Help! M/c

[JOHNNYB]

HI I WAS JUST WONDERING IF ANYONE HAS EVER HERD OF A MASTER CYLINDER BINDING UP FROM DIRT ENTERING BECAUSE OF DIRT IN THE CUPS AND SIMULATING HARD BRAKES LIKE A BAD BOOSTER?
THANX

 

[boomdriver]

HI I WAS JUST WONDERING IF ANYONE HAS EVER HERD OF A MASTER CYLINDER BINDING UP FROM DIRT ENTERING BECAUSE OF DIRT IN THE CUPS AND SIMULATING HARD BRAKES LIKE A BAD BOOSTER?
THANX

Its entirely possible..
The m/c is just a single stroke hyd pump that has a very close tolerence plunger/piston cup to cyl wall difference. Its tight to make sure the fluid moves instead of slipping past. A system that slips is unsafe and brakes need to work everytime..not most of the time.

I've had the pedal go completely soft to the floor with zero braking, then return to normal because of dirt & trash in the M/C holding valves open.

Something else to consider, caliper pistons binding or seizing from dirt. The normal wear of a complicated ABS system with the pumps and added seals causes crud to accumalate and contaminate the fluid. If your fluid is getting dirty, it needs to be flushed before the dirt destroys the ABS as well as the m/c and everything else. Certain C4 yrs have almost no ABS parts available, so take care of the one you have..

 

[JOHNNYB]

Its entirely possible..
The m/c is just a single stroke hyd pump that has a very close tolerence plunger/piston cup to cyl wall difference. Its tight to make sure the fluid moves instead of slipping past. A system that slips is unsafe and brakes need to work everytime..not most of the time.

I've had the pedal go completely soft to the floor with zero braking, then return to normal because of dirt & trash in the M/C holding valves open.

Something else to consider, caliper pistons binding or seizing from dirt. The normal wear of a complicated ABS system with the pumps and added seals causes crud to accumalate and contaminate the fluid. If your fluid is getting dirty, it needs to be flushed before the dirt destroys the ABS as well as the m/c and everything else. Certain C4 yrs have almost no ABS parts available, so take care of the one you have..

HEY THANX FOR THE ADVICE I DIDNT REALIZE THAT THE ABS PARTS WHERE THAT SCARCEAND IM DEF GOING TO FLUSH IT ASAP BUT DO YOU THINK I SHOULD HAVE THE MASTER CYLINDER REBUILT TOO ? A BAD POWER BOOSTER WOULD HISS RITE ?

 

[boomdriver]

HEY THANX FOR THE ADVICE I DIDNT REALIZE THAT THE ABS PARTS WHERE THAT SCARCEAND IM DEF GOING TO FLUSH IT ASAP BUT DO YOU THINK I SHOULD HAVE THE MASTER CYLINDER REBUILT TOO ? A BAD POWER BOOSTER WOULD HISS RITE ?

Not all C4 ABS parts are rare, but a couple yrs were part of an "off-board" diagnostic system that nobody has anymore and many parts are no longer made. I've had to really search for wheel sensors for my 87 and should buy spares the next time I see some since they are ALL different and most cannot be interchanged. I had to buy used or salvage sensors. I ran across guys that knew what they had and were asking $150 for a used sensor that sells for $25 at the parts store...if they can get it.

A booster will hiss a little bit normally because it is sending vac thru there constantly. When the pedal starts getting hard, that is the clue that its failing. And believe me, you'll know. That booster probably does 90% of the work. You'll use both feet to do an aggressive stop...or any kind of stop.

The m/c rebuild...thats a judgement call but getting a new/rebuilt is never a bad idea. It does have wear parts. Get a shop to do the flushing or consult a FSM because of the ABS. The extra mile of tubing and the series of valves and the pump make flushing more complicated. The worst of the brake fluid is mostly at the caliper where the heat and work is happening, so I installed "self-bleeders" or "free-bleeding" screws so I can push the junk fluid out every once in a while. Those can be found in the Corvette catalogs and are worth their weight in gasoline...