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Discussion Starter · #1 ·
SOA with Scout axles so I kept the Jeep D30 calipers and rotors.

Rears are Isuzu Trooper Calipers and Suzuki Sidekick Rotors.

68 Corvette master and S10 dual diaphram booster

New extended rubber lines front and rear.

As I'm getting ready for the local Jamboree last weekend, I noticed the front pads getting thin. I replace them, pushing the caliper pistons back in with a c-clamp.

Now all of a sudden I don't have any front brakes!? They worked great prior to the pad change. Now, even on gravel I can only get the right front to lock up after pumping 2-3 times. The left front never locks up. The pedal is soft 2/3 of the way down until it locks up the rears.

I bled the fronts just because, with no change. There are zero external leaks and no loss of fluid from the master. I did notice that the rubber boot for the left front piston had come loose, but the caliper seemed to be working correctly so I left it.

The master was new (reman) when I did the swap. I'm still using the proportioning valve for the fronts, but bypasssed it for the rears. I'm stumped, any thoughts?? /ubbthreads/images/graemlins/confused.gif
 

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Re: 4 wheel discs stopped working!

many brakes are set up with a valve system that uses only two wheels per line, IE; RF & LR,,, then LF & RR...someplace in the brake line set up did you leave the safety switch that closes off one set of lnes if you have a break line...this switch allows two wheels to stop the Jeep. To reset the mechanical switch you need to have two people...one to press on the brake pedal and one to open a brake line...now if you have a red brake light on the dash blead the line lightly until the light goes out...I would start by bleeding the LF....opening on side of the two line system forces a slug in the switch to a netrual position.
 

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Discussion Starter · #3 ·
Re: 4 wheel discs stopped working!

I see what your saying. As far as I know, this would only effect the fronts on a Jeep. Only one line running to both rear brakes. This was partly why I rebled the system, but even then, I don't know how the valve could have gotten screwed up in the first place unless just from me pushing the pistons back in??
 

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Re: 4 wheel discs stopped working!

[ QUOTE ]
I see what your saying. As far as I know, this would only effect the fronts on a Jeep. Only one line running to both rear brakes. This was partly why I rebled the system, but even then, I don't know how the valve could have gotten screwed up in the first place unless just from me pushing the pistons back in??

[/ QUOTE ]

Just thinking out loud....

One or both of the front calipers are stuck.

There's a problem with the new pads/installation.
Like rock hard "Life Time Warranty Pads"
Or not the correct pad.
Serious misalignment (for some reason).

It worked before... look at everything that's different now.

/ubbthreads/images/graemlins/40BEER.gif
Dale
 

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Re: 4 wheel discs stopped working!

It's not an uncommon problem, and no biggie.

Pushing the pistons in didn't create the problem.
But the first time you pushed the pedal down after you finished did. You should have pushed the pedal down very gently, softly, and a little at a time till it had pressure.

The pistons had to move a long way to get back in position, much more than normal at first. There was no resistance in the front lines, but had some in the rear. Because of the unequal pressure, the valve thought there was a catastrophic failure in the front. The slug moved to the side, allowing all pressure to go to the rear. It did what it's supposed to do.

Have someone GENTLY push on the pedal while you crack a rear line - the slug should center again due to the opposite unequal pressure.
If there's a dash light, it'll go out. If not, but if there's an electrical connection on the valve, use an ohmmeter. The terminal will stop being grounded once the slug's centered.

No terminal? You'll have to guess and try a few times.
 

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Discussion Starter · #6 ·
Re: 4 wheel discs stopped working!

Pads are in correctly, as far as I cen see both calipers are moving freely. The only thing I didn't do was have the rotors turned, and I have the cheapest pads I could buy.

RRich, I actually bypassed the prop-valve for the rears and have it capped off with brass fittings. I know this isn't the safest method, but it has been working great since I did it.

I suppose this would make the "slug" even more likely to slide over so I will take the plug out and see if I can work it back some. Will I have to remove the top plug and get in there with a pick, or can I remove the rear plug and hope a light push of the brake pedal will move it some?
 

