1985 300d trans won't shift out of 1st. - PeachParts Mercedes-Benz Forum

ChrisArnt · #1 05-29-2015, 04:54 PM

1985 300d trans won't shift out of 1st.
Door locks also not working.

I read that the modulator on the side of the trans can go bad.

I haven't seen the car go out of 1st gear.

I've had a dozen of these W123s and haven't had a bad trans yet.

What do you think?

mannys9130 · #2 05-29-2015, 05:37 PM

Kickdown switch stuck or shorted?

No vacuum is a problem too though.

Ceristimo · #3 05-29-2015, 07:42 PM

An '85 doesn't decide shift timing with vacuum though.

@ChrisArnt
So when you keep accelerating, will you get stuck with the engine on the rev-limiter and the car not speeding up anymore, or will it shift up when you hit red line?

mannys9130 · #4 05-29-2015, 08:10 PM

Quote:

Originally Posted by Ceristimo

An '85 doesn't decide shift timing with vacuum though.

@ChrisArnt
So when you keep accelerating, will you get stuck with the engine on the rev-limiter and the car not speeding up anymore, or will it shift up when you hit red line?

No it doesn't. But it does determine shift harshness so once he figures out how to get it to upshift it's going to SLAM into the other gears because the trans sees a full load pedal to the metal vacuum signal.

Ceristimo · #5 05-29-2015, 08:28 PM

@mannys9130
Right. My point was only that his car not shifting up is not caused by a vacuum problem, although a vacuum problem should definitely be fixed as well. Now that I am re-reading your first post I realize you never said it would be caused by a vacuum problem.

I misread that I guess.

pmckechnie · #6 05-30-2015, 08:02 AM

Transmission governor. Do a search on this site and you should find what you need. It is probably a broken plastic gear on the governor. It can be fixed without removing the transmission from the car. Sometimes you will need to replace 2 gears but I only had to replace 1. Cost for repair was less than 3 bucks for the gear from the dealer. I would recommend you service the transmission at the same time so you can get any small broken parts out of the pan.

Good luck

PaulM

ROLLGUY · #7 05-30-2015, 09:12 AM

Quote:

Originally Posted by pmckechnie

Transmission governor. Do a search on this site and you should find what you need. It is probably a broken plastic gear on the governor. It can be fixed without removing the transmission from the car. Sometimes you will need to replace 2 gears but I only had to replace 1. Cost for repair was less than 3 bucks for the gear from the dealer. I would recommend you service the transmission at the same time so you can get any small broken parts out of the pan.

Good luck

PaulM

This exact thing happened to my bro's '91 300D, but I am not sure the '85 has the same setup as the '91. I think the trans in the '91 was a 722.4, and the trans in the '85 is a 722.3. I could be wrong, so please correct me if so. If the trans in your '85 does in fact have the plastic gear on the governor, there is no doubt in my mind that that is the problem. It is replaceable by lowering the rear of the trans, and removing the governor cover. If the gear on the main shaft is also bad, you will need to remove the driveshaft and tail housing to replace it. It is definitely a DIY job. There is a chance that you will do it again if the secondary pump gears are not removed (don't ask me how I know this). The secondary pump is what causes the gear to break in the first place. I started a thread about this a year or so ago, but not sure where it is.....Rich

my123ca · #8 05-30-2015, 11:12 AM

Cali '85 300D has a 722.4 tranny.