Topic: Front brake stuck on

[Shepusa]

Went to get my 350F out of the shed today and found the front brake stuck on. Lever still feels normal. I loosened the two bolts on the outside caliper and it freed it up but when i tighten them up again it is stuck again.
Not a lot of experience outside changing pads.
Thoughts on where to start.
Thanks
Simon

[Stev-o]

The caliper most likely needs a good cleaning, some corrision has prolly "grown" in there.

Remove and clean, a new seal is recommended.

You may want to pump the pad out before disconnecting the brake line.

[TwoTired]

If you have a big rubber hammer, smack the caliper from the side to bang the piston back inward. You can hit it pretty hard without hurting anything.  Rubber is pretty compliant. Apply the brake and see if it sticks again.  Smack with hammer again and test operation.  Repeat this about 5 times.  If the caliper still sticks after some repeat operation, it's time for a caliper rebuild.  Look in the FAQ for a walk though on how to do it.

Yes, this seems barbaric.  But, I have gotten them back to full function with a caliper in otherwise good shape.  Do check the fluid reservoir. If the fluid is NOT clean and clear, you're looking at a rebuild of the front brake system.

Cheers,

[dave500]

like stevo said id pull it all apart and use a new seal,how old is the master assembly?,id be refurbing the whole deal if its an unknown,the front brakes on these aint much good so keep em the best you can,the rears only lock up and skid hardly slowing you down,keep your front brake in good condition.

[scunny]

I've never seen a post from TT suggesting the use of the hammer before. as he said, a soft headed hammer. Worth a shot, if that doesn't work, it's pull apart time.

[dave500]

use TTs head scunny,thats been known to be soft?,don't #$%* around just pull it apart.

[TwoTired]

I've never seen a post from TT suggesting the use of the hammer before. as he said, a soft headed hammer. Worth a shot, if that doesn't work, it's pull apart time.

A Honda motorcycle mechanic taught me the hammer on caliper trick.  Calipers sitting unused get sticky.  There is a lot of pressure on the rubber seal between piston and caliper bore.  Getting them moving again allows the lubes to redistribute. Calipers that have internal corrosion won't get unstuck with the Rubber mallet attack.  Gotta rebuild those.

I rebuilt the front caliper on a 550 two years ago, then let it sit.  Stuck caliper piston.  The mallet trick returned it to function.  A little bit of riding about and in use service and the brake worked as it did just after rebuild.

Cheers,

[dave500]

im glad ya handled my joke as you being hard headed ok loyd,the thought of thumping any pressure sideways on that alloy disc hub makes me cringe!id still be taking it all apart and leave the mallets for cave men who ride british bikes!

[Deltarider]

Why is it the CB350F in particular is prone to a stuck front brake?

[strynboen]

most dont ride them.
..brake systems only get fzuked bu standing still...not if they are used ...

[KeithB]

Went to get my 350F out of the shed today and found the front brake stuck on. Lever still feels normal. I loosened the two bolts on the outside caliper and it freed it up but when i tighten them up again it is stuck again.
Not a lot of experience outside changing pads.
Thoughts on where to start.
Thanks
Simon

How long has it been since the front brake was re-built?
If recently, try the TT suggestion.
If it's been a long time, dig in re-build it.

[Yamahawk]

I have used the hammer on quite a few calipers to get them to release the rotor, and it works 95% of the time. Another thing that you want to check, is the bleed hole in the MC (master cylinder, usually the front of the 2 holes), it gets plugged and won't release the caliper. It is a Very Small Hole, so you will need a piece of wire that is very fine, perhaps the E string on a guitar, or the smallest tip cleaner wire in the set. As TT said, if the fluid is mucky, remove the fluid from the MC, I like to sop it up with a paper towel (Bounty), and being CAREFUL to not drip it on your nicely painted tank, throw the paper towel into a plastic bag. wipe and clean the inside of the MC until all the gunk is removed, then fill it with fresh fluid, and bleed it down at the caliper. The bleed hole is usually plugged because it is so small of a hole. If, after thwacking, poking and bleeding, the darn caliper STILL gives you a tight grip on your rotor, you really should rebuild it.
Charlie

[rotortiller]

Two common things will cause a sticky brake in a correctly assembled, normal, clean and clear (lines) system. They are locked in pressure or a stuck caliper piston. Both are popular LOL. The master cylinder return port can be blocked as mentioned many times by others. The caliper seal can have corrosion under a good looking seal (away from view) pushing on the outside of the clean looking properly sized piston. Hidden damage is usually the hard one to find and stickiness gradually gets worse.

[Stev-o]

If you cant fix it with a rubber hammer it must be a hydraulic issue?

[mrbreeze]

The small port in the reservoir being plugged is what made mine stick around 10 years ago. It's easier to check that before tearing in to the caliper. Open the bleed screw slightly and don't let the fluid go flying out and trashing your paint. If the brake unlocks....the problem is more likely to be a plugged reservoir port.

[Shepusa]

Thanks to all for the ideas.
I gave it the rubber mallet treatment tonight and that seems to have helped. Worked the brake a few times with the mallet between but it still feels sticky so I think a rebuild is coming up.

