'80 240D modulator ruckus - PeachParts Mercedes-Benz Forum

nickofoxford · #1 03-08-2009, 11:34 PM

Hey guys i've been having trouble with Betsy's moody shifting and need some advice..

I've checked all vacuum components and I do know that the valve on the valve cover leaks, so I bypassed that for now and I get 15" hg idle and it slowly goes to 0" at WOT, good numbers as I have read on here. I have adjusted the linkage to the VCV and it will hold about 20" vacuum at idle and not hold at WOT, all is still good here.. right? Shifts are slow, lazy, sloppy, and are probably going to cost my clutch packs here soon.. I have managed to get around on it by letting off the throttle to let in engage, but I want this thing fixed. I have a new valve coming to replace the one on the valve cover, and have tried probably every single notch on the modulator to no avail.. So bottom line what should I do next? Maybe this has to do something with how the vacuum goes down slowly at WOT to 0"? It takes about 15 seconds to do so, I have a neat little vacuum gague strapped to the windshield wiper tee'd into the vac line to the transmission. By the way this is a '80 240D without the bowden cable.

DIESELVOLVO · #2 03-08-2009, 11:40 PM

Put a mity vac on the line going to the modulator. See if it holds vacuum.
I wil bet dollars to donuts it will not. There is an o-ring in the modulator that can allow it to leak vacuum or it could be the bit of oil soaked rubber vacuum line that is attached directly to the modulator.

nickofoxford · #3 03-11-2009, 11:55 AM

Checked the modulator today and it holds for all of 20 seconds, looks like we're having donuts

So im going to stop by NAPA and grab an o-ring later today and get that nasty one swapped out.

kingdoc1 · #4 03-11-2009, 05:33 PM

Quote:

Originally Posted by nickofoxford

Hey guys i've been having trouble with Betsy's moody shifting and need some advice..

I've checked all vacuum components and I do know that the valve on the valve cover leaks, so I bypassed that for now and I get 15" hg idle and it slowly goes to 0" at WOT, good numbers as I have read on here. I have adjusted the linkage to the VCV and it will hold about 20" vacuum at idle and not hold at WOT, all is still good here.. right? Shifts are slow, lazy, sloppy, and are probably going to cost my clutch packs here soon.. I have managed to get around on it by letting off the throttle to let in engage, but I want this thing fixed. I have a new valve coming to replace the one on the valve cover, and have tried probably every single notch on the modulator to no avail.. So bottom line what should I do next? Maybe this has to do something with how the vacuum goes down slowly at WOT to 0"? It takes about 15 seconds to do so, I have a neat little vacuum gague strapped to the windshield wiper tee'd into the vac line to the transmission. By the way this is a '80 240D without the bowden cable.

Any help would really be appriciated. *cough* Brian Carlton *cough*

Am I understanding correctly that when you hold the VCV at WOT it takes 15 seconds for the vacuum bleeds down to Zero? If this is the case, I believe you may have a clogged orfice, as I remember the VCV varys the vacuum by throttle position, more throttle=less vacuum and if it is not bleeding off vaccuum quickly enough you will experience soft shifts. Less vaccum=harder shifts, more= softer shifts. I other words, your VCV may not be allowing enough vacuum to leak off quickly enough. I don't remember if your application has the 3/2 valves on the valve cover-if it does check them too. Do you have a vacuum diagram for your car? If you do it would help alot.

nickofoxford · #5 03-12-2009, 10:08 AM

Quote:

Originally Posted by kingdoc1

Am I understanding correctly that when you hold the VCV at WOT it takes 15 seconds for the vacuum bleeds down to Zero? If this is the case, I believe you may have a clogged orfice, as I remember the VCV varys the vacuum by throttle position, more throttle=less vacuum and if it is not bleeding off vaccuum quickly enough you will experience soft shifts. Less vaccum=harder shifts, more= softer shifts. I other words, your VCV may not be allowing enough vacuum to leak off quickly enough. I don't remember if your application has the 3/2 valves on the valve cover-if it does check them too. Do you have a vacuum diagram for your car? If you do it would help alot.

