Brakes????

[rice_eg]

hey all,

i just got my licence back and i've noticed that when i drive now and am at a set of lights or idling my brake pedalgoes further and further in. I changed the pads today and its stops mad. But the same problem keeps hapening.

any ideas?

mate said that is the master cylinder but theres no leaking fluid. Fluid levels stay the same.

also, i've bleed em too.

cheers

(eh vti)

[Sexc86]

Its the Mastercylinder.

Its the seals inside, doest mean you have to be actually leaking fluid out of your resoviour.

[Limbo]

you need to rebuild the master cylinder. There is a post in the DIY on how to do this

[JohnL]

The fluid (and pressure) leaks past the seals and then back into the reseviour, hence no fluid loss. It's a dangerous condition and needs to be fixed asap.

It may happen more in hot weather or after the MC has been sitting in a hot engine bay when the car is parked. My best guess as to why this sometimes happens is that when the MC is colder the cylinder bore is X diameter, but when it's hotter the metal expands and the diameter becomes X+. The seals may be old and hard, and not able to 'spring' outward to seal adequately when the MC expands. The diameter difference between a cooler and hotter MC may only be very slight, but enough to be the difference between sealing and leaking slightly.

[bennjamin]

did this happen before thebrake fluid change ?

i doubt its your master cylinder - its more than likely user error. You need to rebleed the fluid and make sure there is no air bubbles thru the system. How did you bleed ?

[rice_eg]

cheers guys,
i bleed them for ages. I changed the calipers a month ago but i didnt notice the brakes done that before the calipers were changed.

I hope its something small........

Whats the best way to bleed them?

I had somone pump the brakes and held, then realease the pressure from the 10mm nipple on the caliper. Both sides. Havent doen the rears though.

Could that be it?

[SuiJin]

u need to bleed all the brakes... == u got air in there.

[bennjamin]

Could that be it?

yes it COULD be that.

do it again - you should do it furthest away from the MC (master cylinder) and work your way back in.

So REAR LEFT , REAR RIGHT , FRONT LEFT , FRONT RIGHT.

Make sure there is solid brake fluid coming thru the tube/pipe before you ask your friend to "hold" to the floor as you tighten.

[aaronng]

I had somone pump the brakes and held, then realease the pressure from the 10mm nipple on the caliper. Both sides. Havent doen the rears though.

This method CAUSES leaking master cylinders. You should open the nipple, and then pump the brakes. Time for a rebuild.

[wynode]

A 'leaking' master cylinder won't show a loss of fluid. What happens is the fluild is bypassing the seals.

See this thread for the proper method on 'pumping' the brake pedal.

http://www.ozhonda.com/forum/showthread.php?t=11867&highlight=brake+fluid

[Davo]

i am also having this issue in my crx. is it possible that the brake boost is faulty too???

[JohnL]

The pedal merely being soft with excessive travel is most probably a symptom of air in the hydraulics. This tends to be a fairly consistant problem, i.e. the pedal is always soft and the system needs bleeding

If the pedal sometimes feels soft with excessive travel, but sometimes feels firm with 'normal' travel (or close to it), and particularly if the softness sometimes manifests as a progressively 'sinking' pedal when say waiting at the lights, then the problem is most probably an internally leaking MC, and the MC needs to be replaced.

It wouldn't be impossible to have both problems simultaneously.

[Benson]

This method CAUSES leaking master cylinders. You should open the nipple, and then pump the brakes. Time for a rebuild.

Whats wrong with that method? That what i always do and my brakes are still fine.

Make sure its bleed properly..

Make sure you dont drive around like that... its dangerous

[SPEEDCORE]

This method CAUSES leaking master cylinders.

Interesting view point, not one that I agree with... but I think you on the same page as me.

I bleed my brakes exactly how he described, and it will NOT cause leaking of the M/C.

HOWEVER... I do put a small block of wood I keep in my brake bleeding kit to put under the pedal so as not to go all the way to the floor, or even past the usual point of max pedal travel for that matter.

[aaronng]

Whats wrong with that method? That what i always do and my brakes are still fine.

Make sure its bleed properly..

Make sure you dont drive around like that... its dangerous

Interesting view point, not one that I agree with... but I think you on the same page as me.

I bleed my brakes exactly how he described, and it will NOT cause leaking of the M/C.

HOWEVER... I do put a small block of wood I keep in my brake bleeding kit to put under the pedal so as not to go all the way to the floor, or even past the usual point of max pedal travel for that matter.
The brake system after the master cylinder is sealed if there are no leaks. If you pump hard on the pedal on the sealed system, the internal pressure increases. If you pump too hard, then the weakest part will leak. The weakest part in the brake system are the sealing rings pushing against the wall in the master cylinder. If the pressure is high enough to deform the seal, then your master cylinder will have the tendency to leak/bypass at that deformed spot.

If you don't pump hard, then you'll be ok. But I know of people who use all their strength to pump against the brake pedal, sometimes with both feet in an auto!!!

[SPEEDCORE]

But I know of people who use all their strength to pump against the brake pedal, sometimes with both feet in an auto!!!

Well that's just stupidity.... its not the technique then is it. Its the moron stamping on the pedal with all his strength.

My point in putting the block of wood there, is to prevent more piston travel than usual so the seals do not rub up against walls that have not had the piston move over it, and the greater chance of corrosion being on the walls of the bore further down.

