Sidecar hydraulic brakes

[Rotten Ralph]

A friend recently bought a 2003 V-Rod/Ural sidecar combo. There is a hydraulic disc on the car linked to the rear brake master cylinder.
His problem is that the rear brake won't retain pressure after a few pumps. He did find out that the previous owner had a similar problem that was not resolved completely (even by a Harley dealer).

There are no visible leaks and bleeding the system  thoroughly left no indication of air in the lines. When trying to pump fresh fluid through, many strokes on the brake pedal produce only a trickle of fluid at the caliper end.

Questions are:
1. Would using DOT 4 in a DOT 5 system cause any long term problems?
2. Is it possible that the rear master cylinder with only 3500 miles on it after 13 years has lost its sealing ability?
3. Could the rear master cylinder be too small to work both brakes? The conversion kit for the Harley sidecar doesn't provide a different master cylinder - just a modification for two lines.

[rodekyll]

Try posting this to "trike talk" (www.triketalk.com).  They have a sidecar section and some professional modificators on-site.

[Rotten Ralph]

Thanks.

[Lesman]

Dot4 and dot5 are not compatible. You can get away once(that's a big if) running dot 5 in a dot 4 system. Mixing the dots screws up the seals. . All I'm saying is run one or the other in a clean enviroment.

[Roebling3]

Not at all certain, but. Doesn't Harley use silicone based brake fluid? Or a brake fluid perhaps incompatible with the Harley MC and or the sidecar caliper/wheel cylinder has been used. If such is the case a total system strip & flush needs to be done. Replacement of all elastomers is imperative. i.e. All caliper O-rings, reservoir bellows, piston cups, rubber/silicone brake lines.    Good fortune,  R3~ 

[pat80flh]

DOT4 will work in a DOT5 system,IF the system is totally dismantled, all traces of previous fluid removed, all seals hoses etc replaced. If you mixed 4 with 5, all rubber parts are ruined, a chemical reaction between the two causes rubber to swell and disintegrate.