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  #1  
Old 06-07-2006, 04:40 PM
Cabernet red, actually
 
Join Date: Jan 2006
Location: Willamette Valley, OR
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Question Occasional vac issue-a symptom of something?

Most of the time my car has no vacuum issues. Everything works as it should, at least as far as I know, and the doors will lock/unlock about 5 times, which is what the owner's manual says they should do.

In the last couple weeks, though, the car has occasionally taken a while to shut off when I turn the key and after that I have very little vacuum in the central locking system. But without doing anything at all I can start the car, drive it around, and it will work just fine the next time I shut it down, and the locks will be fine as well.

I can track down a vacuum problem but I can't do it when everything is working right! Are my issues symptomatic of something? Is my shut off valve dying? I know that someone out there has had this same problem so I will await enlightenment, although I think I will see if the white bleeder thing atop the IP will hold vacuum in the meantime.

Thanks!

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1985 300D Turbo, CA model
248,650 miles and counting...
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Old 06-07-2006, 11:50 PM
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Join Date: Nov 2004
Location: LA - the state
Posts: 147
If it helps you any, I am experiencing the same. Have lost my religion and several hours now trying to track down the problem. All vacuum lines, the IP shutoff, and vacuum pump test show nothing.

Took the car twice recently to my indie, who also failed to find the problem.

Even though it's inconsistent, I notice that the symptoms do not appear during the first on/off run of the day. After that run, all bets are off, it may work properly, may not.

Here's a couple threads I started with:

http://www.peachparts.com/shopforum/showthread.php?t=150356&highlight=door+actuators

http://www.peachparts.com/shopforum/showthread.php?t=34852&highlight=repairing+center+vents


When I eventually end this mystery, I'll post.

Good luck to you.
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  #3  
Old 06-07-2006, 11:55 PM
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An intermittent vacuum problem can be due to a faulty check valve on the vacuum pump. (The check valve is inside the nipple where the metal line attaches to the pump.) Especially if you have a complete vacuum loss, evidenced by a loss of brake boost.
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  #4  
Old 06-08-2006, 10:13 AM
Cabernet red, actually
 
Join Date: Jan 2006
Location: Willamette Valley, OR
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Quote:
Originally Posted by tangofox007
An intermittent vacuum problem can be due to a faulty check valve on the vacuum pump. (The check valve is inside the nipple where the metal line attaches to the pump.) Especially if you have a complete vacuum loss, evidenced by a loss of brake boost.
Thanks!

I'll check into this.
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1985 300D Turbo, CA model
248,650 miles and counting...
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  #5  
Old 06-08-2006, 11:13 AM
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Location: West of Ft. Worth. TX
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Another suspect might be the flex fittings. Maybe when they get warm, softening occurs and they don't seal as well or there are dry rot cracks. About $10 to replace them all.
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84 300SD 350K+ miles ( Blue Belle )
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  #6  
Old 06-08-2006, 11:24 AM
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Location: Willamette Valley, OR
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Thanks SDBlue. I've checked those recently, though, and they're all pretty new anyway so I don't think it's the problem in my case.
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Ralph

1985 300D Turbo, CA model
248,650 miles and counting...
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  #7  
Old 06-08-2006, 12:56 PM
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The more I read about it, the more I suspect tangofox007 is right. I'll definitely check out that check valve as soon as I get the chance.

If indeed I do have a broken check valve on my vac pump, is it dangerous to drive around with it? Any chance broken parts could be sucked into the engine or does the whole pump have to fail for that to happen?
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Ralph

1985 300D Turbo, CA model
248,650 miles and counting...
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  #8  
Old 06-08-2006, 01:51 PM
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I don't think so. I believe he may be talking about the main check valve that attaches to the main vac. line for the brake booster and screws into the vacuum pump. Super easy one to change or cleaning might be a cure.
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84 300SD 350K+ miles ( Blue Belle )
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  #9  
Old 06-08-2006, 02:34 PM
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Location: Forestville, NY
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pump valves

The main vac line check valve may be the problem, however
there are two check valves that are part of the pump. One allows air in and the other expels air out. They are easy to replace (at least on my W115) after you take the head of the pump off. A small plate on the front needs to be removed (there are spings pushing the valves in place.) Replacement valves can be found on this site.
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  #10  
Old 06-08-2006, 03:06 PM
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85 300D 4spd+tow+h4
 
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Quote:
Originally Posted by tangofox007
An intermittent vacuum problem can be due to a faulty check valve on the vacuum pump. (The check valve is inside the nipple where the metal line attaches to the pump.) Especially if you have a complete vacuum loss, evidenced by a loss of brake boost.
I could kiss you. This is exactly the problem I have on my TD. I think. Loss of brake boost would mean that pedal goes almost all the way down and only gets firm in last bottom 1/4? (And firm as in no brake boost like firm?).
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  #11  
Old 06-08-2006, 03:10 PM
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Quote:
Originally Posted by winmutt
I could kiss you. This is exactly the problem I have on my TD. I think. Loss of brake boost would mean that pedal goes almost all the way down and only gets firm in last bottom 1/4? (And firm as in no brake boost like firm?).
Don't get puckered up just yet. Loss of boost usually means that applying the brakes is hard from the start. Sounds like you have more of a hydraulic problem than a vacuum problem.
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  #12  
Old 06-09-2006, 11:35 AM
Cabernet red, actually
 
Join Date: Jan 2006
Location: Willamette Valley, OR
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Well I tried to remove the check valve but it was stuck on fast, wouldn't ya' know. I was trying to use an adjustable wrench but I think I will go out and get a socket. I'm guessing it's a 21 or 22, anyone know for sure? I thought about using the anti-seize stuff I have, but it's flammable and the car was still hot, so I figured I'd best wait until it was cold to try that.

I suspect the valve may be dirty. My whole vac pump is covered in so much crap, there could be some ancient treasures buried in there.
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1985 300D Turbo, CA model
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  #13  
Old 06-09-2006, 11:57 AM
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Quote:
Originally Posted by Maroon 300D
I'm guessing it's a 21 or 22, anyone know for sure?
22.
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  #14  
Old 06-09-2006, 11:59 AM
Cabernet red, actually
 
Join Date: Jan 2006
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Thank you once again sir!
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Ralph

1985 300D Turbo, CA model
248,650 miles and counting...
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  #15  
Old 06-12-2006, 12:20 PM
Cabernet red, actually
 
Join Date: Jan 2006
Location: Willamette Valley, OR
Posts: 503
Update

Well I got the check valve out and it's not broken. It did appear to be slightly clogged with oily gunk, however, so I dropped it in some carb cleaner for a couple of hours, dried it off, and re-installed it.

It appears that my vac is better for having done this; the shifting is smoother, perhaps too smooth in some cases. I may need to adjust the vacuum going to the tranny now! I haven't driven the car enough to say for sure whether the intermittent vac issue is gone, but I suspect it is given the slight difference I can feel with the vac while driving. If I find that this didn't fix the internittency issuse I'll post back, but if I don't post here again you can assume cleaning the check valve solved the problem.

Thanks again, all, for your help!

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1985 300D Turbo, CA model
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