Post by entropy on Jul 14, 2008 23:32:25 GMT -5
Well, my '78 rebuild project is almost complete but I seem to be having one problem with the front disc brake. Seems that something is causing the slave cylinder to stick and the brakes are locking up the front wheel.
Here is the maintenance history of the brakes:
1. Fresh rebuild of both the master and slave cylinders using new Yamaha parts rebuild kits.
2. Old fluid was very nasty and I had to spend some time in the solvent tank to get everything clean. All holes and ports were cleaned out in the master cylinder.
3. Close inspection of master cylinder bore revealed that there was absolutly NO pitting or wear in the aluminum. Everything looked perfect.
4. Close inspection of the slave cylinder and piston also showed no wear or pitting in either. Everything looked perfect.
5. I pulled the hoses and squirted liberal amounts of brake cleaner, then soapy water through the hoses. Everything seemed to come out clean. I cleaned all banjo bolts as well. Naturally, I rinsed and dried everything thouroughly prior to reassembly.
6. Put brand new Ferodo pads on.
7. Inspection of disc and mounting bolts shows everything is true and alligned.
8. All parts and components are completely stock (except for the pads).
9. Used fresh DOT 3/4 (Castrol) brake fluid.
Symptoms:
1. I had some trouble at first when I filled the system with brake fluid. It didn't want to bleed very easily. I let the bike sit overnight (per the Yamaha manual) and got it to bleed OK the next morning. Seemed to me at the time that the bleed effort was a little excessive. I, frankly, have never had this much trouble bleeding a brake!
2. When I squeeze the brake lever the slave (caliper) piston doesn't seem to want to "relax" and return to a neutral position so that when I attempt to spin the front wheel, the wheel doesn't spin easily, ie excessive brake pad rubbing on the disc.
3. At first I thought it might just be the new pads not being seated to the disc, so I took the bike around the block (really easily) a few times. I applied the brakes very easily about a dozen times. When I got back into the garage, I couldn't spin the front wheel at all by hand. The brakes were almost locked up (probably from the heat of the disc-expanding). I could roll the bike by pushing with some effort, but could not spin the wheel by hand.
Troubleshooting:
1. I have a disc brake piston pushing tool that I purchased at Napa Auto parts. This tool works by using a screw that tightens into the piston and pushes the piston back into the slave cylinder. It works better than craming a screwdriver between the pads and prying. Anyway, the piston would not budge almost as if there was a hydrolic lock in the system.
2. By loosining the bleeder screw, thus allowing the brake fluid somewhere to go, the piston immediatly and freely pushed back into the slave cylinder. I also tried this with my bare fingers and could also easily move the piston. This symptom led me to believe that my problem was higher up in the system, most likely in the master cylinder.
3. I double checked to make sure that the brake lever adjuster screw was not too tight on the master cylinder piston. I found plenty of free play in the adjustment. not too much, just barely touching. I even experimented by turning the adjustment screw well out of the way. Still no help.
For the life of me I can't think of what the problem could be and I have never experienced anything like it before. Does anyone else out there have any ideas or have experienced a similar problem? I also rebuilt the entire rear disc brake system and didn't have any of these problems. As soon as pressure is taken off the rear brake pedal the disc pads return to a "relaxed" position and the wheel spins almost freely without touching the pads.
HELP! This problem is keeping me from riding my freshly restored '78!
Here is the maintenance history of the brakes:
1. Fresh rebuild of both the master and slave cylinders using new Yamaha parts rebuild kits.
2. Old fluid was very nasty and I had to spend some time in the solvent tank to get everything clean. All holes and ports were cleaned out in the master cylinder.
3. Close inspection of master cylinder bore revealed that there was absolutly NO pitting or wear in the aluminum. Everything looked perfect.
4. Close inspection of the slave cylinder and piston also showed no wear or pitting in either. Everything looked perfect.
5. I pulled the hoses and squirted liberal amounts of brake cleaner, then soapy water through the hoses. Everything seemed to come out clean. I cleaned all banjo bolts as well. Naturally, I rinsed and dried everything thouroughly prior to reassembly.
6. Put brand new Ferodo pads on.
7. Inspection of disc and mounting bolts shows everything is true and alligned.
8. All parts and components are completely stock (except for the pads).
9. Used fresh DOT 3/4 (Castrol) brake fluid.
Symptoms:
1. I had some trouble at first when I filled the system with brake fluid. It didn't want to bleed very easily. I let the bike sit overnight (per the Yamaha manual) and got it to bleed OK the next morning. Seemed to me at the time that the bleed effort was a little excessive. I, frankly, have never had this much trouble bleeding a brake!
2. When I squeeze the brake lever the slave (caliper) piston doesn't seem to want to "relax" and return to a neutral position so that when I attempt to spin the front wheel, the wheel doesn't spin easily, ie excessive brake pad rubbing on the disc.
3. At first I thought it might just be the new pads not being seated to the disc, so I took the bike around the block (really easily) a few times. I applied the brakes very easily about a dozen times. When I got back into the garage, I couldn't spin the front wheel at all by hand. The brakes were almost locked up (probably from the heat of the disc-expanding). I could roll the bike by pushing with some effort, but could not spin the wheel by hand.
Troubleshooting:
1. I have a disc brake piston pushing tool that I purchased at Napa Auto parts. This tool works by using a screw that tightens into the piston and pushes the piston back into the slave cylinder. It works better than craming a screwdriver between the pads and prying. Anyway, the piston would not budge almost as if there was a hydrolic lock in the system.
2. By loosining the bleeder screw, thus allowing the brake fluid somewhere to go, the piston immediatly and freely pushed back into the slave cylinder. I also tried this with my bare fingers and could also easily move the piston. This symptom led me to believe that my problem was higher up in the system, most likely in the master cylinder.
3. I double checked to make sure that the brake lever adjuster screw was not too tight on the master cylinder piston. I found plenty of free play in the adjustment. not too much, just barely touching. I even experimented by turning the adjustment screw well out of the way. Still no help.
For the life of me I can't think of what the problem could be and I have never experienced anything like it before. Does anyone else out there have any ideas or have experienced a similar problem? I also rebuilt the entire rear disc brake system and didn't have any of these problems. As soon as pressure is taken off the rear brake pedal the disc pads return to a "relaxed" position and the wheel spins almost freely without touching the pads.
HELP! This problem is keeping me from riding my freshly restored '78!
