Driver Side Front Caliper Sticking - Faulty HCU?

[rbattelle]

My 2003 has developed what I thought was a sticking driver-side front caliper. Here's my symptoms:

1. On initial brake application the vehicle pulls right. The steering wheel itself rotates to the right, because only the right front caliper is responding. (Note: rear brakes work fine, the only issue here is with the front left caliper).

2. After several seconds of brake application, the right-pull abates as the left side caliper begins to apply.

3. After hard braking, the left side caliper will remain stuck in the applied position, subsequently overheating the brake on that side rapidly.

4. After the vehicle sits for awhile with that left side caliper stuck in the applied position, the pressure abates and the brake will release.

I have verified the asymmetric response of the front wheel brakes by measuring their temperatures after various braking tests. The driver side caliper is definitely slow to apply and to release.

In hopes that the caliper pistons were seizing in their bores, I replaced the left front caliper with a quality remanufactured unit. No change to symptoms.

I now suspect the HCU (hydraulic control unit - the thing sitting under the ABS computer containing the motor and valves that make the ABS work). The part is labeled number 3 in the diagram below. Neither the ABS nor CEL are illuminated, and I have verified by test (panic stop) that the ABS system itself is working.

Unfortunately, the HCU is no longer manufactured and no rebuilt units are available. I was wondering if anyone has ideas on a path forward. I'm considering replumbing the system to eliminate the ABS, but that seems like a somewhat extreme measure.

Or maybe it's something entirely different I should look at.

-Ryan

 

[seafish]

You should know that your symptoms of the LS caliper pistons sticking on application and only slowly releasing is also a symptom of the flexible rubber brake lines that run to the caliper deteriorating on the inside and/or also being pinched by the small clamp that holds it in place. If your flexible brake lines are original to the truck then I suggest you replace both sides first with oem lines and then retest your brakes. My guess is that your problem will go away without needing to replace or rebuild the ABS pump.

 

[rbattelle]

That's a good idea. I didn't think a bad flex hose could cause this kind of problem. I'll change that and see what happens.

 

[dieselshadow]

Change them both. It's not much more money or work. You have to bleed the system anyway. And if one is bad, the other isn't far behind.

 

[Wayne M.]

I’m with shadow.
Our trucks are getting on in age and I’m just waiting for rubber item failures to start happening to me. If you had a internal HCU dump/ pressure issue, you would have a light on/ codes.

 

[Ozymandias]

That's a good idea. I didn't think a bad flex hose could cause this kind of problem. I'll change that and see what happens.

Very common problem, sometimes they deteriorate internally, but in our case the clamp around it at the axle rusts and squeezes the hose close.

 

[MGreer]

View attachment 122512

 

[nibroc]

attachment does not work

 

[MGreer]

I replaced.mine last year with raybestos hoses from rockauto. You can pry up on the holding bracket on the frame and clear way the rust. Then bend the bracket back down, this worked but I eventually replaced both.

 

[rbattelle]

You guys were absolutely correct: the flex line was pinched by the mount bracket. I had to cut the mount bracket off to remove it, and that fixed the issue completely.

The only problem is that the fitting that connects the hard line from the HCU to the flex line at the junction block is stuck. Is it possible the factory put red Loctite at that threaded joint?

If it's rust (rather than Loctite) I will have to plan to replace that hard line from the ECU because it seems unlikely I will be able to disconnect it from the flex line without destroying it.

On edit: the brake lines from the HCU to the junction block (labeled 1 and 2 in the diagram in my original post) are no longer manufactured and unavailable from Dodge.

-Ryan

 

[Ozymandias]

When I bought my new lines, OEM parts, they came with a new junction block.
I used Vise Grips to take them apart, aside from good aid with a heat gun.

For future, after you install the new one, put on a thick layer of grease to the connection so it is safe from rusting.

Hard lines can be made easily DIY, that's why they dont sell them anymore, no one bought them OEM.

 

[MGreer]

The problem with getting the brake line fitting to turn is due to the coating on the lines. What I do is unhook the hose at the caliper and carefully add heat to the metal line. It will melt the coating and let the nut turn. I use one of those micro torches that uses butane.

 

[PLohr]

Guys, I'm also having an issue with a frozen or sticky driver side front brake caliper.

Just wanted to share something I learned from a wise technician somewhere along the road. You guys probably already know this. When diagnosing what may be a frozen caliper, loosen the attaching nut for the brake line at the caliper then try to pry the caliper back. Can the pistons now be compressed? If yes, then the problem is not the caliper but most likely the brake hose.

By the way, this is the second time I've had a brake caliper freeze up on me. Last time could have been 50K to 100K miles ago. I don't have good records on that, wish I did.