Brake issues

[Joe94xj]

Ok just did a quick search for some big bore master upgrades and looks like an 86 E350 will fit with slight mods and 84-86 mustang svo masters will fit. All have a bigger bore. What I think is happening is your not getting enough fluid per stroke of the pedal to the bigger calipers. So you are not actually getting enough fluid in them to give you a hard pedal. Thats why when you pinch off the lines you get your hard pedal back. Make any sense? I am betting my pennies this will fix your issue.

 

[Frank Z]

Only that I don't think its your prop valve -- I ran those same Chevy calipers (waggy version) for years on the XJ with a stock 99 prop valve and no issues whatsoever (with rear discs as well).... Sorry I don't have any other ideas though - its been vac bled at this point?

Rub it in...

How did you clamp them? By pinching the rubber hose or you use plugs in the master cylinder?

Go as close to the calipers as you could get and close the lines there,...just before the calipers.

Visegrips on the new rubber hoses

Frank are there any big bore master cylinder upgrades out there for the cherokee? I am wondering if your master cylinder might be to small for those calipers.

Don't know. I don't believe they are necessary though Joe. This is a very common swap and most folks use the same old XJ M/C.

 

[Joe94xj]

Know anyone that has done a simillar swap where you might be able to swap some parts around?

 

[Frank Z]

I really don't feel comfortable doing that. Worst case scenario is that I break their parts and am out the coin to replace it as well as the money to fix my still busted rig.

 

[Joe94xj]

Makes sense. I still think your master may be too small. The svo master is supposed.to be a direct bolt in. It has 1.125" bore verse the 1" bore cherokee. Terraflex also has a big bore master that they use with there big brake kits. But thats 200 bucks.

 

[techno1154]

Makes sense. I still think your master may be too small. The svo master is supposed.to be a direct bolt in. It has 1.125" bore verse the 1" bore cherokee. Terraflex also has a big bore master that they use with there big brake kits. But thats 200 bucks.

I do understand your point about the MC being too small. Even if this is true, the complaint is that the pedal solwly loses pressure. I have knowingly driven vehicles with faulty breaks that requires several strokes of the pedal to get a good pedal feel and usable brakes. No, it was not in the US. I would not do it in the US. Speeds here is too high, not enough reaction time/distance.

So, let us say the MC do not have enough volume, to sufficiently move the caliper pistons in one stroke, by giving it two or three strokes then holding it (the pedal), it should not go to the floor ie; loose pressure for several minutes even if it was not properly bled of air. Imagine being at a busy intersection with several vehicles infront of you and your break pedal slowly loses pressure. Am I making sence here? The fact that he could have any pressure at all and it slowly leak off indicates there is a fluid loss some where in the system be it internal or external. Based on the items already tested and eliminated in the trouble shooting process, I would look at the wheel calipers again. That fluid have got to be going some where. The question is where?

 

[Joe94xj]

From when i looked at it the pedal never is hard. It is soft all the way to the floor. If you pump it up its still soft and goes to the floor. The only time the pedal is remotely harder.is.when the vehicle is off and after a few pumps. But this will happen because you have depleated the vaccum in the booster making the pedal harder. When you picnch off the hoses at the fron calipers the pedal is good. He had no problems till he added the new larger calipers. So I would say its not a leak, or bad prop valve. It has something to do with the calipers. Either bad calipers which have been replaced again or the master isnt getting enough fluid to the calipers.

 

[Talyn]

I though he said that the pedal sinks under constant pressure, like a leak? Or does it just go to the floor?

 

[Frank Z]

I also used the exact same set up with my WJ (Dual piston Akebono) calipers without issues at all.

XJ-Grin has already stated that his stock M/C handled his Chevy 1/2t calipers without any problems, and I'm fairly certain that Led runs a stock M/C in his MJ truggy as well.

 

[Frank Z]

Sinks under constant pressure.

 

[Joe94xj]

Are they running the same prop valve, rear disc brakes and hoses?

 

[xjbubba]

Did you confirm that your front brake lines are no longer leaking? You said it was leaking at the banjo bolt junction, but I didn't see where you stated it was fixed. Mix up a little joy dish washing soap with water, and spray/brush it on the fittings and around the caliper boot. Have some one keep pressure on the pedal while you look for bubbles. As you know, you'll never get a good bleed with any leaks, anywhere.

