Help!!.. - PeachParts Mercedes-Benz Forum

dannym · #1 11-17-2004, 10:38 AM

Hey,
I was driving to work this morning and all of a sudden the brakes went out. The pedal was very hard and the stopping was hard. Like the power stearing went out.
Also, the engine wouldn't shut off! I had to open the hood and hit the STOP button on the ignition.
It's a 1984 300SD turbo.

I'm thinking it's a broken vacuum line but I'm not sure what it could be.
It's really got me worried.
Anyone got any ideas what it could be and how to fix it?

Thanks

Danny

P.E.Haiges · #2 11-17-2004, 10:52 AM

dannym,

Similar thing happened to me. The vacuum main line came loose from the vacuum pump (VP). This is no big deal, you just reattach the vacuum line.

So its either the vacuum line, the one from the VP to the brake booster or the VP has stopped working.

If the VP has stopped worling, you should check the VP right away because if it has come apart inside, the parts may get into the timing chain and cause engine damage.

P E H

dannym · #3 11-17-2004, 10:59 AM

Thanks P.E.,
I don't think I'll be able to check it until after work.

If it is the (VP) is it still driveable?
In spite of the possible timing chain damage. Is it safe to drive?

Danny

JamesStein · #4 11-17-2004, 11:01 AM

You've either sprung a vacuum leak or you lost your vacuum pump. With the coming colder weather I'd suspect a connector more than the pump.

If you do a search on vacuum leak or something similar you should find a large amount of information on tracking down vacuum leaks.

hawesey_t · #5 11-17-2004, 03:57 PM

Had same problem with mine. Turned out to be the Vacuum Pump Check Valve. Be sure to get all of the pieces that may have come off the old valve before installing the new one.
Part #D3012-25391 $40.50 Much cheaper than a new pump. - th

dannym · #6 11-17-2004, 03:59 PM

Quote:

If you do a search on vacuum leak or something similar you should find a large amount of information on tracking down vacuum leaks.

Worked great!

It's funny because I'm involved in other support forums and I always try to get people to use the search button. But when it comes time for me to use it, do I?? Of course not!

Thanks for your help.

Danny

dannym · #7 11-20-2004, 12:34 PM

Well, I pretty much ruled out the VP. Everything works normal above 1000 rpm. I disconnected the line from the booster and it was sucking.

My problem is I broke a part and I can't positively identify it. It's the plastic piece on the manifold that the vacuum line from the EGR valve goes to. What is this part?
I'm also guessing the part next to it with the brown/white wire coming from it is the coolant temperature sensor. That brown/white wire goes to a connector on top of the driver side wheel well. What is that part also??

This is driving me crazy because I checked every line under the hood and there is nothing wrong. Except for the broken line at the EGR. I disconnected and capped every line going past the firewall and nothing changed.
I'm guessing with that broken part I'm not going to get an accurate reading.

ANY help or suggestions would be awesome!

thanks

Danny

psfred · #8 11-20-2004, 12:51 PM

Go the o auto parts store and buy a MitiVac hand pump. It has a gauge, so you can hook it up and see how much vac you have in the lines, can manually pump down systems, etc.

If the booster isn't working, either the pump itself is shot (and this may be a simple repair like a broken check valve) or the booster or booster check valve is bad. Doesn't take much vac to run the booster.

Note that if you have good power assist above 1000 rpm but not below, you have a bad booster or booster check valve for sure -- once the booster is pumped down, it should stay pumped down until you use it. If the boost goes away below 1000 rpm, something is leaking.

Peter

dannym · #9 11-20-2004, 07:23 PM

Is that the piece on the main line right before the booster?
Can you remove that from the main line and replace it?
I definitely have good brakes above 1000 rpm. What's odd is I was out today and for a long time, at any speed, everything was normal. Like the problem just went away. But not for long though.

Do you know what that broken piece is I that I mentioned in my last post?

I have a magnehelic gauge at work but didn't think to bring it home. Maybe I'll go by tomorrow and get it.

Danny

dannym · #10 11-21-2004, 10:18 AM

Anyone?

I would really like to know what this broken part is so I can get a replacement.

would a bad check valve prevent the car from shutting down? It's a royal pain in the but having to open the hood and manually shut down the engine.

Danny

rg2098 · #11 11-21-2004, 10:43 AM

The broken part is simply a thermo switch that "turns on" the EGR above a certain temp. Just plug the line going into it with a golf tee and be done with it.

tangofox007 · #12 11-21-2004, 12:06 PM

Quote:

Originally Posted by dannym

Is that the piece on the main line right before the booster?
Can you remove that from the main line and replace it?
I definitely have good brakes above 1000 rpm. What's odd is I was out today and for a long time, at any speed, everything was normal. Like the problem just went away. But not for long though.

Danny

The check valve in question is located on the vacuum pump. There is a fitting on the top of the pump where the vacuum line attaches. These are prone to failure and will cause exactly the symptoms that you describe. To check the check valve, disconnect the vacuum line, then remove the check valve fitting from the vacuum pump. Some times you will find broken parts at this point. If not, confirm that air will flow only one way through the valve. It should flow in the direction of the vacuum pump, but not the other way.

tangofox007 · #13 11-21-2004, 12:09 PM

Quote:

Originally Posted by dannym

Anyone?

would a bad check valve prevent the car from shutting down? Danny

It certainly will.

psfred · #14 11-21-2004, 02:17 PM

Get the MitiVac, too -- it's a hand pump plus gauge, and is very handy for vacuum problem troubleshooting.

You can also have the check valve at the booster fail -- it's the fitting in the line or on the booster itself. The grommet on the booster can go bad, too, causing a massive leak.

The plastic multiport fitting in the middle of the main line can crack, too. Not available as a separate part, you have to buy the whole line, but it's not expensive.

Peter

dannym · #15 11-21-2004, 04:41 PM

Thanks RG. I actually had it plugged I just needed to know what it was.

I took everyones advice and bought a MityVac, And your right it's an awesome tool!
Here's what I found:

1-Brake booster held 71/2" and never fell. Yeah!!
2-Check valve was bad, needs replacement.
3-The line going to the Vacuum switches under the black cover on top of the valve cover didn't hold vacuum at all. In fact you can hear the leak as you pump the vac. So I'm going to need 2 new vacuum switches.
4-the vac switch line also doubles back, t's off with 1 line, Black, running back into passenger compartment. That line also does not hold vacuum. I'm not exactly sure what this line does.
5-The EGR valve does not hold vacuum and I could not see it move. Does this mean it's bad?

That's all I found everything else checks out good.

I feel a lot better now knowing what I'm looking at. I really hate vacuum leaks!

Thanks everyone for all your help.

Danny