Brake drags

[chuck hahn]

Front brakes on the 78 1000 started dragging and i had to pull over and loosen the banjo bolt at the master cylinder and they released as expected. So i took the master apart thinking something had plugged the return port....poked it out and blew air through it. Reassembled and went a mile and i could feel them start again so i used back brake only and got it to the shop. Sure enough the rotors were pretty warm and the bike was a bit hard to push.

I thought that since the release of pressure when i loosened the banjo bolt it was telling me fluid wasnt returning...which in turn screamed return port problem. But nope. Ive never had this particular problem. Looking for leads please as to whats holding back fluid. New brake lines made by the same place i always get them made at...im stumped.

 

[chuck hahn]

Since the brakes released by cracking the banjo up at the master cylinder it tells me the problems with the master itself. But the return ports not blocked, so this is why im puzzled as to whats preventing line pressure from being released and causing the pads to drag. Then heat takes over and the brakes get tighter and tighter.

 

[Rijko]

I have seen issues with rebuild kits for the master (plunger length).
Have you rebuilt it ?

Would be interested if you can see fluid returning when pressing the pistons into the caliper.

 

[chuck hahn]

Yes...new kit installed. I was actually just thinking this very thing too. Must be a sign...lol

Its the 16mm bore. Kit came from Dime City. They bought up Z1 from what i gather.

 

[chuck hahn]

Just a thought on the rebuild kit. IF i poke into the return port with the piston installed and it blocked by the rubber seal can i drill an auxillary port to allow pressure relief?. Im thinking add a small hole with a micro drill bit a little bit more toward the brake line??? Think this is a plausible solution?

 

[Rijko]

guess that would work.
But if you have it apart anyway, personally i would compare the plungers (that is, if you still have the old one)
Thing is, the plungers usually don't wear out i hardly ever replace them.
The plunger wears a recess in the master and then it starts bleeding past the seal.
If the seal is old and lost some flexibility. New seal on old plunger usually works a treat.

 

[chuck hahn]

Threw old one out and i dont have another body to try out. All it needs is to release the line pressure and alls well. Im betting youre on track about the rebuild kit. Ill swing by the shop after work tomorrow and poke a fine wire into the return port. I bet it hits that rubber seal on the handle end of the piston. If it does i got micro bits and can relocate a bleeder hole easily enough. Sure cant hurt anything.

 

[Nessism]

K&L strikes again.

 

[chuck hahn]

Actually its an ALL BALLS kit.

RIJKO...you are the winner. wire hit the rubber cup thing when i tried sticking it through. Squeezed the lever to move the cup and wire passed through. I drilled a hole about 1/8 inch toward the banjo bolt end and rode it around the block a dozen times jacking the brakes to heat them up. Must have applied brakes 200 times and no fails. Done.

 

[Rijko]

Glad you got it working Chuck !

 

[Steve]

Did you notice that you had to move the lever more before you got braking pressure?

Personally, I think I would have shaved a bit off the lever end of the pistone to let it retract just a bit more.

.

 

[chuck hahn]

Yes on lever pull Steve. The end of the piston at the lever is irrelivent. The piston contacts the circlip as it's stop point. In any case I'll source a true known 78 1000 master at some point and replace it.

 

[850 Combat]

I had a brake line fail internally on a car. It acted like a check valve,and would make the right front drag. Thought it was a seized caliper. I had heard of that, but I had never experienced it.

Glad you sorted it out.

 

[wymple]

I've had that happen several times on vehicles, including the rear line on a Chinesium 4 wheeler. The line will collapse internally. Pressure from the master will push thru it but it can't return. When the bleeder lets the pressure off it's my 1st suspect.