300D transmission issues - PeachParts Mercedes-Benz Forum

car54 · #1 01-03-2004, 01:40 AM

I am the (less than) proud owner of Turbodiesels 83 300D. About 6 months ago, it began acting up. The first problem was only when cold in the morning, it would seem to jerk very rapidly, as if you were flooring it, then completely backing off, then flooring it again. The whole time, the engine RPM's would stay sort of steady, leading me to believe it was most definently not the engine.

Next, it began slipping out of gear around corners. Specifically hard right handers, such as enterance ramps onto highways. Its especially annoying, when you are trying to accelerate, you suddenly loose power and the engine will freely rev.

Just a few nights ago it developed yet another serious issue. On the highway, anything over 5psi boost or about 1/4 throttle will cause the transmission to slip. The revs will jump almost to redline, and although it still pulls hard, you can tell its slipping like crazy. Once you get to about 80mph, it will handle full throttle just fine (13psi)

I Really dont want to put a new transmission in the car. I know it has a vacuum leak somewhere either in the brake booster or where all the hoses pass thru the firewall because after you shut it off, you can hear a hissing for about 30 seconds. If you dont get the doors locked within 30 seconds, they dont lock. It also takes about 5 minutes of running before it will turn off. If you start it and quickly turn it off, she will keep idling away. Once I made a trip to the trunk, unlocked it, got what I needed out and returned to the car and was able to insert the key before it died (although it was slowing down the whole time, it never made enough vacuum for a complete shut down)

Any ideas what could be wrong? I checked fluid level and it is fine. I changed the fluid and filter about 13 months ago, so I dont think I messed up anything because it ran fine for 6-7 months.

If you think I need a new trans, anybody have a source for a cheap one? I'd love reliability too, but cheap is more important. Its almost exclusively used on the highway so the top gear slipping is somthing that needs to be fixed soon. It doesnt slip in any other gear, if you downshift into 3rd, it will accelerate like crazy. Also the 2-3 and 3-4 shifts are much looser now than before, although they never were firm.

BoostnBenz · #2 01-03-2004, 08:23 PM

While it is very rare for me to say this but I think you may need a new tranny, quite often it is just the vacuum settings which create improper shifting but this is only during shifts you are slipping while driving which is a whole different thing in itself. A few things you can try before bitting the bullet would be to disconnect the vacuum hose to the tranny, does this help at all or just make the shifts worse? Perhaps some Trans-X might be able to clean some of whatever is built up on the clutch face off. Adjust the modulator a little bit for harder shifts (ie more internal pressure) Are you certain that the tranny fluid is at the perfect level (checked after 30mins of driving, and at a idle)? The more it slips the less life your tranny will have so try not to procrastinate this off. If and when it starts to free rev like that let off so it doesn't catch again while the motor is nearing redline.