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#1
09-11-2008, 12:27 AM
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Vacuum Valve Test
I brought my 1982 300SD to Eagle Transmission to have a transmission repair.
After the transmission rebuilt and back on the car, the shop technician said that he can not give me the car back because the transmission is shifting too hard and the reason is because the Vacuum Valve mounted on top of the injection pump is not working properly. He said that he put an used and the problem still the same. I know that there is a Vacuum Dashpot Valve into the vacuum system to make the transmission work properly. I want to know if there are some way to check each valve individually before spend any money and effort to find the vacuum valve, part number 12307000046 from Mercedes Benz not found anywhere in the USA other than used. They said that they try to find in all USA dealers and nothing was found then they try to bring it from Germany and also Germany does not carry it anymore. I whant test it myself with instructions of people from this site to make sure if the problem is really from valves or transmission work. Any help will be appreciated. Thanks Nyck
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Nyck - TX - USA Last edited by nyko46; 09-11-2008 at 12:28 AM. Reason: wront tiping 
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#2
09-11-2008, 02:49 AM
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Another thought; why not "ask Phil" at Fastlane to see if he can find a new valve for you.
Some if the info is in the article: http://www.peachparts.com/Wikka/TransVacTune For other DIY transmission and other repairs: http://www.peachparts.com/shopforum/diy-links-parts-category/
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84 300D, 82 Volvo 244Gl Diesel Last edited by Diesel911; 09-11-2008 at 02:55 AM.
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#3
09-11-2008, 09:13 AM
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Quote:
Take the VCV and connect a Mityvac to the top port. Make sure the the linkage is in the "closed" position...........as if the rack was closed on the engine. Pump up the Mityvac and read the gauge. It should be somewhere in the range of 10-14" of vacuum and be steady. Now, slowly open the linkage (as if you were pressing the go pedal) and watch the gauge. It should slowly fall toward zero as the linkage opens to a greater degree. On the vehicle, you can perform the same test if you T the Mityvac into the transmission line and drive the vehicle. At idle, the vacuum should be 10"-14" and it should steadily decrease as you open the rack with your right foot. This test must be done with the vehicle on the road because you cannot easily open the rack with the engine in neutral (engine runs away). If you do these tests, report back with your findings and we'll determine if the transmission shop knows what it's doing.
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#4
09-11-2008, 01:10 PM
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I brought up a point like this while I was testing my 83' 300SD's vacuum system. I have my Mity Vac and I'm testing the lines finding leaks in them, but I have no specification on what a valid test of each valve is. My specific question was if I put a vacuum on the Modulator Valve on the transmission and it leaks does that mean it is bad or that is the way it operates. But I would also like to validate all the components of the vacuum system and the only way to do that is to know specifically how they work. (i.e. if I put this much vacuum on the valve, this is what happens)
Basically I think if we could (as a community) put together a comprehensive valve by valve test procedure for each vacuum component in all the models, that would answer a lot of questions out there. Last edited by wildbore2000; 09-11-2008 at 01:16 PM.
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#5
09-11-2008, 01:38 PM
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Vacuum Valve Test.
Thanks for your reply and I think the same way.
I was searching on WEB last night about vacuum issues and I found very useful the article under this link. www.dieselgiant.com/mercedesvacuumtroubleshooting.htm I spoke with the transmission technician this morning and he keep saying that the vacuum reading at the Vacuum Valve Regulator is ZERO. I suggested him to do together a swap of the valve from my 1984 MB 300SD to the other one that is in the shop. He extremely agree to make sure that the valve is a real cause of the problem. If you have any idea to share with me I will appreciate. Thanks
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Nyck - TX - USA
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#6
09-11-2008, 02:02 PM
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I wish I could add some more, but I'm in the same boat you are and I think I've read all the same articles. My problem is that while they are very usefull for general knowledge of how vacuum systems work, I still have yet to find any specifics that satisfy me on how to test each valve.
The method of troublshooting you are using is a prime example of what we need to resort to without that knowledge. If we new exactlly what the specification on that Vacuum Valve Regulator are, we can test to those requirements and know if it is bad or not without having to find a replacement to swap it with.
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#7
09-11-2008, 03:35 PM
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Quote:
The principle requirement of the VCV is that it produce some vacuum level when the rack is closed and that vacuum level should drop as the rack is opened. If you have this........you can tune the valve. If the valve dumps all vacuum with a closed rack, it's toast.
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#8
09-11-2008, 08:59 PM
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Quote:
A tolerable leak would be approximately 15 seconds to leakdown from 20" vacuum. Any greater leak and the vacuum levels downstream of the orifice will be too low.
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