Driving I can hear a slight thunk in the rear end when I step on the gas after letting off. So, cruise, let off gas, step on gas clunk at step on gas. I just had the car raised and when you rotate the rear wheels you hear a much more pronounced metal sound thunk.
Any thoughts on that and is there an adjustment that can be made?
thank you
Mark

 

Maybe excessive pinion backlash. Climb under and check for play at the pinion flange.
l would also give all moving parts in the area of rear end a good shake looking for movement.

 

Prop shaft joints ??? See if greasing helps or Pinion backlash ...got any oil in the diff ??? Cut 2 in hole in rear of trunk to gain access to diff plug.

 

Thank you. Novice mechanic gere, no lifts, no experience in differentials seeking clarification. I dont know what Pinion backlash is but it sounds like there is an adjustment for that, is that true? Pistonbroke, do you mean I must cut a hole in the trunk structure to access the fill plug for the differential to check fluid level? I've checked that fluid by removing the bolt plug on the side of American car rear end but the guy who lifted the car could not find a similar check plug. Thank you for trying to help.

 

There is adjustment but you would have to dismantle the diff totally. The fillfer plug is on the rear almost impossible to reach so you cut a hole in the trunk floor to access it . Note the original hole in the video is too low and its simpler to remove the electrical box to the right. You must use a wobble ended extension!!! I suggest if it does have play ( not in prop shafts) then suck out all you can and re fill with EP 140 oil.

 

John thank you. I watched the Video. I have that clunk at acceleration from gas off coast. Does this same apply to the 2001 convertible?
Mark

 

The OP does have a convertible, but it bears pointing out for coupe owners reading this, that the fill plug on the coupes is accessible without cutting any holes. Kinda tight quarters, but even with my large hands I could get to the plug and suck out the old rear end lube.


FWIW, i use the Mobil 1 75w-140. A little more pricey than the 75w-90, but it can take the heat better and should hold up better between changes.


Z

 

Be told its either the diff clearances or the drive shaft UJs or similar in the prop shaft ..get under and check.

 

The prop shaft is a 6bolted rubber thing. Could be worn. As others have said, it could be one or more of the 4 universal joints on the half shafts in the rear. I did the U joints in the half shafts and it wasn't that bad.

Jack up the car and in D or P try turningthe wheels by hand. See if you can reproduce the noise and then, see where it's coming from. Under the car, car in N or P or D you can try (be very careful) to turn the crank shaft listening for noise...

Stuff with the DIF itself... I dont have the experience at all to comment on that.

there are other bits and pieces that actually hold the entire rear end (cage) in place that may SHIFT with starts and stops, acceleration and deceleration... See if you can find some images of the rear end of the xk8 to give you some ideas of what to look for.

 

diff mount square plate, UJ, or pinion slop

 

If it turns out to be pinion slop/ loss of preload causing excessive backlash it will generally also have pinion seal failure so lots of oil and crud around the diff flange area.
Can sometimes be saved in place with some bush mechanics before going to full diff rebuild.

 

There is not a hint of any leak, seepage, absolutely nothing under this car. I read the rear end is sealed for life. Seems odd in that the fluid must brake down and provide less protection.
thank you!!
Mark

 

I am not a believer in "sealed for life" although technically the term is correct in that it is sealed at the beginning of it's life and still sealed when it dies due to loss of lubricating properties of the oil.
Unlikely to be your pinion.

 

I am not sure about your model of Jaguar, but my XK8 had this issue when the car would slam into 1st gear as you approached a stop.

It caused a rear pinion shaft/gear set to be replaced.

After much searching on the internet, I came upon the real fix to solve this problem.

YOU MUST have the engine computer AND the Transmission computer RE-FLASHED at the same time and then someone must drive the car slowly for several miles.

I had this done and I have never once experienced this problem again. I think I used search on transmission thunk.

An experienced Jag dealer would know about this, but my shop's people didn't know about it until I brought in the exact procedure. They then followed the procedure to the letter and I am free of that annoying (and expensive problem).

Good luck

 

It's a good point to make there. And possible to confuse sounds and there location, especially while driving...

So just add a bit. There is an upgrade that has to do with the trans. An A-Drum thing having to do with a pressure regulating valve in the valve body in the 5hp24 transmission... The valve or bore wear allowing an unregulated flow of fluid to improperly engage in 1st and 2nd - 2nd to 1st gear changes... Google transgo 5hp24 upgrade for more info.

Could this be what you are experiencing?
Or do you get sound at any and all speeds?

