Help with 87 tranny issues - PeachParts Mercedes-Benz Forum

burn_your_money · #1 12-05-2010, 02:57 PM

Hello, I am working on a friend's 87 MB. I don't know a whole lot about MB and their naming but I am familiar with VW diesels. Is this a W124? With a 607 engine and a 227 tranny?

The issue is related to the transmission. Before the first to second shift the car shakes and thuds a lot. It sounds and feels similar to a loose wheel that is about to fall off. The knocking appears to be coming from the transmission area. I'm assuming that it is a vacuum issue and possibly the secondary pump thing? that is at the rear of the tranny for push starting. I have read that it sometimes engages at the wrong time. When it does engage at the wrong time, what type of symptoms does it display?

I meant to check the driveshaft for play but forgot to do that.

She came over today for an unrelated issue (the tensioner spring broke) and I was looking under the hood at the various vacuum lines. I noticed that several were unhooked so I hooked them back up. I also noticed that this one was broken

I have found a vacuum diagram for the car and it looks like this is the "switch-over valve, engine overload protection." I can see that it is hooked up to the boost compensator as well as other lines. My question is, is it better to leave this open to atmosphere or to hook line #1 and line #2 up together?

This picture shows where it hooks up to on the pump

Also, is this the vacuum amplifier?

Thank you

europower · #2 12-05-2010, 03:54 PM

Eliminate the saucer, go straight to Tranny from vcv.

burn_your_money · #3 12-05-2010, 04:40 PM

Which saucer? The thing in picture #3?

What is a vcv?

Jeremy5848 · #4 12-05-2010, 04:56 PM

The '87 has a rather complicated vacuum system for control of the transmission. The blue flying saucer or vacuum amplifier (circled in your last picture) combines vacuum from the vacuum pump with pressure from the turbocharger to create a vacuum signal for the transmission. It is supposed to mimic the vacuum from a gasser's intake manifold so the same transmission can be used in gassers and diesels.

The vacuum control valve is at the bottom of your second picture. It decreases the vacuum sent to the transmission as the footfeed is pushed more. Vacuum is used to adjust the firmness of the shift (no vacuum = very hard shifts) while the Bowden cable attached to the throttle linkage determines when upshifts are made.

By the looks of your pictures, your friend has neither cleaned his engine compartment nor replaced any vacuum connectors. They are all pretty rotten and need attention.

Europower's suggestion is to connect the output of the vacuum control valve directly to the transmission. It won't be perfect but it will work and will allow you to eliminate the transmission as a possible problem.

Wodnek · #5 12-05-2010, 08:06 PM

Your desription "sounds like a wheel is about to fall off" makes it sound like a bad center support on the driveshaft. That is exactly what that feels and sounds like.

DieselPaul · #6 12-05-2010, 08:49 PM

So if your hard shift feels like the clunk is coming from the back of the car more than the trans itself would you say it would be the center support bearing?

To the OP. That looks a lot like under the hood of my 1987 300D which is a W124. The motor is an OM603 and the transmission is a 722._ can't remember if it is a 722.3 or 722.4

bigblockchev · #7 12-05-2010, 10:13 PM

It is a whole nother thing to learn. I am having my jollies with my Mercedes automatic as well. Some things are similar to VWs and some things are way different. Cheers Dan

burn_your_money · #8 12-06-2010, 08:50 AM

Hi Dan,

I thought I recognized your username from over yonder.

Thank you everyone for all your input. I will give it a look over and see what I can do. In regards to running a direct line, I think I will do that. Do I need to plug off the rest of the vacuum system where I disconnect it from the VCV?

How hard is this center support bearing to change?

Unfortunately the lady who owns this car does not have a lot of money so basic repairs are often neglected. I'd be surprised if the oil has been changed lately...

What about the LDA? Hook that up directly or do I need that engine overload protector?

bigblockchev · #9 12-06-2010, 08:47 PM

I believe that what Europower is getting at is to take the output line from the VCV on the side of the IP & connect it directly to the modulator line on the transmission. The Modulator is a brown plastic pot on the drivers side of the trans. I believe the plastic line will be black in color. I believe that the connection on top of the VCV line will have a green "damper" in line with it, it also will have a "Keyed" rubber hose connector. This will result in a somewhat more "primitive" version of control of the transmission modulator, but Mercedes does this on some vehicles , I have an original diagram from Mercedes which shows exactly this arrangement on one of their vehicles. Since there are already some broken connectors and lines it may be better than what you have. Or so my thinking goes. I would plug the leftover lines but don't think it will make much difference to anything . The center bearing replacement will probably require removal of the front and rear driveshaft sections and will then be self evident. If I recall correctly the driveshaft bolts are 12mm triple square or 12Pt allen head bolts similar to something on VW's. They are quite tight. It is also possible that one or more the rubber coupling discs which pass for universal joints are shot, just a guess on my part.

compress ignite · #10 12-07-2010, 03:32 AM

Do Not Long Ignore ANY driveline Noises/Vibrations.

rs899 · #11 12-07-2010, 08:52 AM

Tyler-

By all means, check the flex discs and center support bearing, as these are dangerous if left unattended. However, I am a bit confused about the symptoms.

It's pretty normal for a Mercedes transmission to have a very hard 1-2 upshift when there is no vacuum available to the modulator of the transmission. Is that what is happening?

Yes, it is probably best to run a line directly from the VCV to the tranny modulator, and bypass all the other vacuum users ( locks, HVAC) that MB likes to confuse us with.

Not so simple as a 1.6NA, eh?

Rick

burn_your_money · #12 12-08-2010, 11:16 PM

Yeah it certainly makes me appreciate the 1.6NAs in my family...

Rick, which symptoms confuse you?

I personally understand the risks of faulty driveline components however the owner doesn't see the importance...

Yes it is a hard shift from 1-2, very, very hard. I don't own a vacuum gauge yet but I will do some investigating before I just start deleting and bypassing things.

With the direct line to the tranny, should I include or delete the damper?

jonbobshinigin · #13 12-08-2010, 11:34 PM

Start by bypassing the Switch shown in the first picture. Simply unplug the electrical connector and then connect the two vacuum lines together. See how it drives. Then I would get a few feet of vacuum line and replace all the bits here and there. DO NOT ADJUST a thing until you have sorted out vacuum issues. There is also a plastic line that goes from up top to the transmission modulator. It can be accessed on the driver's side and a 1.5" of vacuum hose is all you need to replace it. Trust me on this, get the vacuum issues resolved FIRST! It is cheap and only takes a little bit of time.

How is the car shifting in other gears?

rs899 · #14 12-09-2010, 07:49 AM

Quote:

Before the first to second shift the car shakes and thuds a lot

Tyler- I am confused by this- are you really saying BEFORE the shift, or the shift itself is very harsh?

IMO, the best general course of action is to start with connecting a line directly from the Vacuum control valve to the transmission modulator, and block off all other consumers of vacuum (except the brakes). However, since I don't have one of the later cars, I will defer to those who have them, as there were some improvements made (and complexity added). If that helps, in oreder to fine tune the transmission, you will need to may need to adjust the VCV (if you can on that version) and the modulator. There are plenty of discussions on that here.

Rick