HELP ME PLEASE!!! Is my tranny broken??? - PeachParts Mercedes-Benz Forum

RichardLSU · #1 06-06-2010, 08:29 PM

Two days ago while driving through the city my transmission started missing gears. It would rev up to about 3-4k then shift really hard, even at slow cruising speeds (e.g. 25mpg @ 3k). I stopped and checked the fluid level since I had this problem previously when a belt snapped and snagged a big hole in my transmission cooler lines. So I got some more transmisison fluid (ATF-4) and topped it off. The next day it acted up one time on my way to work but today on my way home it was doing it even worse than the first day. I stopped and checked the fluid, it was full. I'm at a loss guys, is my tranny going out?

tobybul · #2 06-06-2010, 09:01 PM

I'm assumong you fixed the "big hole" ( whatever that means) in the cooler lines.

Sounds like a vacuum issue to me. You may have disconnected a vacuum line when tinkering with it.

vstech · #3 06-06-2010, 09:42 PM

two possibilities.
bad kickdown switch holding the transmission in lowest gear to the shift mark points on your speedometer (could be as simple as floormat stuck under accelerator pedal.)
and
bowden cable popped out/broken.

jonbobshinigin · #4 06-06-2010, 09:48 PM

Lets get a baseline:

When was the last transmission service (oil and filter)?

When was the last time you changed both fuel filters?

How confident are you that you do not have some sort of vacuum leak?

In case you are not familiar with the "Bowden cable", it is the cable that determines at what point, higher or lower rpms, the transmission will shift.

RichardLSU · #5 06-07-2010, 10:26 AM

The transmission fluid and filter were changed about 20,000 miles ago.

I'm not confident that I don't have a vacuum leak. I know NOTHING about transmissions.

What about this "kickdown switch"?

I was looking up similar problems and found some guys had replaced their B2 Piston... could that be it?

I guess I'm gonna need some help diagnosing this. What do I look for?

RichardLSU · #6 06-07-2010, 10:27 AM

Also, both fuel filters were replaced between 10-15K ago. The inline filter gets changed ever 3 times I change my oil. I've replaced the canister filter twice in the 50K I've put on the car.

vstech · #7 06-07-2010, 10:31 AM

not B2. totally different symptoms.
kickdown switch is under your accelerator pedal. round black switch. if it's broken, or depressed, your car will require high rpm's before shifting to the next gear. if that's not a problem, the cable that goes from your throttle linkage on the valve cover to the transmission could be broken. it should have a black rubber boot on it kinda accordion like. about 1/2" diameter.

RichardLSU · #8 06-07-2010, 10:35 AM

No I'm not familiar with the "Bowden Cable"... what do I look for?

vstech · #9 06-07-2010, 10:40 AM

Quote:

Originally Posted by vstech

the bowden cable goes from your throttle linkage on the valve cover to the transmission could be broken. it should have a black rubber boot on it kinda accordion like. about 1/2" diameter.

Quote:

Originally Posted by RichardLSU

No I'm not familiar with the "Bowden Cable"... what do I look for?

ok?

RichardLSU · #10 06-07-2010, 10:50 AM

Lol, yeah. Sorry, its early.

tobybul · #11 06-07-2010, 12:23 PM

[QUOTE=RichardLSU;2481660]Two days ago while driving through the city my transmission started missing gears. It would rev up to about 3-4k then shift really hard, even at slow cruising speeds (e.g. 25mpg @ 3k)......... QUOTE]

I see 2 symptoms here... missing gears and hard shifting...

What does missing gears mean?
Hard shifting. From 1st to 2nd?

RichardLSU · #12 06-08-2010, 11:16 AM

Well the hard shifting comes from the engine revving so high and then finally shifting into gear. Yes, it feels like its missing gears... or a better way to describe it is like the turbo not kicking in (that lump of torque is gone and the engine just revs). Although I know thats not the case. Like I said, its sort of the same symptoms I had when the transmission cooler line got slashed and it dumped tranny fluid out of it, though now its still holding fluid.

I checked the kickdown switch under the pedal and it seems to be ok, that is its not stuck on. I've never had an issue with it before and its always worked. I hardly ever use it.

Second, I checked the Bowden cable. I moved the rubber-accordion-boot back and pulled on the cable and it is flexible but not broken. The engine does rattle around and shake so could that bolt that its hooked to maybe worked its way out a little bit? Should I tighten it or loosen it to cure my symptoms?

Any other ideas?

RichardLSU · #13 06-08-2010, 11:19 AM

Also, on the highway on my way home instead of cruising at 3K at 70mph it was closer to 4k, and then for no apparent reason shifted and then settled down. But then went right back up after I started cruising down a hill and let off the accelerator pedal. I gave it a good jolt on the pedal and then it shifted up again, but once I got into town it was at almost 3k through my 25mph neighborhood, like it wouldn't shift into second.

There doesn't seem to be any rhyme or reason to it. Sometimes it works fine and sometimes it doesn't.

tobybul · #14 06-08-2010, 11:58 AM

Sounds like your tranny is flaring (skipping gears). You still didn't say from what gear to what gear......

Most of these symptoms indicate a vacuum leak. You may also have vacuum-driven parts that are not necessary such as egr, etc but still are connected. In my 84D, I found that removing and sealing the vac lines to unnecessary accessories corrected the flaring and shifting issue.

RichardLSU · #15 06-08-2010, 12:05 PM

Sometimes its 1st to 2nd and sometimes its from 2nd to 3rd. I don't feel it downshift now. There used to be a big CLUNK when it would, but now nothing.

I guess that clunk is a familiar trait of these transmissions, probably the result of a vacuum leak from what I understand.

There is a labyrinth of vacuum lines underneath my hood... where do I begin?

Thanks guys for all your help. My car wouldn't still be running if it wasn't for this forum!