brake question

[mastan]

Hi All:
I'm having issues with my brakes, and I was wondering if anyone could help me out. I have checked and searched through the forum, and have yet to see anyone reach the level of frustration I'm at. I started noticing that my rear rotor was getting hot. Here is what I've done so far:
1. Replaced rear shoes and inspected rear caliper for any obvious problems.
2. Pulled rear M/C and installed rebuild kit.
3. Checked, cleaned, rechecked cleaned again the infamous spooge hole. I don't mean to brag, but I've got the cleanest frigging spooge hole around.
4. Bled through 2 pints of brake fluid, and still couldn't get a firm pedal. Rear brake was slightly spongy to begin with, but now its worse.
5. Installed speed bleeder. Still spongy. Cursed myself for spending $$ on stupid speed bleeder.
6. Went for a ride. Flogged the bike. Hot rotor, spongy pedal.
7. Sat down in front of the computer and tried to calm myself and beg for help.
I know it must be the rear caliper, but there is no evidence of leaking fluid. Its a sealed system, why can't I at least get a firm pedal? Any and all comments would be greatly appreciated.
Mark Stanton
78XS11e

[ratbyk]

Rear Brakes

Mark, first off remove the rear master. Place it in vise more horizontal than it would be on the bike. Hand bleed on the bench. Simply push in on the push rod then place a finger tightly over the brake line hole. Do this three/four times.
Reinstall the the line from the master to rear caliper. (don't put the master back on the bike yet) Again, holding the master at a more horizontal angle than normal, re-bleed the brakes. You can accomplish this by yourself by putting a piece of vacuum hose onto the caliper bleeder screw and run it down into a bottle partially filled with brake fluid. As you pump (slowly down and slowly up)(don't pump like crazy) any air left in the system will appear as bubbles rising in the jar. (easily visible). On the return stroke fluid will be drawn back in/no air. When the bubbles stop reinstall the master. Your pedal should be right there. I have found that I had to bleed this way both times that I have had the master off the Ratbyk.
With the bike on the center stand(in neutral) turn the rear wheel by hand. There should be some resistance, you are turning a lot of stuff on a shaft drive. But! you should be able to turn it without a great deal of effort. If it is really hard to turn, run a screw driver down between the pads and the rotor to force the pads away from the rotor. Now try turning the wheel again. If it turns much easier, step on the rear pedal a couple of times and try turning again. If the effort seems to high then you will have to reseal the rear caliper.
Remember that brakes get hot just normal riding. When you use the brakes you are converting the kinetic energy of a heavy motorcycle into heat energy to stop. Brake pads also drag just slightly on the rotors all the time to keep them clean (in the wet) so that they will warm up a bit just riding without ever touching the brakes.
Ken/Sooke
78E Ratbyk
82 FT 500 "lilRat"

[Jerry]

From personal experience....

Check to make sure the brake pedal comes back all the way up. When I got my XJ the brake pedal shaft was so crudded up it wouldn't return the brake pedal all the way, so rear was always dragging a bit, similar to the spooge hole problem. Pulled the shaft, cleaned and lubbed with white lithium grease, put back together. Problem resolved.

Later I rebuilt the rear master brake cylinder and switched to ss brake lines. The original lines will deteriorate and give you a spongy feel as they expand under pressure. Most common observation after the switch is the 'feel' of the brakes is much better. Even if you don't put on ss lines, replacing the old line with a new one may help.

[sidecarKev]

Another way I have got brakes to firm up is to tie the pedal or lever so it is pressing on the brakes. Leave it that way overnight. It opens up the valve to let the air escape the system. Works almost all the time. Leave the bleeders closed, just bungee the lever to the bar or pedal to something in the floor.

[skids]

That sounds like a good idea!

Originally posted by sidecarKev
Another way I have got brakes to firm up is to tie the pedal or lever so it is pressing on the brakes.

[ratbyk]

?

Originally posted by sidecarKev
Another way I have got brakes to firm up is to tie the pedal or lever so it is pressing on the brakes. Leave it that way overnight. It opens up the valve to let the air escape the system. Works almost all the time. Leave the bleeders closed, just bungee the lever to the bar or pedal to something in the floor.

Can't comprehend how this would help. With the brake in the on position the piston in the master is shoved forward. This covers both the primary and compensating ports in the master cylinder bore. It is now a sealed system. No where for anything to escape!
Any enlightenment appreciated.
Ken/Sooke
78E Ratbyk
82 FT500 "lilRat"

[chevy45412001]

new lines

i'd have to go with Jerry on this one.ss lines are the ticket.Old @ss lines $uck,and they are able to keep presure one the brakes too.they will expand when brakes are applied,when let off brake they are still putting presure on the brakes.

[mastan]

Thank you all for your suggestions. I was able to get a firm pedal yesterday. I noticed that there was a lot of freeplay between the actuating rod and the m/c plunger so I tightened it up and bingo. Could it be that the plunger wasn't going far enough into the cylinder and there was an air pocket in the very top?
Anyway, I think the brakes are still dragging a little too much, so I'm going to attack the caliper. Saw everything I need at parts n more for the rebuild, but the manual says this should only be done by qualified personel which means someone other than myself. Could anyone give me some pointers or point me to some other threads that have dealt with caliper rebuilding?
Thanks again,
Mark Stanton
78XS11e

[ratbyk]

Mark, be careful that you have not adjusted the push rod too far into the M/C bore. If you go too far the piston and rubber cups will not return far enough in the M/C bore to uncover the compensating port to let excess pressure and heat expansion in the brake fluid to escape. This will cause the pressure in the system to build up and the brakes will drag from this to the point that the brakes will drag more and more to the point that the wheel will lock up.
So far as replacing the caliper rubbers it is no big deal. Getting the piston out of the caliper bore is usually the toughest part. Air pressure at the bleeder screw hole will usually pop it out. Caution- wear safety glasses (flying brake fluid) and keep your fingers out of the way of the piston. It some times flies out with considerable force. After disassembly clean everything with brake fluid cleaner or alcohol. (don't use any petroleum based cleaners-it destroys your new rubber seals). Examine the piston for corrosion/pit marks on the portion of the piston that will contact the "O" ring seal. Possibly clean this surface with some fine wet sand paper. Small pock/rust marks a tolerable on this surface as long as they are in an area that will not have to form the-seal between the "O" ring and the piston. Assemble using lots of brake fluid on all internal surfaces-piston, caliper bore, "O" ring.
You can do it. Be careful with brake fluid-it eats paint.
Ken/Sooke
78E Ratbyk
82 FT500 "lilRat"

[sidecarKev]

Hey ratbyk,

Not sure why it works. If you ever get a chance ,give it a try. It really does work. I've talked to more than one person who swears by it. Worked for me!

[Underdog]

Getting the piston out of the caliper bore is usually the toughest part. Air pressure at the bleeder screw hole will usually pop it out. Caution- wear safety glasses (flying brake fluid) and keep your fingers out of the way of the piston. It some times flies out with considerable force.


Thought I'd throw in a tip here that I got from my Brit car buddies. On the old Triumphs they make up a deal for getting the pistons out if they are really stuck. Braze a grease fitting nipple on to an old bleeder then you can use a grease gun (which can build a lot of pressure) to pump the piston out.