Booster and rear disks not working well...

So i did the whole rear disks and bigger booster swap along with the prop valve.... Only thing is they are not working any better than my old brakes did! and i did a full brake job with hawk front pads on new rotors new pads and rotors for the back all at the same time as the swap. They sucked at first which i expected with brake in then all of a sudden they worked amazingly could easily lock up my 35s... That lasted for about a week and they've sucked since... Oh, and i haven't lost any fluid and still get a nice hard petal feel not soft at all. Only thing i can think of is the prop valve is sticking???

Any imput or ideas are welcome!

Rebleed the brakes?

I'm going to. but it seems to be more than that because they worked really well for a while then crappy again. :/ i just don't know what to do.

What components did you use?

I had an issue like this years ago, figured it was the position my caliper bracket held the caliper itself... where the bleeder wasnt at the highest point possible. I had to unmount the caliper, rotate it till the bleeder was at 12o'clock and get the rest of the air out.

OverlandXJ said:

What components did you use?

I had an issue like this years ago, figured it was the position my caliper bracket held the caliper itself... where the bleeder wasnt at the highest point possible. I had to unmount the caliper, rotate it till the bleeder was at 12o'clock and get the rest of the air out.

Click to expand...

I used the booster, disks, callipers, prop valve internals, and master cylender all from a zj... still trying to figure out the e brake....

supposedly the kj e-brake cables are perfect length.

gradon said:

supposedly the kj e-brake cables are perfect length.

Click to expand...

lol thats what i read.. i pulled some from a kj.... NOT the fit i was expecting they're way too long. i'll post pictures...

Bunp, i really need some help. has anyone heard of a prop valve sticking? or maybe i did it wrong...

Yes. Prop valves do stick sometimes. You have antilocks? If so there is a specific bleed procedure that You will have to look up. If not the get a helper. Make sure the master cyl is full. Get all 4 wheels in the air, and check the power of the brakes by hand. If you can move a wheel by hand with the brakes lightly applied then the prop valve has stuck on that end preventing hydraulic pressure on that end. After diagnosing, try opening the bleeders and stomping the pedal. First one end, and check, then the other end and check. If this helps good. If not get another prop valve. Aftermarket adjustable would be best, or a brand new Grand Cherokee prop valve from the dealer.

hows the vac hose that goes to the booster?

and i have modified kj cables on my rig. i had to expose more of the inner cable (shorten the outer sleeve) at the front of the cable to match the length of my stock e brake cable. there is a lot of length to the kj cables so i ran the cables to the opposite side brake and looped them up above the rear axle some to take up some length. its working out great for me

jamiemac said:

Yes. Prop valves do stick sometimes. You have antilocks? If so there is a specific bleed procedure that You will have to look up. If not the get a helper. Make sure the master cyl is full. Get all 4 wheels in the air, and check the power of the brakes by hand. If you can move a wheel by hand with the brakes lightly applied then the prop valve has stuck on that end preventing hydraulic pressure on that end. After diagnosing, try opening the bleeders and stomping the pedal. First one end, and check, then the other end and check. If this helps good. If not get another prop valve. Aftermarket adjustable would be best, or a brand new Grand Cherokee prop valve from the dealer.

Click to expand...

Thanks man it really sucked to do all that work to get brakes worse than before. i'll try to see if its stuck by doing what you said. and also look into an adjustable prop valve.

And no antilocks thank goodnes!

stewie said:

hows the vac hose that goes to the booster?

and i have modified kj cables on my rig. i had to expose more of the inner cable (shorten the outer sleeve) at the front of the cable to match the length of my stock e brake cable. there is a lot of length to the kj cables so i ran the cables to the opposite side brake and looped them up above the rear axle some to take up some length. its working out great for me

Click to expand...

Yeah, thats what i've started doing actually haha. only bad part is my air compressor will run my cut off wheel for about three min before it needs to reload. :smsoap:

And the vac hose looks just fine. Pulled it off an xj with the bigger booster so it fits perfect.

Did you bleed the master cylinder? That made a big difference for me.