Thanks

[Yamahawk]

...remember to clean that tiny return hole inside the MC, as you can rebuild the caliper and STILL have it stuck on the next time you use the brake... as mrbreeze said, crack the bleeder on the caliper, and see if that releases the brake so that the bike rolls freely. If it does, then clean the return hole in the MC, and you should be good to go. If not, then you should rebuild the caliper or at least clean the piston of rust and gunk. Not a bad idea anyway, as the bike is old.
Charlie

[scottly]

If you have a big rubber hammer, smack the caliper from the side to bang the piston back inward. You can hit it pretty hard without hurting anything.  Rubber is pretty compliant. Apply the brake and see if it sticks again.  Smack with hammer again and test operation.  Repeat this about 5 times.

If the caliper adjusting screw is installed, no matter how hard you beat on the caliper the piston won't move any further inward. You need to remove the screw first before you can force the piston back into it's bore more than about .006". If the piston isn't seized, pressing on the caliper with your thumbs with your fingers gripping the disc will be sufficient to move it into the bore.

[TwoTired]

If you have a big rubber hammer, smack the caliper from the side to bang the piston back inward. You can hit it pretty hard without hurting anything.  Rubber is pretty compliant. Apply the brake and see if it sticks again.  Smack with hammer again and test operation.  Repeat this about 5 times.

If the caliper adjusting screw is installed, no matter how hard you beat on the caliper the piston won't move any further inward.

Sounds like you haven't tried it.  It works even with the adjusting screw right where it is.  Only need a few thou to get the disk free.

It's not a cure all for a really gunked up caliper.  But, for disused calipers it can get things moving again.  Worked for me, and got me riding again last summer.

Cheers,

[scottly]

If you have a big rubber hammer, smack the caliper from the side to bang the piston back inward. You can hit it pretty hard without hurting anything.  Rubber is pretty compliant. Apply the brake and see if it sticks again.  Smack with hammer again and test operation.  Repeat this about 5 times.

If the caliper adjusting screw is installed, no matter how hard you beat on the caliper the piston won't move any further inward.

Sounds like you haven't tried it.  It works even with the adjusting screw right where it is. 

Yes, I've tried it, and it worked for me until the next time I applied the brake. Pushing the piston further in than allowed by the adjuster screw did a better job of freeing up a slightly tight piston in my experience. Your mileage may vary, of course.

[minimo]

+1 on TwoTired’s soft mallet whack trick. I personally witnessed Yoshi at Garage Company in Inglewood perform it recently (with a lead hammer) to free a stuck piston from a 400f - whacked it right smack on the flat face of the front brake caliper and freed it loose. Now, whether that will hold over for a good while is questionable. That brake piston when left sitting for a long time will get pitted pretty bad and the brake fluid gums up nice and thick making movement difficult... New seal, new piston, a fresh master cylinder rebuild kit, and I’d recommend investing in some master cylinder pliers; your job will be so much easier. New is always nice; safer too.


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[dave500]

just rebuild the #$%*ing thing!,you can whack it free it up,then later on a longer ride or prolonged steep decent it starts leaking fluid on your pads far from home,its not like rebuilding brembos!#$%* the SLACK attitude to brakes pisses me off!their marginal at best!

[Yamahawk]

.... and after you rebuild your caliper, remember to clean the return orifice in your Master Cylinder with a small piece of wire, if it still sticks on. Personally, this IS the first thing I check when I have a disc brake stuck on, and it is usually the problem. But thwacking it with a hammer is done to move the bike to where I can work on it, not to 'fix' it.
Charlie

[dave500]

you covered your ass there Charlie!if your doing the caliper ya gotta do the master as well on any unknown old #$%*,do the entire thing,the only thing to hit with a hammer is the guy that says to hit it with a hammer!or mallet.

[Yamahawk]

Oh no Dave! I hit the caliper to move the bike, not to 'fix' it. In my 38 years of working on bikes, I have found it expedient to thwack it to get it freed up enough to not only push the bike, but to remove the wheel or caliper from the rotor. Invariably, it is the return hole inside the MC that is clogged up with a small piece of debris that will not allow the caliper to release the pressure that was built up by using the brake. I have not had to rebuild as many calipers as they can be cleaned up, and returned to regular service if necessary. BUT that darn return hole in the MC is so SMALL that it clogs up easily from sediment in the brake fluid, and needs poked out to clean it. I also change the fluid and bleed the lines to remove the old crap in there also. It works well that way. The caliper rebuild is only necessary if the bike has been sitting a really long time. Or, if the seal is damaged in some way. Pulling the caliper, and using a C-clamp to press the pistons in to their proper location usually frees them up. I always clean the outer areas of the piston/seal before I use the C-clamp on a brake pad. Judicious use of Anti-sieze is also part of my caliper maintenance to allow the sliding parts to continue their journey, and not 'seize' up. Be careful to not allow the Anti-sieze lube to contact the brake pad itself, or the rotor. That's not good lol.
Now, if it is a bike that I just purchased, and has been sitting for a long time, I may disassemble the parts that don't work and rebuild them as a matter of course, to provide a know quantity to an unknown one. Other than that, if it has just sat over winter, I will thwack and poke and press and lube it into service lol...
Charlie