I've been working on my 83 300D and am down to trying to soften up the 1st to 2nd gear shift. I put the vacuum gauge on the line to the tranny, and everything appeared normal.

Today, I made the measurement again, and at idle I'm only seeing 10 in of hg. I know that in the past it was always about 15 in of hg at idle. After a few minutes of pulling and pluging lines, I found that the vacuum line to the climate control unit was the cause, but only when the control unit was set to vent. If it was turned off, the vacuum jumped back up to 15 inches of hg.

The cause is another bad vacuum actuator (I found another one last week).

So I put it all back together and took it for a test drive. When the climate control was set to off, the shifts were still sharp, but overall very nice. Then I hit the vent button, and the 1st to 2nd gear shift was again very, very abupt...way too harsh.

I guess the moral of the story is that when vacuum is used to simulate a gas engine for the transmission modulator, and that vacuum runs to many places, make sure when you're troubleshooting you measure the vacuum with all of the climate control settings the same as when you note the problem (either that or plug the line going to the climate control while troubleshooting)

Joe

Joe:

Same problem, different car -- my 87 300D was shifting hard, especially the 2-3 shift, and when I started using the AC this spring, blew only out the defrost vents.

Located the problem to the vacuum switchover valves for the EGR and air recir servos. I plugged the lines pending replacing the switchover valves (or at least pulling the air filter and checking everything out properly). AC and shifting suddenly became normal -- the swithover valves were leaking so badly there wasn't enough vacuum to run the rest of the stuff.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I'm driving an 85 TDT and am finding the shift to be generally late. The RPM too high when gear changes. Abrupt and hard shifts result. I'm curious about the 'switchover' valves. Which components are those? Thanks.

these valves are located just above the push button control unit for the climate control. after changing for the first time, i can now go in a change one in about 5 minutes by accessing these valves from behind the long slneder wood panel that holds the sunroof sw, rear defrost sw, etc. each valve is about 22 or so from fastlane and worth it to replace all 5. good luck

I just started getting the same results as mentioned in this thread. Where is this switchover valve in an '87 300SDL W126 chasis? I really need to get this done. Also, how many do I have, if you know?

Thanx..

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99 C230K Sport
87 300SDL
81 300SD

Jay:

The switchover valves for the EGR and air recirc valve (on the turbo) are under the air filter on the passenger side, down by the turbo.

There are four vacuum lines from the accessory connection on the 603 -- a five way connection right up front just behind the rad. Two go off to the climate control and transmission system on the driver's side and the other two go to the swithover valves.

The best way to check them all out is to get a MitiVac hand pump -- you can then pull one line at a time off and insert the rubber fitting on the pump into the line and pump -- if it won't hold vacuum, something is wrong. There are some vacuum storage tanks in the system that can take a number of pumps to evacuate, so don't assume a system is bad until you have operated the pump several strokes.

Other than the switchover valves, check all the rubber parts of the vacuum lines -- they get old and soft (and sticky) or rock hard, and in either case leak (sometimes the soft ones will collapse, too). Replace any that are iffy with standard vacuum line from the autoparts store. Make sure you don't lose any white or yellow "butt connectors" present -- these are restrictors and must be replaced into the original position.

The transmission control circuit is somewhat complicated -- I have a diagram I can copy and mail you if you need it.

Most likely you have dead switchover valves or a leaking connection someplace -- the rubber is the correct age to fail! Sorry to say, the usual problem with the switchover valves is a failed valve, not leaking connectors.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

PSFRED, thanx alot. Hopefully I'll get to do this investigation on the system this weekend. The first thing I did check when the issue occurred, were the lines in the engine bay. All seemed well.
BTW, if you can, do send me that diagram. Most definitely will come in handy.
Thanx again..

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99 C230K Sport
87 300SDL
81 300SD

I was ready to do my work today on checking the A/C issue with the vents. popped the hood open and was ready to remove the air filter. Then I took a good look at the EGR line. The rubber on the vacuum line was frayed/cracked. Replaced it with another piece of rubber hose and started up the car. The A/C began to work as normal through the vents. ran through all the buttons on the HVAC controller and all is well.

Thanx PSFRED/Peter. Because of people like you, Guys like me love this site !!!

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99 C230K Sport
87 300SDL
81 300SD