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  #16  
Old 05-07-2007, 10:40 AM
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Quote:
Originally Posted by Brian Carlton View Post
It would be of significant benefit if you could connect up a vacuum gauge to the booster line and observe it in the morning after the cold start and idle out of the driveway and over to the stop sign.
Hahahahahahaha!!!

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  #17  
Old 05-07-2007, 11:01 AM
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Exclamation Even in a 123......

Quote:
Originally Posted by deanot442 View Post
FYI
I don't want this to come across the wrong way (after reading it it sounds a little snooty , but not its not meant to be) In a 124 series 300D, your locks work off of an electrical vacuum pump and are not connected to the engine's vac system.
When you turn the key in the door, it is actuating an electrical vac pump just for the locks.
a W123 has an "egg crate" vacuum reservoir......and a check valve separating the car interior portion of the vacuum system from the engine compartment of the system....so when troubleshooting the door locks should work a couple of times regardless.....at least if the interior vacuum system is tight.....

SB
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  #18  
Old 05-07-2007, 04:37 PM
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Vac guage in the morning

Quote:
Originally Posted by Brian Carlton View Post
It would be of significant benefit if you could connect up a vacuum gauge to the booster line and observe it in the morning after the cold start and idle out of the driveway and over to the stop sign.
The shop did the vac in the morning as well, they held the car overnight. They said pump produces 17 inches of vac, and will hold 15 overnight. Specs are 8-10 and 24 hours. Bled down the system to test recovery of vac pump. 0 inches at start. After start, produces 10-15 inches in 3.5 seconds, passing the test. Tested the vac resovoir tank, holds vac. Possible that one of the 5 valves could be sticking, would have to be more frequent to identify.

I replaced the check valve today. I shook it, no rattle. Blew in it in both directions, no air went either way from what I could tell, but it had to be working some, I drove my car fine with brakes. Installed the new one just in case.

The shop did say MB had a problem they never owned up to, that this problem does happen from time to time of hard pedal and nearly no brakes, on older cars like this (mine is 16 years old), and it's a problem with low vac on start up, intermittently. He says to rev it a few times in the morning to help bring the vac up. When I had a hard pedal the next day (the day after I took it in, wouldn't you know), I put it into neutral as he suggested, hit the accelerator, then braked, and it was fine. Of course in that amount of time, it could have cured itself anyways.

Just curious.... if you had no vac whatsoever, it seems to me that you could/should still be able to stop. In my case, the hard pedal, no matter how hard you push, you have nearly no brakes.

Thanks,

Jeff 1991 300d, 105k
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  #19  
Old 05-07-2007, 04:49 PM
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Quote:
Originally Posted by jbach36 View Post
Just curious.... if you had no vac whatsoever, it seems to me that you could/should still be able to stop. In my case, the hard pedal, no matter how hard you push, you have nearly no brakes.

Thanks,

Jeff 1991 300d, 105k
From what I understand, disc brakes are far more dependent on power boost for effectiveness. With drum brakes, you have much more braking power with no boost than with discs.
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  #20  
Old 05-07-2007, 06:06 PM
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All the focus seems to have been on the vacuum system. Have you looked at the linkage to the booster (for interference) and or the master cylinder? These seem a little more far fetched, but it appears that you are too that point that the out of the ordinary may seem plausible.
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  #21  
Old 05-07-2007, 07:30 PM
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Quote:
Originally Posted by deanot442 View Post
All the focus seems to have been on the vacuum system. Have you looked at the linkage to the booster (for interference) and or the master cylinder? These seem a little more far fetched, but it appears that you are too that point that the out of the ordinary may seem plausible.
We'll see how the new check valve has helped or hurt things. If I have this problem once every 2 months, it'll take a while to see what's going on. I called the shop today, they said if it were the brake lines as someone else suggested, then it'd be happening all the time. The mystery has been 1) only in the morning after the first start of the day, and 2) after hitting the brakes lightly a few times, then whammo! Hard pedal and ...almost No Brakes! YIKES!

Hopefully the check valve has finished this problem off. I'll keep ya posted.

Jeff
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  #22  
Old 08-23-2008, 05:28 PM
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Hey guys. Sorry to ressurect an old thread, but I figure it's better to do that than make an entirely new one (just to say the same thing).

Anyway, my problem is very similiar to the original poster's issue, with slight variation. I can go for several months without issue (especially in the summer), but every once in a while - whammo, hard brake pedal that requires a heck of a lot of force to stop the car.

I first noticed the issue about a year ago, and took it right to the mechanic (the car wouldn't shut off, either). He checked a bunch of things, suggested that maybe the vacuum pump had gone bad, and examined the check valve on the pump itself. After discovering that there was hardly any of it left, he stuck a new valve in and I was off on my merry way. Two weeks later, and my brakes were hard again / no vacuum. Frustrated, I bought myself a Mityvac and did my own testing. Whenever the 'incident' occured, I was getting 22+ Hg at the pump, but barely 8-10 at the booster - with a very shaky needle. Convinced that I had a bad main check valve, I replaced the main line.

After that, all was well for ~6 months. Then, the issue started again. Same thing, 20+ Hg at the pump, but miserable vacuum at the other end of the booster line. What do you folks reccomend? Did I just get a dud part, and is that main black line + check valve just faulty, or do I have something else going wrong? Removing the line and slapping it around a bit, then reinstalling it, usually fixes the issue for quite some time.. I'm pretty sure it's a bad check valve again, but I want to be certain.

Thanks!

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