Master Brake Cylinder?

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rubio9800

Greasemonkey
Oct 10, 2020
242
110
43
California
Hello folks,

Happy 4th!

Just got back from a cruise and it was a bit worrisome. When applying the brake it got so soft it went all the way down and the Brake dash light came on.

It went away few seconds and the brake feeling appeared to be normal. As i kept on driving now the brake feeling is either firm (most of the time) to spongy feely(slow to return)

I couldn’t see any brake fluid leaking, and there is fluid when i looked in the cylinder. Can’t tell if it was full or low, got changed less then a year ago.

Could it be the cylinder? Do not feel comfortable driving it now.

Thank you in advance
 

rubio9800

Greasemonkey
Oct 10, 2020
242
110
43
California
i took off the reservoir cap again, something just didn’t feel or look right when i did it the first time.

there is fluid but the rubber piece looks swollen and it’s hard to put back in

doing research i see this could be an indication of contaminated fluid?

Last year i did replace the brake fluid (at a shop) but didn’t think to open it to do a comparison.
 

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Ribbedroof

Comic Book Super Hero
Supporting Member
Jan 4, 2009
4,862
6,891
113
Wellston, OK
The light coming on indicates a pressure imbalance in the system.

I would pull the rear wheels and drums to look for leakage at the rear wheel cylinders, then check the calipers at the front. Other things to inspect are the flex hoses at each caliper, and at the rear axle center section. If these have never been changed, do it NOW. Sometime, the rear wheel cylinders don't leak enough at first to show up on the backside of the backing plate or wheels.

Then I would check the steel hardlines...follow them back from the master cylinder to the distribution block/proportioning valve to each wheel.

While the master can sometimes internally bypass, in my experience, it's not common.

i once owned a Malibu that had a leak in the hardline that came out of the master cylinder. It appeared that a ham-fisted mechanic had managed to move the line to where the upper control arm managed to rub a pinhole in it at the bottom of the vibration coil.
 

CopperNick

Comic Book Super Hero
Supporting Member
Feb 20, 2018
3,347
3,011
113
Canada
Outside possibility that, if the car has one, your brake booster has gone bad on you. Otherwise the list above give a good summary of places to look and things to see.



Nick
 

-dw-

Greasemonkey
Mar 15, 2021
205
376
63
Central MN
The reason for the swelled cap seal and funky brakes is some kind of oil was poured into the master cylinder. Thats guaranteed death to any rubber seal in the brake system. Oil will be slick between your fingers and brake fluid will not.
 

Hurricane77

Master Mechanic
Nov 11, 2020
326
656
93
Ottawa, Canada
i took off the reservoir cap again, something just didn’t feel or look right when i did it the first time.

there is fluid but the rubber piece looks swollen and it’s hard to put back in

doing research i see this could be an indication of contaminated fluid?

Last year i did replace the brake fluid (at a shop) but didn’t think to open it to do a comparison.
That is definitely not right. If the gasket looks like that, good chance the seals in the master cylinder are not is great shape as well. Even a chance that seals in the pistons and drums are gone too.
 

rubio9800

Greasemonkey
Oct 10, 2020
242
110
43
California
when i first got the car i had leaking wheel cylinders and were replaced. Also replaced the calipers.

i’ll be going to a shop later today, see how that goes
 
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