Vacuum Control Valve
 

OK, I had a post a couple days ago about my tranny skipping over 3rd and going into 4th. I suppose you could say when it shifted there was slight flaring on all gears as it shifted soft, much softer than my '79 300. I guess I was being lazy and hoping someone would respond with a precise answer, but I got the good links to the trans adjust articles.
So, putting my laziness aside, I read them all again a started to go through step by step. By the way, I just changed fluid and filter, Mobil 1 ATF and it is at the correct level.
So, first thing is to make sure you have good vacuum flow at the T connection coming off the main vacuum line. Two of the articles sugget to drill with a 1/16" bit to "clean out" the orafice if it is slightly closed. Well, I did that, and there seemed to be some debris or what have you impeding the vacuum flow as I got stuff out and my vacuum readings were instantly in the green after that whereas before they moved more slowly to the green.
Ok, so far so good. I go for a ride and now I have really bad flaring in all gears, bad flaring and slipping and very quick shifts :eek: Great, what have I done. So I move on - linkage looks good. clearance to the stop looks correct. I start getting to the area of how as you accelerate the vacuum should go down to zero or near it and that if you have too much vacuum it will cause the symptoms I just created. So, next I remove the cover of the little finger that pushes on the plunger as you accelerate. Finger looks OK, I have the car running and hook up the vac gauge to the line that feeds the modulator at the trans. I move the pluger in by hand and see the vacuum go down, but nowhere near zero. I am in the green, and it goes down to 10 or so at it's lowest point. So I read further and pop the cap off the vacuum Control Valve and try to adjust that. I get the vac to go down a little bit - so now thew lowest point is between 5 and 10. Took it for a ride and it still flares badly and skips and shifts way too early. Questions:
1. Did I create too much vacuum flow by drilling the 1/16", or did I just get it to where it needed to be?
2. Is the unit with the plastic finger and plunger that moves in and out with the throttle bad?
3. Is the Vacuum Control Valve bad, not bleeding off enough vacuum?
4. Where can i purchase these parts, I am not seeing them here or at other sites?
Man, I want a manual :(

Have you checked that at full throttle the vacuum control lever is within 0.020" of the pin? What vacuum reading do you get when you Mityvac the vacuum control with the lever 10 mm from the pin? (IIRC factory spec is between 6 to 8 inHg) It sounds like you are getting too much vacuum to the vacuum modulator on the trans. causing the soft early shifts. So you have 2 options increase the modular pressure by screwing in the key under the vacuum cap of the vacuum modulator mount on the trans or decrease the vacuum coming out of vacuum control on the IP. I tuned mine to shift the hardest I can tolerate between the 1-2 shift which minimizes the flaring between the 2-3 shift.

http://www.peachparts.com/shopforum/showthread.php?t=121049
This is a link to a current thread on vacuum. I posted some links in that thread that may be useful to you.

Try disconnecting the vacuum line to your transmission and see if the trans shifts hard. That will give you an idea of how far you can go with vacuum adjustments.

Yes, I have the .020" at full throttle. I didn't bother with the 10mm reading because I knew at full throttle I was only getting down to between 10 and 5 in. I played with the vacuum control adjust (under the dome cap) and only could improve it marginally. I also started turning the key on the modulator, bit figured why screw with that when I'm not getting the vacuum down to where it needs to be before it is delivered to the modulator anyway.

So, could my vacuum control be bad because it is not bleeding enough vacuum out, or could it be the little finger actuator on top of the valve cover. It sure is weird that things went really screwy after I drilled the 1/16" at the T. I had done the same drilling on my '79 300D and it didn't go crazy like this is. So I kind of think I just got the vacuum level to where it needs to be coming off the T, but the control valve or something else is not bleeding enough off.

There's an adjusting nut on the valve too, under a dome shaped cap towards the front of the car. You can adjust the vacuum range with that. I wouldn't go crazy with jacking up the modulator on the tranny, mine blew the tranny not long after doing all the same stuff you are going through....

