Brake caliper overhaul questions

[Guest]

So I ordered new piston seals and dust boots to overhaul my front calipers. I also ordered new stainless brake lines from HEL. A week ago I got the calipers reassembled with the new seals, and placed the calipers on the bike. Today I installed the brake lines. The M/C is impeccable with overhaul kit installed at the same time as the calipers were done.

Bleeding the brakes provides a good, firm feel at the lever. Too good, as the pistons are not retracting, thereby locking the front wheel. I read a few threads about the return hole not being clear on the M/C, so I went out and tried again - removed the M/C and reflushed everything (no real need to disasemmble as it was just done a week ago), this time poking a single strand of wire from a bicycle brake cable into the tiny little hole to be sure it's clear. Meanwhile, while I have the M/C completely removed from the braking system (read: open end on brake line), I decide to check if the pistons have released their death grip on the rotors. No luck.

THey are absolutely not retracting. I can move them if I pry with a screwdriver, but they don't move on their own.

My question is this: Are the seals in the calipers directional? Because if they are I'm looking at another week of down time and a big fat mess on my hands.

The bike is an 84 GSX 750SE (Pop up Katana) but uses the calipers off a GS550E/ES 83 on up.

Any help is greatly appreciated....

[hillsy]

The seals are not directional.
Was this happening before the re-build? Did you check the piston / caliper clearance before you put the new seals in to check they were serviceable / not seizing? Did you scrape all the corrosion out of the seal galleys before you put in the new seals?
Did you get new brake pads as well? (I overhauled the brakes on a BMW that locked the front wheel like this and it was the brake pads wearing unevenly that caused the pistons to "skew" and lock the pads on the disc)

If none of these checks out, you may have pinched a seal during the rebuild??

[Smokinapankake]

Hillsy,

Thanks for the suggestions.

No, they were not seizing before the rebuild, just leaking between halves (opposed piston design). They were working pretty good before the rebuild.

Piston/caliper clearance was good. The pistons went into the calipers smooth and even on reassembly, so I dont think I pinched the seal.

Seal galleys were cleaned thoroughly.

No, I didn't put new pads in, and yes, they were worn unevenly, but still with plenty service life left in them. This may be the source of my problem, as the only thing I didn't replace. I'll check them and see if this is my problem.

I didn't notice anything strange or difficult when reassembling the calipers, or when installing the brake lines, or even bleeding them. Everything went normal, until I took it off the centerstand and had to push it forward.....

I'm glad to hear they're not directional.

[Nessism]

You can crack a banjo open to release a little pressure, that will help you positively confirm if the problem is the master or the calipers. Regarding the calipers, did you grease the sliding pins with high temp caliper grease?

[harrythehog]

after thoroughly cleaning the caliper bore, passageways, and body with brake cleaner, were you able to used high compressed air to clean out the remaining residue? did you (very) lightly lubricate the piston, bore, and seal with fresh brake fluid? i find that this has helped me to bring old calipers back to life. i think a new set of pads will definitely get you going in the right direction. good luck!

[Smokinapankake]

Nessism: no sliding pins - opposed piston design. Also, the M/C was completely removed from the bike, with an open end on the hose. The pistons are not retracting.

Harry: Lightly lubed everything with new brake fluid upon reassembly. The M/C was rebuilt, the calipers were spotless, with new seals all around, the only thing not new were the brake pads. At about 30 bucks a pair, needing two pairs, I decided I'd rather spend my money elsewhere and replace the pads when they're due, i.e., down to the wear indicator. I still have a healthy amount left to go.

I'm beginning to see that this blasted motorcycle will never be without its problems. As soon as I fix this, it'll be something else. I'm freakin tired of spending what to me seems like big money for no return on my investment. I have very little time to screw around with it, and with a short riding season (6 months or so), it hardly seems worth the hassle.
Maybe its time to sell.

[Steve]

Did you get new brake pads as well? (I overhauled the brakes on a BMW that locked the front wheel like this and it was the brake pads wearing unevenly that caused the pistons to "skew" and lock the pads on the disc)

No, I didn't put new pads in, and yes, they were worn unevenly, but still with plenty service life left in them. This may be the source of my problem, as the only thing I didn't replace.

... the only thing not new were the brake pads. At about 30 bucks a pair, needing two pairs, I decided I'd rather spend my money elsewhere and replace the pads when they're due, i.e., down to the wear indicator.

