bad brakes

i got a problem my brakes dont work well
you push it once and the pedal goes to the floor then after you let it back up again and push it down you get more pressure behind the pedal and so on and so on it a 73 jeep with a 78 front end and a 78 paportioning valve (i know i spell stuff wrong, deal with it) any hint on getting it better
i have a new master cylinder in the jeep now but its been sitting for a while
thanks for all the help
kuggs

 

Start with a proper bleeding of the system.

Is the master cylinder for the 73 (drum brakes) or the 78 (disc brakes)?

 

i have the disc brakes now they were drums
i have a proper brake bleeding twice bench bleeded the master twice
suckes the air out of the brake lines did everthing i could think of to get the air out i have a brand new master cylinder on the way from napa in just going start replacing everything and go from there
thanks
kuggs

 

73

 

You need the Master cylinder for the 78 for disc brakes.
It should have a larger reservoir and piston in the front for the calipers as they need more fluid to move the caliper pistons.

Also make sure the rear shoes are adjusted up enough. If they are not close to the drum, they need to travel a lot further to grab.

 

thank for the help i was stumped last night
kuggs

 

Mine does that. Original 73, drums all around. My master cylinder is shot and leaking by. Have a rebuild kit for it, same price as a reman MC but the reman MC has shot-peened threads where the lines thread in so I didn't trust them. Rather fix mine than trust some half-butt reman.

 

no he doesn't. disc conversions can be done without changing the master. i've done it. i converted my '75 to front discs about 3 or 4 years ago, and used the original drum MC, with equal-sized chambers. only thing that needs to be altered is to remove the rubber residual valve from the outlet of the MC that leads to the front brakes. i've now got more than 7,000 miles on the conversion as evidence that it DOES work.

his problem with the pedal may be related to his MC, but it isn't because of disc brakes.

 

i put on of those residual valve and still the same thing i have a master for a 78 ordered from napa but its coming from ohio i live in ri its going to take a while what psi residual valve did you use?
thanks
kuggs

 

you misunderstand.

not an external valve, not an added valve. it is original equipment in the drum MC. it's a tiny piece of rubber that sits inside the outlet nipple from the master cylinder. i assume there's two in the drum brake setup, one for the front brake outlet, one for the rear brake outlet. the one you needto remove is the one that leads to the front brakes. a "flapper" valve. the purpose, as i understand it, was to maintain a slight residual pressure within the brake system to allow the drum brakes to function properly. you don't want residual pressure in the disc portion of the system, as it will cause the pads to drag.

 

my problem is that i need to pump the brake pedal a couple of time to get brake pressure i was useing the residual valve to keep the pressure in the front lines to see if the pedal would work like its should i have no idea what is going on in the master but it is all just stuff i am trying to get the brakes to work
i dont have those rubber flapper valves on the MC

 

IMO, understanding the hydraulic system is very important to getting brakes to function properly, esp when modifying your system. Although there is probably more info here than necessary, it is a great place to start: http://www.pirate4x4.com/tech/billavista/Brakes/

 

thanks it looks like i need the corect master cylinder which is coming on the slow boat from ohio to rhode island
thanks y'all
kuggs

 

no. you need a working master cylinder. your original would be fine if it was functioning correctly.

 

i have a brand new one for the corrct year i am going to install tonight

 

so i drove it down the road tonight bad the front calapers are hanging up
they got really hot in less than a miles and a half
i have no idea what is wrong with them now
all i know is i should be driving it right now but i can't

 

i thought everything was fine; you got the new master cylinder.

 

Wrong residual pressure valve, or bad RP valve.
There have been pages of controversy on this, try the search function.

 

i took the rp valve out but with the new master cylinider in and the front calipers are stuck on with out the rp valve in