So I have been getting transmission fault on my 99 VDP for a while now. I have previously been able to shut the car off and get it to clear. For a bit of history, I have already removed the transmission and replaced the A drum and valve body (with updated larger pressure regulator). So knowing that this transmission fault issue was not internal to the trans, I was doing some research on here and found that others had issues with gear position rotary switch. I removed the switch and ran it back and forth a bit and put it back on and no transmission fault. My transmission fault would come up typically when you were putting the car into drive. So I thought I had maybe cured the issue. I drove the car and sooner or later it came back. So I decided that switch must be the cause. I researched a replacement part and I found that this part is almost $500. So I figured at that price I might pull it off and see how it works and see if I could fix it myself. So that is what I did. It is riveted together, so I drilled all of the rivets out and opened it up. See pictures of what I found. So there is a contact block that runs back and forth with tangs that run on a contact surface. I have seen this sort of thing before and know that the tangs sometimes just get compressed from being in the same position for so long, so I gently pried them out a bit to make better contact with the running surface. I then reassembled the case with some bolts and loctite to keep them from backing off. Unfortunately on the the test drive after doing this work my front springs decided to collapse and I could not drive the car to test my fix. I have all new front springs and all new front suspension components on the way to rebuild the front suspension. This was another project that I have put off for a while. I will do another write up on that once I get into that.

 

That's almost exactly the problem I had with my XK8 cruise control. When the engine was hot cruise control was intermittent, so I took the end off the throttle body and bent the spring wipers out a little and the problem was solved.

I think your switch should be good now.

 

A little victory when you can make it 'like new' again, love these fixes.

 

That is some nice investigative work, and one for the archives, just in case ...

On your collapsed front, it is hardly possible your springs or spring components collapsed.
Most likely, it is the front shocks giving way, which will drop the car an inch.

I speak from experience, but new Bilstein solved the problem.
While you in there, check/ change the shock top mount as well.

Link: https://www.jaguarforums.com/forum/x...d-inch-176869/

 

Thought I'd place this here, as this is the post that gave me the idea to open up my bad rotary switch. This switch failed recently, giving me the P0706 code and "transmission fault" message, along with the "limp home" 4th gear only. This switch is the earlier part number (ending in "953"), and it's a completely different design. The shaft is connected to a knobbed plastic cam that presses or releases 6 different contacts (contained in the black boxes at the 10 o'clock and 2 positions). These contacts had plentiful white corrosion on them, which I've cleaned up with lots of contact cleaner and Deoxit D5. I've got another good used switch on the car right now, but I'm planning on putting this original switch back on just to see if this cleaning solved the problem.