Intermittent Brake Seizing

[Bowtie2Bimmer]

After getting the bike running, my buddy has bout about 650 mile son the bike. However he is having intermittent front brake seizing, basically the caliper is locking onto the disk. It will happen sometimes overnight: he will come out and the front wheel is locked. Other times it will be while he is riding. The font starts to drag to the point he just starts slowing down. Once stopped, the wheel is locked, you can't even push it. Again, its intermittent. Some days its fine. After a lockup, he would squeeze the brake lever and open the caliper bleeder valve to relieve pressure. It will work fine after that. Then, some time later (1 or more days) it will lock up again

I assumed water or some other contaminant in the line. I have flushed all the brake fluid and replaced with fresh DOT4. Still having the issue.

I then took the caliper off cleaned the pistons and seals. Still the problem persists.

My next step is to rebuild MC and caliper, but I wanted to check in here. Has anyone heard of this before? Any suggestions?

[csmith12]

I am guessing you have some air trapped around/near the top banjo bolt. Take off the master and turn it upside down and bleed again.

I have a zxg6 doing the same crap, but I haven't dug into it yet. Maybe we can help each other if we find the problem.

[Bowtie2Bimmer]

Originally Posted by csmith12

I am guessing you have some air trapped around/near the top banjo bolt. Take off the master and turn it upside down and bleed again.

I have a zxg6 doing the same crap, but I haven't dug into it yet. Maybe we can help each other if we find the problem.

Sadly, banjo has been bled twice now. I removed all of the fluid to clean the caliper. I literally took the pistons out and cleaned everything. So I had to do a full line bleed.

That's not to say its not still a possibility. I will definitely check again.

[csmith12]

ahh... well, I will be watching for what fixes your problem then.

zxg6?!?!?! I meant zx6r. lol

[Sirref]

Have you checked the front alignment? forks aren't bent at all to cause undue drag from the pads on the rotor?

My first thought was the caliper but if that's been rebuilt already then its likely not the issue. It's likely to be the master cylinder at this point, I'd also check the brake lines for any minor leaks

[Bowtie2Bimmer]

Originally Posted by Sirref

Have you checked the front alignment? forks aren't bent at all to cause undue drag from the pads on the rotor?

My first thought was the caliper but if that's been rebuilt already then its likely not the issue. It's likely to be the master cylinder at this point, I'd also check the brake lines for any minor leaks

Front caliper has been rebuilt per say, just thoroughly cleaned. I'm considering getting all new seals for the caliper and a MC rebuild kit.

What about the line? Could it be swelling for some reason, causing fluid to be pushed out into the caliper?

[Sirref]

A full rebuild kit for the caliper may be the solution

as for the line, its possible that it could have cracks that only show when it expands under use allowing small amounts of air into the lines. You'd be able to see this with your eyes while its sitting so if it looks good it probably is. I've had that issue with a rear line that melted on the exhaust a bit and let air into the system

[RacinNinja]

DO you have aftermarket levers on this bike?

[Bowtie2Bimmer]

Originally Posted by RacinNinja

DO you have aftermarket levers on this bike?

All factory.

[RacinNinja]

SNap. I know there are issues with aftermarket levers holding slight pressure on the master cylinder. This doesn't allow all the fluid to come back in and locks up the brakes.

Might be worth having a look at the lever anyway to be sure it is releasing the master cylinder piston all the way.

[Ghostt]

Write-up time

I recommend that every time you change your pads, you service the calipers, he's my write-up to help you out. It should fix your initial problem, and keep your calipers in top working order.

For those of you whom are scratching their heads, here you go,*


Front Caliper Service (also rear as well)

Many folks have posted here with a Varity of front brake problems.

*Many of which are attributable to the lack of proper maintenance.

*Here’s how you can always have a brake like when your bike was new.

A short list of the problems and the causes.

Soft lever or lever goes to the bar.

The usual cause is the pistons are pushed too far back into the caliper by a flexing a warped, coned, disc.

*Using up too much piston travel before the disc is pinched.

Juddering in sync with wheel rotation.

The disc is worn, and its thickness varies. *This causes the caliper to “sink” into the thin part and when the thick part comes around, it gets wedged into a smaller space causing a tightening of the brake. Then the tight spot passes through and it like the brake is released. Then repeat, repeat.

Cupped, coned, or warped disc.

Unfortunately this is a common problem with EX’s the cause is the disc is stretched in the center due to being rigidly bolted to the wheel. *The huge force of braking is transmitted to the wheel through the webbed center of the disc which gets stretched and becomes larger than the space it occupies in the center of the disc. This causes the center to push to the side trying to find room for itself.

