buddysharp

Howdy,

My new to me 2005 S55, 5 spd trans, 120K is bucking hard on cold shifts between 1-2 on sport and 2-3 on comfort settings. Just completed a full tranny service, looked like an aftermarket fluid had been used. No metal chunks in the pan but more than average clutch material on magnet and bottom of pan. Did a second drive and fluid change draining the pan and found some discoloration of fluid. Torque converter does not have a drain plug. Did one more drive, drain, refill. Fluid looks clean now. Reset adaptation. When warm, fairly smooth up shifting but a little bit of shudder on downshift at low speeds. Also changed the transmission mount.

Did a glycol test and was negative. No leak at the at the wiring adapter plug.
I've used all geniune MB fluids. Removed fluid was thin and brown (did not smell burnt). Changed fluid multiple times using combination of methods (yes, a couple hundred bucks in trans fluid) and problem seemed to improve but returned quickly. Also reset adaptation in the trans..

No stored nor new errors when hooked up to star diagnostics.
When pulling away from stop, if I don't feather the pedal just right, on shift the S will start bucking so hard it'll snap your neck. Doesn't seem to happen after driving a while, but I'm also compensating a bit.

No codes either before flush or after.

I'm at a loss where to go next. Searched the forums and didn't find similar problem other than radiator contamination but my former MB tech, now independent, tells me my radiator was not one of the problematic series.

Looking for where to go next short of replacing the transmission.

Thanks!

Soylent Green

Have you considered replacing the contact plate withing the transmission. Fairly easy to do but procedure must be kept clean. This is a plastic plate with metal contact points imbedded into the plastic.

buddysharp

Considered the plate, but no codes and my independent MB tech said probably not the issue. He believes the apparent use of aftermarket fluid is the more likely cause which is the reason for me performing multiple fluid changes. No apparent leaks or leaching of fluid either.

Soylent Green

With 120k and seeings as how you already did multiple fluid changes I'm still betting on the plate being the culprit codes or not.

PeterUbers

Yup... Replace valve body and you'll be smooth again

buddysharp

Thanks PeterUbers and Soylent. The conductor plate seems cheap enough at about $200. Rebuilt transmission through a reputable SF Bay area shop is about 1250. I just hate to toss money without being able to point to a diagnosis. PeterUbers, have you had or seen similar? Any threads you know of describing?

Flight Test

Sure sounds like the lock up solenoid.

PeterUbers

Search valve body in titles of threads on this entire forum ... Many many threads on it

buddysharp

Yep, I've read them all or at least the majority

The symptoms of my 722.6 though seem different than what I've read and there are no codes. The bucking upon acceleration when cold will snap your neck in low gears This is not a "hard" shift; this is a holy moly watch out for whiplash kinda shift on fairly low acceleration. Paddle shifters don't alleviate it, either. I'm trying to find a way to diagnose rather than change out the plate, try again, rebuild the torque convertor, try again, etc. Hope you can apprecaite my effort. Thank you for the advice and the reference to the articles.

buddysharp

had some trouble with the last posting.

C3Duece

this^^^

buddysharp

I know the name is self explanatory, but what\where\how do I replace a lock up solenoid? Is it in the TC or part of the conductor plate? I searched the forum on the term but nothing in the w220 and w221.