[thepope1986]

i am also having this issue in my crx. is it possible that the brake boost is faulty too???


a faulty brake booster will make your pedal really really hard and wont pull the car up easily

[JohnL]

If any part of the braking system can't easily cope with a strong person pushing with all their strength on the pedal without malfunctioning, then that braking system is poorly designed or faulty.

In reality all braking systems will be physically indestructible in anything remotely approaching the foreseeable extreme of normal usage, and then some. The designing engineers will use a very large MoS (margin of safety) for brakes (consider the lawsuits and damage to public image...).

Keep in mind that in an emergency (with adrenalin pumping) that even a person of only average strength is capable of exerting a very high momentary force on the brake pedal pad. From (vague) memory, something like 200kgs exerted on the pedal is not uncommon during panic braking, which is way more than you are likely to see when bleeding the brakes (even bleeding them brutally).

[aaronng]

If any part of the braking system can't easily cope with a strong person pushing with all their strength on the pedal without malfunctioning, then that braking system is poorly designed or faulty.

In reality all braking systems will be physically indestructible in anything remotely approaching the foreseeable extreme of normal usage, and then some. The designing engineers will use a very large MoS (margin of safety) for brakes (consider the lawsuits and damage to public image...).

If the master cylinder o-ring is that strong, then why do you still get failing master cylinders and siezed calipers occuring to street cars?

Yes, indestructable with normal usage, but pumping on a master cylinder in a system where the brake fluid has no where to go is not normal usage. That means you are putting wear on the o-ring, which is nowhere near indestructable. The caliper, pistons, master cylinder and brake lines are pretty tough, but the o-rings are the weakest link. Nothing lasts forever, and I have many o-rings at work which end up with a flat side on the ring's cylindrical profile, which leads to leakages.

[Webby_roller]

I had a similar thing happen to my ED civic...

When you replaced the front pads, did you notice brake fluid when pushing the caliper back in??? My caliper seals where leaking and required a rebuild...

If this is the case its not expensive to rebuild... My rebuild kit cost 35 ish each side.... Now they feel like new brakes...

hope this helps at all.... good luck

[JohnL]

If the master cylinder o-ring is that strong, then why do you still get failing master cylinders and siezed calipers occuring to street cars?

Calipers often seize due to failure in the lubrication of the sliding guide pins.

Leaks are caused by wear and / or scoring in the cylinder bores and / or rubber seals, corrosion, degradation (elasticity loss / cracking) of rubber seals.

Corrosion, bore and seal wear and bore scoring are likely to be the result of (or at least exacerbated by) old brake fluid (with absorbed water content) and resulting debris in the system. Pistons can seize due to internal corrosion and debris. It's good practice to change the brake fluid annually, which reminds me...


Yes, indestructable with normal usage, but pumping on a master cylinder in a system where the brake fluid has no where to go is not normal usage.

In this sense, the brake fluid has "nowhere to go" whenever any pressure exists in the hydraulic circuit. It doesn't matter whether any movement is occuring, it's only the pressure in the system that is placing any meaningful load on the seals etc. Movement does cause wear, but that's a different issue.

However, this is slightly off the point. I do agree with you that excessive force should be avoided when bleeding brakes, but not for the reasons you suggested.

It's not a good idea to allow the MC piston(s) to bottom out and then force them hard against the end of the cylinder bore and / or each other. This isn't really a hydraulic issue, but more to do with the pistons physically and forcefully contacting each other and / or the end of the MC bore that might cause internal damage to the pistons and related components (more so than the seals I would expect).

In use this never happens unless there is an abnormal condition such as a major leak, or the fluid boils. Normally the fluid prevents the pistons from moving so far that they contact each other or the bore end.


That means you are putting wear on the o-ring, which is nowhere near indestructable. The caliper, pistons, master cylinder and brake lines are pretty tough, but the o-rings are the weakest link. Nothing lasts forever, and I have many o-rings at work which end up with a flat side on the ring's cylindrical profile, which leads to leakages.

O-ring? Of course I know what you mean, but 'O-ring' makes them sound weak and wimpy, which they aren't. The seals aren't as crude as a simple O- ring, which I suspect you know too.

Unless they're damaged, cup seals (as found in MCs) seal more effectively the more pressure is in front of the seal, i.e. the pressure forces the 'cup' lip outward against the cylinder bore. They are able to deal with very substantial pressures because they are very well supported in the piston grooves (in which they sit) and by the bore walls (and lubed by brake fluid).

The amount of rubber (or neoprene like plastic / artificial rubbery substance) that is unsupported and subject to pressure is only that tiny annular area that exists between the piston OD and bore ID, this area being much too small for the seal to 'blow through', and not being where wear is an issue in any case (the fluid seal occurs at the very edge of the cup seal lip).

Rubber (or rather, the rubber analogues used in hydraulics) are very very tough and very wear resistant, but they do eventually wear. This is an issue of rubbing action between the seal and cylinder bore over extended periods of time and many thousands of brake actuations, not to an occasional very high pressure in the brake hydraulics.

This isn't to say that seals that consistantly do see very high pressures won't wear more quickly (than seals that mostly see only moderate pressures), they probably will wear faster to whatever degree, but I don't think it would be a massive difference.