transmission shifting hard - Page 2 - PeachParts Mercedes-Benz Forum

danwashuk · #16 10-28-2007, 04:26 PM

Hi Robert....Thanks for your post. I really don't know if there is vacuum present at the transmission end of the steel vacuum line. I recently purchaned a hand operated vacuum pump with gauge to test my vacuum system, and I think I have figured out a way to attach it to the pecular fitting at the end of the metal line. However I haven't found the time to get back to it yet. Working for a living is really getting in the way of my new hobby!!! I don't see the pressure port that you speak of but I guess I wouldn't know what to look for either. I definately don't see the rubber cap that you refer to, and I have looked very carefully for it. I see that the rubber cap is a part that can be ordered through the internet, so at least I know what it looks like from the picture in the parts catalog. 450slcya replied that this adjustment to the modulator valve on my model has to be done by removing the modulator valve. I haven't done this yet. Thought I would finnish checking out my vacuum system for leaks first. If I do remove the modulator valve, I am wondering if the transmission fluid comes pouring out???? What you say about setting it according to the pressure while driving makes sense to me, do you think this pressure port is behind some sort of cover or screw????

Thanks again for your reply, when time permits I will take some pictures of that part of my transmission, since there seems to be some variation on how the modulator valve is constructed..........Dan

danwashuk · #17 11-05-2007, 09:58 AM

I had a little time to work on the Mercedes yesterday. I put my vacuum guage in right where the line comes off for the transmission and the accessories like door locks etc. At idle speed I have a steady eight inches of Mercury (20 cm Hg). Does anyone know if this is close to the normal value??? I could see that I have some leaks in the door lock circuit so I disconnected all the accessory stuff and plugged the line. I drove the car and found that the transmission still shifts hard, especially going into second gear. When I was a kid I would of loved to have had a car that would get a little scratch going into second gear, but I would like to think I am a little wiser now!!!! I think next weekend I will put the car back up on blocks and test the vacuum line with my gauge at the transmission. If there is vacuum there then I will pull the modulator valve and see if there is an adjustment screw on the inside of it..........Dan

mpierce · #18 11-05-2007, 02:59 PM

Hello
I am a new member to this forum and it looks great. I am also a new (1986 560sl) owner. The car seems to be in great shape with not many miles ~ 36,500. IT does seem to shift much harder than I think is normal (or optimal) . Does anyone have any suggestions on what to check ?
Thank you

danwashuk · #19 11-06-2007, 11:32 AM

Hi mpierce.......sounds like we have the same problem. I have been persuing the vacuum system for my problem. So far nothing I have done has made any differance except changing the transmission oil. This made a slight differance, but the car still barks the rear tires when shifting into second if I am accelerating at a pretty good pace. Next weekend I am going to measure the vacuum pressure at the transmission where it enters the modulator valve. If the vacuum is present there then I am going to remove the modulator valve to see if there is an adjustment on the inside. I believe that your model may have an external adjustment for the modulator valve..............Dan

danwashuk · #20 11-11-2007, 10:47 AM

I had some time yesterday to work on the Mercedes again. I figured out how to measure the vacuum at the transmission, by removing the metal line and turning a thin nut onto the hollow bolt. I was then able to attach my vacuum pressure guage on the end of the hollow bolt, start the engine. amd measure the vacuum. I measured a steady 8 inches of mercury (20 cm of hg).

I removed the modulator valve, about 4 oz. of transmission oil leaked out, and took a close look at it. There is no adjustment inside the valve. I then attached my vacuum pump to the end of the valve and tried to actuate the valve. There is a thin metal pin about and inch and a half long sticking out of the working end of the valve. I pumped up to 23 or 24 inches of vacuum into the valve but the valve never moved. My vacuum pump maxed out could not accuate the valve, so at this point I am going to replace the valve with a new one.

I have attached some photo's of the valve and the side of my transmission......Dan

danwashuk · #21 11-11-2007, 11:02 AM

The first pic is the modulator valve.
Second pic is the working end that goes into the transmission, you can see the pin.
Third pic is the end where the vacuum line is attached.
Fourth pic is the end of the metal vacuum line with the nut attached, so that I could measure the vacuum at the end of the hollow bolt. You can also see the wire that I tied onto the metal line to hold it in place, it's very springy.
The last pic shows the vacuum line and the hole where the modulator valve screws into the transmission. You can see a little oil leaking out of the hole. This pic need to be rotated counterclockwise for best viewing...............Dan

aam · #22 11-11-2007, 03:08 PM

I think you just found the problem.
Get a new one.
Regards, aam.

