Bunk master cylinder?

[Sirshredalot]

First off lemme say id rather rebuild an engine or transmission anyday than bleed brakes.

With that said, Im having some trouble with my trucks brakes.

The pedal is getting softer and the master cylinder cap gasket is sucking itself into the fluid like there is a vacuum inside the cylinder.
Does this mean my MC is bad? My brakes are sticking a little and im getting horid gas mileage.

Please and thank you
God bless
-Shred

[MIKESMONZA]

Shred'; typicaly the master cylnder on the truck or cars with a cap /seal gasket that locks down or clips down will have a couple of round expandble disk's that will pull down (from vacumn) as the fluid level is kept with a false roof above the brake fluid to keep the fluid from having a big area of air,,to push back on while releasing the brakes ,, but when the front disk's are becoming worn and the cups or the pucks in the caliper will retract with a little dirt dust ground up material and corosision near where the seals are they will not retract,, causing a great deal of brake dust on the wheels ,,the over heating of brakes and poor fuel economy,If the fluid is old it probaly needs changing for example some h-body car's have never had a change in brake fliud in 30 plus year's but if you add some fluid alway use an un opened can for best result's ,,,,,,,,Also if the front hose's are breaking down internaly and are restricting flow back you have the same syptoms brake pedal mushy,, master cylnder gasket droping,, most people just push the gasket on the master cynder up and add fluid,,, But when you add new pads on the front you loosen the Master cylnder cover before retracting the pucks or squeezing the calliper,, to fit the thicker pads's the fluid will go back up in the master and flow out of the master cylnder top,, use a cheap vacumn bulb turkey baster and remove the excess fluid if you have been adding . The rear brake's ,,,,whether disk or drum condition's have simular efect on the system,, and also the propotioning valve in some of our cars/ and trucks can get stuck Mike

[Len]

Shred' to check if tou have siezed caliper pistons or faulty ft brake hoses, remove the ft tires, losen the mc cap and try to pry the pistion back into the caliper it will take a little bit of effort. if both go back into the caliper then youre problem is in the rear. however if the pistons dont go back into the caliper loosen the bleader screw and try again if the pistons return all the way you need new brake hoses if the pistons dont returne all the way you need new calipers. If one pistons or brake hoses is faulty replace the other side also.
If the ft checks out ok. Remove the rear tires and drums to ck for leaking wheel cylinders this is easly identified by wet looking shoes ect. Also replace these as a set along with shoes. Dont forget to bleed the brake system after opening the bleeder screws or replacing any of the hydraulic parts
Len

[MIKESMONZA]

Len; that was great , some of those are great diagnotic meathod's ,, ,hope Shred will find it soon,,,,,the cause for sure, Let us know what happen's

[Len]

Thanks , But I see that I forgot about the rear brake hose. To determine it this is at fault. One must hold the pistons solidly of one r wheel cyl while trying to compress the other side if no compresion happens open the bleeder and just like in the front the diaganostics are the same and as always remember to bleed the system any time you open it !!!!!! You must ck both sides this to be shure that all pistons are moving freely either wise reaplace in pairs.
Also if you have rear disc the diaganostic proceedures are the same as ft disc.
To ck the master cyl remove it from the booster without reamoving the lines, pull it away from the booster and look for brake fluid at the back of the master if present replace the master with a new one as rebuilt ones can be very problematic as other members have stated and from my own experances.
Len

[MIKESMONZA]

Shred + Len,,,, we might have to move this to the supension under brake's It would be benefichal' to all with both braking ststem's disk front/ reardrum and disk front and rear.!!!,,Mike