rear brake lockup-help please

[Guest silvertramp]

Last year the rear brake on my '99 RSV locked up. I could barely get to the shoulder. The rotor was too hot to touch. I end up beating the caliper off with a donated hammer and wood block. I pulled the pads-reassembled- and rode home on the front brakes. I had no luck solving the problem, so I bought a brandy new COMPLETE caliper-Installed it, and replaced the fluid. Done deal. This was last fall-didn't get a whole lot of miles before the snow hit. The other day I dragged the beast out of the shed for a new season. Yippee! Well today it happened again after 50 miles or so. This time I cracked the line and bled the fluid out... We don't need no steenkin' brakes.

OK, so what the heck is going on? New caliper--new fluid--same problem. Do you think it's the master cylinder--poltergeists--or what?

Any help would be much appreciated! Thanks:confused24:

[george c]

if when you bled the fluid out did it releas the brake?

if so then it might be the master cylinder is not letting the fluid to return and that would be the problem.

replace the master cylinder

just my 2 cents

George C.

[pegscraper]

Flushed out with new brake fluid, but did you use stuff from the same bottle as last time? A bad batch of brake fluid maybe, that has already absorbed moisture and is rusting the pistons? I suppose it's not impossible. I wonder if a different bottle of fluid would do anything different. WAG really. I don't know what to think.

[BradT]

if so then it might be the master cylinder is not letting the fluid to return and that would be the problem.

replace the master cylinder

.

 

Agree but not sure it has to be replaced. Thought I read there is a small hole that plugs up. (maybe it was something else).

 

I would try to rebuild it first.

 

Brad

[hipshot]

have you , maby, overfilled the reservoir?

if the fluid is too high, and it heats up and expands in the reservoir, there is no where for the brake pressure to be relieved.

just a thought! don't ask me how i know.

just jt

[pegscraper]

How do you know?

[BradT]

have you , maby, overfilled the reservoir?

if the fluid is too high, and it heats up and expands in the reservoir, there is no where for the brake pressure to be relieved.

just a thought! don't ask me how i know.

just jt

 

How do you know?

 

HE posted this last week. Overfilled spilt and then ate away the plastic fairing.

 

Brad

[Yammer Dan]

JT may know the same way I do. It will sure lock them up. Take a 8 mm wrench with you when you ride and some paper towels to catch the fluid. Don't get it on paint!! Just bleed it til it stops locking up.

[hipshot]

JT may know the same way I do. It will sure lock them up. Take a 8 mm wrench with you when you ride and some paper towels to catch the fluid. Don't get it on paint!! Just bleed it til it stops locking up.

!!

 

BINGO!!!!

a man who admits that "he's been there and done that"!

 

thanks , dan.

i thought i was the only dumb-ass, in the group!

just jt

[BuddyRich]

Check to be sure you don't have an exhaust leak or something heating up the brake line if all else fails. Any moisture in the fluid would boil and cause your brake locking problem till the brake lines cooled

[Squeeze]

I ditto anything what has been said, plus, check the Mastercylinder where the feeding Line goes into the Case.

 

There should be two Holes and both of them should be open and free of any Gunk when the Piston is depressed. If the Line heats up, the Fluid should expand into the Reservoir through one of those Holes, if this is blocked or the Reservoir is overfilled, Pressure builds up in the whole System and locks the Brake.

[BOO]

Had a HD that did the same thing, what a pain. In my case there must have been something in the line. I finally took everything off and flushed it all several times, reinstalled and never had another problem.

It's not fun to have the brake lock up and not be able to release it with the pedal.

Good luck,

Jerry

[PrairieStar]

I ditto anything what has been said, plus, check the Mastercylinder where the feeding Line goes into the Case.

 

There should be two Holes and both of them should be open and free of any Gunk when the Piston is depressed. If the Line heats up, the Fluid should expand into the Reservoir through one of those Holes, if this is blocked or the Reservoir is overfilled, Pressure builds up in the whole System and locks the Brake.

 

 

As Squueze stated. There are two holes in the master cylinder bore; one is the breather port and the other is the compensating port. Your problem could be as simple as adjusting the brake pedal linkage. If the linkage is set too long, the piston will not return far enough to clear one of these ports and the brake will build pressure and not release.

 

Rod.

[GeorgeS]

Did you leave 1/2 Inch of space in the Master, for fluid Expansion ??

 

Heat from the Rear Exhaust pipe, heats the master, and Expands the fluid.

 

Also, use Valvoline Synthethic brake fluid.

[Guest silvertramp]

Thanks all for your quick replys. The fluid was from a new sealed can. I thought I was careful not to overfill the resevoir--It is possible, however. It sure ai'nt overfilled now. I'll check the master cyl. I think I can get a new one online for $38. Luckily I've been on back roads and not in the fast lane on the interstate. There is not much time to dive for the side of the road. The motor won't move it----SCARY!!

[hdroyer]

I had the same thing happen, I had to use a piece of wire from a bread tie to clear the return whole.

[Condor]

As Squueze stated. There are two holes in the master cylinder bore; one is the breather port and the other is the compensating port. Your problem could be as simple as adjusting the brake pedal linkage. If the linkage is set too long, the piston will not return far enough to clear one of these ports and the brake will build pressure and not release.

 

Rod.

 

I'm wondering..... and that's dangerous... Why is the master expansion hole so damn small. I would think that it could be made a bit larger and microscopic 'grunge' wouldn't plug it up. I understand that the hole is a potential wear point for the piston cup, but maybe a couple of thousandths bigger would git rid of the rear brake lock ups and clutch slipage, and still not cause premature wear????

