Mercedes-Benz Forum banner

1 - 12 of 12 Posts

·
Registered
Joined
·
58 Posts
Discussion Starter #1
Hi all,

I just picked up an '85 300TD a couple of weeks ago and since I've had it, I have been noticing a very loud and rough CLUNK at about 10-15 MPH when I am braking (I am guessing this is the 2-1 downshift). So far I have replaced:
1) All the vacuum connections in the engine compartment and the connection on the transmission
2) The VCV valve
3) The plastic tube and valve coming from the brake booster to the vacuum pump

I spoke to the guy at the Mercedes Dismantler and he was saying the '85 transmissions were more complicated than previous years. Where should I look next? From replacing all the above parts, the car shifts much better and runs smoother, BUT the loud clunk from 2-1 is still there. Any suggestions? :confused:
 

·
Registered
Joined
·
58 Posts
Discussion Starter #3
Haven't checked anything aft of the trans yet. What kind of/how much damage am I doing driving it with this clunk?
 

·
Registered
1985 380SE
Joined
·
1,939 Posts
While you're under the car it's a good time to check out both flex disks and the center bearing. If you see any hairline cracks in the flex disks replace them.
 

·
Registered
1983 300SD (90K), 1985 300CDT (69K) brand new, 1970 250C, 1989 190D (45K) brand new
Joined
·
164 Posts
And when you solve the clunk that occurs on the 2-1 shift, please let us know. The wife's 83 300DT does the same thing. We've already put over 20K miles on it that way. Though I have fixed or replaced many items for various reasons, I have not found the obvious solution for the clunk.
 

·
Registered
Joined
·
58 Posts
Discussion Starter #8
Ok I will post a reply when I get it fixed. The mechanic says it is definitely a vacuum related issue. Apparently I only have 5 inches of vacuum going to the transmission which is the problem. I have downloaded a few vacuum diagrams of the '85 system to check the connections although I am finding them hard to interpret. Does anyone have a photo on hand for the vacuum connections in the engine compartment for an '85 300D?
 

·
Registered
Joined
·
58 Posts
Discussion Starter #9
I am getting the car back from the shop today. Apparently the mechanic found only 3 inches of vacuum going to the shut off solenoid which is causing the car to keep running when I shut off the key. This has me baffled:
1) There is 19 inches of vacuum coming out of the two way valve between the brake booster and the vacuum pump
2) There is only 5 inches of vacuum going to the transmission
3) There is only 3 inches of vacuum going to the shut off solenoid
4) Door locks show no sign of working.
5) I've replaced all the little X and Y shaped connectors in the engine compartment along with the vacuum connectors.

If anyone has any suggestions where to look, please chime in. I either have a vacuum leak (which I am starting to doubt) or someone hooked up the vacuum system incorrectly. If someone has a good photo of a 1985 engine's vacuum connections on hand, may you please post so I can check if all the connectors are hooked up properly?
 

·
Registered
Joined
·
58 Posts
Discussion Starter #10
Ok, the problem is finally fixed! It turned out to be a faulty vacuum hose that operates the A/C and the door locks. The leak is so large that it depleted almost all the vacuum going to the transmission. I still have yet to find the leak, but simply disconnected the leaking vacuum hose from the rest of the system and the transmission works great for the most part. I now have a good 10 inches of vacuum going to the trans.
 

·
Registered
1982 Mercedes Benz 300D Dark Blue
Joined
·
41 Posts
unfortunately, there are numerous vacuum pods and connections in the system that is faulty, keep in mind that there is a pod for the trunk, fuel door, doors themselves, also numerous switchover valves and pods behind the dashboard. posssibly do the trouble shooting when you have a good amount of time to do it. good luck, i am about to do the same system.
 

·
Registered
1967 300
Joined
·
494 Posts
Interesting. I just got my step fathers '85 300 Turbo Diesel and it has this exact same problem. Then again it's being resurrected after being in storage for almost 10 years.

I'll keep this thread in mind.
 
1 - 12 of 12 Posts
Top