*Resulting is a cone shaped disc.

Soft lever 2

The caliper has pistons only on one side, so as the pads wear the caliper must shift sideways apply even pressure on both sides of the disc.

*To allow this the caliper floats on two pins. *If these pins get dry (no grease) dirty or bent. The caliper won’t center itself and bends the disc to wherever it is.

This take up lever travel and when released pushes the pistons further back than necessary.

*If not fixed will eventually destroy the disc (warp it).


Ok how to prevent all of the above.

When new pad time comes around, resist the temptation to just pop in new one and go.

*Every time you must do these things.

Remove caliper disassemble and clean it.

Clean and re grease the sliding pins.

Polish the caliper pistons to remove dirt. If you just push the pistons back into the caliper leaks will result. Or binding.

Tools required:
12 mm socket
8mm open end wrench
3” or bigger C clamp
a supply of new bake fluid.
wire brush and or steel wool.

Remove the caliper from the fork leg but leave the brake line on.

Remove the old pads and the mounting frame (the sliding pins)

Remove the cover from the Master Cylinder on the Handel bar.

Attach the C clamp to one of the pistons but don’t squeeze it. *Pump the lever on the bar slowly to push out the other piston almost all the way. *Put the C clamp on that piston and push out the other one.

Remove both pistons by hand.

Remove all the rubber part from the caliper, the seals are in the grooves in the caliper and dull pointed thingy will get them out easy.

Disconnect the caliper from the brake line.

Soak all the rubber parts in new clean brake fluid * ONLY!!!!! * Rub them with you fingers till as clean as new.

The caliper can be cleaned with a wire brush or even a Moto tool for the internal grooves, NOW’s the time to paint it if you wish.

Polish the pistons till they are smooth and shinny. They are chrome plated. If any of the plating is chipped or damaged below the dust cap groove. *Replace it.

The master cylinder is the subject of another write up and we’ll assume it in good working order here.

If you suspect your disc is bad, your bets bet is to replace it with an after market one fro EBC or Galpher.

*Don’t remove the disc unless you intend to replace it. *It will assume a new shape if it is * stressed and will not be flat again. You can try to check its condition by placing a straight edge across the face of the pad swept area looking for any distortion.

Re assembly

Take the nice clean rubber seals and install them into the caliper then the Dust covers.
Wet all the rubber with new clean brake fluid and partially fill the caliper with new fluid.

Push the pistons though the dust seals and into the caliper body until the dust covers snap into the grooves.

Fill the MC with new fluid and pump the lever while holding the Line above the MC till clean fluid flows.

Connect the line to the caliper while holding it above the MC.

Pump the lever with the bleeder valve open till fluid flow from the bleeder.

*Hold the caliper so that the bleeder is the highest point.

Close the bleeder and pump more fluid into the caliper but don’t push the pistons all the way out.

Then squeeze the pistons all the way back in and install the new pads.

Re grease the slider pins and assemble the dust seals and re mount the caliper on the forks but leave the bolts loose.

Now clamp the caliper to the disc with the brake lever.

Look at the space between the fork lugs and the caliper, clamp and release a few times as you tighten the bolts by hand. It one lug touches much before the other the odds are you mounting bracket is bent. You can straighten it.

*After you get it the best you can. Some shim washers made from alum can stock can be fitted to the loose side.*

** *What we are doing here is trying to minimize the bedd in time and gets the best pad life.


Ok with everything tight you should be through, Notice we don’t need to bleed the brakes, but if you screwed up in any of the above steps, you might do that here.

Be careful to Bedd in the new pads gently.

*Too much pressure too soon will burn the pad material as only a small area will be gripping at first. You also won’t have full braking power till the pads are fully familiar with the disc

I also recommend flush and fill with new brake fluid, also I'd go with 5.1DOT

This is the one I use



https://m.motul.com/ca/en-us/product...-1-brake-fluid



Also inspect the brake lines, replace is needed, http://faq.ninja250.org/wiki/Stainle..._lines_upgrade

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[Motofool]

Originally Posted by Bowtie2Bimmer

Front caliper has been rebuilt per say, just thoroughly cleaned. I'm considering getting all new seals for the caliper and a MC rebuild kit.

What about the line? Could it be swelling for some reason, causing fluid to be pushed out into the caliper?

There is no mystery about this:
When pressing on the MC's cylinder, there is a volume of fluid trapped inside the system (among the small piston in the MC and the bigger pistons in the caliper).

Case 1:
Heat is transferred into the fluid.
If it is pure fluid, that heat makes that volume grows, but not enough to be noticed.
If the fluid contains humidity, that heat makes that tiny amount of water become steam and the volume of that water grows about 1600 times.
That clamps any pad for as long as the temperature of the fluid+steam remains high enough.