 

[Captain Obvious]

Hey Frank,
I had very similar issues when I upgraded the rear axle that had disc brakes. Pedal would just constantly push to the floor after multiple bleeds, no leakage anywhere. I ended up buying a Dakota master cylinder (almost certain '01), bolted right up to the booster and just had to make 2 lines to adapt it to the proportioning valve. and that resolved the problem. I just needed more volume to move the pistons in the calipers and hold pressure on the pedal. With the stock XJ master piston sitting around 7/8-15/16 it just didn't produce enough volume for me, which I am thinking is the same for you. The Dakota MC sits around 1" and the Ford E350 that was mentioned in the earlier should be around 1 1/16". This is all with a 01 dual diaphragm booster and the stock proportioning valve. If you can't find a leak, I would definitely say that it's a volume issue. This is of course, assuming that the chevy calipers have a larger piston in them, then what you were previously using.
Now with that being said, when it was in 4-Low, I did have to put a heavy amount force on the pedal to get the dang thing to fully stop, which makes me want to lean more to the E350 MC, but I can't be sure since I haven't got my LT1 up and running in my XJ as of yet to see how the Dakota MC stops it.
You are more then welcome to borrow my MC, and give it a try though. Like I said my XJ is down right now as I am finishing up putting the LT1 in it so feel free to borrow it and see if it works for you, not sure if it is a worth while to drive all the way up to Loveland to grab it as opposed to just grabbing one at the store given fuel prices these days.

Semper Fi,

Justin

 

[Frank Z]

Are they running the same prop valve, rear disc brakes and hoses?

I talked to led and he ran 3/4t front calipers and a 14bt out back with a stock M/C.

Did you confirm that your front brake lines are no longer leaking? You said it was leaking at the banjo bolt junction, but I didn't see where you stated it was fixed. Mix up a little joy dish washing soap with water, and spray/brush it on the fittings and around the caliper boot. Have some one keep pressure on the pedal while you look for bubbles. As you know, you'll never get a good bleed with any leaks, anywhere.

Yep, I confirmed no leaks. Soap bubbles won't work unless there's air (gas) to make bubbles. I use the stuff on a regular basis checking refrigeration and A/C systems for leaks.

Hey Frank,
I had very similar issues when I upgraded the rear axle that had disc brakes. Pedal would just constantly push to the floor after multiple bleeds, no leakage anywhere. I ended up buying a Dakota master cylinder (almost certain '01), bolted right up to the booster and just had to make 2 lines to adapt it to the proportioning valve. and that resolved the problem. I just needed more volume to move the pistons in the calipers and hold pressure on the pedal. With the stock XJ master piston sitting around 7/8-15/16 it just didn't produce enough volume for me, which I am thinking is the same for you. The Dakota MC sits around 1" and the Ford E350 that was mentioned in the earlier should be around 1 1/16". This is all with a 01 dual diaphragm booster and the stock proportioning valve. If you can't find a leak, I would definitely say that it's a volume issue. This is of course, assuming that the chevy calipers have a larger piston in them, then what you were previously using.
Now with that being said, when it was in 4-Low, I did have to put a heavy amount force on the pedal to get the dang thing to fully stop, which makes me want to lean more to the E350 MC, but I can't be sure since I haven't got my LT1 up and running in my XJ as of yet to see how the Dakota MC stops it.
You are more then welcome to borrow my MC, and give it a try though. Like I said my XJ is down right now as I am finishing up putting the LT1 in it so feel free to borrow it and see if it works for you, not sure if it is a worth while to drive all the way up to Loveland to grab it as opposed to just grabbing one at the store given fuel prices these days.

Semper Fi,

Justin

Thanks for the offer and info.

FWIW,
I took a few minutes today and tore down the Prop valve. No obvious problems, no torn o-rings.

 

[Frank Z]

I changed out the calipers yesterday. The Reman one's I had on the axle had really bad concentrics around the hole for the banjo bolt.....

Made no difference at all.

I've gone over the brake system countless times looking for leaks and there simply aren't any. I wish there was a massive puddle under the rig cuz that would be a fairly decent indicator that there might possibly be a leak somewhere.....maybe.

So I'll try another prop valve and see if that makes a difference. Neither NAPA or Advance Auto show them on their sites so I'll probably have to yank a used on from the local Pull-n-Pray.

 

[Joe94xj]

Did the other prop valve help?

 

[Frank Z]

Nope.

I'm done screwing with it for a while.

See you all next season.

 

[Joe94xj]

Really. Im still thinkin its the master.

 

[xj-grin]

Again, without any help except to say I ran a 99 stock prop, 99 stock MC with Isuzu rear discs and 1/2 ton chevy front calipers... if anything my pedal was really stiff. Man, I wish I had some wisdom for ya, Frank, but ya know, I'm all book learnin...

 

[montanaman]

Here's an idea ... and I'm not trying to insult your intelligence here. Are the bleeder valves on high part of the calipers? If they are on the low part of the calipers, you could have the cals mounted on the wrong sides. That would make it impossible to bleed the calipers properly.

I just read about this on another forum and thought of your situation. You are obviously very savvy on this subject, but it's worth mentioning.