Topic: Frozen front caliper = BANG! Down goes Frazier

[camelman]

So, as you can guess, I wiped out.  My front caliper froze up when I pulled up to a stop sign, and my front tire skidded out as I was pulling away.  Luckily it was very low speed, so nothing really happened to the bike.  However, I want to figure out this darned caliper.  Please give advice.  Here is what I have done to it so far:

1) remove from bike, clean out, and reassemble,
2) install on bike and bleed out.

That is pretty much it.  Everything was clean inside, and I put on new brake pads.  It hung up a little bit after I put it on and bled it, but I figured it would loosen up once I started moving... boy was I wrong.  After I wiped out, I cracked the bleeder screw to see if there was excessive pressure but there wasn't.  I then loosened the two mounting bolts, and the wheel spun easily.  I pumped up the master, and the front wheel still spun pretty easily.  I tightened the bolts back down, released the pressure in the caliper, and found the wheel was locked again.
So, currently, if I loosen the mounting bolts until they are just touching the caliper, the wheel will turn okay.  However, as soon as I tighten them down, the brake locks and there is nothing I can do to loosen the brake.

Ideas?  Suggestions?

Camelman

[Industrial Cafe]

check out your master cylinder.

[camelman]

Yep, that would make sense.  It seemed fine, but something must be wrong.

[MCRider]

Yep, that would make sense.  It seemed fine, but something must be wrong.

The symptoms as you describe don't quite line up, but the master cylinder is so often the culprit you just have to go there.  Its usually something plugging the fluid return hole which is very small. Can be intermittent. Takes a fine wire to clear it.  Many threads on the topic. Eliminate that variable first, then look for something weirder.


Did you have the piston out of the caliper? Reinstall with a new ORing? Cleaned the Oring groove very well?

[camelman]

I spent a lot of time cleaning out the areas I could see on the caliper.  I even soaked the sucker in parts cleaner, then cleaned it thoroughly with carb cleaner, then water and soap, then brake fluid.  However, I didn't go over each of the small flowpath holes.  I definitely didn't check the master, and I just checked it and noticed it has a catch in it.  So, I'll give the caliper holes a good check/cleaning, and also rebuild the master and check the holes in it.

Thanks for the advice.

Camelman

[crazypj]

 In my experience, the usual culprits are seized  caliper pivot and corrosion under caliper piston seal causing piston to stick.
 Doesn't matter how well you wash caliper, you have to physically scrape out the crud
You can see the fluid moving back to master cylinder if everything there is OK.
The easiest way is to apply pressure to caliper/brake pad using a clamp and push fluid back to M/C.
 If piston/pad is seized you can use brake line pressure to push it back out
 

[Hush]

Same thing happened to me, twin discs froze and over I went, culprit was the tiny second hole in master cylinder was blocked.
I found it with a fine sewing needle, you need to scratch around to find it, once clear front discs spun freely again but disc was forever blued to a lovely colour.

[LoopsAndLogic]

I had my calipers both stick on my 81' CB650C.

Couldn't figure out the problem after rebuilding the complete front brake system.

Soon, my pops told me to hone the piston bores in the calipers, and wouldn't you know, it worked!!!

I went very lightly!!! It seemed the aluminum or pot-metal expanded over the years.

Couldn't explain it otherwise, but it did wonders. Pistons retracted very quickly and boy was my braking power improved.

Probably because of the new system...lol

Cheers

LL

[Spanner 1]

I'm with the posters who say it's the fluid return hole, the tiny one, in the master cylinder...when you pull the brake lever and as you release it you must see a spurt of fluid thru' the front hole ( one nearest the banjo bolt ) or the hole is blocked.......it's happened to loads of us  !!

[IHWillys]

My reservation with it being the return(tiny hole) in the master is based on the lack of any pressure release when the bleeder is opened and that the dragging brake is still occurring after opening the bleeder.   

Ken

[MCRider]

My reservation with it being the return(tiny hole) in the master is based on the lack of any pressure release when the bleeder is opened and that the dragging brake is still occurring after opening the bleeder.   

Ken

Yeah that's why I said your symptoms weren't lining up with the MC return hole problem. . Still, check it cuz you can.

Sounds more like the piston binding in its cylinder, that's why I asked if you'd actually had it all the way out. May need to replace it with one of those trick ones being sold on the internet. Replaced the Oring that seals and retracts it. Cleaned the Oring hole. Or as L&L said, hone the bore lightly.


the pivot shaft being wallowed out something like that.

[super pasty white guy]

Had you done any work to the caliper before?  Some members have reported that re-mounting the brake arm incorrectly can cause the pad to jam in the bore and result in what you experienced.

Also, you might check that the pad is wearing evenly and not becoming cocked in the bore.  I had a pad wear very unevenly and I'm sure that this would have been the eventual result had I not managed to realize what was happening.

I'll second the advice to make sure the pivot is clean and operating freely.  Hard to imagine that it could cause a full lock-up, but it's definitely something that can cause some significant dragging.

spwg

[camelman]

Well, I went back to the bike and got it off the street today.  I loosened up the caliper bolts, and drove it back to my friend's garage.  It worked perfectly with the bolts loose... and then I figured it out.  The pads are sitting too proud in the caliper.  It is either from the pads not seating all the way into the caliper, the piston being partly stuck, or the nylon washer being too thick (or maybe even the pads not being designed to work with a nylon washer).  Anyway, that's the answer, the pads were too proud, so that when I tightened the bolts down the disc was clamped solid.

Thanks for all the advice.

Camelman

[bryanj]

If the pads were too thick it would jam up immediately not just apter its been used!

Still check out the master return and the pivot pin

[camelman]

It was pretty darn tight to begin with actually.  The stop just put it over the edge.  It worked perfectly once I loosened the bolts.

[L.A. Nomad........]

My experience with people locking up their brakes are always when they take off the front fender! You need the fender brace to be assembled with your caliper!

I always here about guys having to loosen their caliper bolts to free up the brakes. This is my experiences with Cb550s only.

L.A. Nomad

 

[MCRider]

Well, I went back to the bike and got it off the street today.  I loosened up the caliper bolts, and drove it back to my friend's garage.  It worked perfectly with the bolts loose... and then I figured it out.  The pads are sitting too proud in the caliper.  It is either from the pads not seating all the way into the caliper, the piston being partly stuck, or the nylon washer being too thick (or maybe even the pads not being designed to work with a nylon washer).  Anyway, that's the answer, the pads were too proud, so that when I tightened the bolts down the disc was clamped solid.

Thanks for all the advice.

Camelman

Hmmm that just doesn't sound right, but hard to say without seeing...

The A pad should self adjust, by moving against the fluid deeper into the caliper. The B side has a mechanical adjuster, when its set right doesn't matter how thick (proud) the pads are, there should still be an air gap between the pad and disk.


Are you completely fixed now? What did you do?

[crazypj]

Without the fender bracket the caliper is tilted over,there isn't enough clearance with new pads to allow this.
 It also happens when bracket is put on wrong side of caliper mount

PJ