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  #1  
Old 03-01-2001, 12:38 AM
300D
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My car is w123 300D,

hydraulic brake is working properly when I depress it as normal or suddenly.Yesterday,I would like to check its system, so
I drove it with low speed and I depress it a little but several time before sharp depress.

The result was : It 's very hard (strength)to depress it and the car was not stop. It ran for a long distance.
Itseem to be the brake was not applied.

Is it abnormal ? How to solve this problem ?


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  #2  
Old 03-01-2001, 02:13 AM
unkl300d's Avatar
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Location: San Francisco, Ca
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my 2 cents..... might be your master cylinder.
A bad diaphram? Did somebody bleed the brakes at some point
and step on the pedal all the way to the floor as they pumped air out?
This can mess up the master cylinder.
Good luck.
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  #3  
Old 03-01-2001, 05:51 AM
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Posts: 269
This type of symptom is typical of MB diesels with some vacuum problems. Each time you depress the brake pedal you use some of the vacuum the pump has produced. If there are other consumers of Vacuum (leaks in ACC,or door locks) or the pump is beginning to fail. You will get a hard pedal. The brakes will still work fine but you have no power assist. If you push down on the pedal and hold it and after a few seconds it gets hard or pushes back your booster is probably on the way out.

Bob D.
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  #4  
Old 03-01-2001, 06:32 AM
LarryBible
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Yes, this is most definitely a vacuum problem. You could have anything from a leaky reservoir to a serious leak somewhere in the accessories.

The best way to begin isolating the problem would be to disconnect and plug everything except the brake booster and see if the problem remains.

If it works normally during this temporary arrangement, you need to look for a leak in the accessories, if not you need to check the pump and associated plumbing.

Good luck,
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Old 03-02-2001, 12:47 AM
300D
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Last night I checked the vacuum system and found that
1.The vacuum central lock system was replace with electrical system by the former onwer.
2.The vacuum line between vac. pump and booster has 3 way connection and contected with small vac.line to start switch.(If i am incorrect)
3.The vac. line from the end of injection fuel pump is connected to start switch (same switch in item 2 but another port)
4. Other vac. line are disconcected from the system and remain open.

I would like to know the operation of this system,Why it has vac. line from injection pump to start switch and
tab from vac.main line with small one to start swich also.

I do not know this is normal or has been modified by
former onwer.

Can i plug the small line that connected from main line to start switch? I do not want to use vac. central lock anymore
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  #6  
Old 03-02-2001, 01:28 AM
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Join Date: Apr 2000
Location: So. Cal
Posts: 4,430
That vacuum line running to the ignition switch needs to be there. That is what "turns" the vacuum on/off to the shut off valve, allowing you to start/stop the engine.
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  #7  
Old 03-05-2001, 05:15 AM
300D
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What is the purpose of another main line from vac. pump
to air filter cover?

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