At idle, what is the vacuum reading in the line to the modulator (downstream from the vacuum control valve)?

Thanks - I turned it clockwise to to harden the shifts, but this was before I started doing too much upline. I stopped adjusting the modulator figuring my probelm was upline. I probably turned it 3/4 of the way around. I think I'll turn it back to it's original position tonight before I start monkeying around again.

I'll check tonight, but going from memory I think it was too high based on some reading I'm doing this morning. I think it was up in or near the green zone. I'm taking the reading from the rubber connector up at the valve cover (the vacuum valve with the plastic finger that pushes a plunger in when throttle is increased) where the black line departs on it's journey down to the modulator on the trans.

I think what I'm reading is maybe I have too much vacuum going from the assembly on the valve cover down to the vac Control Valve that bleeds of vacuum. If the vacuum is too great the control valves' range does not get it down to 0???

So did I open a can of worms by drilling the T to a 1/16" opening?? or is the valve unit with the plunger and plastic finger bad and allowing too much vacuum to go down to the Vac Control Valve.

YES, you opened up a restriction which was designed to allow the vacuum to drop close to 0.
can you get a plastic bead which will fit into the tube and drill a tiny hole in it (1/64" would be close)
Try that and report back later.
Tony

I believe that the recommendation was to clean the orifice, not "drill it out." So if you materially changed the size of the orifice, you likely caused more problems than you solved.

I just posted this DIY Article today that may be helpful. It has been referenced here before but, I pulled it into our DIY section.

Also

Please remember that only a SMALL PORTION of the parts we have available are in the Fastlane catalog. Call Phil at 888-333-4642 or email him if you need something not listed.

I know this is a possibility, but 2 of the articles in the trans adjust area said to do this. Also, I did the same thing on my "79 300D last summer and it didn't change anything.

I thought perhaps you were referring to this article:
http://transmission.articles.mbz.org/adjust/
It says "Take a small wire or 1/16" drill bit and make sure the opening is clean of any carbon or build up."

I'm at home for lunch - gotta love these Mercedes :D I checked - it's 22 lb. The line that goes form the vac valve with finger and plunger on top of the valve cover to the Vac Control Valve reads 0 lb at idle and immediately jumps up when throttle is applied.

No, I was referring to this one in the DIY link - it is from Sun Valley Mercedes.

The supply is taken from the Power Brake Booster vacuum line ("T" in line). With the engine running, and the transmission full of oil, unplug the supply and install a vacuum gauge. The gauge's needle should jump up to 15" - 20" of vacuum. If the needle rises slowly, your supply is restricted. Remove the gauge and drill the orafice with a 1/16" drill bit. Make sure you do not drill all the way through the supply tube.
Now that the supply is good, you need to re-connect the vacuum line to the Booster Supply Line. Now disconnect the vacuum modulator line from the White Bleed Valve. Plug in the Vacuum gauge in the modulator line's place and take a vacuum reading. It should read 10" - 20" of vacuum. If not, check the white vacuum switches located on the top of the valve cover, blocking each one off to test for a vacuum leak. Check all the vacuum hose connections for leaks and check the EGR valve for leaks, as well. If any are leaking, replace them. Make sure that the linkage arm from the White Bleed Valve to the Injection pump is hooked in properly. If you are getting a good vacuum supply to the White Bleed Valve, but no vacuum to the modulator line, replace the bleed valve. If you are getting good supply to the bleed valve and you are getting 10"-20" of vacuum to the modulator, open and close the throttle slowly, with the engine running, and watch the vacuum gauge. It should drop according to throttle position. I.E.: Half throttle, half vacuum. Full throttle, no vacuum. If you don't get the proper regulation, you must replace the White Bleed Valve. When you finally get good vacuum regulation to the modulator, you are done. Follow the adjustment page for proper modulator adjustments.