Question About 722.120 Kickdown:

[Doktor Bert]

Quick question for those of you with experience with the 722.120 transmission. I'm pretty good with these units, but I do have an operating characteristic question for the forum at large.

When I rebuilt the engine in my 1879 300SD (116.120) I also rebuilt the transmission, replacing all of the bands, frictions, steels and bushings. There really wasn't anything wrong with it, I just thought it made sense to build it while I had everything out of the chassis.

The only thing about this unit that puzzles me is how kickdown behaves below 50 mph. Above 50 mph, the unit downshifts a single speed range and accelerates strong all the way to about 80-85 mph when it upshifts into high speed range.

However, if you mash the throttle below 50 mph, the unit downshifts two speed ranges and this results in engine rpm quickly reaching the governed limit and no increase in vehicle speed. If you keep your foot on the throttle, you can just hold the engine speed and vehicle speed constant. The unit will not upshift until you let up on the throttle. I have also checked all the requisite adjustments to ensure they are in accordance with the FSM.

This isn't a big deal for me as I know just when and where the unit likes to upshift and downshift. I have also driven a few other similar 300SD's that all exhibited a similar characteristic. However, I recently drove an all original 1978 300SD that did not do this.

Curiously, I examined the shift linkage on this car and found it to be no different than mine and all adjustments were similar in nature. Notwithstanding some internal changes, I was unable to find an externally recognizable reason for this.

Any have a similar experience???...Robert


Obviously,

[Doktor Bert]

Any similar experiences???

[79Mercy]

my 722.112 tranny will only kickdown 1 gear. I have never tried to kickdown above 50MPH.

Where did you get the new bands and friction discs steels and bushings from?

[Doktor Bert]

Transmission Supply Center in Fresno, California...Robert

[Doktor Bert]

Mine will downshift (1) speed range at any speed between 50 and 80 mph. Below 50 mph, I downshifts (2) speed ranges, maxes out the engine rpm and just hangs there until you let up on the throttle. Car has done this since I have owned it and I bought it from the original onwers.

I've adjusted all the linkage to specification. I just thought maybe I missed something...Robert

[pawoSD]

Mine does that, I can get it to double-kickdown when going around 40-50mph....but it will quickly leave 2nd gear and go back to third if it goes into high rpms....it does not hold it until I let off....it does it on its own. Mine will readily kickdown 1 gear at pretty much any speed under 72mph.....

[Doktor Bert]

I may look into the adjustment on the detent linkage and back it off a bit, even though I set it to factory specificatiuon pursuant to the MBFSM...Robert

[Doktor Bert]

I'm working on a turoial for the correct adjustment procedure.....

[pawoSD]

My 300E also does this, it will drop all the way to 1st if under 50mph during a hard kickdown but will immediately shift to 2nd. Its rather annoying.

[Doktor Bert]

The adjustment between the throttle rod and the kickdown switch is like a teeter-totter. I have been working with this and gaining ground on it. I will post in detail when I am done...:-)

[ckamila]

Doktor Bert - Have you completed this adjustment procedure? I have FSM to set linkages to spec but Bowden rod (not cable) to transmission hits a oil line that goes to turbo i believe. Not getting a double kickdown under 50 and seems a little sluggish...could not get above 50MPH on a 12% grade

I have the 1980 CA version of the 116

[ckamila]

Update - Found linkage rod connecting to IP 10mm too long. Setting to spec helped....less pedal/better acceleration. Still can't always get double kick-down while under 50 even if i mash the pedal. Might still be the Bowden rod hitting the oil line at back of engine block. Happy with the current shift points.

[Doktor Bert]

Ok,

What I am wroking with at present is an intermittant 2-1 downshift on takeoff. As many of you know, the 722.120 with the 617.950 stays in 2nd speed range at a traffic light and downshifts to 1st speed range when you release the brake and apply throttle.

I do know that there is a control unit in the RF passenger's footwell that wroks with the overboost protection circuit to influence transmisson downshift, but I am not sure if this is what controls the 2-1 downshift on takeoff.

The 2-1 shift works fine most of the time, but then it will stop working for several days, then start working again. I have checked to see the connector on the electric valve is secure, so I am beginning to think this could be a bad solder joint in the control unit.

Anyone have more experience with this system???

Thanks....Robert

[kerry]

I was under the impression from discussions on other threads that the 116 tranny didn't shift down to 1st then you release the brake and apply throttle, but when the car came to a complete stop, as if the mechanism was a pendulum which swung backward after a forward swing from braking. Perhaps I misunderstood what was happening. I know that on my 116, if I didn't come to a complete stop, it wouldn't downshift into 1st upon re-accelerating unless I hit the kickdown switch or manually moved the shift lever.

[Doktor Bert]

Originally Posted by kerry

I was under the impression from discussions on other threads that the 116 tranny didn't shift down to 1st then you release the brake and apply throttle, but when the car came to a complete stop, as if the mechanism was a pendulum which swung backward after a forward swing from braking. Perhaps I misunderstood what was happening. I know that on my 116, if I didn't come to a complete stop, it wouldn't downshift into 1st upon re-accelerating unless I hit the kickdown switch or manually moved the shift lever.

I used to work for a private MBZ shop in Visalia ran by George Curtis. He told me about a pendulum too!!!!!

Perhaps this is true????