Slipping tranny? - PeachParts Mercedes-Benz Forum

mdlwolf · #1 12-24-2002, 01:41 AM

O.K. On my 83' 300D I've replaced the 2 white vacuum switches on the valve cover and the vacuum switch on the injection pump. My tranny shifts just about perfectly except for a periodic flairing between 2nd and 3rd. It seems worse when under load, like going up a hill, or when the tranny only downshifts to second and then has to upshift to thrid again, as in stop and go traffic where I don't come to a complete stop and the tranny is still in second gear when I start going again.
I've checked the system with a vacuum gauge and it idles at about 14" and drops to about 1.5" at full throttle. The vacuum unit on the injection pump that I got from fast lane doesn't have an adjustment on the lever like the old one did. I took it to the local Mercedes dealer and was told that the new one I have without the adjustment is the only part that is available. I've also tightened the bowden cable and found that to give me more RPM's before the tranny shifts. The shifts are very firm other than the flairing between 2nd and third, in fact if you really get on the throttle the car will chirp the tires on the shift from 1st to second.

My question is, would adjusting the modulator help any? Could the modulator itself be bad? Any help would be greatly appreciated as this problem has really got me stumped.

diesel don · #2 12-24-2002, 08:15 AM

Mdlwolf:

I have had the identical symptoms on my '83DT.

It sounds like you are traveling the right path. Have you exhausted the following articles?

www.continentalimports.com

click on "articles" and then "mercedes-benz transmissions".

www.mercedesdismantlers.com

check out the Auto Transmission Tech Information

I have gone through those two articles in depth and still have a slight problem. What I've done is a bit radical. I'm driving without vacuum currently and its the best attempt so far. I have the line (that is going to the tranny) plugged. What that does in effect is to tell the tranny that the car is under full acceleration (as there is not supposed to be any vacuum delivered under hard pedal). As a result I notice the following:

1. Under slow acceleration (usually when cold), I can manipulate the shifting without a "flare".
2. Under hard acceleration, it functions as new
3. Under medium acceleration it will "flare" if not warmed up

I wish you the best. As for me, I know that it is a tranny problem and not vacuum as I've exhausted the possible solutions.

Don

adamb · #3 12-24-2002, 08:16 AM

A ways back someone posted a website with Mercedes shift improvement kits which I assume includes parts to rebuild the valve body. Based on what your conditions are, maybe something like this would be good for you, as it seems that you have the proper vacuum drop-off with rpm.
I think I'll order one of these today. Has anyone else here had any luck with this valve body kit before? here is the link...

http://www.bulkparts.com

Superior Shift correction 722.3 / 722.4 Diesel
# 85931 Superior Kit K722A-D This valve body kit deals with these problems: Harsh 1-2 shift Soft or flare 2-3 shifts Slip or flare 2-3 (cold) Soft or flare 3-4 shifts Stacked 2-3 shifts

$46.55

when I get it in and install it I'll let everyone know what it's like.

Adam

#4 12-24-2002, 12:45 PM

Adjusting the modulator may be what is called for. I have found that it is a simple matter to undo any adjustment you make. Worst case is you spend some time messing with it. Just pry the cap off, and there is a Tee there. Pull it out, and for the symptoms you have, turn it 1/8 counter clockwise. Then reassemble and test drive. If any improvement, you are on the right track. Keep making the 1/8 turns until it is set right. If this makes worse just turn it back to the last setting.
By the way, if you want to source the problem, after setting the vacuum as you have done, just remove the vacuum line from the trans module. If the shift improves, your problem still lies, at least partly, with the vacuum system.

diesel don · #5 12-24-2002, 03:54 PM

Adam:

I would appreciate you keeping us posted. That would be a great price to solve my "flaring" condition.

Thanks

Don

per eriksson · #6 12-26-2002, 11:27 AM

I've been looking to get one of these kits as well but shipping international would make it more than twice as expensive and there's also a 100$ miniumum on international orders.

Would be interesting to know if it is useful if I should pursue this further.

#7 12-26-2002, 07:32 PM

A simple solution for the 2-3 flare is to just completely unplug the black vacuum line going to the trans, as stated above. Only problem with that is, you get hard 1-2 and 3-4 shifts, but a really nice 2-3 shift. It will make your trans last damn near forever though because of such a hasrh shift and no slippage.

EricSilver · #8 11-10-2004, 11:41 AM

Quote:

Originally Posted by turbodiesel

A simple solution for the 2-3 flare is to just completely unplug the black vacuum line going to the trans, as stated above. Only problem with that is, you get hard 1-2 and 3-4 shifts, but a really nice 2-3 shift. It will make your trans last damn near forever though because of such a hasrh shift and no slippage.

Really? Sounds odd. But here is my question:

While having my car inspected, I had the fuel injector/air cleaner service done, in which they add cleaning fluid through the vacuum line coming from the brake booster to the engine. I had this done this past saturday (11/6) On Monday morning, and this morning (Tuesday) the transmission flared between 2 & 3.

Could I have a vacumm leak as a result of the line not being secured properly after the injector service?

I also know that my fluid was very low, and have added more to compensate. Prioor to the injector service, the tranny was fine, except for some hard shifting (need to adjust modulator perhaps).

Prior

boneheaddoctor · #9 11-10-2004, 12:17 PM

Quote:

Originally Posted by EricSilver

Really? Sounds odd. But here is my question:

While having my car inspected, I had the fuel injector/air cleaner service done, in which they add cleaning fluid through the vacuum line coming from the brake booster to the engine. I had this done this past saturday (11/6) On Monday morning, and this morning (Tuesday) the transmission flared between 2 & 3.

Could I have a vacumm leak as a result of the line not being secured properly after the injector service?

I also know that my fluid was very low, and have added more to compensate. Prioor to the injector service, the tranny was fine, except for some hard shifting (need to adjust modulator perhaps).

Prior

Check your vacume connectors under the hood, are they tight or loose? they should be tight. I can barely feel my shifts now. but I did like how and when it shifted with vacume line off.... Later shifts. before you adjust modulator check the other stuff, when that is right then do the modulator, otherwise you are trying to use a band-aid on an amputation.

EricSilver · #10 11-10-2004, 12:28 PM

Thanks Doc, will definitely do that. Seems there is a definite cause and effect relationship to the disconnection of that vacuum line, then the tranny issues two days later.

I noticed after this morning's flare that subsequent shifting was exceptionally smooth.

JamesStein · #11 11-10-2004, 01:01 PM

Right now with the laundry list of things I have on the 300D and the 300CD... A slippy tranny that works is far down the list.

rg2098 · #12 11-10-2004, 01:18 PM

I have the vacuum thing on the valve cover completely disconnected right now, one less place for leaks to occur. Next I replaced the vacuum modulator on the transmission, not a fun job but pretty straight forward. Last thing I did was fiddle with the modulator setting to attempt to get it perfect. Its impossible to get the smooth 1->2 shift with out slipping, with out a new updated transmission as there was a design flaw from the factory that caused the harsh shift. In many cases people softed the modulator adjustment to soften the shift and just lived with minor slipping NOT GOOD. Since you have the correct vaccum to the modulator, turn it clockwise in small incruments to firm it up to prevent the slips and flares.