~Scott

I did the zj swap on my 98, no booster change + bled the brakes really well.
At first it was unimpressive, then it was inconsistent, then it worked really really well. Seemed to take care of itself right up until I blew a rear brake line - fixed that, bled it, it performs great.
I wonder if your booster is causing the inconsistency / problems. Don't know a ton about them but you've changed three things - the problem is in one of them.
Did you use new calipers?
Are the bleeders at the highest points?
Are you sure the system is air-free?
Have you tried going to OEM prop valve or otherwise troubleshooting the prop valve?
After that.. its the booster. I'm rolling on ZJ discs, cheapo pads / rotors and have awesome braking performance. No reason you shouldn't be better off.

But like I said - I had mystery issues for a coupla-few thousand miles before things seemed to settle in and perform consistently well. To this day I don't know WTF was going on.

EDIT: Also. Check your pads for glaze or abnormal shininess / wear. I wouldn't mention it but I put a solid glaze on my front pads about 5 months ago and wound up replacing them. Made a HUGE difference, even just buying cheapo pads. If you use the brakes on a long downhill (like we tend to get out west) you'll quickly burn up the brakes and even boil the brake fluid, causing sponginess in the pedal. Put the trans in a lower gear instead - I put my AW4 in "3" and it never breaks 53 MPH. Sorry if this is a "duh" but I grew up in Maryland and had to learn this the hard way out west.

Muddy Beast said:

Did you bleed the master cylinder? That made a big difference for me.

~Scott

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x2 did you properly bench bleed the booster? if not then you need to!

G

yossarian19 said:

I did the zj swap on my 98, no booster change + bled the brakes really well.
At first it was unimpressive, then it was inconsistent, then it worked really really well. Seemed to take care of itself right up until I blew a rear brake line - fixed that, bled it, it performs great.
I wonder if your booster is causing the inconsistency / problems. Don't know a ton about them but you've changed three things - the problem is in one of them.
Did you use new calipers?
Are the bleeders at the highest points?
Are you sure the system is air-free?
Have you tried going to OEM prop valve or otherwise troubleshooting the prop valve?
After that.. its the booster. I'm rolling on ZJ discs, cheapo pads / rotors and have awesome braking performance. No reason you shouldn't be better off.

But like I said - I had mystery issues for a coupla-few thousand miles before things seemed to settle in and perform consistently well. To this day I don't know WTF was going on.

EDIT: Also. Check your pads for glaze or abnormal shininess / wear. I wouldn't mention it but I put a solid glaze on my front pads about 5 months ago and wound up replacing them. Made a HUGE difference, even just buying cheapo pads. If you use the brakes on a long downhill (like we tend to get out west) you'll quickly burn up the brakes and even boil the brake fluid, causing sponginess in the pedal. Put the trans in a lower gear instead - I put my AW4 in "3" and it never breaks 53 MPH. Sorry if this is a "duh" but I grew up in Maryland and had to learn this the hard way out west.

Click to expand...

I replaced all the calipers when i did the swap. Full brake job front and rear, also i probly should check the pads because the first time i drove it around the block i was pretty hard on them and they ended up smoking... I'm hoping my brakes work them selves out like yours did though lol.

dgrigorenko said:

x2 did you properly bench bleed the booster? if not then you need to!

G

Click to expand...

I dont remember to be honest... I had a short deadline to have a car to drive and i might have forgottten to do it.. But like i said, i have really firm petal feel... i'll do it just to be safe i guess. Come to think of it i probably focused on the booster then i was worried abot the lines i had to bend and flare... CRAP i hate it when you know your wrong!

Jack up the back of your Jeep run it in gear and see if the rears are working. Be sure to put it on stands.

If you dont want those KJ cables, how much would ya sell them for? I would pm ya but I think your box is full.

If the pedal is firm than I doubt its an air in your system problem... Sounds like a lack of pressure which could be the booster? Maybe you don't need the prop valve after all, I know in some cases it isn't advantageous to use the zj one.

ausi02 said:

If you dont want those KJ cables, how much would ya sell them for? I would pm ya but I think your box is full.

If the pedal is firm than I doubt its an air in your system problem... Sounds like a lack of pressure which could be the booster? Maybe you don't need the prop valve after all, I know in some cases it isn't advantageous to use the zj one.

Click to expand...

Sorry man, i only have one and i'm playing with it trying to get it to work. I was just lucky in the jy one day... Well kinda i only got one.