My 87 tdt still won't kick down - PeachParts Mercedes-Benz Forum

biopete · #1 12-24-2012, 10:26 PM

My transmission hasn't kicked down for a year now when i put my foot to the floor and hit the switch. My reverse was out and so i finally put in a rebuilt transmission and thought this would solve all my problems.

Yet, my transmission still does not kick down. Also, it still likes to shift very early -- ie it will shift into fourth at like 25 mph unless i floor it. I have the bowden cable adjusted all the way out.

I read here that early shifting could be caused by the kick down switch so i went to the parts car where i got my transmission to get the kick down switch and it is the 2 wire kind and I have the 4 wire kind. So i went to my 1992 w124 and stole the kick down switch. I think that it worked great although reverse it out on it and i stole the battery like 3 months ago so I can't really remember.

Still no luck.

So, I'm going to verify i have voltage at the transmission wire -- could be a broken whire from the switch to transmission but apart from that -- what could it be.

Is the solenoid in the transmission different for the 2 and 4 wire switch maybe?

Or could it be my throttle linkage is so out of wack that it is affecting it? My understanding of the 722.3's is that the bowden cable handles shift points, the vacuum modulator handles the hardness of the shifts and the kickdown switch will just do it's thing electrically with a solenoid.

So if I verify my switch at the pedal is working and i have voltage at the transmission -- then next thing is to replace the solenoid in the tranny?

Thanks all. Hope you have a merry christmass. And first one that needs a two wire tranny kick down switch gets a christmas present

PM me your address.

vstech · #2 12-24-2012, 10:50 PM

bowden adjusted all the way out will do what you are describing.
you need to tighten the bowden to extend the gear shifts.

once this is accomplished, see how the kickdown is working.

biopete · #3 12-24-2012, 11:09 PM

Thanks vstech. I've tried it both ways. Now It is "loosened" -- turned counter clockwise until it wont go any more. That seems to make it so that when i give it pedal it shifts to lower gear to speed up . But no matter what it still stays in wont kick down when i hit the switch.

All the way loosened -- does that make it shift early or late? Mine just always seems to shift early no matter the state of the bowden cable. If i take my foot of the accelarator at 25 mph, it will shift itself to fourth gear. If i put it to floor, it will shift to 3rd but then when i hit kickdown switch, it won't shift to 2nd. I want it to not shift to 4th until at about 40 mph if i have my foot on pedal at all.

(Background info hopefully irrelevant

) I did take out my blue flying saucer disc and alda a couple years back just to simplify things. That shouldn't affect shift points or kick down right? Or hard shifting?

scottmcphee · #4 12-24-2012, 11:15 PM

Could be a combo of the condition of your VCV on the IP, and missing blue UFO.

Too much vacuum to tranny communicates leisurely pace stay in high gear.

What does a vacuum gauge read on the tranny line under driving conditions?

biopete · #5 12-25-2012, 12:18 AM

Quote:

Originally Posted by scottmcphee

Could be a combo of the condition of your VCV on the IP, and missing blue UFO.

Too much vacuum to tranny communicates leisurely pace stay in high gear.

What does a vacuum gauge read on the tranny line under driving conditions?

I'm trying to remember. My friend tested that with me a month ago and the Vcv was doing its job and read like 14 hg and then went to 0 or close to it I think. I recall us assessing everything was good with the Vcv and modulator. I'll have to ask him what we did.

One thing I've been trying to firm up shifts and turning modulator a few clicks hasn't made a difference that I can tell. I'll turn some more. I should be able to get some hard clunks from this thing right?

Thanks

vstech · #6 12-25-2012, 08:24 AM

... ahh, the additional info makes more sense still.
no. the alda being out will not affect transmission, except your pedal foot no longer needs to be pressed as hard to get the car moving. this causes the transmission to shift earlier than you intend because it thinks you are coasting.
If bowden adjustment makes little to no difference, then it may be damaged, or disconnected in the pan.

the bowden senses how hard you are pressing on the pedal, and holds gears longer when floored/heavily accelerating, and shifts rapidly if the pedal is barely pressed.
so.
tightening the bowden will keep the lower gears engaged longer and prevent rapid shifts.
HOWEVER, if you have it tight, and you barely step on the pedal to get going, because your alda is out, and the car moves so well at part throttle, or if you floor it, you get a huge cloud of black smoke... then the transmission is doing what it's supposed to. it's upshifting based on your throttle position.