[Squeeze]

I'm wondering..... and that's dangerous... Why is the master expansion hole so damn small. I would think that it could be made a bit larger and microscopic 'grunge' wouldn't plug it up. I understand that the hole is a potential wear point for the piston cup, but maybe a couple of thousandths bigger would git rid of the rear brake lock ups and clutch slipage, and still not cause premature wear????

 

The bigger the Hole, the bigger the Travel of the Piston needs to be to seal it before any Pressure builds up.

[Condor]

The bigger the Hole, the bigger the Travel of the Piston needs to be to seal it before any Pressure builds up.

 

Squeeze, over all, the effective compression seal of the piston cup, with an expansion hole a couple of thousandths bigger diameter would be insignificant.

Now granted the bleeding process might get a little more messy due to the increased flow of fluid out of the hole on the initial piston stroke....

[Squeeze]

You may believe the Boring Diameter is nearly insignificant, but it simply would lengthen the Way the Piston needs to travel to reach a specific Amount of Pressure. And the bigger the Hole is, the more free Way(unpressured) is in Action.

 

Next would be to see this not in pure Length, but in Percent of the traveled Way.

 

Not that i want to defend those Engineers in any Factory, it's just a Fact.You asked for an Explanation, now you got it

[Yammer Dan]

Flush system as you should and size of return hole would not be a concern would it?

YEAH I don't do it as should be either.

[Condor]

You may believe the Boring Diameter is nearly insignificant, but it simply would lengthen the Way the Piston needs to travel to reach a specific Amount of Pressure. And the bigger the Hole is, the more free Way(unpressured) is in Action.

 

Next would be to see this not in pure Length, but in Percent of the traveled Way.

 

Not that i want to defend those Engineers in any Factory, it's just a Fact.You asked for an Explanation, now you got it

 

OK Squeeze, I'm open to learning something here. Let's say for discussion that the OEM opening of the hole is 5 microns and we opened it to say 10 microns, and since hydralics doesn't occur until the lip of the cup moves past the hole, what would the difference in hydralic movement be with that little difference in hole size??? Also remember that the edge of the cup only retracts just past the opening when at rest, and sits in front of the fluid supply hole. So the piston cup edge only has to move slightly before the hole is closed off and hydralic action occurs. I personally think that the difference would be very little, but perhaps there's something I'm overlooking??? I understand that Honda actually has a larger hole and puts a baffle over the opening to prevent fluid from going airborn....

[Squeeze]

OK Squeeze, I'm open to learning something here. Let's say for discussion that the OEM opening of the hole is 5 microns and we opened it to say 10 microns, and since hydralics doesn't occur until the lip of the cup moves past the hole, what would the difference in hydralic movement be with that little difference in hole size??? Also remember that the edge of the cup only retracts just past the opening when at rest, and sits in front of the fluid supply hole. So the piston cup edge only has to move slightly before the hole is closed off and hydralic action occurs. I personally think that the difference would be very little, but perhaps there's something I'm overlooking??? I understand that Honda actually has a larger hole and puts a baffle over the opening to prevent fluid from going airborn....

 

Well i'm sorry, i have nothing to teach you more than you already know.

 

I'm with you, the Difference in your Example is 5 Micron and i wouldn't make a huge Difference. But it would change the Point where the Lever bytes to a later Point.

 

But with only 5 Microns more Diameter what would you gain other than a bigger Boring? The Chances that this Hole will get plugged are not essentially better than a with the smaller Boring. If you want to play it safe, the Hole has to a be lot bigger, e.G. 1.5 or 2 mm. This would make a Difference in both Aspects, premature plugged and effects the Lever Range.

 

I'm sorry, no further Education from me at this Point ... :D

 

P.S.

not only Hondas have Baffles in the M/C. My Friends FZ750R has Baffles in both, Brake and Clutch M/C.

[Condor]

Well i'm sorry, i have nothing to teach you more than you already know.

 

I'm with you, the Difference in your Example is 5 Micron and i wouldn't make a huge Difference. But it would change the Point where the Lever bytes to a later Point.

 

But with only 5 Microns more Diameter what would you gain other than a bigger Boring? The Chances that this Hole will get plugged are not essentially better than a with the smaller Boring. If you want to play it safe, the Hole has to a be lot bigger, e.G. 1.5 or 2 mm. This would make a Difference in both Aspects, premature plugged and effects the Lever Range.

 

I'm sorry, no further Education from me at this Point ... :D

 

P.S.

not only Hondas have Baffles in the M/C. My Friends FZ750R has Baffles in both, Brake and Clutch M/C.

 

Shoot? You're no fun.... :) The only difference between the 5 and the 10 micron hole (example) would be that larger particles would pass thru and reduce the possibility of brakes locking up and clutches slipping due to fluid expansion, rather than the hole plugging up with the tiniest particle. And it seems that this problem is quite common with our bikes, right next to reserves that are over filled. The next time I get into rebuilding a brake master I'm going to modify an extra one by enlarging the hole and install it to see the effect...if any. That said, nothing beats regular fluid changes, to keep clutch and brake systems happy......

[Squeeze]

Shoot? You're no fun.... :) The only difference between the 5 and the 10 micron hole (example) would be that larger particles would pass thru and reduce the possibility of brakes locking up and clutches slipping due to fluid expansion, rather than the hole plugging up with the tiniest particle. And it seems that this problem is quite common with our bikes, right next to reserves that are over filled. The next time I get into rebuilding a brake master I'm going to modify an extra one by enlarging the hole and install it to see the effect...if any. That said, nothing beats regular fluid changes, to keep clutch and brake systems happy......

 

Sorry for your Inconvenience :rotf:

 

 

My only Question is ...

 

What the Heck do any Particles in any Size in the M/C or the Fluid ??