'95 E34 540 - auto trans speed sensor control - shifting problem

[trading10]

I have a 1995 E34 540 with an automatic, and it is exhibiting signs that I think might be related to a speed sensor failure. An auto transmission specialist I know says it could also be a problem with a check ball in the valve body.

I need another brain to think about this and come up with a theory.

When coasting along at 45 mph, if you give it some gas, it seems to either shift up then down suddenly, or the torque converter clutch is kicking in at the wrong time. I can't seem to tell which it's doing.

The second thing it does is when you approach a stop light, if you brake to a stop quickly, sometimes it will not shift down fast enough, and it will act like it's bogging down and going to die - just like a manual transmission car would die if you didn't push in the clutch at a stop light. If you gradually brake up to a light, it will shift down as expected.

The third thing it does is, if you're going down a steep hill, it will shift down and run the RPMs way up. It will continue to shift down until it's in 1st or 2nd gear (not sure how low of a gear it reaches). This makes going down any steep hill almost impossible without drastically affecting the speed of the traffic behind.

I have a PEAK code reader that is reporting a faulty 'speed control sensor' (or something like that). I have been told that there are three speed control sensors on the E34 540 - one in the engine bay somewhere, one in the instrument cluster (of all places!!), and one on/in the rear differential.

An auto transmission specialist here in Portland suggested getting a different transmission computer, which I did (off ebay), and see if the behavior changes - just to see if it's the computer that is faulty. Well, I put in a different computer, and it still does the 'shuttle shift' at 45 mph, but also does that incorrect down shift going down hills. So that behavior is different with the transmission computer I got off ebay. He was trying to determine if this transmission needs a valve body rebuild.


Has anyone had shifting problems with their 540 automatic like this??

I'm about to give up on troubleshooting this thing and sell it, but it's the most beautiful BMW body style of all I have ever seen - so I am torn.

Theories anyone??

[3050rpm]

Go to this site and see if it might help http://www.continentalimports.com/ser_ic100076.html . I seem to recall coming across a different problem affecting these transmissions in doing an Internet search, having to do with some disintegration of internal seals or some such thing, but I can't place it right now. If the site provided above isn't applicable, I'd suggest doing a more thorough search, you might find a solution that isn't all that costly, and you can hold to what I agree is a very nice body style.

[Big Evil]

Other things too. Faulty speed sensor, which one is faulty? They're fairly cheap and most likely it's going to be the one on the diff. I doubt your tranny or controller are bad. If they're getting bad information (you know, bad sensor data) they will not behave as expected or desired. Fix the sensors your problems will most likely go away. I've seen tranny "pros" replace a tranny 3 times only to have the real problem end up being be a bad TPS (throttle position SENSOR). I also have an E34 and yes, one of the best looking designs out there. Good luck

[trading10]

Big Evil - I'm going to look into the diff speed sensor. The transmission specialist guy I have talked with in the past probably has the right test equipment to see if that sensor is outputting bad data, as well as the TPS.

3050rpm, that writeup was informative, but what I appreciated even more than that was that they were committed to 'learning' something, even if it meant paying for work that turned out to not fix the problem.

I'll call him on Tuesday and see what happens. I'll report back here.

[trading10]

Kuni BMW parts guy tells me that the diff speed sensor is only for the speedo cable to the instrument cluster.

Is that right??

He said there are two speed sensors in the transmission - identical parts - called a 'pulse generator'. Maybe they measure input speed and output speed??

From his drawing, he couldn't tell if you could change these two parts without cracking open the valve body.

Does this ring true with you guys??

I don't have the equipment or skills to crack open the trans at my house, so I'd have to pay my trans specialist guy to do it for me. When I had the fluid and filter changed, it was about $350 - yikes! I suspect I'd have to pay that all over again too.

[Big Evil]

All the speed sensors are the same thing (pulse generator). Just find where the wires come out and check for AC (yes AC) voltage while things are turning. If they're not turning then the generators won't generate. He should be able to test them at the harness without cracking open the case. If he thinks he can bench test them by pulling them out, go somewhere else. The other side of this is the wiring harness. If a wire has been worn through then the signal can't get to the computer. You need a guy who can do electrical first, the Tranny is secondary at this point. First fix the faults, THEN if it still doesn't work, look at the larger components.

[trading10]

Big Evil, am I correct to say that my transmission specialty guy hook up a meter to the wires from those two transmission speed sensors, and have the meter sitting on the dash while he drives the car to see if they produce the a/c pulse? ie - meter wires stretched from the engine bay through the driver's window (or passenger's window if that's where the leads are located).

[Big Evil]

That is one way of doing it

[trading10]

Ok. I'll ask him to test the two transmission 'read switches', and report back here with the results.

Thanks guys.

[dynamicdoctor]

top of the evening to all lovers of bmw tech.