biopete · #7 01-31-2013, 11:36 PM

Quote:

Originally Posted by vstech

... ahh, the additional info makes more sense still.
no. the alda being out will not affect transmission, except your pedal foot no longer needs to be pressed as hard to get the car moving. this causes the transmission to shift earlier than you intend because it thinks you are coasting.
If bowden adjustment makes little to no difference, then it may be damaged, or disconnected in the pan.

the bowden senses how hard you are pressing on the pedal, and holds gears longer when floored/heavily accelerating, and shifts rapidly if the pedal is barely pressed.
so.
tightening the bowden will keep the lower gears engaged longer and prevent rapid shifts.
HOWEVER, if you have it tight, and you barely step on the pedal to get going, because your alda is out, and the car moves so well at part throttle, or if you floor it, you get a huge cloud of black smoke... then the transmission is doing what it's supposed to. it's upshifting based on your throttle position.

Thanks Vstech. Nice thinking. I like it. I'm going to try a valve body. A tranny guy said if bowden cable is tight and it still wont stay in lows gears its a collpsed spring behind the bowden. This guy has been rebuilding trans for 35 years and knows Mercedes and just did my 1992 722.4 rebuild . So now i have a 722.3 and 722.4 transmission cars with same problem -- no kick down and upshifting right away no matter how i adjust it. So hopefully the valve body is it and that will explain alot . I'll post and update.

vstech · #8 02-01-2013, 06:20 AM

I was wondering how this was going. thanks for the update, keep us posted.

fredws · #9 01-17-2020, 09:44 AM

I realize this thread is really old, but I came across it while trying to figure out my problem, so I thought I would post what I found in case someone else is looking for an answer.

Anyway, my case was similar to the OP, I have a 1991 350SDL, and it would shift through all of the gears by 25MPH, no matter how fast I accelerated, or how I adjusted the Bowden cable. Ended up I checked the vacuum going to the modulator, at idle it was right at 15, and would increase as one increased throttle. This is of course opposite of what it is supposed to do, it is supposed to go to zero as throttle is applied. Replaced the Vacuum Control Valve, now all is good.

I hope this solution helps someone else out.

tdoublenastywitit · #10 01-17-2020, 03:27 PM

Adjust the air pressure on the side of the tranny.

I've had this problem with 3 different cars. And it was always this. I messed with all the bowdens and the ofv valve or whatever it's called by the pump. Never fixed it

Mxfrank · #11 01-17-2020, 05:37 PM

The ALDA supplies power to the kickdown solenoid on diesel powered 201's and 124's. What can happen is that dirt and water trapped under the switch shorts out the circuit, and burns out a trace in the ALDA relay. To check this, pull up the carpet around the accelerator pedal and check for power at the kickdown switch (car should be running for this test). If there's no power, clean out the switch and replace the ALDA. A less common problem is that the solenoid wire is broken at the transmission end. As for the weird shifts, I would guess that he screwed up the vacuum plumbing when he removed the BUFO. Technicians love problems like this. Sell a major transmission repair, and then do fifteen minutes of work to "unsimplify".

StatusQuo · #12 09-11-2020, 05:08 PM

Hi Guys, I‘m new to this Forum.
I‘m from Germany and it‘s very difficult to find some usefull informations on german pages or forums about the 722.3 transmission. Everybody want to hide their knowledge or wants a lot of money for that.
That is the reason why I entered this forum because I found so many helpfull informations in here via google. Great knowledge in here. I like.

I‘ve got the same problem with my W124 300CE M103.
It upshifts early to the 4th gear and no kickdown.

I changed oil, filter, k1 and k2 valve. First I thought I have found the problem cause the big spring of K2 valve was destroyed in 4 pieces. But after I put a new K2 valve kit in it, nothing changed.

Now I found this thread here and fredws write the vcv was the problem in his case. Does mine 300CE got also a vcv or is it just a diesel thing? Where can I find it?

Does somebody know where I can look after to solve this problem?

Sorry for bad english and have a nice weekend!

Best regards from Germany

Sebastian

fredws · #13 10-25-2020, 09:37 AM

Sebastian,
Sorry I am a couple months late in answering, but no, your car doesn't have a vcv, that's just a diesel thing. The vcv simulates the vacuum that a petrol engine would have, since your car is petrol, the vcv is not needed.

In regards to your problem, have you checked the tension of your Bowden cable?
Fred