My 1980 300D is making a buzzing (vibrating noise). It started when I changed the vacuum lines that run from a vacuum T which branches from the main line and feeds the modulator valve and the white plactic item on the top rear of the injector pump. The noise started then. All I think I did was shorten the lines. What does the plastic part do and why is it making noise?

The lines to the modulator valve have been bypassing the valve device mounted on top of the valve cover for some time. When I inserted a vacuum conector tube in place of that vavle, which is activated by the accelator pedal, a late shift problem stopped.

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tadco


82 300TD Wagon

previous diesels
82 OLDS 5.7
84 Ford with 6.9 LT
80 300D

The buzzing sound is normal. The vacuum control valve leaks by design, hence the noise. If bypassing the VCV improved your transmission performance, you have a problem somewhere. A vacuum leak or bad modulator are good possibilities. It is time to round up a vacuum tester and investigate.

At the time I bypassed the valve atop the valve cover I used a hand pump tester on the modulator and it had a bad o-ring under a plastic cap which the vacuum tube attached to. When I replaced the o-ring my slipping/late shift was unchanged. After bypassing the valve I had a nice shift.

I put a new vacuum pump kit in about 2 years ago and at the time I saw no difference in any of the symptoms that prompted me to install it. All works well except the engine will not stop if it has been just started, it must run for 2 to 3 minutes before it has sufficent vacuum to stop. The power locks will function for about 2 or 3 minutes aftrer the car is shut off.

Should I find ALL vacuum leaks and repair them?

Should I replace the modulator?

What should the vacuum be at the main truck line at idle?

Thanks,

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tadco


82 300TD Wagon

previous diesels
82 OLDS 5.7
84 Ford with 6.9 LT
80 300D

That would be consistent with a leak in the door lock system. The 2-3 minute delay for shut-down would be due, in part, to the need to "recharge" the vacuum reservoir.

A vacuum leak anywhere can translate to low vacuum everywhere. You could disconnect and cap the lock supply line for testing purposes.

Somewhere in the vicinity of 20" Hg. If your power brakes are working, your pump is probably okay.

Sounds like a pretty heavy vac leak somewhere...

If this is the case, it will upset the operation of the transmission especially the point and the quality of its shifts....

That white-thing on the IP the vac line and the Trans. Modulator are connected to is the (Transmission) Vacuum Control Valve, or VCV. Its job is basically to tell the trans the position of the accelerator, (Via linkage) and the I.P. throttle-shaft, Via Vacuum Intensity.

The trans. 'expects' to see a Vacuum of somewhere around 10 In Hg, with accelerator Not pressed, engine Idling.

The VCV is supplied with Vac, from a metered 'Orifice' which is in the main vac line from the brake-booster to Vac. pump. (The small side-barbs connected to the smaller vac. lines) The purpose of the orifice is to reduce the 20 in Hg to around 15 in. Hg

The VCV varies the vac from around 10 in Hg to Zero or thereabouts at full throttle position, This is important as the shifts will be either very harsh or will flare horribly depending on whether the Vac at a certain accel. position/engine-speed is either too high or too low.--MANY Transmissions have been replaced Needlessly due to Incorrectly diagnosed Vac. issues!

Personally, first I would check all the vac components in engine-bay--Especially the rubber joints and pipes. A small leak can drastically upset the trans. operation as the vac level will not be as intended, messing up all the vac. levels.

Check out petershmidt's site for the vac. diagrams for your car's trans system to make sure someone hasnt 'Fixed' it before and messed it all about--(Very common)!

--Its a good idea to plug the door-lock circuit to rule this out in the testing to locate leaks as others have said.

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http://i190.photobucket.com/albums/z...0TDnoplate.jpg

Alastair AKA H.C.II South Wales, U.K. based member

W123, 1985 300TD Wagon, 256K,
-Most recent M.B. purchase, Cost-a-plenty, Gulps BioDiesel extravagantly, and I love it like an old dog.

W114, 1975 280E Custard Yellow,
-Great above decks needs chassis welding--Really will do it this year....

Thank you for the help,

I have not gotten the VCV back in line but I am back where I was working faily well without it. I will get a vacuum guage and get the VCV back in line soon.

Thanks again.

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tadco


82 300TD Wagon

previous diesels
82 OLDS 5.7
84 Ford with 6.9 LT
80 300D

Does anybody have a list of the orifice size and colors? I went to the MB dealer to try and buy an assortment and they were unable to find information, saying something about part numbers no longer available...

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83 300TD, 260,000 miles, aka "Dusty"
6 vehicles, 2 cup holders (both in the dump truck)

It's here on the forum somewhere. Someone posted all the colors and MB part numbers for them.

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)