W108 transmission shifting late

[TWOEIGHTY_SE]

Originally Posted by tram

The only difference is that I don't think the W108 has the access plate on the tunnel. I think you're on the right track, though. Does your kickdown work?

Hahah... I drive this thing like an old lady so I didn't really know. On the w108 the kick down switch is activated when the throttle pedal hits the floor right? On the way home from work I put the pedal to the metal so to speak and it felt more like the car only went full throttle and there is no downshift. But to be honest I'm not sure because I don't know what is "normal" feels like on this car. Or on any vintage car with an automatic transmission. This car is way fancier than what I am used to.

I'm super bummed about the w108 not having an inspection plate- that sure sounds convenient. I'm going to check the solenoid function this weekend by just watching from underneath while someone else does all the shifting/kick down switch activating for me.

Originally Posted by Frank Reiner

TWOEIGHTY:

The selector arm positions on the trans are the same for K4A and for K4C, that is, Park is aft for both.

I just figured out what you meant by the "P" position for the shift selection. You were referring to the dash display of the gear selected rather than the selector arm position at the transmission itself. The column shift in my car has the "P" to the left which matches the K4C transmission installation. So it sounds like I may need to adapt the 4 bolt transmission style throttle position linkage for the conversion to work as long as the mounting of the transmission is the same.

[tram]

TWOEIGHTY- there's a switch under the throttle pedal that should 'click' and activate the kickdown. Check the fuse in the fuse box for the automatic trans and make sure it's there, and it's good. test it with a VOM to make sure there's continuity.

[TWOEIGHTY_SE]

It turns out that my W108 does have the inspection plate!



The solenoid and kickdown switch are working. I didn't have time to adjust it tonight but tomorrow I'll see what lengthening the rod does.

[tram]

Originally Posted by TWOEIGHTY_SE

It turns out that my W108 does have the inspection plate!



The solenoid and kickdown switch are working. I didn't have time to adjust it tonight but tomorrow I'll see what lengthening the rod does.

Well, that's great news- AFAIR the W108s didn't have that plate- at least not the early ones.

IIRC the solenoid finger pulls the rod forward, yes?

[TWOEIGHTY_SE]

Originally Posted by tram

Well, that's great news- AFAIR the W108s didn't have that plate- at least not the early ones.

IIRC the solenoid finger pulls the rod forward, yes?

Yes the solenoid pulls the rod when the kick down switch is depressed. Ignition on, it pushes the rod aft. Off idle, the rod moves to a middle position that is the same as when the ignition is off.

Lengthening the rod did not seem to change the shift point. It mostly felt like it was slipping through second gear into third. I kept lengthening the rod until it was too long to be moved by the solenoid. I think at that point it was stuck in the "aft" position.

For kicks I set it back to one full turn shorter than it was originally. It pretty much shifts at the same speeds as before. I might try shortening it more but I think my modulator just isn't working.

From the Pagoda tech wiki:

As last resort the control pressure linkage on the transmission (between the three position solenoid and the modulator can be adjusted. (make sure everything else is correct first). Since your kickdown is now working, your probably on the right track. Just doublecheck yourself. Some additional and more unusual things to check: Tom found that his linkage had been bent. Also there is a modulator diaphram that can fail and cause shifting problems also. If this happens the car usually puts out some white smoke and spark plug cylinder #6 will foul out from transmission fluid getting sucked up the vacume line going from the modulator to the intake manifold. This diaphram can be changed from under the car without removal of the transmission.

Which Diaphragm are they talking about, is it this?

1969 Mercedes-Benz 280SE All - Automatic Transmission - Page 3