Brakes

Pressure problem to the rear...possibly all around.
-Vanco up front.
-SSBC disks in back.
-New soft lines, no leaks.
-System bled pedal feels hard with prop valve adjusted to about ~60/40.
-Stock prop valve has stem and cap only. (washer on the stem blocks all rear flow and was removed.)
-Working prop valve is on the common hardline to the rear. (SSBC)
-New booster (stock).
-New -and larger- MC (bench bled).

Thinking of completely gutting the stock prop valve and plugging it?

Thoughts?

I totally bypassed the prop valve when went with rear disks, works great.

What year XJ?What exactly do you mean by "larger" MC?What did you use?

RCP Phx said:

What year XJ?What exactly do you mean by "larger" MC?What did you use?

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01' The SSBC kit came with a MC that is longer, possibly larger in diameter and has a larger reservoir. They refuse to tell you what vehicle it is stock to.

robsjeepxj said:

I totally bypassed the prop valve when went with rear disks, works great.

Click to expand...

How?

I was thinking of just gutting the internals and plugging the hole in the bleeder cap...somehow...

My problem was that with a 50/50 flow the vehicle was spinning. Then I started having pressure problems and now the adjustable prop valve set to somehting like 70/30 or 60/40 stopped the rears from locking early but the whole system is garbage because I have very little pressure all around and so little in the back that I can't even bleed the brakes with the valve open for a 50/50 flow. Also, the pedal is mush with free flow.

look at your m/c. if you are not getting pressure to the rear with the adjustable prop valve set to 50/50, perhaps a seal has folded in the master? the prop valve is also another place to check. maybe one out of a zj or wj could help. im just spit ballin' tho...

maybe a booster issue as well... any vac leaks? pinhole in diaphragms?

tribalmentality said:

look at your m/c. if you are not getting pressure to the rear with the adjustable prop valve set to 50/50, perhaps a seal has folded in the master? the prop valve is also another place to check. maybe one out of a zj or wj could help. im just spit ballin' tho...

maybe a booster issue as well... any vac leaks? pinhole in diaphragms?

Click to expand...

I should get 50/50 with the adjustable valve 100% open. If i set it to 100% open, the pedal is squishy...I don't think this is right either.

I attempted ZJ internals but they, like the XJ internals, didn't give me enough rear pressure. When I pulled the o-ring on the ZJ internal and got 50/50 without an adjustable prop valve, the brakes worked too well and the Jeep would spin above 40MPH with heavy braking.

If I adjust the prop valve just right I can get a nice hard pedal...maybe there is air or gunk trapped back there somewhere? I should be able to get a good pedal with that valve open...I think...maybe a pressure bleed with the valve open?

it sounds to me like you have master cylinder problems, or possibly you have the front and rear brakes plumbed backward.

What prop valve are you currently using? I need to do something about mine because my rear discs are barely working.

I didn't do the hardlines myself...they could have screwed it up. I guess it's worth figuring out which MC the kit came with and getting another one...it may be the Durango one or something close to it. Bah!

sunburned said:

What prop valve are you currently using? I need to do something about mine because my rear discs are barely working.

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I have a ZJ stem without an o-ring, spring removed and ZJ cap. midway down the unibody rail I have an SSBC valve in-line on the common hardline to the rear...something about the setup is messed up though....

http://www.thewedgeshopstore.com/products/SSBC-Inline-Proportioning-Valve.html

What rear axle are we talking about?

EMSJEEP said:

I didn't do the hardlines myself...they could have screwed it up. I guess it's worth figuring out which MC the kit came with and getting another one...it may be the Durango one or something close to it. Bah!

Click to expand...

I did a drum to disc conversion on a jeep some time back (rear, of course), and after I did the brakes went to hell. Could not get a firm pedal no matter what. Replaced the prop valve 3 times, bled the system about 9 times, replaced the master and booster.

Turned out the front/rear hard lines had been reversed when adding line locks to the system (between the master and prop valve). With drums, for whatever reason, it still worked fine - but once they went to discs, no firm pedal could be found. Fixed the hard lines and all was good.

RCP Phx said:

What rear axle are we talking about?

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A 35 that will get tossed as soon as I have the $$$. Based on past experience I have about 20k miles left on it.

cal said:

I did a drum to disc conversion on a jeep some time back (rear, of course), and after I did the brakes went to hell. Could not get a firm pedal no matter what. Replaced the prop valve 3 times, bled the system about 9 times, replaced the master and booster.

Turned out the front/rear hard lines had been reversed when adding line locks to the system (between the master and prop valve). With drums, for whatever reason, it still worked fine - but once they went to discs, no firm pedal could be found. Fixed the hard lines and all was good.

Click to expand...

Hmm...I'm trying to think what was actually done between the time when I was locking the rears too early at 50/50 and when the system took a dump. It wasn't the addition of the prop valve, it already sucked at that point. In fact, the whole thing was kinda terrible from the get go compared to the drums, except the drums were a maintenance nightmare. I'll look into this. Thanks.

How does this look? The SSBC valve froze and the internals fell out when I wrenched on the valve stem with some locking pliers. Reinstalled the frozen stem and bled the system. I can get a good solid stream when bleeding all around now but still no grab in the brakes. I get a nasty squeak on the downstroke of the pedal. Pedal is firm but pressing it does very little. I'm starting to think booster now.

Looks to be correct to me....

I was able to take a look at the system again but unfortunately I didn't get too far, the SSBC adjustable valve has corroded and seized. It was dealer installed in about November and the vehicle has been off the road since January. It has been just fine up until very recently. The valve stem threads corroded and froze. The plastic knob promptly broke off and my attempts to lubricate and free it only succeeded in removing the entire valve stem and losing about a cup of brake fluid.

After hemorrhaging fluid from the SSBC valve and reintroducing the spring into the stock prop valve in the distribution block, I bled the system and got a decent pedal feel back. I am now able to extract fluid from the rear calipers at whatever setting the SSBC valve is frozen at, something I was unable to do in the past. I'm not set up to be able to take pressure measurements at this time.

One thing I did notice while the SSBC valve was working was that at a certain point, if I increased pressure to the rear as much as possible to achieve a 50/50 distribution (the stock prop valve being non functioning) the pedal be noticeably softer upon application. As the SSBC valve is now frozen I don't know if this would still be the case after the system was successfully bled.

In any event, the plumbing looks correct with the rear line feeding the front and the front line feeding the rear (http://i1003.photobucket.com/albums/af152/emsjeep/IMG_20110605_173226.jpg http://i1003.photobucket.com/albums/af152/emsjeep/IMG_20110605_173207.jpg ). A firm pedal with no bite makes me want to look at the booster, but that has changed in the past depending on the position of the SSBC prop valve and I won't know more until I can get that fixed. I may have a soft pedal hiding behind whatever effect the SSBC valve is having on the system.

If you are using an aftermarket prop valve you should bypass the stock prop valve completely. When I was messing with the prop valve I removed the o-ring and ended up with a very mushy pedal with little bite. I'll probably go with an aftermarket prop valve sometime in the future just to dial it in better.

I was driving around with a 50/50 system on the stock valve for a while. It was dangerous, I almost rolled it twice. That system eventually failed and sometime later I added the SSBC valve anticipating that I would fix whatever else was not working correctly later. It certainly didn't help the problem, but it didn't cause it...

Removing the o-ring does not make the system 50/50. It just merges the two brake systems letting the fluid take the path of least resistance.