spongy brakepedal

i have never had much luck getting brakes working in a cherokee.

i recently swapped in a 99 brake booster and master in my 88. bled the brakes twice and still the pedal will go to the floor. it does stop but it would not lock any of the wheels up as it hits the limit before it can.

when the jeep is off it still feels squishy. the rear drum adjusters are adjusted i believe. i set them possibly a little on the tight side. the only thing I haven't done is adjust the parking brake. it will hold the jeep if its pulled.

i have checked for leaks and it has new rear wheel cylinders and rubber lines to the front wheels and rear axle. i have ordered on of those "bleeding" tools that lock the prop valve to see if that helps the at all.

any suggestions?

When replacing the master cylinder it's critical to
bench bleed it before installation. Air can get trapped
there and is very hard to get out.

You could remove the brake lines at the MC and bleed
back into the reservoir just to remove that possibility.

Also the pushrod length is critical, where it seats into the
master cylinder. Don't recall the specs, but it's probably
.005=.010 inch clearance.

I forgot to say I did bench bleed the master. Pumped until it had no bubbles coming out of both circuits.

And I bought a new master and booster when I did the conversion and I believe it had the correct clearance. I feel like it's air stuck somewhere. I have bled two bottles of DOT3 through the master. And also replaced the hard lines on the rear axle too. Does air get stuck in the prop valve? It's the only part I haven't changed.

Went out today and re bled the brakes. Got no air. Looks like parking brake is set to the maximum adjustment with newer cables so I'm not sure what to do there.

I did take the master off and pressed the pedal down and there is slack before the booster engages.

I'm going to try and drive it some and see how it does.

There's a critical adjustment between the booster and master.

https://www.youtube.com/results?search_query=adjust+booster+to+master+rod

There is a loooong thread here of mine from battling that for years on my 87 Wagoneer. One issue was air trapped in the Combination (equalizer) valve, and the only solution was bleeding the combination valve (at the front nut, 2 person job). Another was rotors that were worn with a taper, and only 10% of the pad was touching the rotor, and third was worn-notched knuckles the pads rode on, and got hung up on, and another was a worn and stretched cable on the adjusters on the rear drum brakes that let the adjusters loosen on the rear brakes..... For starters. Find that old super thread of mine, it is a gold mine of info. Oh, and I found out the brand new rear brake cylinders may NOT leak brake fluid when new, but can draw air in adding air after bleeding the rear lines.



None of which are common, known brake issues.

90xj06 said:

I forgot to say I did bench bleed the master. Pumped until it had no bubbles coming out of both circuits.

And I bought a new master and booster when I did the conversion and I believe it had the correct clearance. I feel like it's air stuck somewhere. I have bled two bottles of DOT3 through the master. And also replaced the hard lines on the rear axle too. Does air get stuck in the prop valve? It's the only part I haven't changed.

Click to expand...

Happy Holidays sir.

cruiser54 said:

There's a critical adjustment between the booster and master.

https://www.youtube.com/results?search_query=adjust+booster+to+master+rod

Click to expand...

90xj06 said:

........
I did take the master off and pressed the pedal down and there is slack before the booster engages........

Click to expand...

From what I can tell, there's no Jeep specification for the
booster to master cylinder gap. The booster and MC seem
to be assembled with a preload.

You might try extending the pushrod length for zero clearance
and see if that gives an acceptable pedal without causing the
brakes to drag...

No preload. The brakes would drag.

Too much slack equals brakes like you're complaining about.

These brake boosters and masters are just like a jillion other cars out there.

Go to YouTube and search booster to master clearance and about 10 videos pop up.

I haven't gotten a chance to work on it. But I did drive around on Friday and although the pedal is soft I can feel the rear brakes grabbing. Almost as if those are doing the brunt of the braking.the front rotors do have some rust on them from sitting. And I'm wondering if the have air stuck in the caliper. I'm tempted to swap in newer knuckles and calipers. I can't find replacement brackets for the calipers.

Also it looks kind of tricky adjusting the pushrod on the wj booster.

One day this week I'm going to clamp off the brake line and push the caliper pistons in and see if I can get any air out. And I'll throw pads and rotors on again too

1) Sounds like air trapped in the Combination (Proportioning valve) valve, or even a tripped Combination valve that closed off flow to the front or rear brake side, that needs to be reset? I think it is inside under the brake light switch?



2) Put the parking brake on, then test with the engine off, pump it even, and report back with one push and after pumping, differences.



3) repeat #2 with the engine running. Check the vacuum hose to brake booster vacuum check valve, and check the vacuum valve it self for leaks. It is one way valve.

90xj06 said:

i have never had much luck getting brakes working in a cherokee.

i recently swapped in a 99 brake booster and master in my 88. bled the brakes twice and still the pedal will go to the floor. it does stop but it would not lock any of the wheels up as it hits the limit before it can.

when the jeep is off it still feels squishy. the rear drum adjusters are adjusted i believe. i set them possibly a little on the tight side. the only thing I haven't done is adjust the parking brake. it will hold the jeep if its pulled.

i have checked for leaks and it has new rear wheel cylinders and rubber lines to the front wheels and rear axle. i have ordered on of those "bleeding" tools that lock the prop valve to see if that helps the at all.

any suggestions?

Click to expand...

Some more information on this. Spongyness is better. The parking brake cables were adjusted to the maximum and started overheating the drums and causing a really bad vibration.

The front pads have a shim for noise or something and it was all rusted and expanding because of it acting like a spring. I removed the shims and it's not as spongy. The front brakes don't seem to be doing anything really. But I'm going to put new rotors and pads on as the rotors are rusty and yucky. But in the snow just touching the brake locks the rears up. So they are working. Maybe a bit too well.

90xj06 said:

Some more information on this. Spongyness is better. The parking brake cables were adjusted to the maximum and started overheating the drums and causing a really bad vibration.

The front pads have a shim for noise or something and it was all rusted and expanding because of it acting like a spring. I removed the shims and it's not as spongy. The front brakes don't seem to be doing anything really. But I'm going to put new rotors and pads on as the rotors are rusty and yucky. But in the snow just touching the brake locks the rears up. So they are working. Maybe a bit too well.

Click to expand...

The way you are describing the rears reminds me of an 88 2 door sport 5spd i had.

Make sure you didnt install the parking shoes incorrectly. I could lock and squeal tires for 1/4 mile with barely a touch of the pedal (kinda scary when your slave cyl is bad and you cant engine brake instead). This was after a full brake job with Napa AdaptiveONE shoes, and according to the mechanicenthat got it after i traded it in, i reversed the shoes on install * dunno if theres any truth to that, wasnt my problem anymore


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