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Discussion Starter · #8 ·
Re: 4 wheel discs stopped working!

I had heard (rumors mostly) that it would restrict the fluid to the rear calipers and make them ineffective.

So I've been meaning to plumb the proportioning valve back in and did that today. The I did what RRich suggested, only the bleeder on the right rear broke off /ubbthreads/images/graemlins/cussing.gif so I could only crack the left rear.

The result, driving on gravel road:

Hit brakes, only very slight braking, seems even side to side and front to rear.

Two pumps, rears will lock, fronts start to grab but don't lock

Three pumps all four lock fairly well, sometimes the driver's front will not.

Four pumps, lock up is nearly at the top of the pedal, although the rears seem to lock up a bit earlier, the pressure seems good right to left.

One wierd thing, when I bleed the brakes, the pedal goes to the floor. But when I test drive it the pedal only goes about 3/4 down, stops and gets very hard to press, even on the initial stroke when there is little braking taking place.

Geez this is getting really frustrating /ubbthreads/images/graemlins/wall.gif
 

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Discussion Starter · #9 ·
Re: 4 wheel discs stopped working!

Well I still cant get the proportioning valve to budge. I don't want bypass it if I don't have to.

I unscrewed the front of the valve and tried to move the slug. However, when I unscrewed it, I only lost fluid from the resevior for the front brakes. So I actually think the slug needs to move forwards and not back.

If I unscrew the back of the asssembly can I manually access the slug and get it to move?

Overall the brakes keep getting worse. I have rock hard pedal less than half way down with almost no braking front or rear, and pumping is being less and less effective. I've tried several times to break open rear lines and bleeders to re-center the prop valve with no luck.

Any thoughts are appreciated.
 

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Re: 4 wheel discs stopped working!

That's not a proportioning valve. The valve with the sliding slug is an equalizer valve, sometimes called an isolator valve.

It keeps the systems separated until there's a catastophic failure on one side. With one side pressurized and the other failed side not, the slug moves off center and re-directs the fluid to the failed side. It gives you a few more pumps before they fail completely.

Yours has slid to one side - it'll go towards the side that's not getting presure. Once it moves, it stays there until the pressure is unequal - but opposite. Sometimes it's a pain, you open the side it's NOT on and GENTLY apply pedal pressure - the slug moves to center again. But - sometimes it goes all the way to the other side - oops, too far. Back and forth. Ya gotta be gentle to get it to stop in the middle.

Try from the other side -- but if it moves hard it's no good anyway. It won't work when you need it.
Do a search on the web - there are pictures of equalizer valves, proportioning valves, hold-off valves etc. for braking systems. And then there's combination valves, incorporating several valves in one body. Find the one that looks like yours - look at the cut-away drawings to see how they work.

Through the years they've been called by wrong names all the time.
 

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Discussion Starter · #11 ·
Re: 4 wheel discs stopped working!

Sorry, I've been calling it a proportioning valve out of habit. Mine is the type W combination valve. Here's where I am at now.

Too little space to access the combo valve. I got frustrated and figured what the hey, cut all lines to it so I could get it out and look it over. Figured while I was at it, I'd just plumb things back together in case I mess the combo valve up... and to see how the braking changed.

It wasn't a ton of work, a couple of hours with the double flaring tool, some fittings and a chunk of line.....

NO CHANGE WHATSOEVER!!!!!!!! /ubbthreads/images/graemlins/cussing.gif

I even put new pads on the rear again becuse they were wearing prematurely and locking up before the fronts.

I'm right back at square 1. The pedal is rock hard less than half way down. If I really stand on it I can get the right rear to lock up...but it's raining out so that's not saying anything. If I pump, it gets slightly better but not even close to acceptable.

So no proportioning (oops Combo) valve in the way...straight plumbing to a "T" for both fronts and a single line to the rear.

I am thouroughly confused and frustrated. Please keep throwing ideas my way. I don't think I've ever been this stumped about something that started so harmlessly. /ubbthreads/images/graemlins/crybaby.gif /ubbthreads/images/graemlins/confused.gif
 
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