Troubleshoot kickdown switch

[Graham]

The kickdown on my 1972 350sL is not working. (I imagine other model early benzes would have a similar design)

Checked wiring diagram and there is not much to it - just a foot switch that operates a solenoid valve on transmission.

Power comes from a fuse that I think is OK (but will recheck). Cable is connected at transmission end.

If fuse is good, either solenoid or switch must be bad or a wire must be disconnected.

Anyone know where I can check continuity? (Diagram shows a terminal strip but I don't know where it is.)

[79Mercy]

put the car on ramps and check for power at the solenoid when the key is on and the pedal pushed on the floor. If you have power than you need to replace the kickdown soleniod on the tranny.

I need to do this, I have the same problem except my tranny will downshift in 4th gear if im not going over 40MPH.

[Lexxani]

you test the kick down switch by simply kicking it down. . .

[Graham]

Originally Posted by 79Mercy

put the car on ramps and check for power at the soleniod when the key is on and the pedal pushed on the floor. If you have power than you need to replace the kickdown soleniod on the tranny.

I need to do this, I have the same porblem except my tranny will downshift in 4th gear if im not going over 40MPH.

If that turns out to be the problem, can solenoid be removed without fluid running out? My car has a 3-speed 722.004 transmission.

I suppose I could connect 12v t the solenoid and listen to see if it actuates. Wonder if solenoid needs engine running before testing?

[79Mercy]

when you remove the solenoid some fluid will run out but not much. I don't know how to test it other than if its getting 12V and not working then its bad. I did a search and it seems that these soleniods do fail.

[Tom Drew]

Hi Graham,

I had to replace both the kickdown switch under the accelerator and the solenoid at the trans. to restore proper kickdown. Check the kickdown switch under the accelerator with a voltmeter by hooking the + lead to the power wire at the trans solenoid, and the negative meter lead to ground. Turn on the ignition and have a helper floor the acclerator. You should see 12 volts at the meter, indicating that power is arriving at the solenoid when the kickdown switch is activated. If not, move over under the driver floorboard to the kickdown switch terminals, see if you have 12 volts feeding the switch. If yes, the the switch is bad and needs to be replaced. If no, the fuse is blown or there is a break or short in the power wire to the kickdown switch.

When I removed the solenoid from the trans, a small amount of fluid leaked, but I stopped it up with a correct-sized plastic hole plug until I installed the new one. Save the small aluminum sealing ring and note where it goes when you remove it, so when you install the new one it will be leak-free. Solenoid is not available from MB. Did some sniffing around and was able to source one from Sun Valley Mercedes Dismantlers, Sun Valley CA. for $50.00. Installed it and I'm back to proper trans operation with kickdown on hard acceleration.


www.mercedesdismantlers.com

[Graham]

Originally Posted by Tom Drew

Hi Graham,

I had to replace both the kickdown switch under the accelerator and the solenoid at the trans. to restore proper kickdown. Check the kickdown switch under the accelerator with a voltmeter by hooking the + lead to the power wire at the trans solenoid, and the negative meter lead to ground. Turn on the ignition and have a helper floor the acclerator. You should see 12 volts at the meter, indicating that power is arriving at the solenoid when the kickdown switch is activated. If not, move over under the driver floorboard to the kickdown switch terminals, see if you have 12 volts feeding the switch. If yes, the the switch is bad and needs to be replaced. If no, the fuse is blown or there is a break or short in the power wire to the kickdown switch.

When I removed the solenoid from the trans, a small amount of fluid leaked, but I stopped it up with a correct-sized plastic hole plug until I installed the new one. Save the small aluminum sealing ring and note where it goes when you remove it, so when you install the new one it will be leak-free. Solenoid is not available from MB. Did some sniffing around and was able to source one from Sun Valley Mercedes Dismantlers, Sun Valley CA. for $50.00. Installed it and I'm back to proper trans operation with kickdown on hard acceleration.


www.mercedesdismantlers.com

Thanks Tom,

I have been tied up on other things, but had a quick look and see there is a plug that I can use to check that switch is working. I have also had a look at the solenoid connections and it should be easy to check.

