[22lyons]

imported post

ok. I rebuilt my rear caliper and cleaned the pistons, etc. been riding for several hundred miles and the rear started to tighten up. got her stopped and used a screw driver to pry the pads off to free her up to get home.



now on center stand here is what i have found:

1. apply brakes and she is not locking up (a little tight)

2. pistons are rusted evidently from taking too much material off when polishing.



conclusion:

replace pistons @ $50 each from honda



questions:

1. do you agree the pistons are the culprit?

2. is that the going rate for new pistons?

2. should i replace the new seals since it tightened up and got so hot?

3. likely cost of good used replacement caliper instead?



thanks...

 

[Keno]

imported post

Before placing all the blame on the caliper, make sure the small return port in the m/cyl is open and not sealed shut. The caliper pistons do not retract a measurable distance. Only relax, leaveing the pad and caliper surface barely touching. When the small port is stopped up the system is closed off and heat buildup will expand the fluid enough to lock the brakes. On cool down they will relax until the next build up from use or dragging. Could be the caliper but the return port gives a lot of misery. The calipers do seize when dirty or corroded and the pistons can stick in the oring seals causing a severve drag and heat. Butalock up points to the return port and pressurized lines. Crack a line or bleeder when locked and if fluid squirts out and brakes release you have a plugged port. :waving:Keno



My 82 was dragging the rear pads real bad and it was the piston and seals sticking,had toclean pistons and lubed with silicone and worked back and forth several timesbefore it loosened up.

 

[Bagmaster]

imported post

You could also have a line coming apart on the inside and collapsing, which would not allow fluid to return to the master cylinder. Had this happen on one of the front lines on my Grand Prix so I replaced both front flex lines. It happens on these older bikes also.

 

[GSMacLean]

imported post

The pistons would have to be mighty seized in order for them to lock up the wheel - and it would take longer than a few hundred miles.

I agree, the likely (and usual) culprit is the return port in the master cylinder.

 

[22lyons]

imported post

well, i found some new pistons at a good deal and since the others are rusted pretty bad i will replace. i will try to find the return hole in the rear m/c.

 

[22lyons]

imported post

looked at your rebuild of the rear mc and don't see where the return hole is located? some help.


Also, got the caliper off and pumped up the pistons and opened the bleeder and no fluid came out. Am i correct in understanding that when it heats up it can slowly clog if the return hole is partially plugged?

thanks

 

[GSMacLean]

imported post

I didn't have a problem with my MC return when I rebuilt, and did not show the return hole. It looks like a very small depression near the far end when looking in the cylinder. At the bottom of the depression is a tiny hole. Best way to clean it out is to use a single wire from a wire brush, to ream out the hole - it's that tiny.

If you pump up the pistons when the caliper is off the wheel, there will be no pressure to push the fluid out - the pressure comes from the pistons pushing the pads against the rotor. When the pads are tight against the rotor, and the pistons can't push any further, but you continue to apply pressure - that's when there is pressure to bleed off.

Put the caliper back on the rotor (you don't even have to bolt it in place - just make sure the brake pads are on the rotor in their normal position), then pump the pedal until it is firm. At that point you should open the bleeder and you will get fluid to come out.

And you're correct - if the return hole in the master cylinder is plugged, as the brakes heat up, heating up the fluid, the fluid expands. It can't go back into the master cylinder, where it would normally go, because the return port is plugged. The only thing it can do is push the pistons out - which pushes the pads against the rotor, and eventually locks the wheel up, until it cools down.

 

[22lyons]

imported post

when i pumped it up the caliper was on and it did not build up any pressure to push fluid out the bleeder. therefore, it may be partially blocked since it started to tighten up when hot.



the pistons are corroded so replacing also.

 

[GSMacLean]

imported post

If the caliper is on the rotor, you pumped the pedal until you felt resistance (pressure), and then opened the bleeder and nothing came out, then you've got problems other than the return port.

 

[22lyons]

imported post

that's why i was thinking new pistons.



I was wondering if the port wasjust a bit clogged would the heat cause it to swell enough to make the brake start to tighten up?

 

[namsgt1946]

imported post

I ran into a similar thing on my fronts-----after much thot I found the new seal in Mcyl kit was slightly different ----( still don't know why ) but I machined .020 of the end of Mcyl piston and allowed seal to clear bleed hole and all is well. You can check this by gently putting a small wire thru the bleed hole in mastercyl and it should NOT hit the seal when inserted straight.