Mercedes 508D (1981) Brake problem (1 Viewer)

[Wildman]

Hi as most of you know I have a 1981 Mercedes 508d Motorhome. I have just replaced the rear brake shoes/wheel Cyls//Drums/Rubber hose/brake pipes. I am not able to get fluid through when trying to bleed them. I have tried manually pumping the pedal and also used a pressurised reservoir system. I vaguely remember something about reverse bleeding being mentioned, what is this how do I do it. The front brakes are totally unaffected :thumb:even with rear hoses removed so assume it is a duel system. However the master cyl appears to be single piston (though not removed and checked) anyone cast light on why I'm having problems before I jump off a cliff. I need it sorted in time for Shepton or will there be in a tent.

 

[chris v]

Brake problem?

Hi,
The only thought I have after reading your post is... does your van have a brake pressure limiter? If you have the van jacked up with the axle hanging it will give the impression of no weight on the back wheels and cut the fluid pressure. Try sticking a jack under the diff.and see if you get any fluid. If this is the problem reverse bleeding will not make any difference. Let me know how you get on, or back up.
Regards,
Chris.

 

[Wildman]

No idea about a pressure limiter but van is on axle stands anyway. With the wheels still off. I am stuck trying to do it single handed.

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[vwalan]

hi roger, if you want to reverse bleed use a clean trigger pump type oil can .connect a rubber tube to blleed nipple on one rear w.cyl other end to oil can make sure other bleed nipple is shut .pump can .be carefull as brake fluid will eventually come out of filler resevoir. .do it to both w,cyl. some times its easier to use a vacum pump on the w,cyl and suck the fluid through. you may have to put wheels on and drop to ground . in the garage we used to cap the brake pipes so the fluid never ran out . let us know how you get on .cheers alan.

 

[hilldweller]

No idea about a pressure limiter but van is on axle stands anyway. With the wheels still off. I am stuck trying to do it single handed.

That was a good suggestion, I was looking at ours 'tother day as it was being MOTed.

Ours is a rod from the back axle to the chassis, one end, I forget which has a valve with two pipes.

Can you see anything like that ?

If you can maybe you can undo one end to release it.

I thought split brakes always did one front plus one back so you got a sort of balanced brake if half failed, so this too points to a valve OR it could be why your brakes were knackered, you have a blockage front to rear which kept the rears on a lot of the time.

 

[scotjimland]

Hi Roger

I think there is a check valve in each line which is designed to close if there is a loss of pressure.. so bleeding in the conventional manner won't work.. but you know that already..
Reverse brake bleeding is the way to go .. you can use a syringe and a short piece of plastic pipe to push fluid back to the reservoir .. I'm sure you can knock something up to do the job.. and it's a one man job.
the other option is vacuum bleeding but the kit is expensive..

hth

jim

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[Wildman]

That was a good suggestion, I was looking at ours 'tother day as it was being MOTed.

Ours is a rod from the back axle to the chassis, one end, I forget which has a valve with two pipes.

Can you see anything like that ?

If you can maybe you can undo one end to release it.

I thought split brakes always did one front plus one back so you got a sort of balanced brake if half failed, so this too points to a valve OR it could be why your brakes were knackered, you have a blockage front to rear which kept the rears on a lot of the time.

blockage front to rear was caused by a collapsed rubber hose. The valve you describe is a brake compensator to ensure even pressure independant on loading. This is not fitted to mine, too old, hee hee. There is only one brake supply pipe to both rear brakes.

 

[Wildman]

Hi Roger

I think there is a check valve in each line which is designed to close if there is a loss of pressure.. so bleeding in the conventional manner won't work.. but you know that already..
Reverse brake bleeding is the way to go .. you can use a syringe and a short piece of plastic pipe to push fluid back to the reservoir .. I'm sure you can knock something up to do the job.. and it's a one man job.
the other option is vacuum bleeding but the kit is expensive..

hth

jim

Cheers jim I hope it is that simple

 

[Wildman]

hi roger, if you want to reverse bleed use a clean trigger pump type oil can .connect a rubber tube to blleed nipple on one rear w.cyl other end to oil can make sure other bleed nipple is shut .pump can .be carefull as brake fluid will eventually come out of filler resevoir. .do it to both w,cyl. some times its easier to use a vacum pump on the w,cyl and suck the fluid through. you may have to put wheels on and drop to ground . in the garage we used to cap the brake pipes so the fluid never ran out . let us know how you get on .cheers alan.

Cheers Alan, looks like I may finally get it sorted.

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[tradmad]

410

hi. i just retired my 89transit camper.:i cant spend anymore time or money on it.. it had a good life680000 kms. i am new to merc.. i just bought a 92 410d. 170000mls all good except there is two different pressure in back brakes. it failed test because of this. will this be a easy job to correct .. thanks allot ..