brake woes." pun intended"

[black87yj]

i just sold my 98 TJ and bought back the 87 YJ i had my Daughter buy. LONG STORY. anyway the Yj has new brakes all around (everything replaced by former owner) but the rears do not work. at idle there is a hissing sound inside the jeep cab. it stops when you press the brake pedal. at stop signs the pedal "fades" to the floor , but at road speeds its firm and stops fine . what should my first move be , replace the proportioning valve , or the rear wheel cyl. ( they look new too ?) the master cyl has a tag on it from a bone yard indicating its a 89 ..maybe it is bad ? :?
all things considered , i like the jy better than the tj....its more "jeepy" ( and the wife has stopped complaining about payments and washing it. I said jeeps DON'T GET WASHED !!!)
any help from you guys will be greatly appreciated !

 

[larry870]

How do you know the back brakes are your problem?
Are the rear cylinders leaking fluid?
Is there fluid missing from the reservoir?

The hissing indicates that the master cylinder, or the vacuum hose may be leaking.
I would check for vacuum leaks before anything else.

 

[black87yj]

thanks for the input ! we bought the jeep from a guy who said it just had a brake job. i saw my daughter stopping at the end of the driveway with it and the back wheels were turning and the fronts were plowing in the snow . it stopps fine but im sure it would be better with all 4 brakes ! so this spring i looked at them briefly. everything is brand new. with the wheel hub off i stepped on the brakes and there was no movement at all. no leaks . the master hisses at the firewall ??? i'm waiting for a good day and some time away from the "honey do " lists to look closer at this. :?:

 

[black87yj]

must be a proportioning valve problem. anyone ever bypass the thing ? also the pedal is firm after running 35 mph or so and only fades at full stop..must be a vacuume problem ?

 

[cjcrazy]

Check your brake lines to because it sounds like when your pedal fades to the floor it must be leaking fluid somewhere. Also check your vacuum line because it sounds like there is a leaking one. Replace any vacuum lines that are cracked to. Hope that helps. Also bleed your brakes.

 

[almostcj7]

8) It should be VERY obvious if a brake line is leaking. For one thing (if you didn't notice the fluid, witch could be possible in snow.) is after a few stops, you would have no brakes at all. The braking system dose use a vacuum assist. the first thing I would do is look for the line that goes from the TB or the intake. As fo the fronts working and the backs not, do you have disks front and drums rear?8)

 

[black87yj]

update..either the "new" brake booster was no good or the poportioning valve as i changed out the booster master cyl and booster from a cherokee and all is well.
I know, a cherokee part has too short of brake rod but i put a longer adjustable one on it. works great

 

[Jeeper99]

Not to Hi-Jack the post, but on the subject of the brakes and proportion valve. does anyone know if a 50/50 proportion valve off a 97 Grand Cherokee will fit a 99 TJ with the 4.0?

I had a problem with the front wheels locking and the back wheels rolling while braking and backing down steep banks. I know the discs will catch first and foremost on the front, but I was wondering if it was logical for the 50/50 valve change.

Jeeper99

 

[Dragin]

The way all factory braking systems are set up is about 70/30 front rear, usually the fronts will lock up first on almost all pre anti lock vehicals and even some current anti lock cars. If you want to go 50/50 for off road or something like that I would use and adjustable proportioning valve that you can set back to the factory for normal street driving. They can be found at most aftermarket performance stores as the are used on alot of race applications and Im sure for some of the tunner cars as well.

Steve