Hello all,

My 85 300SD transmission flares from 2-3 and 3-4 slightly when the transmission is cold. Once everything is warmed up, it seems to shift fine.

I took some vacuum measurements yesterday and have attached an image. (Hopefully you can read the measurements in red)

The system shows 20 in-Hg @ idle when I tap into the white line and plug the other end. 15 in-Hg inline measurement.

It seems as if the VCV shows 0 in-Hg the entire time with no metering as I drive it around.

The transmission line does show a change from 6in-Hg to 1in-Hg as I depress the pedal to full throttle.

Does this mean the VCV valve is bad?

Should I test the vacuum modulated on the transmission next? Or just adjust the setting?

I am confused at what the purpose of valve #125 is in the attachment.

Sorry for any confusion. I am attempting to follow some of the basic diagonistics to see if I can get rid of this 2-3 flare.

Fluid (including TC) and filter was changed 5k miles ago.

Any help is appreciated.

Thanks.

Attached Thumbnails

 

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1985 300SD 200K

Cant read your vacuum readings even after downloading it and opening it here.

What Hg reading are you getting out of your vacuum pump ?

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1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

I get 20 in-Hg when I plug the white line and measure directly off the brake booster.

I'll try to describe the readings I got below:

White - 20 in-Hg (plugged line), 15in-Hg (inline measurement)
White/Blue - 17 in-Hg

black and green - 15-17 in-Hg
black - 12-15 in-HG (cold), 0 in-HG warm engine (This line goes into the blue disk)
black/red (from #72) - 0 in Hg
black (transmission line) - 6-1 in-HG (idle to WOT)

Hopefully that helps. Thanks.

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1985 300SD 200K

On the w123 the solid Black line is the Vent line.
"black (transmission line) - 6-1 in-HG (idle to WOT)" If this is between the Vacuum Valve and the Modulator that is normal. (On a 300D the upper end at idle is 5-10 and the low end at wide open throttle can be as low as zero.)

Transmission Vacuum and Adjustment
http://www.continentalimports.com/ser_ic20242.html

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84 300D, 82 Volvo 244Gl Diesel

The 6-1 in-Hg is from the vacuum amplifier to the transmission vacuum modulator.

Measuring directly off from the top of VCV (on the IP) to the vacuum amplifier (blue disk) is 0 in-Hg the entire time. I thought this should control the vacuum, by modulating from 20 in-Hg to 0 in-Hg based on throttle position?

I guess I need to get a vacuum pump and test the VCV to see if it holds vacuum.

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1985 300SD 200K

I was able to rent a vacuum pump from the parts store and the transmission modulator holds 15 in-Hg without any leakdown (about two minutes).

I then connected the vacuum pump to the top of the vacuum control valve on the injection pump and it will not hold a vacuum? Does this mean the valve is bad.

By the looks of things this valve just happens to open the vacuum system up to the atmosphere as the throttle is increased creating a leak?

Should I attempt to adjust the valve? I checked the amount of clearance between the valve lever and stop with a feeler gauge at WOT and it looks to be in spec.

Any help is appreciated. Thanks.

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1985 300SD 200K

i think you may have problems upstream of the VCV? whats the measurement at the line going into the top of the VCV? i think it takes 20" and like you said, bleeds some off into the atmosphere. the VCV shouldn't output a full 20 to the trans.. i think it's something like 10 at idle down to 0 at wide throttle. mine isn't fully functioning so its like 5 or 6 at idle and 1 at WOT.. but even that results in smooth shifts. you can make adjustments by popping off the white dome on the front left of the VCV.. go slow with the adjustments because i guess it's really easy to break the thing !

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1981 NA 300D 310k miles

Hello all again,

I did some more investigating, and it looks like the VCV valve is not holding much vacuum. It holds 5 in hg before it leaks down when tested off the car with a vacuum pump. After messing around with this my shut off system quit working as often, leaving me to pop the hood and manually stop the engine.

I decided to start over and check the vacuum directly from the pump by blocking off all other branches. It quickly read up to 20 in HG.

One at a time I decided to check the systems by adding one system at a time back to the main vacuum line and comparing vacuum pump down time. The climate control system seemed to have the slowest pump down (red/gr?).

With the car off I tested the key switch and it held vacuum and allowed it to pass by when on.

So my question is, typically how long does it take the car to build a vacuum?

Additionally, how hard it is to get to most of the climate control vacuum modulators for vacuum testing?

Any help is appreciated.

Thanks.

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1985 300SD 200K

This data tells all you need to know. If the maximum vacuum seen by the transmission is 6" hg, and the transmission is still flaring, you're basically out of options.

As a final check, disconnect the line to the transmission and plug the supply side and see if the flaring improves. I'd guess that it won't improve.

At that point, you've got no choice but to increase modulator pressure to try to stop the flare.

Chasing a non-functional VCV is not going to affect your flare in any way. In fact, if the VCV was functional, the vacuum to the trans would range from 12 to 0 and the flaring would be much worse.

Brian,

Thanks for the reply. I will try what you suggested. As far as adjusting the modulator, do you recommend the procedure of attaching a gauge to the transmission and adjusting the pressure to the spec or just adjusting by feel, a half a turn at a time?

Additionally, do you think a leak in the climate control system (Intermittent shut off issues) would have a significant affect on the transmission modulator pressure? This car has a vacuum amplifier.

I appreciate any advice. Thanks.

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1985 300SD 200K

I would take a 1/2 turn on the modulator and see if the flaring situation improves.

Vacuum leaks cannot affect modulator pressure in any way. That's an internal function of the transmission. They do affect the vacuum that the modulator eventually sees. However, in your case, it only sees 6", maximum, so it would be unlikely that the trans is flaring due to high vacuum. If you correct your vacuum issues, the flaring will likely get worse.

Before adjusting the modulator, you definitely should remove the vacuum supply to the modulator and take it for a drive to determine the flaring condition. You could definitely drive it without any vacuum if it does not flare and it does not clunk ( a miracle, but it could happen).

Thanks for the response.

I did take it for a drive when the engine was cold (when flaring occurs) and disconnected the vacuum supply to the modulator. It up-shifted with no flaring, but clunked on downshifts?

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1985 300SD 200K

in my own experience that is caused my little or no vacuum. which makes sense if you disconnected the vac. line. so what the previous poster was saying sounds right on.

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1981 NA 300D 310k miles

OK, that's encouraging.

The new challenge is to adjust the vacuum to the modulator to reduce it from the current level of 6" to somewhat less............maybe 4" or so.

You'd need to take some photos of the setup in the '85 to see if that's doable. I understand that it has the blue amplifier which will complicate the adjustment somewhat. It may be necessary to eliminate this device and use only the VCV (if you can get it functional).

I believe my car is a 1985 300SD California car based on the diagrams. I looked it over and everything looks factory, nobody has removed any line as far as I can tell when i trace the diagram, but I will try and get some photos to upload also. I believe the diagram is the link below.

http://www.peterschmidtransmission.com/vacuum/1977_1985/617_95/1985_cal.jpg

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1985 300SD 200K