Case 2:
The relief orifice (compensating port) in the MC is dirty/clogged and/or the return spring is broken/weaken.
In both cases, the problem does not allow part of the fluid trapped among the small piston in the MC and the bigger pistons in the caliper to normally return back to the container (compensating for any variation of volume due to temperature), reducing the volume and pressure inside the caliper enough to release pad's pressure over the disc.

Any deformation of the hose under pressure would have the opposite effect: it becomes harder to clamp/lock the pads.

Click on Theory Video and on Animation:
http://search.lv2014.integr8cms.net/...aster-cylinder

[verboten1]

Originally Posted by Motofool

Case 2:
The relief orifice in the MC is dirty/clogged and/or the return spring is broken/weaken

This is what I came to say after thinking about it a little bit.

[SLOWn60]

It has to be master cylinder.
"It's seized in the morning": the only possible way it can be seized in the morning is if it was seized at night or the rider applied the brake in the morning (common practice for many and should be for all to give the brakes a few pumps to confirm they are fully operational). If the brake seizes and won't release but does when bled then it has to be the master cylinder.
All symptoms described except the impossible "it seized overnight" describe a master cylinder issue.
Sorry, curt & brevity because I'm madly hammering this out on my phone and my thumbs are sore!

[RuthlessZ]

I've been having intermittent dragging issues on my front caliper since about February. When it started, I naturally, bled the brakes and changed the fluid. This fixed the problem briefly, but it returned shortly after all was well though, and I rode just being cautious with the front brake, and honestly using the rear excessively. Now about 2 weeks ago I swapped my master cylinder for a brand new one, and the issue got much better but was still there sometimes.

Now the fun bit, 4/5 I was at a car meet, leaving, touched my front brakes, and they just locked hard around 15mph, I low sided and was more or less unscathed. Bike not so lucky.

So I've torn the bike apart to fix everything, taken my caliper apart, 2 week old master cylinder is trashed, and I threw away my 12 year old brake hose.

My bike has ~25k mi on it, yes it was dumb to not replace all that **** earlier, but moving on I just wanna guarantee everything functions when it goes back together. I have a few questions.

1. The bike was roll-able after I picked it up, but after 10 minutes of sitting my front wheel wouldn't even rotate, tire just dragged. Does this provide me any info as to why the caliper locked? I don't think it was input error on my part.

2. New master cylinder, SS brake hose, new rotor, and caliper rebuild should mean this won't happen again?

3. Clutch cover is scraped, and sight glass broke, should I replace the whole cover or just the glass? It's scratched right on top of the actuator arm bit of the casing.

4. I just measured my front rotor and it's 4.25mm thick, the under-spec rotor couldn't have caused this right?

ETA: Sorry for threadjacking

[ducatiman]

OP....there exists a relief port (bleed back) in the master cylinder... def need to examine, possibly cleanout

[Bowtie2Bimmer]

Now that it is mentioned, it would not surprise me to find that MC relief port was clogged. The fluid was exceptionally bad when I flushed it the first time. I had began to solidify in the reservoir.

I think I will disconnect, clean and reassemble

[csmith12]

That is a bummer Jon, hope everything goes well.

[SLOWn60]

There's always a silver lining: through your experience and posting up here; you learn and others benefit from your experience too! You'll have a good idea of what is the problem and how to fix it as will others when these symptoms occur again or to someone else.

[Ghostt]

As long as your in the neighborhood, address the caliper as well, don't forget the slider pins as well, also check the rear too.

Don't take any changes with brakes.

[Mohawk]

So the brakes were full of congealed fluid & you just bled them right ? Well there your problem. Brake fluid will ONLY congeal in the presence of contamination which is usuall water ! Water causes corrosion of the other components especially allow, this will lead to corrosion solids in the brake system that will NOT be forced out with a bleed, because the bleed hole is to small & the caliper will still be full of congealed fluid, unless it was stripped & cleaned.

Even if you change your fluid regularly at the 2 year interval recommended by most manufacturers, the caliper will always remain filled with old fluid, unless you take the caliper off the bike & remove the bleed nipple, allow fluid to drain from the hose & M/C then invert the caliper & press the pistons fully in to expel all the old fluid. Mount back to bike loosely replace bleed nipple & bleed like a new dry system.

When rebuilding calipers or M/C you do NOT need to change the seals if the they & the system are in good condition. If there is contamination always replace all seals after a thorough clean of the metal components.

Hope that helps. I know it's a PITA job, but good performance & your life could depend on it !