Rear End differential thunk

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Sep 2, 2021 | 06:17 PM

#21

Kongo1

Senior Member

Joined: May 2012

Posts: 344

Likes: 121

From: PA

Quote:

Originally Posted by hofslr

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

I believe this scenario is commonly referred to as the type 1 zf lurch?? The OP's scenario sounds like it could be the type 2 ZF lurch?? Google "ZF Lurch" and you will find both described in detail.

Sep 2, 2021 | 06:30 PM

#22

xalty

Veteran Member

Joined: Dec 2019

Posts: 3,695

Likes: 1,222

Quote:

Originally Posted by Rearaxle

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.

the 14HU rear end in the XK8 is different, a total POS and not worth repairing for any reason. the pinion breaks teeth and it’s game over

the 15HU in your XJ6 is a domestic rear end, a dana44. you’re right that setup is hard and time consuming. so just let a jeep shop do it instead

Last edited by xalty; Sep 2, 2021 at 06:51 PM.

Sep 2, 2021 | 06:34 PM

#23

Markmbaha1

Thread Starter

Senior Member

Joined: Aug 2021

Posts: 381

Likes: 41

Quote:

Originally Posted by Kongo1

I believe this scenario is commonly referred to as the type 1 zf lurch?? The OP's scenario sounds like it could be the type 2 ZF lurch?? Google "ZF Lurch" and you will find both described in detail.

I'm taking it that the reflash did not fix your problem I think you saud parts were replaced. Or am I wrong about that?
Thank you

Sep 2, 2021 | 11:35 PM

#24

zray

Veteran Member

Joined: Jan 2018

Posts: 3,722

Likes: 2,319

From: on the road in NE Oklahoma

Quote:

Originally Posted by Markmbaha1

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

if you changed many rear end fluids you would have a different viewpoint of “odd”. The smell alone coming from well used rear end line that’s been supposedly “sealed for life” would convince you that’s that indeed it can and does break down and does loose it’s ability to lubricate. Changing the rear end fluid every 50,000 miles will do wonders to keep it working as new for the life of the car.

my personal favorite is Mobil 1 75w-140. It does cost more than the same brand of the 75w-90 weight, but will keep working when the lighter weight lube fails .