Now, all I have to do is find time to check it out!

[79Mercy]

in my case I can use a solenoid off of a 300D, I checked EPC and they use the same part #. I'll grab as many as I can find at the JY next time I go.

[Graham]

Spent an hour on this problem today.

Tested the switch and it seems to work.

While doing this, it seemed to me that it is difficult to push pedal as far as switch. So, it seems step one should be to make sure switch actuates when pedal is pushed!

I disconnected linkages and found that the firewall mounted bearing for the longitudinal shaft is badly worn. The shaft moves up and down 1/4" before it turns. The bearing seems to fit into a bracket, but not sure how. Does it just clip in? (I changed the other end bearing a little while back)

The foot switch seems from the parts diagrams, to be adjustable. How is it adjusted and/or removed? It has a hex on it, but I did not try turning it - want to be sure I don't break it!

[79Mercy]

I don't think the switch is adjustable, just use a pair of pliers and turn it like 1/2 turn and it will come out.

You need to adjust some of the linkage so its isn't as long so the pedal hits the switch.

[Graham]

I did a little more trouble shooting today. I found that the foot switch works. Checked resistance across solenoid and it is zero. Had wife push pedal and I had 12v at solenoid, so solenoid must be burned out.

Will try and get a replacement.

added:

Looked up part numbers and this seemed to confirm that the solenoid is no longer available. BUT, it seems that perhaps parts may be available.

For those who have removed the solenoid, does it have a separate coil that could be replaced?

Does the solenoid just screw out?

[Tom Drew]

Hey Graham,

The solenoid is removed by unscrewing the large hex bolt. The coil is actually within the body of the solenoid. The hex bolt is hollow and contains a spring loaded sliding pin that moves to open or close the fluid passage in the trans. The source I referenced in my earlier post (Sun Valley Mercedes Dismantlers, Sun Valley CA.) for a replacement solenoid was the result of quite a bit of my time and effort spent to try and find the correct part for a reasonable price ($50). These guys rebuild MB Transmissions for a living and know their stuff. I was able to find 2 other sources, but both quoted me prices well over $100.00, and who knows if their part would be correct?. I'm sure that if the part was available from MB it would be at least $150.00 or more. No disrespect intended, but take advantage of my experience, order the part, install it, and unless there are other trans issues, it should solve your problem.

Tom

[79Mercy]

I also tested my switch and solenoid today. When the pedal is pushed I get 12v at the solenoid but doesn't kickdown above 40mph or in any other gear than 4th gear. Im guessing the solenoid isn't sending out enough signal or something to make it kickdown at high speeds or in a lower gear. I'll pull one out of a Junkyard an see if it helps my problem.

[Graham]

Originally Posted by Tom Drew

No disrespect intended, but take advantage of my experience, order the part, install it, and unless there are other trans issues, it should solve your problem.

Tom

Tom,

I am not ignoring your advice, but being in Canada, I thought that if I could get a new coil for the solenoid overnight from MB Canada, that would be the quickest fix. I could afford to pay about C$100 and still break even because of shipping and other cross border costs.

The epc says that a new solenoid is not available.

But, it says that the component parts are. The part (item 405)they call the "magnet coil" is what appears to be the valve body. The "bolt" (item 410) is called the "magnet frame".

I was interested in perhaps buying the "magnet coil" and assuming I could re-use the "bolt"

Either way, I need to get the number off the tranny! Maybe tomorrow. EDIT (Just found it - 107 270 0101002734)

Thanks for the lead on the solenoid from Sun Valley - I may still go that way.

[Tom Drew]

Graham,

Thank you for your gracious reply to my rather ungracious post. I can only say that upon re-reading what I wrote, I must have allowed my frustration from another unrelated event to influence my reply. My sincerest apologies to you.

I appreciate all of the help I've found here over the years and tried to help others in kind. I'll promise to be on my best behavior in the future.

Tom