Rear brake / master cylinder problem after attempting fluid change

[vandy]

1987 FJ1200. I was changing out fluids the other day and ran into a problem with the rear brake. The clutch and front brake fluid changes went fine with no issues. Got to the rear brake, pumped the brake pedal a couple of times, opened the bleeder valve, brake pedal went down, a couple of inches of brake fluid went into my hose, I closed the bleeder valve, and released the brake pedal. Pumped the brake pedal several times to repeat the process, and couldn't get any kind of resistance on the brake pedal again.  It just pushes down easily. Got out the Mityvac and tried to suck the fluid through the system but nothing came out. Could the piston or something inside the master cylinder have gotten stuck when the pedal went down the first time?

Greg

[CutterBill]

Could the piston in the master cylinder have gotten stuck? Sure, I suppose it could. I've never seen that happen but it's possible. More likely that the bypass port is plugged, thus not allowing the cylinder to refill. Take the cylinder apart and inspect/repair as needed.
Bill

[vandy]

Thanks. It's kind of strange that the brake was working fine before. I will take it apart and have a look. It's going to be messy since I can't get all of the brake fluid out first.

[ryanschoebel]

Thanks. It's kind of strange that the brake was working fine before. I will take it apart and have a look. It's going to be messy since I can't get all of the brake fluid out first.

If you need all the fluid out, just open the lowest point in the system, and pump the hell outta the brake. or use a syringe, and suck the fluid out of the master. That said, its not unheard of for ports to get clogged in a change, because you are stirring up anything and everything thats in that system.

[PaulG]

Could the piston in the master cylinder have gotten stuck? Sure, I suppose it could. I've never seen that happen but it's possible.

My OEM Sumitomo front caliper(s) seized open coming down the offramp from the freeway in '07, the first summer I had my '92ABS.  When I took the calipers apart I had to use dental picks to clean out the crap that had embedded with the piston seals. So yes it can happen, esp if the brakes haven't been serviced in a long time (or never in my case from the three POs).

As suggested, if you're going to take it apart to clean them, you might as well put in a new seal kit while it's open. Also do a good inspection of the dust boot, any holes in it will let the crud in.

[vandy]

Thanks for the additional info....