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1990 W124 230E
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67 Posts
Discussion Starter #1 (Edited)
Gentlemen - After reading the extensive literature on the W123 brake system, my issue of: the brake pedal hitting the floor once in a while and the engine not turning off, especially when parking on an incline with the brake pedal pressed down; was in fact a problem of a worn out brake master cylinder. The MC was replaced with a new one followed by a new brake booster and the scheduled bleeding and replenishing of the brake system with DOT 4. I can't thank you all enough for the priceless information provided via this forum.

Coming on to another issue that I currently face: my central locking has failed in addition to which, as per the mechanic at the local MB dealership, my vacuum pump needs replacement. A conclusion he came too while putting on the new MC and booster. I am assuming that the central locking has gone out of order due to a leak in the vacuum system. Since the vacuum pump has been suggested to be changed, I might as well update the entire system with new lines and valves where ever necessary.

In order to better understand the dynamics behind this system I seek your help and would appreciate if any one could provide me with the diagrams/flow charts; educating me on how the entire pump system correlates to the mechanics of the car along with the color coded lines that run through out the structure of the vehicle; under the vacuum distribution system in a Euro 1982 W123 300D under discussion.

I believe my hard gear shifting transmission issues are also symptoms of a weak vacuum pump?

An expensive undertaking, nevertheless in order to have this piece of automobile ingenuity run in the family for another 60 years, the above project needs to be undertaken and performed. All help rendered in this regard would be highly appreciated.
 

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Registered
1990 W124 230E
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67 Posts
Discussion Starter #3
Govert - Agreed but correct me if I am wrong here, the vacuum pump also controls the locking system and does have an affect on the gear shifting? I might be horribly wrong here but as per my understanding the vacuum system is connected extensively to almost every component in the car
 

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2001 Volvo V40
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2,954 Posts
What normally occurs is that a leak in the central locking system or the valves controlling the EGR (there are some other common vacuum leak points) affect the shifting. Only if the brake booster doesn't work, you have a possibility of the vacuum pump failing.

The main function of the vacuum pump is to provide the brake booster with vacuum, that is why there is a big vacuum line running from the pump to the booster. From that big line there are one or two vacuum tap points for all the other systems (central locking, shifting, A/C etc). The orifices of those tap points are calibrated so that a leakage in one of the systems doesn't affect the brake booster system.

If you want to be sure, you have to do some measurements with a vacuum gauge.

There are repair sets available for the vacuum pump, you don't have to replace the entire pump if it is found to be faulty.
 

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1990 W124 230E
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67 Posts
Discussion Starter #5
Govert - in order to check my points, when you say certain levels on a vacuum gauge, what amounts of pressure am i suppose to be looking at and specifically what reading in supply line is to be observed and read? any diagrams depicting this?

i appreciate the help that you are providing me with!
 

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2001 Volvo V40
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2,954 Posts
The testing of the vacuum pump is described in the FSM:
43 Brake Booster
select 43-660
You measure the time it takes to reach -0,5 bar of vacuum.

A good vacuum pump should be able to create around -0.75 bar (or 22 inHg) of vacuum.

Piston-type vacuum pumps usually don't fail or only after a very long time and if something fails, it is the bearings (causing engine damage when parts of the bearing come between camshaft and timing chain), not the vacuum piston.

Vacuum diagrams exist of the EGR system (probably not installed on a 300D in Pakistan), the central locking (frequently published on this forum and elsewhere, can be found with a search) and of the automatic A/C.
 
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