Blocked Brake Hose/ABS Channel

[roosri]

For a few months leading into covid, my ZHP was starting to have a weird pull under braking. The wheel would dart right under braking with increasing intensity. I transitioned to WFH in March of 2020, and the car basically sat in that state until the last few weeks trying to get her road worthy again.

To that end, I bought a set of rebuilt calipers with new pads + rotors. After doing the parts swapping, I went to bleed the system. I bled three calipers just fine with a vacuum bleeder, but my front left caliper wouldn't let any fluid out of the bleed nipple, even with a lot of pressure on the brake pedal. The pedal has plenty of pressure, and the other three calipers work, but that front left just doesn't do anything at all.

Needless to say, I'm a little frustrated that instead of diagnosing the real issue I spent money on parts I didn't need to buy. Because of a storm warning, I had to kick the ZHP out of the garage to pull in the other car. Through the week, I want to actually diagnose the real root cause and get to the bottom of this.

What I've checked so far;
- The metal line between the rubber brake line and the DSC unit: no obvious kinks.
- Fittings into DSC have no leaks, no leaks from the MC or reservoir.
- The reservoir itself did have some grey goo when I cleaned it and filled with fresh fluid. When troubleshooting the single failing caliper, I found more goo all around the bottom of the filter basket.

Planned next steps;
- Remove, empty, and inspect reservoir
- Disconnect front left hardline from DSC and from caliper, use compressed air to ensure line isn't blocked
- Inspect DSC unit for any obvious blockage.
- Use compressed air to blow air through DSC while using a computer + cable to open the valves in the unit.

Anything else I could check? I have a cable coming in a few days, so I won't be able to do much until then.

[TenMorePlease]

I would start by disconnecting the brake line going into the caliper. Check to see if brake fluid flows out, could get lucky and it just be a defect with the new caliper. Crazier things have happened.

Then just work your way back through the line in question checking at each removable connection until you find flowing brake fluid.

The wheel pulling problem you originally had. How many miles would you say you drove on that before addressing it? If it was long enough you may be able to see some wear differences on between the drivers and passenger side pads. That would back up your theory of the brake line issue causing the pulling.

During the abnormal braking events with the right pull, would it ever feel like abs was engaging through the brake pedal? Even if there were no dash indicators? Only reason I ask is because I’ve seen corroded tone rings cause speed sensors inputs be intermittent enough to not cause any faults but enough to actually engage the stability program/abs prevention measures but again with no dash lights! Really frightening tbh.

Probably not your case but just figured I’d share as tone ring issues happen more frequently as the cars age and get up in mileage.

Curious where you end up finding the blockage. The rest of your strategy sounds good.

Now that I’m thinking about it, have you considered doing a full dsc brake bleed as a first step since you have access to the computer and everything is together still?

Good luck! ��