv. has an added plate between the boot and the diff. which makes drilling an access hole more complicated. I'm not sure if all 4.2 conv. have this plate, but I know the 4.0 do not.

I have just put some duct tape over it at the moment, and no there is no increase in road noise. I will probably just glue a piece of plastic over it when I get more time, but I don't think it's critical. It was much easier than fiddling in the dirt under the car, and if you're going to cut a hole, then make it big enough to get your hand through otherwise you're grovelling in the dirt form underneath to get the damn thing back on the thread. This way you can fill from the top, and the car will be level when you do it, which is so important. Most of us don't have a lift at our convenience. Just my opinion of course. Good luck. The 4.2 doesn't have a plate, and mine is a 2003 coupe.

Mike, I wrote that my 06 4.2 conv. has the plate. It may be just the conv., not the coupe, or even just the 05-06 conv.