I nailed down the slow leak-down problem yesterday turns out the modulator line had been cut by the P.O and was really pinched, fixed that right up. I did have the 3/4 valve but bypassed that because it did nothing but leak. Can you explain what the 3/4 valve actually does? I do have a diagram saved from one of the stickys on here.

kingdoc1 · #6 03-12-2009, 08:41 PM

The valves on the valve cover are on/off valves and will completely shutoff or allow vacuum to the VCV depending on IP linkage position. I am relying heavily on memory for this one, so if anyone wants to step in and correct me, I won't be offended. I believe one valve shuts off vacuum to the VCV at off idle, then transfers control to the VCV later in the IP linkage travel. I think one of the other valves is related to the egr system. You stated that your car does not have the bowden cable, so I am assuming you have the 1981 version which used only vaccum to control the trans, as opposed to the early version with just a mechanical linkage and the later version with vaccum controls and a bowden cable. You might have to refer to 1981 vacuum diagrams to match your car. Btw, did your modulator line repair fix your problem?

nickofoxford · #7 03-15-2009, 10:51 PM

Quote:

Originally Posted by kingdoc1

The valves on the valve cover are on/off valves and will completely shutoff or allow vacuum to the VCV depending on IP linkage position. I am relying heavily on memory for this one, so if anyone wants to step in and correct me, I won't be offended. I believe one valve shuts off vacuum to the VCV at off idle, then transfers control to the VCV later in the IP linkage travel. I think one of the other valves is related to the egr system. You stated that your car does not have the bowden cable, so I am assuming you have the 1981 version which used only vaccum to control the trans, as opposed to the early version with just a mechanical linkage and the later version with vaccum controls and a bowden cable. You might have to refer to 1981 vacuum diagrams to match your car. Btw, did your modulator line repair fix your problem?

Weird, it might be an 81 motor and trans in there.. there's parts with "617" on them all over the place so I wouldn't doubt it being a transplant engine..

The pinched line did nothing to shift quality or timing, it just made the gauge slam down to 0" at WOT instead of kinda meander down to 0". Right now the modulator is adjusted almost to the outer CCW limit which should restrict vacuum, right? Does the 3/4 valve shut off vacuum supply to the VCV at WOT? Also, my kickdown doesn't work and it does click and has worked before this all started happening.. Guys im stuck here

What I am thinking is the modulator needs readjusting, but I need some guidance on how to do so.

Can someone verify this?

- WOT= 0" hg
- Idle= ~15" hg
- Higher vacuum= smoother, sooner shifts
- Lower vacuum= tighter shifts with more latency for acceleration
- Modulator key CW= more vacuum
- Modulator key CCW= less vacuum

nickofoxford · #8 03-17-2009, 10:56 PM

Anybody?

gregszustak · #9 03-18-2009, 06:52 AM

On a 240d
The vacuum starts off the main vacuum line.
It goes through the u-shaped hose on the 3/2 valve DIRECTLY to the transmission.
If you disconnect or bypass the 3/2 valve you will have constant vacuum at the modulator, hence early and sloppy shifts.
The other line off the 3/2 valve is a bleeder line. It bleeds vacuum via the VCV to reduce vacuum at the modulator.
If the 3/2 valve is disconnected or bypassed the VCV valve has nothing to do with shifting, it is not being used.

gregszustak · #10 03-18-2009, 09:07 AM

Quote:

Originally Posted by gregszustak

On a 240d
The vacuum starts off the main vacuum line.
It goes through the u-shaped hose on the 3/2 valve DIRECTLY to the transmission.
If you disconnect or bypass the 3/2 valve you will have constant vacuum at the modulator, hence early and sloppy shifts.
The other line off the 3/2 valve is a bleeder line. It bleeds vacuum via the VCV to reduce vacuum at the modulator.
If the 3/2 valve is disconnected or bypassed the VCV valve has nothing to do with shifting, it is not being used.

