Automatic transmission stuck in Parking mode

Well, quicker then anticipated I ran already into my first trouble. Not sure if this is a bad omen or just bad luck. So rather then writing my first blogs on some history and the buying traject I have to write about problem fixes. Perhaps the quickest way to learn and know more about the car. For sure the past two days has been a steep learning curve.

After the purchase I drove the car back home. The missus was at her work and obviously also interested to see the car. As the car was not washed or cleaned for a while I thought it was a good idea to drive it thru the carwash first. And then onwards to her work to present the shiny XJS. Underway I noticed the brake warning light popped up when I had to slow down. Typical, did a bit of water caused already electrical gremlins? On arrival I parked it but when I stepped out I noticed the back was slightly popping out. So I figured to move it a little more so people would not hit it.
To my surprise the automatic gearbox was stuck in parking mode and would not move to R or N. What the heck was going on?

During my pre-inspection testdrive I noticed the gearbox did not went smooth into R, N or D.

I was not overly concerned about that as the GM THM400 is more or less a bomb proof transmission. In fact it’s also equipped on my Ferrari 400. As such the automatic gearbox was the least of my worries. Furthermore the car was idling high when running stationair, around 1500 rpm. So clearly to high and as such very likely negatively influencing the automatic gearbox usage.

In any case, it remained stuck. So I thought that it might need to cool down a little, thus went to see the missus and shown her the car and had a coffee break. Afterwards it still remained stuck. My first thought was to have the oil level inspected. The dispstick was two-sided to measure, one side being cold and the other being hot. I also noticed it was stamped 400 which I found funny.

The oil was clear red, indicating it was fresh but also quite above the maximum level. I learned later (on Google) that the appropriate way to measure is to put it in N with the engine running.
My gut feel said this would be potential another contributing factor of why shifting the stick did not went smooth but not explained why it would not shift at all.

So I drove back home (using the car of the missus) and spend some time on the computer. Then on a forum I saw an older post which did mention a failing brake light switch preventing the car to shift, this was however on a modern Jaguar. Then I recalled I had this silly brake light failure as well. I didn’t expect this to be the cause but you never know. Apart from this I couldn’t find much more relevant information that potentially could explain or help to identify the root cause. As it had became dark already there was no option to further look into this.

So the car had to stay overnight out of sight (on the first day of ownership). Another worry that crept up is that an automatic car is going to be very difficult to move, in case I was unable to fix it. And towing it away and get it fixed in a garage was going to be a very expensive undertaking I was not looking forward to. So the plan for the next day was to check the brake switch first, disconnect the battery (potentially resetting some electrical gremlin, ie solenoid or switch).

The next morning I first checked the transmission oil again, being in a cold state. To my surprise it was way above the maximum level. That certainly was not good but could it be the real cause?

As you can see the oil level was all the way up to the spiral, both in cold and hot condition.

Starting up and tried to shift it but still it remained stuck. Then fiddling around and disconnecting the brake switch without joy. Disconnect/connecting  the battery did not worked out either. As such I started to remove the gearbox-shift-housing. When removed it became apparent that the solid metal pin between the gearstick and the cable, which pushes the actual lever on the gearbox, was bend.

This had happened when I forced the stick as I managed to get it into R and N position (but it never went actually in that state because it bend). So when holding that pin firmly, so it would not bend, I forced the stick again and now the gearbox lever was firmly pushed and presto it was working again. Phew!

I was glad I could move the car again and get it back to my home. The next plan was to get the transmission oil at the right level again and see if that would make any difference. And the other step would be looking at the idle RPM. More on this on the next blog.