I think I am detecting a trend here. If the brake pads are worn unevenly and you have just replaced everything else with NEW, I think the pads are due, too.

.

[hampshirehog]

If you really squeeze hard on the lever and don't get any leaks (dribbles or squirts) or gentle 'farting' noises your seals are in correctly. I'd pull the pistons out again and check there's nothing wrong inside and try again. I've had this happen and did that - always worked fine and don't know what was causing it. (Though if your pads are pretty skewiff they could be the root of the problem).

[silverhorse47]

Another thing to do before taking drastic measures is to put a couple or four credit cards or some other shim material between the pads, on both sides, and the rotor, and sqeeze the brake lever a few times. Sometimes both pistons aren't pushed into the bore of the cylinder the same amount, causing one to engage with the rotor before the other. Then it will stay 'on'. The idea with the shims is to get the pistons balanced over the rotor, or centered may be a better word. Sometimes loosening the bolts holding the caliper on the fork a bit can help this process.
I have always understood that the seal is the return mechanism for disk brakes, and that the seal flexes against the piston when hydraulic pressure is applied, and the rubber 'unwinding' when the pressure is released is what moves the piston back into the bore, releasing the pad. It is a very small amount of movement. So I think the seals may be directional. I don't know...there has always been a lip on the ones I've worked with. Was yours a square profile ring? It is generally quite hard to push a piston back into a brake cylinder, often a clamp is required. Was yours tight like that? Could you have been given the wrong rubber bits?
Good luck, and don't give up on your bike. You will get this sorted out.
S.

[exdirtbiker]

brake lines ????

This might be a little "out there"...
My 73 corvette locked BOTH front calipers at the same time !!!!
They were 'new' !!!
Found out that BOTH front brake hoses had fallen apart, and the inner lining had become a 'one way flap valve'... so the pressure never released when I took my foot off the pedal.
( I found this as I tried to 'hot dog' it around the block one night, and got stuck 100 yards from my driveway )( with no insurance, or front bodywork) ( or mufflers)
So... are you sure the lines are good?
Is the M/C retracting all the way??? If it doesn't pull back far enough, it will never let out the pressure... but it sounds like you would've caught that already.

[Big T]

To confirm the master cylinder is working properly, take the top off and gently squeeze the lever to full pressure

Now release - you should see a small spout of fluid come out of the return hole. That confirms that the pressure is releasing at the master

[Smokinapankake]

Okay, I pulled everything apart again and here's what I found:

NOTHING.

New Brake lines.
New seals with no lip or taper or anything to indicate any kind of direction. Square profile.
Pistons clean, not scratched, pitted, or in any way suspect.
Bores clean, seal channel clean with nothing suspect.
Master cylinder spotless and squirting when squeezed/released (I forget which one) with new seals/spring. This was before I took everything apart again.
Pistons can be retracted by hand, pushing fluid up toward the master cylinder. They move smoove and easy.

Nothing blocking the passage between halves.
Nothing blocking bleed valve/nipple.
Nothing blocking fluid flow in any way anywhere I can see (including the splitter at the bottom triple crown).

So in a nutshell, there is absolutely no reason my brakes should lock up and not retract. NONE. What the hell?

Steve,
Can pads really be the root of the problem? I mean, if I were to put in wooden shims in lieu of the pads, and the calipers still don't retract, I doubt I can blame the pads, right? That might not be a bad idea to give it a whirl.....

And now the new thing it's doing is nothing. I squeeze the brake lever and nothing. No fluid pumps, no little squirts, just a few meager bubbles up out of the tiny little hole, and then nothing. The spring is retracting and pushing the lever back, but otherwise it doesn't do a damm thing. What the bloody hell? Why is this so damm difficult?

[chef1366]

Are you using the junction box for the lines or are they running from the M/C to the calipers?

[Colin Green]

Looked around (search function ) and found these threads that deal with lock ups

http://www.thegsresources.com/_forum/showthread.php?t=133078&highlight=Front+brake+lever+travel

This one has posts about dot 5 fluid (silicone) and problems re piston lock

http://www.thegsresources.com/_forum/showthread.php?t=101172&highlight=Front+brake+lever+travel&page=2

[Nessism]

Sorry for all the problems. Only thing I can think of is the unevenly worn brake pads are forcing the pistons to skew in the caliper bore and binding them up. How about removing the pads and dressing them square with a belt or disc sander?