Topic: My Never Ending Brake Problems

[GizmoDuck]

So I rebuilt my front brakes and my front wheel won't budge. I can take the calper off and move the pad in and out with pressure from my thumbs but when I bolt it back on the pad slides out and applies a ton of pressure on the disc. How do I stop this? Cleaned everything new piston, new seals, new pads.

Also I replaced the clutch cable and I think it has too much play in it. How should I adjust this to get it dialed in?

[MCRider]

So I rebuilt my front brakes and my front wheel won't budge. I can take the calper off and move the pad in and out with pressure from my thumbs but when I bolt it back on the pad slides out and applies a ton of pressure on the disc. How do I stop this? Cleaned everything new piston, new seals, new pads.

Also I replaced the clutch cable and I think it has too much play in it. How should I adjust this to get it dialed in?

Once the pad moves towards the disc, you release the lever, and it is drawn away from the disc by the flex and unflex of the sealing rectangular ORing. When it withdraws it pushes fluid back into the master cylinder. If the return hole in the MC is clogged, fluid can't enter and it becomes a one way system, ever so tight. So, clean the return hole in MC. 99% of the time, this is the problem.

[Bodi]

Brake advice is good, but if you can push the piston in by hand then the relief hole is clear. Description is a bit unclear: is the brake free with the piston pushed in as far as it can go? (beware of overflowing the reservoir when doing that) If yes, and it stays locked only after applying the brake, check that relief hole and maybe a MC rebuild is a good plan. If it locks up when you bolt down the caliper... I have seen replacement pads too thick that do that. You can return them and get ones that fit or spend some time with coarse sandpaper and make them thinner.
Is the piston pad sliding freely in the caliper? Many aftermarket pads have the steel backing plate too big, and they need to be filed down to fit. Put some rust paint on the now bare metal afterwards to delay corrosion.
The clutch has adjustments at the lever and at the engine. Different bikes do the engine end differently but get a service manual and do as described. You want the clutch lever adjustment roughly centred with the lever feel correct. If correct engine adjustment doesn't get that, the free cable length of your new cable may be wrong. There's no easy fix for that, you can move a ferrule in and resolder it if it's too long but a propane torch is not hot enough for the bronze or silver solder decent cable makers use (and you should).

[MCRider]

Brake advice is good, but if you can push the piston in by hand then the relief hole is clear. Description is a bit unclear: is the brake free with the piston pushed in as far as it can go? (beware of overflowing the reservoir when doing that) If yes, and it stays locked only after applying the brake, check that relief hole and maybe a MC rebuild is a good plan. If it locks up when you bolt down the caliper... I have seen replacement pads too thick that do that. You can return them and get ones that fit or spend some time with coarse sandpaper and make them thinner.
Is the piston pad sliding freely in the caliper? Many aftermarket pads have the steel backing plate too big, and they need to be filed down to fit. Put some rust paint on the now bare metal afterwards to delay corrosion.
The clutch has adjustments at the lever and at the engine. Different bikes do the engine end differently but get a service manual and do as described. You want the clutch lever adjustment roughly centred with the lever feel correct. If correct engine adjustment doesn't get that, the free cable length of your new cable may be wrong. There's no easy fix for that, you can move a ferrule in and resolder it if it's too long but a propane torch is not hot enough for the bronze or silver solder decent cable makers use (and you should).

Oops, that's right.   

[Tia813]

Did you happen to replace the brake lever the same time you rebuilt your brakes? I replaced my lever on my other bike and had the same condition as yours. Chased it for a while till I saw the lever nub, that presses the piston in, was too long. Soooo the piston was always pushed in causing my caliper to seem to be "locked" but all along the brakes were applied due to the length of that "nub". I guess remove the brake lever and pay attention if the piston comes out. Just a thought

[NobleHops]

Once the pad moves towards the disc, you release the lever, and it is drawn away from the disc by the flex and unflex of the sealing rectangular ORing.

With all due respect, I do not believe this part of your otherwise good advice is true. The hydraulic brake is nothing more than a pump, and it has a return spring, in the master cylinder where the pumping force is generated. When the lever is released, the return spring pushes the piston back in the MC, withdrawing the pumped fluid, creating suction in the system. The effect of the square sealing ring in the caliper bore in returning the piston to a retracted position is minimal, if any.

[Bodi]

"With all due respect, I do not believe this part of your otherwise good advice is true. The hydraulic brake is nothing more than a pump, and it has a return spring, in the master cylinder where the pumping force is generated. When the lever is released, the return spring pushes the piston back in the MC, withdrawing the pumped fluid, creating suction in the system. The effect of the square sealing ring in the caliper bore in returning the piston to a retracted position is minimal, if any."

