Hi All. I get a pretty significant clunk when I first engage reverse when everything is cold. After the first selection all is smooth. Any idea’s?

 

I had something similar on my XK8 2001 - putting in TransGo pressure regulator valve and fresh trans fluid fixed it for me.....and hopefully postponed/prevented the dreaded A-drum failure

 

My wife’s XK8 (’99) had exactly the same problem as you described. I found a hairline crack in the valve body of the ZF5HP-24 transmission. I ordered a refurbished one from World Wide Speciality Parts. It solved the problem of delayed shift between Park, Reverse and Drive. I also had a delay sometimes after stop & go at traffic lights. Here is a picture of the crack in the valve body.

 

Let the start-up RPM drop to normal running RPM before engaging reverse gear. I used to get the clunk
before I started doing this. There might still be an underlying issue though which I know nothing about.

 

Amazing. I was just fitting a new handbrake light switch and sport mode switch and thought “why don’t I let the revs drop before engaging reverse. Wat do you know no clunk. I just checked the forum and @mcook gave be this exact same advice. I think this forum must have psychic element!

 

I haven't encountered this on the XK, but I think I instinctively pause long enough for the revs to drop to idle before selecting drive, and also for the gear to engage before giving it some throttle. My first Jaguar (around 25 years ago) was a '91 XJ40 and that had a habit of triggering the gearbox limp home mode if you didn't do this. I did always find it somewhat amusing that the so called limp home mode would theoretically allow you to limp home at around 115mph though!

 

Not familiar with TransGo pressure regulator valve, assume it requires dropping the transmission to replace.
My transmission was rebuilt and the clunk is still there when the car is warm. When my 1999 XK8 is warm the RPMs drop to around 550 and the clunk showers up. I can increase the RPMs manually to around 700 and the clunk goes away.
So is my problem RPM related or does increasing the RPMs just overcoming the real problem?

 

It can be changed without dropping the transmission.

Pan, filter and lower valve body only.