jons87mj Posted August 13, 2012 Share Posted August 13, 2012 Hi I'm having trouble with my brakes they work but only when the pedal is down at its stop. so i put a new master cylinder on it, bleed the hole thing and its still the same :fs1: any help would be great :yes: thanks Jon Link to comment Share on other sites More sharing options...
Harley Posted August 13, 2012 Share Posted August 13, 2012 Booster.......? Link to comment Share on other sites More sharing options...
Comanche County Posted August 13, 2012 Share Posted August 13, 2012 Did you bleed the Master Cylinder? It must be bled or you'll never have brakes. You can bench bleed them or just install, fill, then use two extra hard lines and bend them over into the MC reservoir. Pump until there's no more bubbles. Then bleed each corner again. There's a trick to bleeding the brakes on an MJ due to the rear proportioning valve....lots of topics on it here. Link to comment Share on other sites More sharing options...
jons87mj Posted August 14, 2012 Author Share Posted August 14, 2012 yes i did bleed the master by using the steel lines and i bleed the brakes like they say to know what :dunno: thanks for the replys Jon Link to comment Share on other sites More sharing options...
Harley Posted August 14, 2012 Share Posted August 14, 2012 Booster.......? Link to comment Share on other sites More sharing options...
jons87mj Posted August 14, 2012 Author Share Posted August 14, 2012 the booster? why ? isent it a rod that goes all the way thru the booster and into the master :dunno: sorry i just don't understand :oops: Link to comment Share on other sites More sharing options...
Harley Posted August 14, 2012 Share Posted August 14, 2012 Never had any issues with mine but have read where others have had minimal pressure, swapped the booster and it cured it. I'm sure somebody can chime in on the specifics. If the master is fine and you bled it properly and are sure no air is in the system then i'd target the booster. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 14, 2012 Share Posted August 14, 2012 Try adjusting up the rear brake shoes. Link to comment Share on other sites More sharing options...
jons87mj Posted August 14, 2012 Author Share Posted August 14, 2012 The back shoes are tight so it's not them. And if I do a wj booster do I have to change masters? Link to comment Share on other sites More sharing options...
Harley Posted August 14, 2012 Share Posted August 14, 2012 This may help ya......http://www.jpmagazine.com/techarticles/ ... _upgrades/ Link to comment Share on other sites More sharing options...
Comanche County Posted August 14, 2012 Share Posted August 14, 2012 If everything is properly bled, then I'd agree with Harley....I'd have to say its the booster. Link to comment Share on other sites More sharing options...
Pete M Posted August 14, 2012 Share Posted August 14, 2012 do you still have the factory prop valve out back? Link to comment Share on other sites More sharing options...
jons87mj Posted August 14, 2012 Author Share Posted August 14, 2012 yes all is there :help: Link to comment Share on other sites More sharing options...
Gork Posted August 14, 2012 Share Posted August 14, 2012 General question: Why would the booster not functioning make the pedal soft? Wouldn't the problem be the master since the booster is there to soften the pedal? Topic: If you pump your brakes does the pedal get harder? IMHO you should check the master and re-bleed the brakes IAW the forum. If you're convinced its the booster you could always test it: Vacuum Leak Test Operate the engine at idle without touching the brake pedal for at least one minute. Turn off the engine and wait one minute. Test for the presence of assist vacuum by depressing the brake pedal and releasing it several times. If vacuum is present in the system, light application will produce less and less pedal travel. If there is no vacuum, air is leaking into the system. System Operation Test With the engine OFF, pump the brake pedal until the supply vacuum is entirely gone. Put light, steady pressure on the brake pedal. Start the engine and let it idle. If the system is operating correctly, the brake pedal should fall toward the floor if the constant pressure is maintained. Power brake systems may be tested for hydraulic leaks just as ordinary systems are tested. Link to comment Share on other sites More sharing options...
Pete M Posted August 14, 2012 Share Posted August 14, 2012 I do believe there is something special in the procedure to account for that extra line going to the rear. brain is failing on me though. Eagle knows. maybe he'll chime in. a bad booster caused my pedal to become soft only when the engine was on. if off, the pedal felt fine. Link to comment Share on other sites More sharing options...
Lee21490 Posted August 15, 2012 Share Posted August 15, 2012 I do believe there is something special in the procedure to account for that extra line going to the rear. brain is failing on me though. Eagle knows. maybe he'll chime in. a bad booster caused my pedal to become soft only when the engine was on. if off, the pedal felt fine. From the little googling i did about it, It supposedly is a backup for the front brakes, So if they fail it makes it so the backs work at 100% Link to comment Share on other sites More sharing options...
jons87mj Posted August 15, 2012 Author Share Posted August 15, 2012 when i bought the truck it only had back brakes and it was because the prop. valve under the master was froze. so i replaced it with a working one i had. bled the brakes and tryed it out , they we soft. ok no problem replaced the master, bled the master and all the lines again. tryed it out and had the same thaing happen, it was soft and went to the floor. took it for a drive and if i was going 30mph and stomped the brakes it would slow down but would not stop, it would slow down alote but then it would roll to a stop. with the truck off the pedal felt fine and was were you would want it but when it would be running it would go down so i pulled the vac hose off and ran it like that and the brakes worked great. put the vac hose back on and the pedal would go down and the truck would not stop like it should :dunno: thanks Jon Link to comment Share on other sites More sharing options...
Pete M Posted August 15, 2012 Share Posted August 15, 2012 sounds like a bad booster Link to comment Share on other sites More sharing options...
Eagle Posted August 16, 2012 Share Posted August 16, 2012 when i bought the truck it only had back brakes and it was because the prop. valve under the master was froze. so i replaced it with a working one i had. bled the brakes and tryed it out , ??? Huh? That distribution block just beneath the master cylinder is NOT a proportioning valve in the Comanche, and there is nothing inside it that could "freeze." It's function is completely different from the XJ proportioning valve, which IS built into that metering block. Link to comment Share on other sites More sharing options...
jons87mj Posted August 16, 2012 Author Share Posted August 16, 2012 idk but if your unscrow the nut on it there is a slid in it and it rides on a stude made to the nut and mine was slide forward and made the brake light come on. i don't know its just what i found inside of the block. but the spare one i had everthang would move and the light went off :dunno: Link to comment Share on other sites More sharing options...
Eagle Posted August 16, 2012 Share Posted August 16, 2012 idk but if your unscrow the nut on it there is a slid in it and it rides on a stude made to the nut and mine was slide forward and made the brake light come on. i don't know its just what i found inside of the block.but the spare one i had everthang would move and the light went off :dunno: Right, but that's only the slider that triggers the brake warning light. If either the front or the rear circuit fails, the pressure differential moves that slider, which then activates the switch (that off-white plastic thing screwed into the top of the metering block). Once the brakes have been repaired and bled, a couple of good, hard stomps on the brakes generally is all that's needed to reset the switch and slider. Doesn't affect the braking. (Except to allow full pressure to the rear circuit if the front brakes fail.) Here's what they look like inside: Link to comment Share on other sites More sharing options...
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