Topic: Mushey Breaks

[Bolt]

I'm running a 1991 4 runner, lifted and locked, I do rocks and mud. I use to have good solid breaks. Then they poped. I had both rear wheel cyclinders leaking. I put cheep advanced auto ones on. Two months later they blew out. I put OEM back on. I had the mushey breaks ever since the original ones blew out. I replaced the master cyclinder and the booster. I do stop but when I smash on the breaks the pedel hits the floor and the tires do not lock up. I am suspecting the break fluid. I have no leaks and front calibers work great. I even put new pads and shoes on. Is there maybe an rod adjustment between the master cyclinder and the booster? I have heard of others having this same problem. If I use silicone break fluid will that ruin all my seals. I have had seals swell up and lock up calibers due to silicone break fluid.

[brainlessfool]

off the top sounds like you need to bleed them, it's ez to not get all the air out so I'd say sec. time's the charm 

[KYOTA]

I thought air brakes were the shizzle 

[Bolt [OP]]

Ok I blead them again and this time we ran the truck for maxium pressure to blow out the air. They are still the same and I went thru a quort of fluid and got no air out.

[WHITE_TRASH]

Bleed the load valve for the rear brakes and make sure that the rear brakes are adjusted correctly. 

[79coyotefrg]

Ok I blead them again and this time we ran the truck for maxium pressure to blow out the air. They are still the same and I went thru a quort of fluid and got no air out.

um  how are you bleeding your brakes???  i never use those bull crap bleeder things, get a helper to mash the peddle and hold it to the floor, crack the bleeder, make sure its tight again befor they let off the pedal or you will suck air back in.

did you bleed your front brakes also??  your load proportioning valve may be bad

[GrimReaper]

Gravity bleed them if you don't have a helper. Just simply crack open the bleed screw and let it drip.
If that doesnt work there is a trick to draw air back up to the reservior. Get a junk yard reservior cap and put a fitting in it to hook it to a mighty vac. Pull about 5 hg of Vacuum into the reservior. This will draw air back to the reservior. Might need to let it sit that way for a couple hours. YOU DO NOT want to pull much more then 5hg because you can pull air in past the seals at the wheel cylinders or calipers.

[yotaboy79]

heres a lazy person way to bleed breaks dunno if it will work on a truck but its worked on my motorcycle take a pipe or somthing like that jam it between the brake pedal and the seat so the pedal is pushed down as far as it will go and leave it like that over night all the air in the fluid should work its way up to the resivore i do this to my motorcycle when theres just a small amount of air in the brake lines i just ziptie the lever to the handel so in theory it should work on a truck it may take longer than over night with a truck too

[Skinny_Pedal]

or just get a friend and do it right

[yotaboy79]

 

[79coyotefrg]

or just get a friend and do it right

[FVF_SAS]

Hmmm, Is this mushey thing only occuring in the rear brakes? What type of Brake fluid are you running? As far as seals popping due to sillicon brake fluid keep in mind that sillicon is just very fine sand; the seals are affected more by the chemical it's suspended in. Seals are all designed to work with certain compounds IE don't put esther based fluid in a system designed for mineral or petroleum based fluids...

[Bolt [OP]]

Ok I blead them again and this time we ran the truck for maxium pressure to blow out the air. They are still the same and I went thru a quort of fluid and got no air out.

um  how are you bleeding your brakes???  i never use those bull crap bleeder things, get a helper to mash the peddle and hold it to the floor, crack the bleeder, make sure its tight again befor they let off the pedal or you will suck air back in.

did you bleed your front brakes also??  your load proportioning valve may be bad

I'm bleading them just as you said. But with the engine running for maximum spirt. I'll try bleading at the proportioning valve. Thanks.

[Bolt [OP]]

Hmmm, Is this mushey thing only occuring in the rear brakes? What type of Brake fluid are you running? As far as seals popping due to sillicon brake fluid keep in mind that sillicon is just very fine sand; the seals are affected more by the chemical it's suspended in. Seals are all designed to work with certain compounds IE don't put esther based fluid in a system designed for mineral or petroleum based fluids...

I'm using dot4 Valvealine break fluid from advanced auto. Thanks for the info on not crossing over types of fluids.

[79coyotefrg]

with the  motor running mash the brake pedal and listen for a sucking air sound if you hear one, replace your vacuum booster

[Bolt [OP]]

Vacume booster is replaced. Still mushey. I gota buy a different brand of fluid and try that. Any suggestions on a good brand.

[79coyotefrg]

the dot 4 your using is fine,  ive thought about this and if you got all the air out the only thing it could be is the master cylinder is letting fluid bypass the plunger

take the cap off and hit the pedal if fluid flies all over the place,  thats it