From hard shifts to flaring - PeachParts Mercedes-Benz Forum

firemediceric · #1 11-19-2006, 01:06 PM

I followed the instructions to remove the EGR vacuum lines from the top of the valve cover on my 1981 300 SD.

The hard shifts disappeared, but I now have SEVERE flaring. From what I have learned from Brian Carlton, this is caused by too much vacuum. This makes sense, as one of the pieces of tubing I removed exhibited a lot of little dry rot type cracks. Perhaps those cracks made it so it was shifting hard, but not flaring?

I am stuck at work but I have sent my wife to Sears to buy a Mighty Vac for me. As you can tell, I have no experience with one and have not had the need for one until now.

I have been searching the archives, but I’m running out of time, as my employer’s computer system only allows us 2 hours of internet time a day. I am looking to find exactly where the vac modulator is located and how I go about adjusting it.

rg2098 · #2 11-19-2006, 03:52 PM

Modulator is located on the driver side of the transmission. It's green and should have a black cap on it. You remove the black cap and their should be a little metal knob. I believe you turn it clockwise to firm up the shifts.

Brian Carlton · #3 11-19-2006, 07:08 PM

You're not interested in the vacuum modulator.

You're interested in the vacuum control valve. This shall henceforth be known as "VCV".

This valve is white in color and sits atop the IP. It has a vaccum line going into the top of the valve with a green damper inline. You'll see this green damper and will know that this is the valve.

The line with the green damper is connected to the main vacuum line with a T. One side of the T goes to the supply vaccum and the opposite side of the T goes to the transmission.

What you will do is to remove the supply vacuum line and connect up your Mityvac. Now, you've got a Mityvac on one side of the T and the transmission on the other side of the T and the VCV on the bull.

Pump up the Mityvac and see if it holds vacuum. I presume that it will. Get a reading and report back with the result.

Watch the Mityvac and slowly open the rack. The Mityvac gauge should fall gradually the further the rack is opened. When the rack is fully open, the reading should be close to zero.

All these tests are performed with the engine not running.

Report back with results.

rrgrassi · #4 11-20-2006, 11:14 AM

Brian,

How do you "open the rack"? It that by moving the throttle linkage from idle position to WOT?

Oh, BTW, thanks again for your help. I ordered the orifice #63 from the diagram. It will be in this week. MB showed it to be 2mm inner diameter for the Federal emissions group. Also, MB does not list the part as an orifice any more. They now call it a nozzle. FYI, thier vacuum diagram was a bit different than the diagram posted here, and they had to find an older parts guy who knew about the vacuum systems on out older MB's

I will post a part number when I get it.

tobybul · #5 11-20-2006, 11:33 AM

Brian, I'll be watching this thread as I need to do the same with mine.

Brian Carlton · #6 11-20-2006, 12:43 PM

Quote:

Originally Posted by rrgrassi

Brian,

How do you "open the rack"? It that by moving the throttle linkage from idle position to WOT?

Oh, BTW, thanks again for your help. I ordered the orifice #63 from the diagram. It will be in this week. MB showed it to be 2mm inner diameter for the Federal emissions group. Also, MB does not list the part as an orifice any more. They now call it a nozzle. FYI, thier vacuum diagram was a bit different than the diagram posted here, and they had to find an older parts guy who knew about the vacuum systems on out older MB's

I will post a part number when I get it.

Yep, that's how you do it.

Good job. It's quite difficult to find a parts man that knows what you're speaking of.

Please post that p/n. It's desperately needed by many members.

firemediceric · #7 11-20-2006, 01:09 PM

Brian,
I believe I followed your instructions to the letter. I left the first hose from the "T" to the damper and on into the VCV in place. I left the second hose from the "T" to the transmission in place. I removed the third hose from the "T", the one coming from the vac. pump. Into this hole on the "T" I placed the Mity Vac.

When the Mity Vac handle is squeezed I read 11 on the guage, but it does not hold. I start losing vacuum immediately, down to 0 over the course of 23 seconds. When I open the rack, the guage falls to zero almost instantly.

I take it these results are a little different than you had expected?

For my drive home from work today I disconnected the vac line at the damper above the VCV. The flaring went away, but the hard shifts were back, as would be expected. Of course, I reconnected the vac line in order to turn the car off.

What do you recommend I do from here?

rrgrassi · #8 11-20-2006, 04:24 PM

Quote:

Originally Posted by Brian Carlton

Yep, that's how you do it.

Good job. It's quite difficult to find a parts man that knows what you're speaking of.

Please post that p/n. It's desperately needed by many members.

Brian, thanks for the confirmation on moving the rack.

I'll get part number for all of them, including the CA emission cars. IIRC, when I looked at their monitor the Cali cars called for 1.1 mm diameter for #63. I do remember the part number started with 116. I found and copied the part numbers posted by Sam Ross, but they did not match, according to the parts guy, what is on the MB part file. I did bring a copy of the diagram to show them exactly what I was looking for. At first they told me it was just a connector. I told them that was incorrect, and after some back and forth, they called out the older guy. The younger ones apologized and said they just learned something new. The older guy also told me that part names in the FSM are sometimes different than what the parts dept has recorded and looks at.