If you remove the 3/2 valve from the top and connect the bleeder line directly to the u-shaped vacuum line your transmission should work, more or less, somewhat normal.

If you remove and plug the line coming from the main vacuum line to the u-shaped rubber on top of the valve cover your transmission will not get any vacuum and your shifts will be very late and hard. This would indicate your modulator is working to some extent (at least at the extremes.)

nickofoxford · #11 03-19-2009, 11:17 PM

Quote:

Originally Posted by gregszustak

If you remove the 3/2 valve from the top and connect the bleeder line directly to the u-shaped vacuum line your transmission should work, more or less, somewhat normal.

If you remove and plug the line coming from the main vacuum line to the u-shaped rubber on top of the valve cover your transmission will not get any vacuum and your shifts will be very late and hard. This would indicate your modulator is working to some extent (at least at the extremes.)

I have the VCV tee'd in with the vacuum supply and the modulator line. I still get 15" idle and 0" WOT with a gauge tee'd into the modulator line.

From what you guys are saying the 3/4 valve would do the same exact thing and would more or less only be there to prevent leak-down when the car is off.

I tried disconnecting the vacuum line to the modulator all together and I have the same exact problems, so Im going to say the modulator is poop. I read iandiam's post about how the spring can rust out in the modulator and give the symptoms I have.

Here's the link.
a bad modulator valve can cause flare in older 722.3x

Any recomendations with pulling the modulator? Tips, tricks?

gregszustak · #12 03-21-2009, 06:29 AM

I haven't had to change mine yet but it looks like it just unscrews as opposed to the 300 series which is clamped in.

Anybody change a 240d modulator?

2/3 valve on top of the cover is basically an on/off switch

nickofoxford · #13 03-25-2009, 04:41 PM

Quote:

Originally Posted by gregszustak

2/3 valve on top of the cover is basically an on/off switch

Sounds like it is basically there to prevent leakdown after the engine is not supplying vacuum, maybe that makes it easier on the vacuum pump.

My other thought was the 2/3 valve supplies full vacuum to the modulator at idle, with the VCV blocked out of the whole circuit. With some throttle the 2/3 valve introduces leak from the VCV and allows the vacuum curve with throttle travel. Now I don't know if I am right, at all, that is my theory. I have a dead 2/3 valve and couldn't test it out to see how it actually works. I wish someone could clarify this for me.

Throwing this out there..

My transmission fluid is god only knows how old, should I change it and see what that does?

I've read that sometimes the PO will put additives in the transmission and with a fluid flush the seals are rendered useless without the additive.

Also, my dad has told me about how the particulate clutch matter helps the transmission work and without it, it will make things worse. I think the particulate matter would only clog the filter in there and again, make things worse..

Opinions, opinions. Anyone have facts?

gregszustak · #14 03-25-2009, 08:31 PM

"My other thought was the 2/3 valve supplies full vacuum to the modulator at idle, with the VCV blocked out of the whole circuit. With some throttle the 2/3 valve introduces leak from the VCV and allows the vacuum curve with throttle travel."

Yup.
Pull the hoses off the 3/2 valve and connect them together, leaving the 3/2 valve out of the circuit. It may start off in second or seem a little squirrely starting off.

Tranny opinion, change the fluid, DON'T FLUSH IT!

nickofoxford · #15 03-29-2009, 01:03 AM

Quote:

Originally Posted by gregszustak

"My other thought was the 2/3 valve supplies full vacuum to the modulator at idle, with the VCV blocked out of the whole circuit. With some throttle the 2/3 valve introduces leak from the VCV and allows the vacuum curve with throttle travel."

Yup.
Pull the hoses off the 3/2 valve and connect them together, leaving the 3/2 valve out of the circuit. It may start off in second or seem a little squirrely starting off.

Tranny opinion, change the fluid, DON'T FLUSH IT!

Good stuff, thanks for the clarification

I'll change the fluid tomorrow, I guess I should throw a new filter and throw a filter at it as well and report back. What's the difference in flushing and changing? Should I put a small amount of additives in the new fluid as a precaution? I mean small amount

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