Brake mystery

plymouth
voyager

#1

I’ve got a 1999 Plymouth Grand Voyager with brake issues. After running for 30-45 mins, the front brakes begin to apply pressure and stick. If you put it on the rack and run it with no pedal pressure applied at all they do the same thing. I replaced the pads & calipers & master cylinder in a brake job 6-8 months ago. There are no code error warnings coming up when we run a diagnostic. We have disconnected the ABS system. Still the same results so it is not the ABS electrical system. Also replaced the brake vacume booster. Nothing. All we can figure is the ABS hydraulic control unit (HCU) but this is VERY expensive and I certainly don’t want to buy it unless I have to.

We are stumped on this one!

Any ideas???



Thanks,

99VanDriver


#2

I believe that your flexible brake lines are deteriorating on the inside and that they are collapsing.
When they collapse, fluid is trapped and pressure is applied to the brake calipers just as if you stepped on the brake pedal.

The likely cause of this situation is not having changed the brake fluid on schedule, namely every 3 years/30k miles, whichever comes first. With an 11 year old vehicle, the brake fluid should have been changed at least 3 times already, so if that has not been done, that would explain the situation.

At this point, you need to replace ALL of the flexible brake lines in the car and install new brake fluid of the correct specification. It won’t be cheap, but at least it will be cheaper than replacing the ABS control unit.


#3

Thanks for the great information. Bad news though is I talked to my mechanic and he said he DID replace the hoses when he put the calipers on earlier so they are new hoses. On this van the other lines are metal. Only the front brakes have rubber lines. Anyone got another idea??


#4

There have to be flexible lines running to the rear brakes, otherwise the brake lines would be damaged the first time that the rear suspension reacted to a bump or a pothole.


#5

Did someone top up the fluid ? you need to leave room for expansion. Try removing some fluid. Sounds simple but try easy things first Next try opening the clamps that hold the flex lines in the middle not too much ! do not want rubber loose but sometimes evan new ones can restrict the flow


#6

If you can get the front brakes to apply on the rack, do some troubleshooting. With the wheel locked up, unbolt the master cylinder from the brake booster. If that doesn’t work, crack the line for the front brakes on the master cylinder. If the calipers do not release, crack the line to each front caliper at the ABS hydraulic module. If the calipers still do not release, crack the bleed screw on each caliper.

In the first instance there is a problem with the brake booster; the adjustment of the booster push rod; or the fit of the master cylinder to the booster (wrong part?). In the second instance, something is wrong with the master cylinder. In the third instance the problem is in the ABS hydraulic module. In the fourth instance, there is a problem in the lines from the ABS module to the calipers. If the calipers still do not release in the last instance, the problem is in the calipers or pads.

Hope that helps. Let us know what you finally find out.


#7

They did flush out all of the old brake fluid didn’t they? Aged brake fluid will have a much lower boiling point than fresh fluid so I’m just wondering if heat expansion of the fluid could be behind this problem.

This could possibly be exacerbated some if the master cylinder pushrod that attaches to the brake pedal is a bit too snug and keeping the piston in the master cylinder depressed more than it should be.