sstrickstein

Ok here we go again. My 84 928S auto has recently started doing a goofy thing. After warmed up and on the freeway at speed in top drive, the transmission downshifts out of 4th down to 3rd on its own. Some further details. Once it starts doing this it will hold off shifting back into 4th until im going well over 80 MPH. It also becomes more sensitive to throttle input and further downshift. I pulled out my Factory repair manual and looked this up under the transmission section troubleshooting. I read that it could be either a bad O ring on the kick down solenoid valve( I replaced it) or a stuck Solenoid Valve itself( I cleaned the valve good today. I have ordered a spair kick down solenoid valve anyway. Has anyone else seen this before? If you followed my previous post I just had coolant enter my transmission from a bad radiator. I have changed the fluid twice since. Input would be appreciated.

sstrickstein

I received the kick down valve today. So I replaced it. From the drivers seat I can hear a very audible Click when I press the peddle to the floor. I hope this solves the problem. Today on my way in the transmission went into kick down mode several times. The old valve was part number 000 304 229 0. The part I put in was 000 304 289 0. Seemed to be the same from the outside. Any input is appreciated.

Mark Anderson

The superceded switch you bought requires a superceded control magnet
Check PET 308-55

sstrickstein

Mark

Those part numbers are from the Magnets I have just installed the valve part number 0003042890 into a switch 0003041890. I had a failed valve part number 0003042290 in the car with the 0003042790 switch. It went bad. I tested the set up and I am getting the loud click from under the car.

GregBBRD

Unless you have a short circuit causing the solenoid to be activated without you pushing on the kickdown switch, this is not your problem.

Hook up an small current (LED?) light to the kickdown signal wire and put that light somewhere you can see it. Monitor the light. If the light magically comes on without you hitting the kickdown switch, you have isolated the problem and then will only need to repair the wiring/triggering issue. If the transmission kicks down, without the light turning on....you have an problem somewhere besides the kickdown solenoid (Kickdown cable? Valve body?)

sstrickstein

I just adjusted the transmission throttle cable. It was a little too tight. I took all the tension out of it so it. I then drained off the fluid and replaced it again. I think some of the sludge that I didn't get when I had my trans cooler blow last month is stuck somewhere. I put some trans x in the fluid and Ill baby it till the stuff gets cleaned out.

sstrickstein

My drive home started out ok but after an uphill downshift out if top gear the car wouldn't go back I to forth. The only weird thing was I put my HVAC on differant setting. After I set it back to what I normally do it shifted better. Could a bad vacuum line cause lack of up shifts ?

GregBBRD

The modulator affects shifting and is vacuum dependent....

sstrickstein

So let's say I've got a large vacuum leak after the cars hot. Would that cause these issues?

Mrmerlin

yes

sstrickstein

So today I checked my vacuum source and the line to the Trans both check our ok. No change in what the car is doing. To be exact now, once the Trans is up to temps it holds gears. Most of the time it won't shift out of second. The kick down works so if I full throttle it at 40 it downshifts and then kicks into third and then back to second. My Trans cable is correct and the kick down solenoid and valve are new. I'm afraid I need a rebuild due to the coolant getting into it. Anyone else have a suggestion?

Kiln_Red

Does fourth gear ever engage at this point?

sstrickstein

No

GregBBRD

Getting all of the water and coolant out of the valve body does seem like it could be problematic.

Why not take the valve body out, separate the two halves, completely clean it with a spray cleaner and compressed air, put it back together, and re-install it?

You've got very little to risk....and chances are, from what I get sent to re-rebuild that the "local Mercedes transmission hacks" have worked on, uou would be way farther ahead!

sstrickstein

At this point the shop manual says I either have a problem with the shift valve or the centrifuge. It depends on the unit pressures. I put Trans x in the mix to see if it would clean put that stuff. My plan is to only drive it short hops each day this week to see if that will unstick what's clogged. This just started to appear. My fear is that the coolant damaged the clutches and the car is driving this way because Both clutches are engaged at the same time when the unit gets hot.