Brakes Dragging After WJ Booster/MC Swap

[sean87xj]

Whats up JF, been a long time. My Cherokee has been out of commission for the last year and a half....finally got it up and running again. I finished swapping in a '04 WJ booster & master cylinder - which went pretty smooth - but now it appears that my brakes are dragging pretty bad and I've got a hard pedal.

This is what happens:

1) When I first start the car, the brakes don't drag at all. The pedal feels normal through about 2" of travel, then gets extremely hard but stops fine.
2) After pressing the pedal several times, the brakes begin to drag. It gets progressively worse until they're basically locked and excessive amounts of throttle need to be applied to move the vehicle.
3) As the calipers dragging gets worse and worse, the pedal gets harder until there is no longer any amount of "normal" feel to the first couple inches of travel.

This has only happened since the new booster/MC was installed so it's gotta be one of those. I'm pretty sure it's all four calipers....should I just buy a new master cylinder? I think I might have screwed it hooking the brake lines to the prop valve up backwards at first.

[sean87xj]

BUMP!

Anybody??

[balloo93]

I'd suspect the prop valve. They are designed to hold a little line pressure even with the pedal up, but it sounds like they are holding way too much pressure. Remove the prop valve and take the small rubber bushing off of the rod and see if they bleed out once used.

Does the rod to the booster align well? When you release the pedal does it float back to the UP position?

[sean87xj]

Originally Posted by balloo93

I'd suspect the prop valve. They are designed to hold a little line pressure even with the pedal up, but it sounds like they are holding way too much pressure. Remove the prop valve and take the small rubber bushing off of the rod and see if they bleed out once used.

Do you mean tiny rod that is (I think) surrounded by a coil inside the prop valve?

Originally Posted by balloo93

Does the rod to the booster align well? When you release the pedal does it float back to the UP position?

The rod from the pedal to the booster aligned almost perfectly. It was off by maybe a centimeter or less, but still slid onto the nub on the brake pedal fine. It does float back up....but here's another weird thing: there's almost no pedal travel. The pedal gets extremely hard, so it does require a bit of effort, but if I press it not even halfway down it'll be equal to slamming on the brakes on a normally functioning brake system.

The drag definitely gets progressively worse, I drove it around for about a half hour the other day and when I parked it in my driveway the rotors were smoking and I could barely get up my driveway in the ice. I'm now almost positive it's all four brakes as well. I'm thinking it's gotta be something at the rod or master cylinder....I'm going to detach the rod from the brake pedal and pump it by hand to see if I get the same results.

Is the rod that goes from the booster to master cylinder different from the one that goes from pedal to booster? Any way to adjust the former?

Thanks a lot!

[balloo93]

Yes, the small rod in the Prop valve is what I would remove and take the rubber bushing off of.

It sounds like the Rod and pedal are okay. Sounds like the system is just pressurizing and not bleeding out.

[sean87xj]

Originally Posted by balloo93

Yes, the small rod in the Prop valve is what I would remove and take the rubber bushing off of.

It sounds like the Rod and pedal are okay. Sounds like the system is just pressurizing and not bleeding out.

Well balloo, you're a man much wiser than me and your advice has been a life saver in the past....so I will take it again. I'll report back with results, thanks again!

[sean87xj]

Originally Posted by balloo93

Yes, the small rod in the Prop valve is what I would remove and take the rubber bushing off of.

This is the side you meant, right?



I got it all apart and got confused, because there was no rod inside.....just a spring....but anyway, results of testing this were very inconclusive. I'm gonna grab a new prop valve tomorrow anyway, they're cheap enough and it can't hurt.

I haven't really messed with it since I posted this thread, but here are the other pictures I have of the install....in case you notice anything else bogus that might be problematic:





...and here's the thread on NAXJA I've been posting progress in since I started doing this almost 2 years ago

Thanks dudes

[XJLI]

I'd suspect the drums- how are the shoes? and are they adjusted? The WJ swap gav me weird brakes, but the pedal is more mushy, not like your problem.. still stops better though

[sean87xj]

Originally Posted by XJLI

I'd suspect the drums- how are the shoes? and are they adjusted? The WJ swap gav me weird brakes, but the pedal is more mushy, not like your problem.. still stops better though

All four corners are dragging, so it's gotta be something between the pedal and the calipers. It's bad enough that when I drove it in the snow, smoke was billowing out of all four wheelwells and I had a hard time getting up my driveway in 4LO!!! That's when I decided I would only do VERY short trips until it got sorted out.

Did you reuse the XJ prop valve when you did your swap? I'm wondering if maybe there is something to the ABS prop valve (the one I'm using, from the Bendix-9 system) that is effing this up. It looked identical to the 87-91 non-ABS units, but it was hooked up to the Rube Goldberg-looking master cylinder much differently than the normal ones are. I had to uncap a couple ends, and the lines from the calipers went directly into the MC unit, then to the prop valve and back in....weird system.

BTW - Noticed you're in Huntington, you know any honest shops in Nassau/Western Suffolk that could possibly sort this out? I've never had any luck with mechanics on LI....and it'd hurt my pride taking her in, but I'm really sick of driving my Grand Marquis and don't have a lot of free time to fiddle anymore, as evidenced by this fairly simple project taking me 2 years to complete

[XJLI]

Originally Posted by sean87xj

All four corners are dragging, so it's gotta be something between the pedal and the calipers. It's bad enough that when I drove it in the snow, smoke was billowing out of all four wheelwells and I had a hard time getting up my driveway in 4LO!!! That's when I decided I would only do VERY short trips until it got sorted out.

Did you reuse the XJ prop valve when you did your swap? I'm wondering if maybe there is something to the ABS prop valve (the one I'm using, from the Bendix-9 system) that is effing this up. It looked identical to the 87-91 non-ABS units, but it was hooked up to the Rube Goldberg-looking master cylinder much differently than the normal ones are. I had to uncap a couple ends, and the lines from the calipers went directly into the MC unit, then to the prop valve and back in....weird system.

BTW - Noticed you're in Huntington, you know any honest shops in Nassau/Western Suffolk that could possibly sort this out? I've never had any luck with mechanics on LI....and it'd hurt my pride taking her in, but I'm really sick of driving my Grand Marquis and don't have a lot of free time to fiddle anymore, as evidenced by this fairly simple project taking me 2 years to complete

I used my stocker 93.... give a regular non-abs valve a try i suppose. the one shop i know of (never had any work done there though) is faithful automotive on NY ave in huntington, near the village. my neighbor recommended them when i needed an inspection... and my jeep wont pass a NY dyno test at some random shop.