Om642. Hard brake pedal. Engine issue?

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DarioD85

New Member
Joined
Nov 19, 2018
Messages
15
Location
London
Car
Mercedes cls 350 cdi
Hi everyone, new to this forum.
Car: Cls Grand edition 350 cdi
Year 2010
Engine om642
Milage 108000
This car is mystery!
Having issues on hard brake pedal in stop start traffic, if I release brake pedal while the engine is still on idle not revving or driving on idle not pressing accelerator. The second press on brakes is hard as rock no stopping force. But as soon as I accelerate brakes worked fine.
So I realised not enough vacuum produced for brake booster.

-First I checked vacuum pump very little vacuum produced( ordered new pump from main dealer) , fitted
Nothing same result.
-Second. Change new vacuum line to booster including check valve.
Nothing
-Third . Order new brake booster
Changed and Nothing

Now my other guesses changed:
Engine breather, new drive belt and tensioner, turbo seals oil cooler seals, full service etc.....

No help.
Then I brought my friends Eclass with same engine. His vacuum pump sucking very well. So I took it off put it on my car but guess no lack. His pump still doesn’t work properly on my car. Then I realised that his drive belt turns a lot faster on idle then mine. So I put my pump on his car and it works fine.
Ok now the revs on his car and on mine are the same on idle 600 rpm

Now the vacuum pump is turned by camshaft so is everything else by engine chain and alternator belt

Now why is my engine turning slowly on idle even everything else works fine and no screen faults. But not enough for pump to produce vacuum.
The only difference on my engine and my friends is I have factory fitted brabus chip when w219 was ending yr 2010 and he doesn’t.

Does anyone have any idea where to look next???
Please help
MUCH APPRECIATED GUYS
THANK YOU!!!
 
Pulled No.They are all original from day one.
But what confuses me, vacuum pump driven by camshaft on this V engine.
The chain is not stretched.
To get point adding some pictures
Where the vacuum pump is mechanically attached . Red paint on the right.
( not my engine )
78FCA1A5-0909-4BC0-BE47-5880FC2C5800.jpeg
 
Vacuum pump directly attached to this camshaft which is driven by main chain and everything else
 
The schematic for my ‘08 OM642 (US) shows a BAS travel sensor mounted below the master cylinder.
Not sure if this means anything for your situation, but figured I’d offer it.


Sent from my iPad using Tapatalk
 
Symptoms are typical of a brake booster not holding vacuum for some reason. Mystery symptoms are often the result of a simple fault and often down to a mechanic assuming something is true when its not.- like the new check valve/vacuum line is working correctly- did you swap it as well as the pump for your test? Otherwise it remains an untested common factor[ among several others] for both pumps failure on your car and not your mates.
 
Other possibility is if there are other vacuum branch takeoffs beyond the check valve. If there are any leaks in any of the branches of the vacuum that would have the same effect Certain engine components are elecrically controlled but vacuum operated by solenoid controlled vacuum valves-things like turbo variable vanes or waterpump impellers? To test these components might require a vacuum pump like a mityvac?
Hand Vacuum/Pressure Pumps | Mityvac
 
Last edited:
Thanks for reply.
The Vacuum pump has only one entry point and it goes to only and directly to Brake Booster.
I have brought new vacuum line direct from Mercedes which has check valve on it. No help!
Then I have changed brake booster thinking the same. But looks like booster has only little vacuum to brake once and that’s it. Vacuum pump barley sucks if I put my finger while idle it’s like nothing, compering mates car where it wants to suck my finger in.
So could it be something else?
 
I could be wrong, but I believe it relies to some extent on an oil supply to enhance the internal sealing of the pump. I think the oil feeds up through a small drilling in the side of the cylinder head where the nose of the pump pokes in to. It might be worth checking there is not a blockage in this area, perhaps if someone has used silicone sealant or something to try to cure an oil leak.
 
It’s crush metal gasket.

Oil supply to pump though of that one as well.
When I took the pump off and start the car, don’t know whether it should but no oil coming thru that little hole on cylinder head. So was curious put a flexible wire in and only goes about 15cm and hits something. Don’t know if it should is there check valve or something?
But when I opened pump there is oil in there it’s not dry so I guess pump sucks oil from that little hole?
 
DarioD85 said:
It’s crush metal gasket.
Click to expand...
Just wonder if there's a degree of end float required between the cam end drive and the mounted pump shaft to give the PUMP impeller the ability to seal properly internally?A used crushed gasket might seal adequately but clearance might be reduced?
 
D9FE7AA5-99F7-434B-8BFF-704BD59CB02D.jpeg Pump can be fitted only one way finding degree of camshaft and then turn the pump to allocated holes for screws.
Also measured distance between camshaft and impeller looks fine.
Here is the picture of pump
 
I think you should run your friends car and see if oil comes out of that hole. Afaik early cars with SBC and no vacuum pump have that drilling sealed with a small ball bearing down at the head gasket face
 
Last edited:
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