Honda Car Forum

When I work at the shop where I work part time we have had a
number of master cylinders or slave cylinders fail all of a sudden
while bleeding or changing brake parts and we (me and the boss) think
it is because when you bleed a brake since there is no fluid to stop
piston travel the piston goes further down the bore than it usually
does and dirt and corrosion might have accumulated there to rip up the
seals. Like 3 months back I changed an old toyota camry rear brakes
and we pressed on brake pedal and started to adjust it. Then we
noticed it leaked a huge leak from cylinder, had to change cylinder, it
was not leaking at all before. Only difference was brake unadjusted so
pistons in brake cylinder traveled further in bore to dirty rusty
surface that ripped up seals. Also I just bled my clutch slave
cylinder, was alone so I had to use clear tube in glass bottle
technique, and I filled clutch master about 7 times and pumped out
fluid. Boy you should have seen all the black stuff in the bottle.
Also if you understand how a brake master cylinder works you will
see how if one circuit fails the pedal will go further to floor. In a
typical master you have 2 pistons one for each circuit. In normal
operation when you press on pedal it pushes rear piston forward, The
rear seal will push fluid lightly and push front piston forward, then
front piston and rear piston will start to apply brakes. If front
piston circuit loses pressure then front piston will go into bore till
the metal part of piston hits end of bore and rear piston will also
travel further (remember there is a rear facing seal on front piston. )
Now if rear piston circuit loses pressure then the rear piston will go
forward till the front part of it hits the front piston and pushes it
forward where good forward piston circuit pressure will stop the front
piston and rear piston. If both circuits fail the when you push the
pedal then the rear piston will run into the front piston and the front
piston will run into the end of the bore( in this case the pedal will
travel the furthest toward the floor.


duckbill wrote:
> Over the past few weeks the brake pedal on my 95 Civic Ex (195,000
> miles)with ABS would sometimes sink a little at stoplights and statrted
> feeling a little funny the first time I applied them lightly in the
> morning. My first thought was to bleed the brakes. And, while bleeding the
> brake pedal yesterday, I lost all pressure and the brake pedal consistently
> went to the floor. I had placed a piece of wood under the pedal so the
> brake stroke would be the same. The search feature of this wonderful forum
> led me to purchasing a master cylinder. The problem is now fixed.
> What I don't understand is how a master cylinder could fail so
> completely because you have two seperate hydraulic brake systems? When my
> pedal went to the foor, it meant I had lost both of these brake systems.
> There were no external leaks, and I never had to add brake fluid. Had one
> of my brake systems failed a while back and I was not aware of it? Thanks
> in advace of any thoughts on the issue.

Thanks Elle, Jim Y, Jim B, Michael, and Edokamoto. And a special thanks for
Tegger for the awsome master cylinder information. I did take it out on the
gravel and exercise the abs. I changed the brake fluid in the reservoir
tank again because it was now looking very (amber) used Bleeding all the
brakes again will have to wait. Happy 4th to all.

edokamoto@netzero.net wrote:
> When I work at the shop where I work part time we have had a
> number of master cylinders or slave cylinders fail all of a sudden
> while bleeding or changing brake parts and we (me and the boss) think
> it is because when you bleed a brake since there is no fluid to stop
> piston travel the piston goes further down the bore than it usually
> does and dirt and corrosion might have accumulated there to rip up the
> seals.

potentially true, but two things:

1. if you flush the fluid regularly, like it says in the book, this
doesn't happen. tegger's obsessed by this stuff more than any normal
person, and his cylinder was absolutely /pristine/. but his seals still
wore out.

2. the system /has/ to be able to function in an emergency stop without
seal failure. if using the full bore of the cylinder unearths such an
issue, it's a /good/ thing, not bad.

> Like 3 months back I changed an old toyota camry rear brakes
> and we pressed on brake pedal and started to adjust it. Then we
> noticed it leaked a huge leak from cylinder, had to change cylinder, it
> was not leaking at all before. Only difference was brake unadjusted so
> pistons in brake cylinder traveled further in bore to dirty rusty
> surface that ripped up seals. Also I just bled my clutch slave
> cylinder, was alone so I had to use clear tube in glass bottle
> technique, and I filled clutch master about 7 times and pumped out
> fluid. Boy you should have seen all the black stuff in the bottle.
> Also if you understand how a brake master cylinder works you will
> see how if one circuit fails the pedal will go further to floor. In a
> typical master you have 2 pistons one for each circuit. In normal
> operation when you press on pedal it pushes rear piston forward, The
> rear seal will push fluid lightly and push front piston forward, then
> front piston and rear piston will start to apply brakes. If front
> piston circuit loses pressure then front piston will go into bore till
> the metal part of piston hits end of bore and rear piston will also
> travel further (remember there is a rear facing seal on front piston. )
> Now if rear piston circuit loses pressure then the rear piston will go
> forward till the front part of it hits the front piston and pushes it
> forward where good forward piston circuit pressure will stop the front
> piston and rear piston. If both circuits fail the when you push the
> pedal then the rear piston will run into the front piston and the front
> piston will run into the end of the bore( in this case the pedal will
> travel the furthest toward the floor.
>
>
> duckbill wrote:
>
>>Over the past few weeks the brake pedal on my 95 Civic Ex (195,000
>>miles)with ABS would sometimes sink a little at stoplights and statrted
>>feeling a little funny the first time I applied them lightly in the
>>morning. My first thought was to bleed the brakes. And, while bleeding the
>>brake pedal yesterday, I lost all pressure and the brake pedal consistently
>>went to the floor. I had placed a piece of wood under the pedal so the
>>brake stroke would be the same. The search feature of this wonderful forum
>>led me to purchasing a master cylinder. The problem is now fixed.
>> What I don't understand is how a master cylinder could fail so
>>completely because you have two seperate hydraulic brake systems? When my
>>pedal went to the foor, it meant I had lost both of these brake systems.
>>There were no external leaks, and I never had to add brake fluid. Had one
>>of my brake systems failed a while back and I was not aware of it? Thanks
>>in advace of any thoughts on the issue.
>
>