Rear caliper seizing help!

[AshyLarry]

Hi Guys, let me start by listing the recent work done to the bike so you know what I'm working with.

2002 620 dark (17.3K miles)
4k miles ago - rear pads
2k miles ago - rear sprocket/chain
700 miles ago - rear tire
100 miles ago - QD exbox installed

Yesterday on my way home while coming to a stop, the rear brake seized, almost locking the rear tire completely. I was able to get into a parking lot (instead getting smashed into in a busy intersection). The rear brake pedal was stuck in the up position, all the way. It could not be depressed at all. Oh, and the pads were smoking as you would guess.

After about 5-10 minutes, it cooled down and the pedal was able to be moved, (pads loosened?) so I rode home with front brake only. No problems.

I let it sit for a few hours then went out to do it again so I could mess with it while it was locked. After 5 minutes of rear brake only stops, it seized again, pedal stuck up all the way. Limped back into the garage and everything seemed fine, this time it took 30 minutes to cool enough to move the pedal.

After searching threads I decided to bleed the brakes as a quick try fix. I bleed the rear (bench bleed the master). I also greased the guide pin and checked to make sure the retainer clip was on ok. Everything looked good.

Test ride, 5 minutes and it seized again. Back into the garage, checked the rear pads and they were stuck to the rotor again (obviously). This time I cooled it off with a fan, removed the pads and inspected for uneven wear scoring etc... Found that opposite corners of each pads were worn more than the other corners, and the other typical scoring glazing you'd expect. Also, the set screw on the lever appears normal, not overly long or short. There is the 1-2mm play the manual states.

I compressed the pistons individually and they appeared to be ok, noting though that when depressing the brake pedal, the front (facing me) piston fired further than the rear, and retracted less. For the hell of it, I unbolted the caliper and squeezed each piston (and shooting fluid all over ) each worked fine. Reassembled caliper, reinstalled pads, retainer, pin. Bleed again and spun the wheel manually and hitting the brake, all seemed well.

Too late to go for another test ride so I'm posting here because my friend and I are out of ideas. Everything seems to be working properly, but not! Is the caliper shot? I'm beginning to think so. I'm open to anything, I'm desperate to get the bike working by the weekend.

Thanks for reading!

[Howie]

Increase the free play.  You need 1.5 - 2mm free play.  This is done at the master cylinder push rod.  You will need to check your brake light adjustment after adjusting free play.

[Slide Panda]

If it's not the free play- pull the pads. I had a similar but worse incident due to a the guide/retainer pin being caked with crap and causing the pads to hang and skim the rotor. The result was A LOT of heat, locked up rear brake, cooked rotor etc etc

[Artful]

Just had a similar issue with a buddy's bike.

Took off the caliper, pulled the pads, pressed the brake lever to push out the pistons themselves, and found a lot of pad debris buildup, road gunk, etc on the pistons. When he reset the piston during the pad install that junk got jammed up in the piston sleeve.

Little bit of steel wool on the piston itself to remove the buildup, a lot of brake cleaner on the caliper, and voila, perfect operation.

[AshyLarry]

Tried everything said still has the problem, I pulled the pistons and they were fine no build up at all really. I cleaned everything and am reassembling now. Don't have high hopes though. Very confused as to what could cause this so suddenly.

Any more ideas?

[Speeddog]

Points towards a plugged bleed orifice in your master cylinder.

Usual routine is that folks fit rearsets, or adjust the pedal position without checking for freeplay.
Then the piston is too far into the master, and it blocks the bleed orifice.
Caliper seizing, blown brake lines, blown piston seals, fire, etc. ensue......

[AshyLarry]

Hmm... Come to think of it, I forgot to mention that at 12800 miles (so 4500 miles ago) I had to replace the brake lever due to a drop. Could it take this long for the improper adjustment to cause problems?

How would I remedy that then? The screw? I turned that and still seized up. Maybe the damage was just already done? I really appreciate your feedback.

I just won a used caliper and master on ebay so hopefully I get it by saturday so I can spend more time working on it.

[Speeddog]

Dunno if the replacement brake lever was the issue or not.

The pushrod that goes from the lever to the master is adjustable.
That's what you adjust to get freeplay, *after* you set the pedal position with the stop screw.

[beatcat]

woah! i have an 02 620 w/ 18k on it---just replaced the rear tire and the same damn thing happend to me! Unfortunately on a 95 degree day and i rode it home a mile before i realized it was the brake was locked up. Pretty much shot the pads and dusted everything down real good. I cooled it down and pryed the pads off the rotor and haven't had any problems since. Although I did just replace the pads and clean the hell out of everything with cleaner. see what happens I guess! Good luck!

[bdfinally]

I've had that happen a couple of times. Took the pushrod off and it it with emory cloth to beat off the corrosion and re-installed & adjusted and worked fine.

[AshyLarry]

Hey guys, so I adjusted the height first with the screw, then I adjusted the freeplay so I had a few mm's before the pushrod hit the piston. Went for a ride and after 20-30 10-0 stops the rear caliper began to seize again. The pedal has no play now at all, just stuck at the top. Should I try adjusting it for even more freeplay? Or should I take the master apart? I bought another caliper and master which should be here soon (hopefully tomorrow), but I realllly want to figure this out.

Thanks for all the help thus far!

[beatcat]

do you mean the pin that holds the pads or the thing that pushes the pads together.? sorry---first time bleeder.....you said "beat off"  BTW ;-)

[AshyLarry]

Well, just in case anyone stumbles on this thread having a similar issue I'll updated here with the conclusion.

After taking the master off and ensuring it was working I was totally stumped. I put the entire system back on, adjusted freeplay, bleed once more and went for a ride. Seized again! I was pretty discouraged so I just left the garage.

About 1 hour later everything kind of clicked. I reread the posts here and it all made sense.

The QD exhaust was vibrating the set screw to the point of max pedal depression, ie leaving the pedal down and dragging! I had noticed that the set screw was not on the same place I left after one of the test rides, but didn't think anything of it because the pedal hadn't seized yet. Dumb!

So, some locktite, checked the freeplay and off for a test ride.

200 miles later I can say that its "fixed". No problems at all. Other than feeling like a dumbass I'm ecstatic that its fixed and I can ride again!

Thanks for all the help, if only I'd listened to it better!

[Speeddog]

The screw that sets the pedal position should have a nut on it to lock it in place.

[BlackKat]

interesting...I have the same issue and I too just installed an Ex-Box.....