'85 300D vacuum modulator missing parts - PeachParts Mercedes-Benz Forum

engatwork · #1 08-03-2002, 11:58 AM

I pulled the existing vacuum modulator out this morning to replace it and was surprised to see that there is no modulating pressure control valve nor the spring that goes between it and the thermal thrust pin. I have had this car for a year and a half and have slowly been going through every external component of the tranny to get it to shift right. The problem with it is that it shifts into high gear by the time it gets to 30 mph. I put the existing vacuum modulator back on because there does not seem to be any problem with it. I feel that missing these parts will cause shifting issues and will get them coming over the next few days to install next weekend.

edited part In reviewing the exploded drawing in the ATSG manual at the front of the manual it shows a spring between the modulating pressure control valve and the thermal thrust pin. In a later section of the book it does not show this spring. Can anyone tell me if a spring goes in here or not. It looks like the part number for the modulating "slide" valve is 126 277 21 32.

psfred · #2 08-03-2002, 07:05 PM

Jim:

I don't know if the spring belongs there for sure, but I would bet it does -- I've suspected since you first described the shifting problem you have that there was something missing in there. The modulator must move the valve to have any effect, and it seemed to me it wasn't.

We are going to the Brickyard 400 tomorrow -- taking lots of Gatorade and water, it's going to be hot!

Peter

engatwork · #3 08-03-2002, 07:15 PM

Peter - ya'll drive careful and have a good time - drink water whether you are thirsty or not

.

Early tomorrow morning I am driving 180 miles to go take a look at an original owner 240D with manual tranny (26x,xxx miles). Maybe it won't follow me home

. I will post the phone no, etc. on this site if I don't purchase it and it looks as good as it sounds.

I am planning on going by the dealer Monday morning and take a look at the picture they have for the vacuum modulator area and get whatever I need. Like you, I am pretty sure there is supposed to be a spring in there, otherwise what pushes the modulator pin back. Hopefully, this will get the tranny working the way it should. I messed myself up by driving a 300D and SD with a properly working tranny. Oh yea, the downshift solenoid is inoperative too so I will be getting it back into service over the next couple weeks. I have power to the switch and the switch works.

psfred · #4 08-03-2002, 07:38 PM

Jim:

My 220D shifted like that when I first got it -- no hill climbing ability at all!

I have a new project, too -- bought a 1972 280 SE 4.5 for $50, would be driving it if the PO hadn't left water in it after he decided not to replace the water pump. Runs great, now that I got the fuel pump turning, even on the residual dead gas I couldn't get out of the system and one gallon of clean fuel! Unfortunately, the block is split down the valley on both sides, water runs out as fast as I can pour it in! Heats up like crazy, but I can spin the tires on dry pavement!

Peter