Cb750 front Brake question

J

jinsonphoto

Active Member
So I pulled the forks off to pull the headlight ears. To do so I had to pull the caliper mount loose to get the forks out. Anyways after I put it all back together I'm now having break issues. Once I get everything adjusted with the wheel spinning free and I pull on the brake handle the piston doesn't go all the way back in once I release the handle. Does this mean the break now needs to be bled? I didn't think I did anything to get air in the lines??

I didn't touch the handle when it was off the bike. Any ideas or thoughts would be very much appreciated.

Thanks in advance,
Anthony


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What year is your 750? Some of them had floating pistons, so it doesn't actually "pull" the piston back out after you hit the brakes. It more or less is "pushed" off the rotor once the pressure is released while the wheel is spinning.
 
if the piston wont retract with a bit of help

it could be that the return hole in your master cylinder has a bit of dirt plugging it or corrosion
 
Jewbacca it's a 78 with the newer style caliper. Do you think that could be the issue?


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Cxman the piston will retract with a c-clamp, but even after doing that and re-pressing the lever when it's all back together it's not fulling releasing?


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That sounds like either A: You have a piston seal that's rolled over, or B: a faulty/dirty master cylinder.
 
Can't say for sure what it would be then. Best guess would be to drain all the fluid, tear down the caliper, check your piston seals, clear out your lines, master cylinder, everything. Check for trash in the MC, put it all back together and re-bleed the system. Something obviously isn't right, and without being able to see it, it's hard to pinpoint the problem.
 
Jewbacca or anyone else.. I pulled the caliper apart and cleaned it out. The seal didn't seem to be rolled over and visually it didn't look like either of the holes in the master cylinder were clogged. It's actually pretty clean. Do you guys have any recommendations for checking or cleaning the MC without taking the whole thing apart? Or is disassembling it the only way to clear it?


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The caliper seals form corrosion underneath and this makes the seals "tight" around the piston. Did you pull out the seals and scrape out the seal channels? You should be able to move the piston by hand when it's disconnected from the M/C.


And "pretty clean" isn't really good enough for a M/C - it needs to be spotless. They are not hard to dis-assemble - normally it's only a circlip behind the lever and the whole thing comes out.
 
Ok thanks hillsy! I was kinda intimidated by the master cylinder. I'll give it go.

And yeah I didn't clean out the channel where the seal is. In fact even after I cleaned it the piston was tight when i reinserted it and the only way it would come out was with air. I thought it was supposed to be tight? I have now have a new seal I can put in there after I clean the channel.

I guess I better get a circlip pliers?




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