Car down! Need help sourcing Vacuum Control Valve VCV '84 300SD W126 - Page 2 - PeachParts Mercedes-Benz Forum

sleepstar · #16 07-06-2014, 04:56 PM

hmm. if you have 8 to 10" coming off of the vcv, how are you losing all that between the vcv and the T? and yeah, bench testing these things isnt really that great. they have to be testing in the car with a constant 15" or more being supplied by the vacuum pump.

bodyart27 · #17 07-06-2014, 05:22 PM

I've wondered that as well. I've tested the hard line from the motor to the trans (by plugging the end by the trans and applying vac at the engine side of the line) and it holds rock steady. I've replaced the rubber connector at the green disc on the side of the trans where the hard vacuum line connects to try to ensure a good seal.

So, I would assume the transmission is consuming some vacuum, but I don't know if it is excessive. I would think the vac just past the VCV would have to be in the high teens to 20 give the trans a fighting chance of having 15 at the "T"

tangofox007 · #18 07-06-2014, 05:29 PM

Quote:

Originally Posted by bodyart27

So, I would assume the transmission is consuming some vacuum, but I don't know if it is excessive.

The transmission should not "consume" any vacuum. If your modulator is leaking, it needs to be replaced.

Quote:

Originally Posted by bodyart27

I would think the vac just past the VCV would have to be in the high teens to 20 give the trans a fighting chance of having 15 at the "T"

I just checked my VCV. At idle, it relieves anything above 14" Hg immediately. Then it will leak down to zero after 20 seconds once the vacuum source is eliminated. (My transmission shifts very nicely.)

sleepstar · #19 07-06-2014, 05:59 PM

yes, test if the modulator holds vacuum. since you verified the hard line is OK you can just do it from inside the engine compartment. pull vacuum on the line going to the trans and it should hold vacuum.

not sure what your routing circuits are for the SD, but the VCV should essentially be on its own circuit with the transmission. what else is attached to that T?

what i'm saying is, just attach the transmission line directly to B, at least to test. in my opinon 10" should be enough to make the transmission shift smoothly.

whunter · #20 07-06-2014, 06:25 PM

Quote:

Originally Posted by bodyart27

Howdy! I was just looking at my User stats and it's been almost 4 years since I've posted. I used to be a rabid "How To" contributor. Then I went off and started a business and had a child.... well you get the picture (no more free time).

So, the real reason for the post is my '84 300SD W126 needs a Vacuum Control Valve or "VCV" and everything I'm reading says the part is no longer made. Part numbers look like it can be either 1230700046 or 6170700246. I could REALLY use a lead on sourcing good one as it's sidelined the car (shifts very hard and I'm afraid it's going to trash the transmission slamming up and down gears).

I've done quite a bit of testing - great vacuum supply up to the "T" to the VCV and off to the transmission. Tested line to transmission - no leaks, replaced rubber where it joins to transmission to make sure I'm not losing vacuum downstream to transmission. MityVac attached to the top of the VCV - won't hold vacuum and the vacuum does not vary when I move the throttle. When I "T" in between the VCV and the transmission with a gauge I get super low levels (almost none) and again no change with throttle or monitoring while driving around. I've adjusted the VCV with the 8mm nut on the front but it's making no difference in performance. Years ago I've tested at that point before when I tuned my transmission shifting and used to get in the "teens," now it's reading like 0-3. Seems like the VCV is not operating and bleeding off way too much vacuum so I can never get an adequate supply to reach the Transmission to soften the shifts.

Any leads on where to get a VCV in good order would be appreciated. Hopefully someone has benefited from one of my "How Tos" write-ups and can return the favor? Scouring eBay the past month and no luck. If you have one for sale please email me info@shellblack.com - Thanks everyone!!!!

My number is in your PM box.

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bodyart27 · #21 07-06-2014, 06:37 PM

Well I just tested to see if the transmission will hold vacuum (from engine fro hard line going down to the transmission modulator) - it does not. Tested engine running and not running.

As you can see in the picture, there is nothing else hooked up in between the VCV and the transmission

sleepstar · #22 07-06-2014, 07:10 PM

that might be your answer! might be time for a new modulator

tangofox007 · #23 07-06-2014, 07:55 PM

Quote:

Originally Posted by bodyart27

Well I just tested to see if the transmission will hold vacuum (from engine fro hard line going down to the transmission modulator) - it does not. Tested engine running and not running.