I agree - this has been said before lots of times. The seal does maybe pull back a bit but the MC is key to retraction and brake drag reduction. The MC piston, once past the relief hole, compresses the hydraulic fluid and forces the caliper piston out for braking. On return, there's some suction on the caliper piston as the MC piston retracts. The MC piston is cupped, though: much resistance to retraction and it will pull more fluid past the cup. If the caliper piston is stiff then it won't retract properly.
And, more usually the issue, any air bubbles in the system will be compressed and shrink as pressure increases: when the lever is released they expand again and use up the MC volume that should be causing suction and retracting the caliper piston.
Eliminating all trapped air in the braking system really helps reduce dragging.

[NobleHops]

Example: How do we think a hydraulic piston on a bulldozer retracts? From the resistance of some deformed square seal? Nope.

[enwri]

Example: How do we think a hydraulic piston on a bulldozer retracts? From the resistance of some deformed square seal? Nope.

By being "pushed" back by fluid being pumped into the other end of a double acting cylinder.
Or by being "pushed" back by load, like a  jack.
Hydraulics never "suck"  Hydraulic pressure can be thousands of times atmospheric pressure.
Master cylinder seals are a cup designed to allow fluid to flow past the edges of the cup in only one direction when the cylinder needs more fluid.
You would not be able to bleed them otherwise.

[MCRider]

I got my info first from the forum, then confirmed by page 17-4 of the Honda Common Service Manual to wit:

"When the brake lever is released, hydraulic pressure decreases and the pads cease to press against the disc. Unlike drum brake systems where a spring retracts the shoes from the drum surface, on disc brake systems, the resilience of the caliper piston seal retracts the pads from the disc and automatically self-adjust for wear."

I will repeat the follow thru, if that return hole in the MC is not clear, the fluid displaced by the action of the seal has nowhere to go and the pad remains rubbing hard on the disc, even when the lever is released.

There is a graphic on that page entitled "Return of piston due to the resilience of the seal".

There is also a really neat video showing the path of fluid and action of the seal as it flexes somewhere on this site, I'll look for it.

[MCRider]

Here it is:
http://forums.sohc4.net/index.php?topic=129993.0

[NobleHops]

Example: How do we think a hydraulic piston on a bulldozer retracts? From the resistance of some deformed square seal? Nope.

By being "pushed" back by fluid being pumped into the other end of a double acting cylinder.
Or by being "pushed" back by load, like a  jack.
Hydraulics never "suck"  Hydraulic pressure can be thousands of times atmospheric pressure.
Master cylinder seals are a cup designed to allow fluid to flow past the edges of the cup in only one direction when the cylinder needs more fluid.
You would not be able to bleed them otherwise.

Alright, I just spent a good 30 minutes looking at diagrams of various hydraulic systems, and I see what you're describing WRT dual acting cylinders, and I understand the jack reference, I have seen it in action. And so I think I had it wrong.

[GizmoDuck]

If I look in the master cylinder is the return hole the smaller one on the left? If so it bubbles when I squeeze the brake with the cap off does that mean its clear? Also while I completely rebuilt my master cylinder it seems to be leaking around the brake lever. Should I take it apart and rebuild it again or what?

[flybox1]

if its leaking, it wont supply the pressure to slow you down.  rebuild it.

[NobleHops]

if its leaking, it wont supply the pressure to slow you down.  rebuild it.

He did rebuild it. If it's still leaking after rebuild then either the bore wasn't cleaned well enough, or it is pitted beyond reuse, which is all too common I'm afraid. You have nothing to lose by trying to rebuild it with the same parts again - take it back apart on top of a spotless surface, and see if you find any grit or schmutz - if you do that could be your culprit. If not, you can try to hone it - I have a set of transmission bore brushes I use in my drill for the purpose. Hone it and reassemble it, and see if it will seal. If it won't, you're best off replacing it altogether with something new. it's the same cost as a resleeve and you'll get a better master cylinder.

N.

[enwri]

Or, I read on here somewhere else, (everything has been covered on here before, searching is difficult though. lots of results that aren't really related.)
That if you pull the lever all the way to the handlebars, the edge of the cup in the cylinder can move (too far in) and go past the reservoir feed hole and get fluid on the wrong side (lever side) and leak out.
It's recommended to place a 15mm block between the lever and bars to stop it happening while bleeding.
Might not be anything wrong with it, just over travel inside the cylinder.
Could also be all of the above suggestions as well. You'll have to eliminate them all one by one.