 

Checking for backlash is a simple process. Repairing it, is not. Usually, a U-joint will not clunk like this. The sound you describe has the earmarks of excessive backlash in the pinion gear.
About a year after picking up our 95 XJ6, we began hearing a rumble in the rear end. The rear end bearing were failing. The average DYI guy cannot rebuild a Jaguar rear-end. My background is
in automation and machine repair. My father was an auto mechanic and he used to rebuild rear-ends for a few guys that raced. It's been over 20 years since I rebuilt that XJ6 rear end, but I remember
it vividly. I had access to all sorts of equipment. You will need a 20 ton bearing press for starters. The domestic brands I'm most familiar with (Ford or GM) are easy for most guys to rebuild. There are still
plenty of ways to screw things up, but ordinary tools will work and it can be done. For example, a Ford rear-end has threaded caps that are adjusted and used to set the bearing preload. Jaguar uses shims.
This means that every time you need to set the bearing preload. The unit will need to be disassembled. In addition to that problem, the Keepers are press fit. Jaguar technicians must have some very special
equipment for this. There is no way to get behind these press fit keepers to remove them. I solved this problem by cutting the old bearing off and splitting them. This gave me the space to get behind this
Keeper ring. Using a conventional bearing press, I was able to remove these press fit rings. These parts did not come off easily and the sound was similar to a gunshot when they released. That's a whole
lot of pressure. I believe that Jaguar heats these rings before they are pressed on and I suspect that if they cut them to remove them. Then they replace them with new parts.
That was the easy part. With a Jaguar rear end. You need to be able to accurately measure the clearances. Preload is nothing more than a gap that exists between the ring gear and the pinion gear. When
that gap gets too large, you will hear a clunk when that clearance gets excessive. Some would think that this is easy to solve. Remove the ring gear assemble. Pop out the pinion gear and add more shims
to move the ring gear in closer to take up the space. It's not that simple. The pinion gear would no longer run in the center of ring gear and most likely, you would end up breaking teeth. The proper way
would be to move the pinion half the distance and then move the ring gear the other half of that distance to reach proper alignment. The dicey part of this would be that you basically get one shot at getting
this right. Whoever built or rebuilt the rear-end in my Jag, did it wrong. The bearing ended up failing due to incorrect preload. I know this because I've rebuilt high speed spindles in machining centers.
Bearing preload has to take into account thermal expansion. The bearings need to room to expand so they don't run to tight. Adjusting the clearances for backlash is simple. But you also need to account
for thermal expansion. This needs to be calculated into your measurements when calculating the shim thickness.
If you plan to rebuild the rear-end, then you should also replace all the bearings. There is a chance that you pinion bearing is wearing and that is where this space came from. You should check for metal
in the grease.
(I don't recommend cutting any holes in your trunk. I would drop the entire assembly before I cut holes in the body. This is the direction your headed anyway. Sooner or later. The rear-end has to come out).
In an ideal world, you could just replace the bad pinion bearing and all the clearances would be good. Unfortunately with any bearing failure. Metal has been circulating in the rear end and the entire
assemble in compromised. Your most simple solution would be to replace the rear end. The idea of rebuilding a rear-end is a complex process that you may not be equipped to do. Replacing the rear-end
is not so bad. You end up pulling it out regardless. I think the best method is to drop the entire suspension assembly and roll it out where you can work on it.
There are a few other possible causes for the cluck. Although, I believe it is highly unlikely. Loose bolts on the flex plates connection to the ring gear. Highly unlikely if the engine has never been removed.
Or possibly a broken motor mount.
I took the time to write this long opinion in an effort to "scare" you away from attempting to repair this rear-end. Unless you have seen this done and have the equipment. You chance of success is small.
Of course another option would be to remove the rear-end and have a shop rebuild it. You may find it more economical to replace the rear-end. Personally, I have trust issues with these shops and their
quality.
If you feel you have the expertise needed and you have access to this type of equipment. That changes everything. But your questions don't lead me to that conclusion.
So, welcome to the world of Jaguar. Where nothing is as simple as it looks. Jaguar just does things a little differently sometimes. After driving a Jaguar, it's hard to say no.

 

I did not notice it when the xk8 was in S mode which I did not find out about until later (no manual).
I had it up in the air the other day and the mechanic then raised the ut further making the rear wheels free. When he turned them, there was a metal clunk seemingly coming from the differential. I've not tried it back in S mode which is how i test drove it.

 

Not in the VIN range but info for the XK propshaft.

 

What does Minstral 2001 XJ8 Mistral mean that's new to me?
Thanks
mark

 

It still clunks on S but not as bad.
mark