I am having an odd issue with me transmission. I have a 97 840 steptronic. While driving in D the cluster will suddenly display S3 and the car goes into 3rd gear only. If I shift nothing happens. If I pull over and restart the car, the problem goes away until the next random occurance. Any suggestions?

Thanks

Douglas

most likely the problem is coming from your transmition switch (position switch).look at part number 5.
http://www.realoem.com/bmw/showparts.do?model=EF83&mospid=47332&btnr=24_0776&hg=24&fg=15

Laszlo over on RF had the same problem while we were all in Florida in April. Here is the thread to see what he did to "cure" this problem.

http://forums.roadfly.com/forums/bmw/bmw-8-series-e31/8912256-5.html

Hope that helps

I remeber Laszlo's problem. I thought his was water related

Just an update on the symptom. I only have problems when the car is in D. If I put it in sport mode, the problem never occurs. I am going to tear into it (probably tomorrow) and see what I can find.

I will post pictures of what I find.

Still open to suggestions.

-Douglas

Well I got impatient and tore into it tonight. The switch and wiring is located under the car on the tranny on the passenger side. Removal is fairly straight forward. Lift the car, remove the front passenger wheel, and go under. There are four 10 mm bolts to remove. Two of the bolts hold a cover over the switch and two hold the switch. The it take a little gentle persuation to pull the switch off the transmission. There is a shaft that mates with the switch and mine was a little stuck. You must be careful when removing because it is a metal shaft/plastic gear interface. One that is off the wires are connected using a standard round BMW plug.

What I found was the same as Lazslo and the same as I found on my headlight wiring harness. Insulation failure. The insulation is failing all along the length of the wire. The problem here is one end terminates into a BMW plug and the other end terminates into the switch. The switch end is soldered in manufacturing and then cast in epoxy. I am going to have to cut the harness and splice wiring in on both ends. I have a plan and will post the results when done.

-Douglas

you might want to give Laszlo a shout and pick his brain for some "pointers", I recall he did a great job and solved all the problems.

I solved my transmission problem today. I disassembled the switch and rewired the harness. My digital camera was at the office so no pictures. Laszlo's pictures pretty much tell the story but I did things a little differently.

The inside of my switch was is good condition so no need to do any repairs there. I drilled out the old rivets and replaced them with new ones when I was done inside.

The big thing is that the insulation is failing on this part. It is not because of an oil leak. My harness was fairly clean for something that rides a few inches above the ground.

Because of the the BMW plug and the wires being encased in epoxy at the switch, I could not completely rewire the switch from point to point. What I did was cut away the old harness and left approx 1.5 inches of wire at both ends.

Next, I removed the insulation from the remaining 1.5 inches of wire. I stripped away approx 1.25 inches of insulation from the new wire and slipped it over the old bare wire. Then I soldered the old wire to new wire on both ends. I used the factory sheath as the final outer layer of protection just like the original harness. To seal each connection, I used high-temperature heat shrink tubing with a high-temp glue inside. When you heat the tubing, it shirnks and the glue flows to form a water tight seal and bond around the solder joint.

I put a single large piece of the same heat shrink around the entire harness at both ends. Finally, I encapsulated the ends with high-temperature silicone and let it dry.

I reinstalled everything and it works. Much better than buying the part for over a grand at the dealer.

-Douglas

Good Job, Brother. Excellent write up

Very nice thread, Douglas. Thank you for posting this & I'm glad to hear that all is well in the land of 8.

Cheers