Mercedes 811d - 1989

[Alchemist]

Please can someone give some advice on bleeding the brakes on a Mercedes 811d bus?
It has a twin brake system with pdwa - the brake light on the dash comes on.

Does the load sensing valve have to be wide open to bleed rear brakes?

I have a noise like a foot pump when I press the brakes - I think this is the brake servo - have replaced once though and is the same - have another part on order.

Only thing making me wonder is that sometimes now the engine wont stop so makes me wonder if its a vacuum problem?

Even when I press the brakes hard the pedal goes to the floor as if there is air in the system still.

I have had the brake servo and master cylinder off.

Please help!

 

[turbopete]

i have very little knowledge of your vehicle BUT it does sound like you have a vacuum problem if the engine doesnt shut off, HOWEVER that would usually make the brake pedal hard after a couple of applications. if i remember right, the smaller 411d used to make a similar noise when the brakes were applied and that was normal for those.

is it a recently aquired vehicle or is this a new sound thats appeared?
is the master cylinder in good order (sounds like the most likely cause of your problem)
load sensing valve shouldnt affect the bleeding of the brakes. pressing the pedal right to the floor when bleeding them can, however, cause the seals to fail in the master cylinder

 

[WG M-B]

I thought they were full air brakes??????
You have an air solenoid that acts as a fuel shut off to turn the engine off. An air problem I would imagine?
Is the compressor working correctly???

 

[Alchemist]

No not air brakes - vacuum assisted as on a car
Brake servo, master cylinder, pdwa sensor, ride level sensor,
Do all these need bleeding in a certain order?
Or does the ride level sensor need to be wide open to bleed rear brakes properly?

 

[mike_hornsey]

Thanks Alchemist for resolving this. I had similar problem

 

[Alchemist]

Problem not solved! - How did you solve your problem please???

 

[Alchemist]

Mike Any info please?

 

[Rockron]

The 609d 709d 711d 811d 814d known (even more versions available on the Continent) as the MB Type 2 commercial all had conventional vacuum assisted braking as standard, the vacuum being produced by a piston/cylinder and the vacuum stored in 2 chambers, but an air assisted system was an option as was an exhaust brake "jake brake" these options are often to be found in these vehicles.
As for bleeding the conventional vacuum system, I find this to be easier than on many a car.... using the good old Gunson kit at a pressure of less than 10 psi. Furthest bleed point first etc. I change the fluid annually; 17 times so far with no probs. Hope this helps

 

[jomojo32]

HI, I have a similar problem with my 709d horsebox. It doesnt switch off and my brakes aren't working and they are vacuum brakes. Really appreciate any advice and where on earth can get a 709d vacuum pump from??? I know most of these lorries seem to have been exported to Africa. Appreciate any advice possible, even if anyone has a picture of the pump so at least i know what i am looking for.

 

[Rockron]

Hi Jomojo, The standard setup main components on the vacuum side of the braking system (as opposed to the hydraulic side of the system) is vacuum pump/brake booster/vacuum reservoir.
The vacuum is created by the vacuum pump which is like a 5th piston and cylinder arrangement, driven by engine power. There are various valves and pipe lines which you should check for vacuum leakage before replacing anything. The pump creates the vacuum which is stored in steel reservoirs when there's sufficient vacuum a switch turns the red dash warning light off.
Vacuum also stops the engine by shutting off the fuel supply via a soleniod operated by the ignition switch.

The brake booster is more likely to fail than the exhauster. Perhaps the brake boster diaphrgm has perished.
Erith Commercials in Dartford Kent specialise in breaking and sellng type 2 van and bus parts you'd likely get what you want there. Have to be careful you don't get a booster as old as the one that "may" have to replace and as a result also has perished rubbery parts. But as I've suggested first thing is to look and if you can get the engine running listen for leaks. Not easy on the OM364 engine the listening that is.

 

[philawsonheatingplumbing]

Hi my 811d engine will.start no probs but just pulsates when I rev it and moves so slow it kangaroos thanks phil

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