tranny clunks - PeachParts Mercedes-Benz Forum

Maroon 300D · #1 03-19-2006, 10:02 PM

Well there's a lot of info. here on clunking trannies, but I would like some advice on my problem as I'm not quite sure where to begin. The car is clunking extremely hard going into second and third gears when the engine is cold. It's a pretty violent clunk that moves you in your seat. Once it gets warm the problem pretty much goes away, although there are less violent clunks at times.

I just got my car running again yesterday after two weeks of sitting while I put new glow plugs in, cleaned the banjo bolt, and put in a new ignition cylinder and made an attempt at fixing the clock. It never clunked so violently before I did this work, just a little and I thought it was probably fairly normal.

Now from what I've read on here it seems I could have a vacuum problem, but there was also one thread that referenced the boost control valve as something that can cause clunky shifts. It seems likely that there is more air going in there now that I've cleaned the banjo bolt and replaced half the hose that goes from the BB to said valve. Could my problem have something to do with this?

If it's the tranny itself then it should still be under warranty as it was installed in Sept. That was by the previous owner, though, so I'm not sure if I have a warranty or not....

Diesel Giant · #2 03-20-2006, 08:28 AM

The clunking is usually a vacuum modulator not working properly. It is there to dampen the internal pistons as they shift. Vacuum leaks is the main cause to the modulator not working, although the modulator can go bad also.

Maroon 300D · #3 03-20-2006, 11:20 AM

Thanks for the reply. I wonder if I knocked a vaccuum line loose while changing the glow plugs...that's how I ended up cleaning the banjo bolt; I accidentally broke the hose connecting to it.

I'll have a look around, I guess.

I would like to say, DG, that your posts on here and the various DIY things you've got on your website are enormously helpful. I have used them and do appreciate them. You are one of the people that make these cars affordable for people like me.

barry123400 · #4 03-20-2006, 12:17 PM

There is a better than average chance you did disturb the vaccum circuits in some way to some extent. Coincidence is usually over ruled when a problem surfaces immediately after working on something. Now at least I know the origin of old clunker.

Learn something new every day.