richamor

I'm at a loss here. So far I've replaced the master cylinder (twice) and have bled multiple times. I've replaced the proportioning valve twice. No leaks and have run a gallon or more of brake fluid through it it trying to get the brakes up. The pedal goes all the way to the floor. I do have brakes. They're just all the way at the bottom. The only thing I haven't replaced is the brake booster and it does whoosh when the brakes are pushed.

The ONLY thing not stock is the 98 rear with disc brakes. I have fluid there and no leaks. Both calipers were rebuilt and new pads installed. I'm using an 89 valve and master cylinder.

I'm stumped. I've worked on cars for 50 years and have never had brakes do me like this. I forgot to specify I'm working on a 1989.

Any help is appreciated. Thanks!!

RockyMtn96XJ

vacuum leak?

richamor

none I can find. and the engine runs great.

dmoe69

Are the bleeders at the top of all four caliper pistons?

4.3L XJ

Do you have ABS?

richamor

all bleeders are at the top of the calipers. No ABS

tech

I would check all the brake pad shims and pad guides to make sure that they are not holding the pads away from the rotors . If that is okay , then maybe push all the caliper piston back in and pumping the brakes back up and do that a couple of times see if that does any good .

richamor

I'll have a look at that tomorrow tech. And just to clarify I went outside and checked again. The pedal doesn't go ALL the way to the floor. There's maybe an inch or so from the floor when it stops. I can lock the brakes but the pedal just go down so far it's uncomfortable. And it takes a hard push to lock the brakes.

tech

Are the brakes new ? Have they been seated ? Because if they are not seated the pedal will be soft and go down farther , And is the rear disc a new change over ? because 4 wheel disc brakes will have a lower pedal .

richamor

The brakes were all done a while back but the Jeep has been sitting for a while. Partly because of this. The rear is a new changeovers and this has been an issue ever since. The pads seem to be seated fine. Brakes are fine….at the bottom of the stroke
I read somewhere that the original master and prop valve would work ok but it would allow more fluid to the rear brakes. Since the fronts do most of the work maybe that’s my problem. Excess fluid going to the rear brakes slowing but no stopping unless I keep pushing the pedal? Maybe?
My plan to address this was an adjustable valve inline with the rear brakes.

tech

The prop valve for disc / drum brakes will hold a little more pressure to the rear when your not on the brakes because of the brake springs a prop valve for a 4 wheel disc brake system will not hold as much pressure to the rear when you are not on the brakes , the only thing it can do is wear out the rear pads faster because the prop valve for a disc / drum system is holding the rear brake on a little . The only other thing I can think of is that the rod in the power booster is adjusted to short that will give you a low pedal .

Roler

What proportioning valve have you installed; PV2 or PV4?

Roler

I was thinking the same. But the booster hasnt been replaced yet....

cruiser54

And the "whoosh" noise?
Sounds like a bad booster to me.
You might consider going to the WJ booster/master at this point. HUGE improvement in brake performance along with those rear discs.
You could check the pushrod adjustment first though. But, before I did that I would verify the booster is working like it should.

richamor

Thanks for all the input folks!! The prop valve is a PV8796J 12M1220. If that makes any sense. It was ordered for a 1989 XJ same as the master.

Odd that you mention it but I did adjust the rod in the booster out just a bit before I installed the second master. Maybe needs a bit more????

And I'm leaning towards the brake booster. The only thing is that even with the booster disconnected (removed and plugged vacuum line) the brakes go down to the floor. Not as fast or as easy but they do go down to about the same spot.

The WJ booster/master sounds intriguing but at this point I just want to get the brakes working as they should. I'd settle for that for a while.