W124 transmission problems

We test drove and bought an '87 300TE this weekend. The car drove fine on the test drive and about 10 miles after that. Then it started downshifting on it's own into 3rd or 2nd and seemed to get stuck in the lower gear once it did it.

After driving the 25 miles home at 45mph we made it home.

I then took it for a drive and if I was easy on the throttle it would shift ok for awhile - maybe 10 minutes before it started acting up again. Occasionally putting it in Neutral and then back down into D would get it to go into 3rd or 4th, but not always and not for long.

This car has a MBz 722.3 transmission.

I checked and disconnected the kickdown switch, thinking it was stuck but that didn't help.

It seems like it could be a governor issue, as I've read they are prone to having a plastic gear break - but I'm uncertain if that would cause intermittent issues like this.

Any ideas? The trans fluid doesn't smell burnt at all.

I'd hit benzworld.org for an expert's opinion. It doesn't sound like the governor problems I'd read about there, but it's been a while.

I did just that Tom, thanks.

Nothing useful to add other than I hate it when everything works great on the test drive and then on the way home the car takes a dump!

Does the shifter move left and right to hold the trans in gear? I'm not familiar with your exact model, newer cars will hold in gear by pushing the shifter left or right. There could be an issue with the shifter or its electrical connections.

Chas_H wrote: Does the shifter move left and right to hold the trans in gear? I'm not familiar with your exact model, newer cars will hold in gear by pushing the shifter left or right. There could be an issue with the shifter or its electrical connections.

Oops, that was supposed to be '87, I've corrected the initial post.

No, the only electrical component of the transmission is the kickdown solenoid.

Draining all fluid (including the torque converter), transmission filter, and renewing all fluid seems to have resolved the issue.

Though, it's hard to say since it drove fine on the initial test drive.

My working theory is that the car was sitting for a number of months and the during the test drive it sucked up what trash had settled in the pan up into the filter, causing low pressure to the governor.

The hydraulic self leveling suspension worked correctly on test drive, but now behaves as the actuator diaphragms have ruptured.

yay me.

Tom Heath wrote: I'd hit benzworld.org for an expert's opinion. It doesn't sound like the governor problems I'd read about there, but it's been a while.

Sadly I never got a response at benzworld or peach parts.

Peach parts is usually much better for technical questions.

m4ff3w wrote:

Tom Heath wrote: I'd hit benzworld.org for an expert's opinion. It doesn't sound like the governor problems I'd read about there, but it's been a while.

Sadly I never got a response at benzworld or peach parts.

That's a shame. Benzworld was jumping with activity not too long ago.

I enjoyed my Benz 300TE quite a bit, and sang its praises to anyone who would listen...until it broke. After pricing replacement parts and looking at the err...labor intensive...process of replacing simple underhood components, my enthusiasm cooled.

If I'd had more time/money/space, I would have loved trying a V-8 swap.

m4ff3w wrote:

Tom Heath wrote: I'd hit benzworld.org for an expert's opinion. It doesn't sound like the governor problems I'd read about there, but it's been a while.

Sadly I never got a response at benzworld or peach parts.

m4ff3w, you posted in the tech section of Peachparts. That would seem to make sense, but the diesel section gets more traffic and the regulars are knowledgeable. If you explain (and I've seen this done before) that you got no response on the general tech section and just wanted to get as much exposure as possible before giving up, I'll bet somebody will help. Those are good transmissions and it's probably that plastic gear or a sticking valve. Mine's been good so far, so I just don't have a lot of experience...yet.

carzan wrote:

m4ff3w wrote:

Tom Heath wrote: I'd hit benzworld.org for an expert's opinion. It doesn't sound like the governor problems I'd read about there, but it's been a while.

Sadly I never got a response at benzworld or peach parts.

m4ff3w, you posted in the tech section of Peachparts. That would seem to make sense, but the diesel section gets more traffic and the regulars are knowledgeable. If you explain (and I've seen this done before) that you got no response on the general tech section and just wanted to get as much exposure as possible before giving up, I'll bet somebody will help. Those are good transmissions and it's probably that plastic gear or a sticking valve. Mine's been good so far, so I just don't have a lot of experience...yet.

Thanks for the tip.

The intermittent nature of it makes me doubt it is the plastic gear, we'll see how it goes with fresh filter and fluid.

Our 190E 2.6 is very similar mechnically and has been a good car in the year we've had it with over 200k on it.

I had an issue with the vacuum modulator on my car where it would give me a clunky downshift. I'd would just go for a fluid filter change then drive the crap out of it, run it through the selector to push the oil through the passages then after a 1000 miles or so change the fluid again. Worse comes to worse you are 300$ from a junkyard transmission. I would check the bushings/kickdown/vacuum modulator/tranny mounts and all the BS before replacing the thing.

Good luck and keep us posted!