Brake line failure

[Marlin]

My wife called me at work today to tell me that she had no brakes in the VX!!! Fortunately she was in a parking lot and ditched it on the curb. She didn't think to use the ebrake:confused:

Anyway, when I got there, there was a puddle of brake fluid under passenger side front tire. I crawled under and found the culprit. The new SS lines I just installed about a month ago, one of em ruptured, about 2-3 inches below the top fitting!!!! I am in the process of contacting the company for replacement. They have a lifetime warranty.

Here is my real question, I thought the purpose of the proportioning valve was to prevent a failure of this nature from affecting both front and rear brakes? I have absolutely no brakes whatsoever. I thought I should still have rear? Maybe my VX brakes suck because I have never had rear brakes? That would explain another scenario I experienced. When I installed my front locker, I had the whole front end off, and when I went to back out of the stall, VX wouldn't stop until I pumped the brakes a few times to get the front caliper pistons to engage. I should have had rear brakes then as well? Hmm, I will wait to let some others chime in on what they think. I have never really messed with this stuff before. I was thinking about plugging the front port on the proportioning valve and seeing if the rears worked. The rotors are shiny, so they at least move some, but maybe not enough to be effective? That would also explain the extreme nose diving on hard braking, I just assumed the front EBC pads were badass.


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[MSHardeman]

Marlin, I'm no brake expert, but here I go talking out of the side of my neck:
A proportioning valve just regulates the amount of force going to the front and rear brakes, it doesn't totally separate the systems. Because of that if you lose fluid (particularly all of it) then the whole system goes down and your wife gets to ride the VX roller coaster in the parking lot.

I'm shocked that the stainless lines would do that. I can't imagine that they would blow out, and I have to believe that the line was kinked or cut by something under the car to make it fail. I suppose anything is possible, but those stainless lines should be able to handle anything that you might throw at them. Heck, the stock lines are just squishy rubber and they held up to a lot of abuse (I saw you wheel in Moab :biggringr) before you put the stainless lines on. When you put the new line in make sure that there isn't anyting binding the line or rubbing against it.

[Marlin]

Marlin, I'm no brake expert, but here I go talking out of the side of my neck:
A proportioning valve just regulates the amount of force going to the front and rear brakes, it doesn't totally separate the systems. Because of that if you lose fluid (particularly all of it) then the whole system goes down and your wife gets to ride the VX roller coaster in the parking lot.

I'm shocked that the stainless lines would do that. I can't imagine that they would blow out, and I have to believe that the line was kinked or cut by something under the car to make it fail. I suppose anything is possible, but those stainless lines should be able to handle anything that you might throw at them. Heck, the stock lines are just squishy rubber and they held up to a lot of abuse (I saw you wheel in Moab :biggringr) before you put the stainless lines on. When you put the new line in make sure that there isn't anyting binding the line or rubbing against it.

Yep, there is nothing really to rub on under there. I can't find any nicks or anything. I checked the other side, it looks fine. It is possible that there was a preexisting flaw in the hose itself?

Here is some info about the proportioning valve, it should prevent a front failure from affecting the rear brakes, this is from the VX shop manual:

The P&B valve contains two sections, each serving a
different function.
The proportioning section of the P&B valve proportions
outlet pressure to the rear brakes after a predetermined
rear input pressure has been reached. This is done to
prevent rear wheel lock up on the vehicles with light rear
wheel loads. The valve has a pass feature which assures
full system pressure to the rear brakes in the event of front
brake system malfunction. Also full front pressure is
retained in the event of rear brake malfunction.
The combination valve has a pressure differential
warning switch which is designed to constantly compare
front and rear brake pressure from the master cylinder
and turn on the brake system warning light on the
instrument panel in the event of a front or rear system
malfunction. The valve and switch are so designed that
the switch will latch in the warning position once a
malfunction has occured. The only way the light can be
turned off is to repair the malfunction and apply a pedal
forced required to developed line pressure. The P&B
valve is not repairable and must be replaced as a
complete assembly

[MSHardeman]

Well I'll be. I had no idea a proportioning valve could do that. I just thought it regulated the amount of pressure going fore and aft, not that it would allow the front or rear to work if the other went out. Maybe I'll have to disconnect some of my brake lines to see if mine works or not. Since I don't have an idiot light for my brakes showing on my dash I guess it is working.

I suppose the line could have had a flaw in it to begin with, but I can't imagine the amount of pressure that would be required to blow out the inner rubber lining AND the braided stainless. Impressive.:thumbup:

[Marlin]

Well I'll be. I had no idea a proportioning valve could do that. I just thought it regulated the amount of pressure going fore and aft, not that it would allow the front or rear to work if the other went out. Maybe I'll have to disconnect some of my brake lines to see if mine works or not. Since I don't have an idiot light for my brakes showing on my dash I guess it is working.

I suppose the line could have had a flaw in it to begin with, but I can't imagine the amount of pressure that would be required to blow out the inner rubber lining AND the braided stainless. Impressive.:thumbup:

I think my proportioning valve may be bad, or I have a huge clog somewhere between the front and rear, or I suppose it could be in the ABS garbage somewhere.
I may put a bolt in the front proportioning line tomorrow and see if I magically get rear brakes, if not, I will get the valve off the junk VX here in town. Probably a good time for me to remove all the ABS junk and hardline from the proportioning valve to the calipers.

[rowhard]

it's that master cylinder that does the split. This is from 'How Stuff Works' web page:

To increase safety, most modern car brake systems (http://auto.howstuffworks.com/auto-parts/brakes/brake-types/brake.htm) are broken into two circuits, with two wheels on each circuit. If a fluid leak occurs in one circuit, only two of the wheels will lose their brakes and your car will still be able to stop when you press the brake pedal. The master cylinder supplies pressure to both circuits of the car. It is a remarkable device that uses two pistons in the same cylinder in a way that makes the cylinder relatively failsafe. The combination valve warns the driver if there is a problem with the brake system, and also does a few more things to make your car safer to drive.

Sounds like you might have a few problems Chris

[Triathlete]

If you had a "clog" that should of showed itself when you bled the new lines.

[Marlin]

Not if the clog is not 100%, which would explain why the rotors stay clean, I need to pull the pads and check wear. They only have 10K miles on em.
As for the proportioning valve only being a warning, its straight out of the VX shop manual that it has a bypass to separate front and rear. I will figure it out tomorrow when I block the front port.

[Marlin]

Apex sales rep called yesterday, sending two new front hoses, should be overnighted on Monday, Tuesday at the latest. That means no VX for the next 4 or 5 days:( That means the rear diff rebuild can't happen until the VX is back up and running. Too bad I didn't save the crappy rubber hoses.