danwashuk · #23 11-12-2007, 09:36 AM

Hi aam.....Thanks for your post.............
I have ordered a new modulator valve, the price was $67.00. If it fixes the problem it will be much cheaper than a trip to the Mercedes shop!!!! It's a good idea to keep in mind that, "It's always the last thing I do that fixes the problem!!!!!"..........Dan

aam · #24 11-13-2007, 11:50 PM

Quote:

Originally Posted by danwashuk

Hi aam.....Thanks for your post.............
I have ordered a new modulator valve, the price was $67.00. If it fixes the problem it will be much cheaper than a trip to the Mercedes shop!!!! It's a good idea to keep in mind that, "It's always the last thing I do that fixes the problem!!!!!"..........Dan

Have faith.

Regards,
aam.

danwashuk · #25 11-19-2007, 09:41 AM

I have great news to report today. I have fixed my transmission!!!!!!!!!

I installed the new modulator valve yesterday, took the car out for a test drive and it shifted great!! No more burning rubber shifting to second even when I held the gas pedel to the floor through the shift. I think I sprained my elbow patting myself on the back!!!!!!

When I got the new modulator valve I tested it with my hand vacuum pump. I could see the working end move with vacuum applied, this didn't happen with the old valve. Of course there are always a few unanswered questions when working on a problem like this. I was unable to effect an adjustment of the new valve by turning the threaded piece inside. It has a 4mm allen screw inside the valve but I could not turn it. I really was afraid that I would round out the whole if I put any more force on it. I decided I would just put it in and see what happened, since the old valve didn't seem to work at all. Also there was a disclaimer note that came with the new valve stating that it would require adjustment or the transmission could be damaged. My feeling was that the way it was shifting now was the biggest risk so I put the new valve in anyway. I am thrilled with the way it is shifting now.

I want to thank all of you that replied to my thread. Please take pride in yourselves for a job well done..................Dan

danwashuk · #26 11-21-2007, 03:10 PM

I have one more experience to relate regarding the modulator valve. I went back under the car to put the skid plate back on and found that the modulator valve was leaking a little oil from the point of attachment to the transmission. After tightening it up a little more I discovered that the car did not shift as smoothly as before. Aparently tightening it caused an adjustment problem to the valve. I removed the vacuum line from the valve and with much effort was able to turn the 4mm slug inside the valve. They must have put something on the threads to prevent the adjustment from changing through vibration because it was really hard to turn. Since I had screwed the valve in tighter to stop the leak I just turned the slug out about the same amount and now the car shifts like a dream again.............Dan

aam · #27 11-21-2007, 09:36 PM

Quote:

Originally Posted by danwashuk

I have one more experience to relate regarding the modulator valve. I went back under the car to put the skid plate back on and found that the modulator valve was leaking a little oil from the point of attachment to the transmission. After tightening it up a little more I discovered that the car did not shift as smoothly as before. Aparently tightening it caused an adjustment problem to the valve. I removed the vacuum line from the valve and with much effort was able to turn the 4mm slug inside the valve. They must have put something on the threads to prevent the adjustment from changing through vibration because it was really hard to turn. Since I had screwed the valve in tighter to stop the leak I just turned the slug out about the same amount and now the car shifts like a dream again.............Dan

Next time put some Teflon tape on the threads, make sure nothing goes in
the transmission.

Congrats,
aam.

danwashuk · #28 11-22-2007, 09:27 AM

In retrospect the teflon tape is a good idea. I thought about it but was afraid of getting it inside the transmission. The old valve did not appear to have anything on it, and there was no washer of any sort either. I thought about making a washer out of some gasket paper if I could not stop the leak by tightening it some more, but it has now stopped leaking...................Dan

aam · #29 11-22-2007, 01:18 PM

Quote:

Originally Posted by danwashuk

In retrospect the teflon tape is a good idea. I thought about it but was afraid of getting it inside the transmission. The old valve did not appear to have anything on it, and there was no washer of any sort either. I thought about making a washer out of some gasket paper if I could not stop the leak by tightening it some more, but it has now stopped leaking...................Dan

Hi danwashuk.
Some times when I want to seal something difficult I will twist the Teflon
tape so it will form like an O ring.
So you can seal, with out anything going in.

Regards,
aam.

richardr · #30 08-09-2012, 01:34 PM

I have a 560 sl 86 I may have a problem with Transmission Modulator my shift from park to rev to come out of drive way it is hard shifting a cluck
after the engine warms up it seems to get better
dose that sound like a Transmission Modulator 2-3-4-gear fine
to you ???
7724850326
richard