rear brakes started working on their own

[jprissel]

they quit working about a year ago.there was massive pulsating when the brakes were applied.after not driving it for about four weeks i went out to get it started and take it out on the ice the brake light was on so i checked the fluid res. it was just down to the min mark.checked for leaks, none obvious.topped off the fluid and drove away.brakes have worked sweet since and still full of fluid. any ideas whats going on.84 fj60

 

[Jukelemon]

Well, here is my guess. You have shot rotors and the cold is actually cutting down on the friction applied to the rotors i.e. making the grooves and indentations on your rotors less apparent. Pulsating usually means rotor or caliper issues. Lack of fluid in the braking sytem really does not correlate with pulsating. If you had a leak, air in the system or no fluid at all, your brakes would either work at a percentage of full capacity or (in the case of no fluid) not work at all. So, my guess to the riddle is rotor issue. Could be a caliper mount but I suspect that would not change regardless of temp and year. I had an old Ford with bad rotors that did this exact thing.

 

[jprissel]

10-4 on the rotors,but every things fine now.no pulsating, just brakes working right.ii'm worried they're going to stop working again and looking for suggestions on were to start.it seems like the slave cylinders were pulsating.it would also pull left quit hard at first(high speed) then at 35mph it would staighten out and stop pulsating, however i still couldn't get the rear brakes to lock up.now there working fine.they will lock up and stops staight as an arrow on dry pav.

 

[Jukelemon]

You could have a leak and that would explain the pressure loss on the cylinders but you would notice the leak at the reservoir....unless...you mentioning the lockup, I bet it is a leak and you have not driven enough to take down the fluid i.e. air in system causing the issues but very small crack so little fluid loss. It will be hard to see the brake fluid on the lines if you are in snow/ice weather. If it is your daily driver, better dry it off on Friday and hit all brakelines on Saturday.

 

[jprissel]

driving around yesterday they stop working again.icouldn't get them to lock up on ice.then on the way home pulling into the driveway i tryied um and they locked up.could the proportioning valve be junk.

 

[talkinggoat]

are the brakes soggy? do they go all the way to the floor when it doesn't want to stop? do they feel firm when it does stop?

you said "10-04 on the rotors, but everything's fine, now" did you change the rotors? did the pulsating problem continue?

check those rotors and drums and see if you have fluid on them. make sure you don't have a leak from one of the cylinders or pistons. fluid getting on the rotors and pads will cause a hard pull in either direction, and will cause them to not lock up. that would also explain your fluid loss... but, it would be weird if it were working, then just quit, then started again. it isn't common for it to just randomly start leaking and then stop. it's worth a look, though.

i'm not sure of the setup on 60's; i have a 40. if you think that proportioning valve is not any good, change it. at this point, you are trouble shooting. it won't hurt to eliminate that problem; plus, you will have a brand new valve in there.

 

[jprissel]

the front brakes work fine.drove it 6mi. this morning, rear brakes never did start working again.fuid is still full.no visable leaks around drums.both rear brakes work evenly when working and neither work when they don't.there was no pulsating today or pulling,just no rear brakes.it seems strange to be systematic like this.

 

[jprissel]

the peddle is firm and doesn't fade.

 

[talkinggoat]

will they bleed? if so, bleed them all the way. change that proportioning valve.