Auto trans - Help needed

[dum]

This is my first post, so I wish to say hello to all.
I bought a 1967 250sl, US model sold in 1968. I took the car to have a general service and fix some instabiltiy in revs I could see while the engine was idle. Until then, the trans was OK, not very smooth, but OK. The only thing I noticed was that when I did not press the throttle (with the gearshift in 4 and say 3rd gear) the revs remained at high levels unlike what I am used to see in modern autos. Is that normal?
The problem, however, started when I took the car back. The trans started slipping, a lot... The mechanic (familiar with old Mercs, but not too much so with pagodas) diagnosed a complete failure of the trans. Since then we have exchanged a few (used) boxes without too much luck. After reading some of the posts in here, though, I started realizing that probably the slip was created by the engine fine-tuning and it could be that the very first one is OK...
My question: Could you please help me in determining possible causes of the slipping and how to fix them? I would appreciate if you kept it simple (language is also a problem, imagine that I am still wondering what a solenoid is...) and use some photos if possible.

Many thanks in advance!

[ja17]

Hello,

Yes, some changes in linkage can cause drastic changes in the automatic transmission function. Remove the carpet on the right side of the tunnel inside the car. Remove the inspection cover and view the modulator pressure linkage rod on the side of the transmission. the linkage rod is controled by the three position solenoid on top of the automatic transmission. If the rod does not move to the middle position when the acclerator is pushed, the modulator pressure in the transmission will be low and the transmission will slip. The transmission linkage should be in the forward position at idle, in the center position after the pedal is moved and in the rear-most position when the pedal contacts the kick-down switch on the floor.

Let us know what you find. Ask more questions!

Most likely something is out of sync or stuck. Review the "Linkage Tour" to start off with.

[Peter van Es]

A solenoid is an electrical actuator (a device that moves something, a rod, a valve, or a switch) when an electrical current is applied. Have a look here: http://en.wikipedia.org/wiki/Solenoid

If Wikipedia has a Greek version you can select that on the left and read that.

Also check our Technical Manual... it has lots of info in there already!

Peter

[dum]

Many thanks to both, I will keep you informed!

[dum]

Good news...!
Observing the solenoid through the "window" to the transmission from the passenger's side proved that the problem of slipping occurred due to the solenoid not responding to the throttle's position.
After searching for the reason, I realized that the solenoid next to the venturi (which informs the transmission solenoid about the throttle's position) was not functioning. I opened and removed dirt and after a while fixed it. The slipping is completely over and the trnasmission works! So thanks for the advice!

One problem remaining: the gearbox will not shift from 3rd to 4th if engine does not reach 4,000 rpm. And when this happens I cannot drive in low rpm with 4th as 4th is kept only if I further increase speed. This is nerve breaking as it happens at normal cruising speeds for most circumstances. Any ideas?

[lurtch]

Hi dum - - there are two vacuum taps at the rear of the intake plenum. The upper one goes down to the vacuum modulator on the transmission. Make sure the banjo fitting is tight at the top end and at the bottom end.  When I was sorting my car out four years ago I found that this tube had chaffed through and and the air bleeding in was messing up the shift points. Repaired it by flooding the crack with silver solder.

Regards, Larry in CA

[dum]

Many thanks for the help lurtch.

I would appreciate if somebody could send me a photo of those vaccum taps, so as to be sure with what I am dealing with !

Many thanks,