Under normal circumstances, the engine would have nothing to do with whether the modulator holds vacuum. A modulator that won't hold vacuum cannot do its job.

whunter · #24 07-07-2014, 12:31 AM

Quote:

Originally Posted by bodyart27

Well I just tested to see if the transmission will hold vacuum (from engine fro hard line going down to the transmission modulator) - it does not. Tested engine running and not running.

As you can see in the picture, there is nothing else hooked up in between the VCV and the transmission

It was great talking with you again.

FYI other members:

The vacuum modulator has a new (several months old) rubber cap.
The modulator suddenly will not hold vacuum.
He is seeking a new or good used modulator ASAP..
The VCV may NOT be bad.
He will experiment with the four used VCV units, after the modulator is replaced.

====================

Assuming your tool does not leak...
Assuming the vacuum modulator is good.

You should be able to connect a Mityvac directly to the vacuum modulator, pump it up to roughly 20 inches Mercury (vacuum), walk away for 15 minutes, with NO change of reading when you return.

If your modulator leaks during this simple test = the rubber cap and/or modulator is failing or ruptured.

*************************

A special attention note:
In some cases, the failed modulator allows the vacuum system to suck transmission fluid.

#1. This can cause a runaway engine or excess smoking on some early vacuum systems exhausting/venting into the intake manifold.

#2. On later models, the vacuum system exhausts/vents into the crankcase, this can cause several issues.
A#. Transmission fluid thins the engine oil = no longer protects crankshaft main/rod bearings.
B#. Transmission fluid thins the engine oil = it can aerosolize/mist enough oil to cause a runaway engine.
C#. The most extreme cases where owners constantly filling their transmission with no visible leak, this usually ended with hydraulic lock from excess crankcase oil or a terminal runaway.

Run away diesel, why does it happen?
Run away diesel, why does it happen? - PeachParts Mercedes ShopForum

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Silber Adler · #25 07-07-2014, 07:37 AM

I don't have the problem here but great response hunter.

bodyart27 · #26 07-13-2014, 01:51 PM

And we have vacuum! The problem was not the VCV but the transmission vacuum modulator. I did a full trans service (drain torque converter, new filter new gasket) and then did the vacuum modulator. 2 little 5mm bolts hold a little bracket so the modulator doesn't back out. Looks like the original part has been superseded. The new one (black, not green) comes with a key - the finger, the modulator, o-ring, key, and cap. The design allows the key to be adjusted by turning the cap (rather than remove the rubber cover to get to the key as in the original design).

As you can see in the first pick I finally have vacuum when I "T" in between the VCV and the transmission. I did one minor adjustment to bump up the Vacuum to ~15 and then tuned the shift firmness with the vacuum modulator. I had to soften the shifts a bit. 1-2, 2-3 are awesome, 3-4 is a little more firm but and more noticeable but a far cry from the smack / slam we had earlier due to no vacuum. Downshift on full throttle are very nice as well.

Now she drives like a luxury car again! Thanks everyone for their help and support and helping me see my misdiagnosis.

Last pic is the gratuitous engine bay pick. It's the only part of the car worth showing - interior and paint have succumbed to too many Texas summers

On a side note, having come back to the forum after many years away, I'm still impressed how "functional" these forums are in the age of social media. There really isn't anything better for this type of thing.

bullethawk · #27 11-04-2014, 03:54 PM

Quote:

Originally Posted by charmalu

Wow, two old relics from the past.

I have a few of the VCV`s. have no idea if they work, just grab them when I see them in the yards since they are NLA and I have the SD, only one with a auto trans.

Let me know.

Charlie

Hi, I need a VCV for my 84 300d, how do I get it from you? you can test them with a hand held vacuume tester.

#28 11-13-2014, 01:28 PM

Hello All,

I'm a late joiner to this forum, been part of Benzworld.org for years. I've had some challenges with the shift quality of the automatic in my car. End result was that I ended up writing a rather lengthy article with a ton of pictures about vacuum adjustment (incl. the VCV), and the transmission.

Unfortunately the PDF is too large for my attachment limit. So send me a PM and include your personal e-mail address and I will forward the document. Maybe one of you can attach a 1.8 Mb file to this e-mail thread.

bullethawk · #29 01-16-2015, 09:08 PM

I just bought one from w123suv. also Phillytwotank said he had one maybe.