MOAB Hydroboost and Seized Calipers

[staleb00]

I redid the brakes calipers and brake pads earlier this year and installed a WH MOAB hydroboost unit last spring. I’ve been dealing with a slow pedal return since the hydroboost install but didn’t seem to affect braking so just kinda let it be. I noticed recently that at higher speeds when I brake, it pulls to the left slightly. Then when I release it pulls to the right slightly. Figured it was maybe a seized caliper on the front passenger side. And sure enough it was. However, when I bled it. The caliper didn’t release. Checked the driver side and same thing. Piston was jammed and didn’t release when bled. So both were jammed basically and weren’t releasing. I took the driver side off emptied the brake fluid and was easily able to push the piston back in. Going to go ahead and replace the entire front brake lines to make sure it’s not a collapsed hose. But this has me wondering if the pushrod in the master cylinder might be jammed or too long? Seems the most logical with the slow pedal return and both front calipers seizing. Not as familiar with how to diagnose or even address that. Any thoughts on where to begin?

Also, I didn’t catch this when I replaced the calipers but my knuckles aren’t ground down. I originally assumed they were bc it had calipers from the PO. I had no issues installing the new ones but wondering if this has a role too.

 

[gr8scott]

Also, I didn’t catch this when I replaced the calipers but my knuckles aren’t ground down. I originally assumed they were bc it had calipers from the PO. I had no issues installing the new ones but wondering if this has a role too.

The lack of clearance between calipers/knuckles is the cause of all your issues.
Grind down the knuckles and your brakes should work properly.

 

[toddz69]

X2 - grind the proper clearance and then check things before going too crazy on the troubleshooting.

Todd Z.

 

[ntsqd]

Likely that the PO ground the calipers, a no-no - for this and other reasons.

Can confirm that it's the interference by pressing on the pedal, releasing it, and then cracking open the bleed screws. If fluid only dribbles out then it's the interference. If fluid blasts out (watch the eyeballs) then something else is going on.

 

[ba123]

Yeah, your calipers can't release if they can't even move!!! (assuming I'm understanding correctly).

 

[staleb00]

Thanks guys. I’ll grind them down tomorrow, reinstall the calipers and see what happens.