Rear caliper sticks after new SS lines and rebuilding MC and caliper.

[chuck hahn]

Return ports are only in front masters. His rear problem is most likely seal bind

[sinkankan]

Been there done that, many frustrating hours and replacing every part. Turned out it was because the rear calliper piston seals just needed some lubricating grease to help them. The master cylinder had been resleeved and the brake shop covered up the return hole, so the old cylinder was tossed out and a new one installed.
Once everything was reinstalled it took five minutes to bleed and get a solid brake, don't fool around with second hand parts because it's a total waste of time and energy.

[cowboyup3371]

Actually Chuck, the rear MC also has a small return port which can become blocked and needs to be cleaned. Use a single strand of wire from a piece of electrical wire

[chuck hahn]

Got a pic?? Ive torn down several and never seen one that I recall. Dont recall that on my 78 750 that I had either. Just a straight bore, the brass nipple screwed in the side that the feed tube connects to, and the output for the brake line that I can remember.


But then again some days i cant remember what I had for lunch 4 hrs later...NO JOKE!!! I actually have had that brain fart before!!

[cowboyup3371]

Got a pic?? Ive torn down several and never seen one that I recall. Dont recall that on my 78 750 that I had either. Just a straight bore, the brass nipple screwed in the side that the feed tube connects to, and the output for the brake line that I can remember.


But then again some days i cant remember what I had for lunch 4 hrs later...NO JOKE!!! I actually have had that brain fart before!!

I don't have a good picture on the computer so I'll try to take one tomorrow

[Cyrano]

I've only ever had 2 sticky callipers (plenty of poor ones) one was down to a blocked return port (this was after cleaning and flushing the master cylinder) and it was relived, albeit temporarily by releasing the bleed nipple.

The second one was after the master cylinder (front brake again) was 'modified' and the piston wasn't allowed to retract fully to allow the return port to function. I wonder if it is possible to assemble the rear brake in such a way (no play in the lever) to create this?
On the subject of calliper piston seals, Chuck is correct, they should be able to be pushed in by hand (a little dip in some brake fluid helps the pistons go in). If it doesn't, it usually means there is still some crusty crud in the grooves. Just had to do my neighbours rear brake on her Bandit 600, it's an annual event due to the poor underslung location.

Carbs and brakes... just because you think you've cleaned them doesn't mean they're clean.

[derwood]

Return ports are only in front masters. His rear problem is most likely seal bind

Now I am sure that you don't realize there are 2 ports in a master cylinder bore.

It wouldn't make any sense that the rear would only have 1 port. It wouldn't work.
Master cylinders have 2 ports, "fill / inlet port" and "return / compensating port " ( there are exceptions, but there has to be a way of allowing fluid to expand so the brake doesn't get applied) the same physics apply to front and rear brake systems.

Testing before tearing it apart costs nothing. It is important to diagnose the problem before ripping and tearing.
If it is just the caliper piston seal, (which it may be), then the brake will not tend to apply itself, the fluid will expand up into the reservoir as it heats up rather than apply the brake.

The O.P. stated that pressure builds in the hydraulic system that is relieved when the bleeder is opened and the brake then releases, I don't think a a binding seal would not cause the system to pressurize unless the compensating port is plugged or the pushrod / linkage is adjusted a little tight.

[chuck hahn]

I know what fixed mine and it was tight seals from K&L..New Suzuki ones and problem gone. Had nothing to do with any port being plugged.

[Strobot]

I appreciate all of the advice and experience from this community. As an update, I went to my local dealer yesterday and was able to order new seals for the rear caliper. The parts guy also suggested new slides. I'll put the oem's on next week and see what happens. Thanks again for not making me justify a new GSX-S750Z!

[Strobot]

The OEM seals were not the issue. I tore the rear caliper apart again and cleaned out the channel the seal sits in with a dremel. I put bake fluid on the seals and the pistons to make sure it was nice and lubricated. They slid in much easier this time. I went for a ride after I bled the air out, and after about 5 miles, my bike started lugging. I pulled over and the pads were smoking. Same exact issue. I am at a loss for sure. Any other ideas???

[derwood]

read post 15, 21, and 22 of this thread

[btbarb]

click here, see post 10 for pic of return hole

[Strobot]

should I be able to poke a small wire through the hole like the other hole? It looks like the hole is on the bottom end of the cup. I cannot push a wire through. I am using a wire from a bread tie. It's a very small diameter and keeps bedding on me. The m/c is soaking in some kleen diesel right now to break up whatever is in there.

[chef1366]

It's the master cylinder

[derwood]

should I be able to poke a small wire through the hole like the other hole? It looks like the hole is on the bottom end of the cup. I cannot push a wire through. I am using a wire from a bread tie. It's a very small diameter and keeps bedding on me. The m/c is soaking in some kleen diesel right now to break up whatever is in there.

Yes, you should be able to poke a very small wire through the hole. (the hole looks like it was started with a drill the same size as the fill port, but it is actually finished with a tiny drill). Bread tie wire is too soft, a wire brush whisker should do it. If a wire can't be forced through I have used the smallest drill in a welding tip cleaner to open them up.

Like this one .... http://www.amazon.com/Hobart-770086-.../dp/B0017Z1SXA