2005 Sportster Rear Master Cylinder

[Pog]

Here's the setup. My wife has a 2005 Sportster 883l. I have changed the rear brakes 3 times since 05 and every time I can not get any pressure at the brake pedal.

First it was done by a shop. They rebuilt the master cylinder. No problems until I changed the brake pads a second time in 2014. Same issue. Couldn't get pressure to build up in the caliper. That time I replaced the entire master cylinder and reservoir.

So today I replaced the rear pads again and no pressure at the pedal again. Bleeding doesn't help. I know the drill. Rebuild or replace the master cylinder.

I was wondering if anyone else has had this issue and is there something I can do to avoid the problem. Any advise would be appreciated.

[Panzer]

How are you bleeding the brakes?   Vac. gun bleeder or manually pumping pedal?

[Pog]

I've tried both methods and just can't build pressure. This is the 3rd time it's happened on this bike. The first was a rebuild done by a shop, last time I replaced the entire Master Cylinder thinking perhaps the original was somehow defective. So I know that the fix is a rebuild or to replace the master cylinder.

My question I guess is why it happens. Is it a poor design or does it require special handling? The entire process was done exactly as described in the HDshop manual. I've done brakes in my different bikes numerous times. This sportster is the only one that spreading the pistons on the caliper damages the master cylinder(m/c) somehow.

I always take the cap off the m/c before spreading the caliper to relieve pressure build up but it hasn't helped with this bike. I'm thinking the m/c is poorly designed because this just shouldn't happen.

The next time I change the brakes I will completely disengage the m/c before spreading the caliper, that's the only other thing I can think of. Never had to do that on any other vehicle I've ever worked on.

[Wicked]

I don't think you're ruining the master cylinder. Problem is - not much stroke on the m/cyl piston because of design/linkage. After replacing pads, I've had to pump the pedal 50+ times to get the pads to seat proper. Helps considerably if you clean the protruding portions of the caliper pistons and clean/lube the caliper mounts. Still may take quite a few pumps.....
Common quirk on these rear brakes.... 

[Pog]

Thanks for the tip. That worked, pumped it a bunch and it brought the pedal back. Saved me a few sheckles. Thanks again.

[fbn ent]

Reverse bleeding (pushing the fluid TO the master cyl) has worked for me with problematic systems.