[flybox1]

if its leaking, it wont supply the pressure to slow you down.  rebuild it.

He did rebuild it. If it's still leaking after rebuild then either the bore wasn't cleaned well enough, or it is pitted beyond reuse, which is all too common I'm afraid. You have nothing to lose by trying to rebuild it with the same parts again - take it back apart on top of a spotless surface, and see if you find any grit or schmutz - if you do that could be your culprit. If not, you can try to hone it - I have a set of transmission bore brushes I use in my drill for the purpose. Hone it and reassemble it, and see if it will seal. If it won't, you're best off replacing it altogether with something new. it's the same cost as a resleeve and you'll get a better master cylinder.

N.

Yeah....i know he rebuilt it.  But its leaking, and it needs to be done, again, with better attention to detail.

[NobleHops]

if its leaking, it wont supply the pressure to slow you down.  rebuild it.

He did rebuild it. If it's still leaking after rebuild then either the bore wasn't cleaned well enough, or it is pitted beyond reuse, which is all too common I'm afraid. You have nothing to lose by trying to rebuild it with the same parts again - take it back apart on top of a spotless surface, and see if you find any grit or schmutz - if you do that could be your culprit. If not, you can try to hone it - I have a set of transmission bore brushes I use in my drill for the purpose. Hone it and reassemble it, and see if it will seal. If it won't, you're best off replacing it altogether with something new. it's the same cost as a resleeve and you'll get a better master cylinder.

N.

Yeah....i know he rebuilt it.  But its leaking, and it needs to be done, again, with better attention to detail.

I guess I said "I agree" but with more detail :-)

[GizmoDuck]

Taking it all apart today to make sure I didn't tear any of the rubber pieces and that everything is clean inside will let you know what I find. If it doesn't end well what would you recommend as a replacement master cylinder?

[NobleHops]

Taking it all apart today to make sure I didn't tear any of the rubber pieces and that everything is clean inside will let you know what I find. If it doesn't end well what would you recommend as a replacement master cylinder?

There are a dozen well reviewed units on Amazon, for $50 or less, depends how original you want it to appear. No specific reference though - I bought a replacement Nissin for $125 or so for another project. Not quite the bargain these Amazon units are, but a name brand and I'll likely be able to get rebuild parts for it down the road.

[przjohn]

Are you assembling the caliper while it is on the disc, or are you assembling the caliper and then sliding onto the disc. The reason I ask is it wouldn't be the first time I have seen pads that are too big and incorrect for the installation. Sometimes it is from reproduction pistons that are not correct. When you assemble the caliper and the pads are too big it clamps the pads down and you won't be able to move the disc. If you have a decent bench grinder and a good eye you can face off the pads using the side of the wheel, it usually doesn't take much. Just don't go bananas on the thing the first ride and break the pads in REAL good.

 If you can move the piston back and forth with your thumb then it doesn't sound like you have hydraulic lock on the caliper. Still, you have a master that is leaking and must be rebuilt. Since it is leaking you have either rebuilt it incorrectly or it is damaged or pitted, that could be a problem. Personally I have been using the reproduction master cylinders now available from many sources for about $70.00 instead of rebuilding on recent bikes. David Silver has them and they are all over Ebay. Much easier, are a damn close replica of the OEM unit, and they work well. For the money I think they are a good way to go.

[GizmoDuck]

Figured out the piston and brake pads, the nylon washer between the pad and piston had slipped and was not positioned properly.  Silly mistake.  As for the Master cylinder the rebuild parts were great and no dirt but there is some pitting inside.  Here are a few pics.

[NobleHops]

Yeah, that probably means "punt". Too bad :-(

[GizmoDuck]

Bought a new MC put it on today, filled it, bled it, and the brakes are Sooooo squishy.  I read that using a rubber band to hold the brake lever closed and leaving it over night may allow some of the air to escape.  If that doesn't do the trick what else should I try?  I spent an hour today trying to get this resolved.

[NobleHops]

Bought a new MC put it on today, filled it, bled it, and the brakes are Sooooo squishy.  I read that using a rubber band to hold the brake lever closed and leaving it over night may allow some of the air to escape.  If that doesn't do the trick what else should I try?  I spent an hour today trying to get this resolved.

Tap the lines with a screwdriver handle with the lever strapped, bottom to top, and leave it a couple of days, report back.