Problems with drum brake

Hi Newsgroup,

i have a problem with the drum brake from my ford mondeo (1993). On the brake test stand the brake power of the right back wheel is nearly zero. So I have changed the brake shoes on both back wheels. But without success. So I have changed the brake cylinder of that brake. Nothing happens. During the bleeding of the brakes the flow of the brake fluid was normal, so I dont think, that there is a problem with the brake pipe.

Tests on a sandy underground shows, that all wheels are blocking, except the right back wheel. But when I do the test with the parking brake, both back wheels are blocking directly.

So I think, it has something to do with the hydraulic, not with the brake itself.

Is it possible, that the brake pressure reducing valve is out of order? Or can it be, that the main brake cylinder is faulty?

Any help would be appreciated.

Kind regards from Germany,

Bernd.

P.S.: Sorry for my bad english. I have the technical expressions from a technical german - english dictionary, so I hope, that you understand it!

Given that the parking brake block the wheel, it seems a reasonable hypothesis that there is a hydraulic issue, but what about the condition of the drum? Was it cut when you added the new shoes, warped perhaps? Not sure if this would cause the problem, even a warped drum should slow the wheel down.

Also, how was the system bled, power/pressure bled, using the brake pedal, or a vacuum pump? Perhaps the flow might look normal at a low bleeding pressure, but might not behave correctly under load when braking, due to a partial blockage.

How about taking out the reducing valve and cleaning it out, then re-install, re-bleed and re-test? If that does not work, how about bench-testing the master cylinder? The last resort might be replacing the entire line to that particular wheel. A partial blockage in the line might be causing the problem, but hard to tell, really.

Good luck, Matt