Vacuum question......again problems - PeachParts Mercedes-Benz Forum

BIGRED · #1 04-13-2003, 05:49 PM

I have a 300TD. I ahve been through the vaccum system soooo many times, I proably hold the speed record of removing door panels and replacing them.

After about 10 minutes the vacuum drains and the remote door locks don't operate.

The following is what I have done.

First I disconnect green-yellow from the circuit (climate control) because that whole system needs lots of work.

I am feeding the brown (ignition), yellow (door locks) and black-yellow (storage tank) from a 4-way connector. When I tap into this group and check vacuum it holds. This shouild mean the the ignition switch, ignition shut down valve, all door related vacuum components and the storage tank are ok.

The line that feed to the transmission and up to the micro swiches on the valve cover also hold vacuum. This should mean the modulator, the micro switches and the leak valve are ok.

When checking the main vacum line from each of the two vacuum connectors it holds vacuum. This should mean the pump, the line and the booster are ok.

Am I missing / overlooking something?

Thanks for any input.

Don

psfred · #2 04-13-2003, 07:01 PM

Red:

Two things:

One: the vac switch on the driver's door can go bad and leak down, sometimes in only one postion (lock or unlock).

Two: A bad check valve will vent off the vac reguardless of the condition of the rest of the system.

Make sure you hold vac with the check valve in the circuit (use a T for the hand pump). We had to replace both on my brother's 300D, they buzzed when the engine was shut off.

If the locks leak down, then only that check valve is bad, probably.

Otherwise, if it only leaks down locked or unlocked and not both, then you still have a leaky diaphram somewhere.

Peter

BIGRED · #3 04-14-2003, 01:38 AM

No leak locked or unlocked. The vacuum tester holds pressure on all lines at the driver door main valve.

I wonder if it showing up when warm to hot and not when it is cold.

I guess I will have to give that a shot, next.

Thanks for the input.

ewstan · #4 04-14-2003, 12:00 PM

Vacuum hoses and connections will often leak when hot and not when cold.

ewstan

erubin · #5 04-14-2003, 08:52 PM

You may want to replace the 4-way. maybe it is leaking but you bypass it when you're testing. They may leak where the plastic line slips into the rubber 4-way. Just a guess.

If you're sure the door lock circuit doesn't leak you may want to isolate the lock circuit from the other systems with a devoted check valve. Maybe you're missing a check valve as I was when i bought my 300D. Single port (see attached) vacuum check valves are not too bad ($6.41).

Why do you keep taking the door panels off. You should be able to isolate the problem without doing this each time. I assume you have a vac pump.

BIGRED · #6 04-14-2003, 10:16 PM

I had just been thinking about using a check valve for the different circuits, just what I am going to do.

I am a new owner of this TD and it had / has a number of different vacuum related issues. Not having the vacuum expertise as yet I am sure I do more work than I need too.

Between the transmission, door locks, climate control, storage tank and engine shutdown, lets just say the thought of a 12 guage shootgun up its tailpipe has crossed my mind (don't own any guns).

Thanks for the tip.

Don

Big Ron · #7 04-14-2003, 10:52 PM

START CHECKING FROM THE FRONT OF THE CAR NEAR THE VACUUM PUMP, oops, with a couple of golf tees. Pull a line ,plug it, if it's OK hook it back up and move along to the next and soforth. You must have a slow leak, so leave the plug in the line for a while to see if it bleeds out. Good luck, Big Ron

'79 Super Turtle · #8 04-19-2003, 02:10 PM

Does your vacuum pump supply vacuum to your brake booster and your cruise control like mine does? If so, I'd check those as well.

BIGRED · #9 04-19-2003, 02:48 PM

I am done checking....I hope. Today I am installing 1 way check valves for the storage tank and the door lock feed. Being that those don't appear to be leaking and the only issue is getting the doors unlocked after she's been sitting for a few minutes, let alone overnight.

Thanks for the tips!

'79 Super Turtle · #10 04-19-2003, 06:34 PM

Big Red, I'm not sure, but did you ever check how much vacuum you were getting from the pump? I've had to rebuild one pump because it was only getting 15 In. Hg on the mityvacII. That solved all of my vacuum problems. Now my other car is not shutting off promptly, and has a brake pedal that loses vacuum every so often. It is only putting out 18 In. HG on the tester. I think 24 is normal. If you are not putting out enough vacuum the components will starve.

If you can't find any leaks, this seems likely to me.

I know that rebuilding my pump will solve this problem.

I also wanted to add that when I got my first 300SD, the blue/black check valve going to the door locks had been reversed by some crafty soul in an attempt to allow more vacuum to the other components. It worked for a bit.

BIGRED · #11 04-19-2003, 07:43 PM

I will re-check it later on today, I checked it when I got it and it was strong, however maybe it went pppppppppssssssssssssssssssssssssssssssssssssssttttttttttt POP.

Thanks for the reminder!

erubin · #12 04-19-2003, 09:47 PM

I also had low vacuum problems that also included a leaking brake booster. Because of the booster leak the pump created 4" Hg less vacuum than when measured without the booster connected. A salvage yard booster set me back $75.

You can check this quickly by connecting a vacuum gauge (or mityvac) to the main vac line, disconnecting the hose to the booster, starting the car and putting you thumb over the hose you disconnected from the booster. Compare that vacuum reading (and the steadyness of the gauge) with the reading when the booster is connected.

Before changing the booster make one final check which is to test the booster alone with a Mityvac. This is done by somehow connecting your mityvac to only the booster and pumping it down. I would only be concerned about a gross leak since it won't effect the other components because of the CV. A gross leak like i had never allowed the vacuum level to go deep enough and CVs will not help that.

BTW, I hate the tapered end on my Mityvac. It is large diameter and damages the small MB vacuum hose ends. The Snap-on brand hand vacuum testing pump has a perfect dia for MB hoses but it's probably a lot more $ than the Mityvac. All the MB techs at the dealer I know only use Snap-on ones for this very reason.

BIGRED · #13 04-19-2003, 10:06 PM

Got it.

I am getting close to 25 lbs inline. It is the leak vacuum valve attached to the injection. It was fine about 3 weeks ago. Maybe the engine was did it in (shrugging sholders).

Using a one way check valve solved the problem with the door lock. Now when we go somewhere I don't have climb through the interior to open doors.

This also esplains the recent bout of trans shfiting issues. Had it perfect and then it acted up.

Don

'79 Super Turtle · #14 04-19-2003, 10:14 PM

erubin, that is an excellent way to diagnose a leaking booster. I thank you for the input.

Is it the different sized rubber bits that you don't like on the mityvac? What is the snap-on pump like? I've always had to make my own hoses and end pieces in conjunction with the tapered bits that come with the mityvac to fit on different vacuum mechanisms.

JHZR2 · #15 05-06-2003, 02:12 PM

Quick question... On a check valv like those displayed above, which do not havea flow-direction arrow on them, how do you know which way to put them inline?
Thanks

JMH