Weird C10 Front Brake Problem - One Locking Brake

[JohnIL]

Hey fellas,
I need some help with the front brakes on a '77 C10. This is my son's daily driver. He's fine under controlled braking. But, if he's in traffic and he has to get on the brakes hard, the left front locks. of course, it's much worse on wet roads. My uneducated guess was that he either had a stuck caliper or collapsed hose on the right. In the name of caution, we replaced both calipers and both hoses. After bleeding the system, the problem is exactly the same.

The brake system is stock. Front discs, rear drums. Stock master cylinder and proportioning valve. Original steel hard lines.

Any ideas? What else would cause one disc brake to be MUCH stronger than the other?

John

[maxx442a1]

My first guess would be proportioning valve. Here is an alternative thought though. What if the right side isn't braking enough and causing the left to lock up?

[Dead Parrot]

Same type of tires on both fronts? Some tires really are that much better then others.

2nd the prop valve as a suspect. Does the brake warning light work? Possible the bulb is burned out and you are missing the warning light about a prop valve issue.

[kwmech]

Check the steel hard lines for dents or being smashed. Not unusual after 50 years of various people working on them, stuff gets dropped and banged around. If they're ok, take the hard line off the rubber hose and blow the lines out with brake clean, maybe a chink of something somewhere. If I'm refreshing a brake system I always do this before I hook the lines back up to the Master. Got a 71 I'm working on right now for a customer. The master had (I kid you not) close to 1/2'' of mud/gunk in the bottom of the reservoirs. Original master cylinder from 71

[Pontiac1976]

I would have to agree proportioning valve. But make sure there no bet hit hard line in the front to the calipers. How dirty or long was the last time the brake fluid was replaced may tell you that line and valve rust or blocking. May try blowing the front lines out with air see what come out first.

[JohnIL]

Thanks for the suggestions. Unfortunately, we don't have time to open the brake lines and/or replace the proportioning valve right now. My son has to head back to college in a few days. I'll get a new proportioning valve ordered and we'll dig into it when my son is back home for spring break.

We took a few minutes this afternoon to clean and lubricate the caliper sliders. There was a bit of surface rust on the sliders. We pulled the new calipers back off, cleaned up the slider mating surfaces, gave them a fresh coat of brake grease and reinstalled the calipers. I don't know yet if this will help, but it certainly won't hurt anything.

My son is getting a new set of Firestone Destination LE3's installed on the truck tomorrow. The new tires may provide some better grip. That feels like a long shot, but the tires were on his to do list anyway.

Hopefully all of this makes the brakes behave themselves. Thanks again for the help. If we find a definitive solution, I'll post it back her.

John

[72c20customcamper]

I had a similar problem turned out the caliper that didn’t lock up was a defective rebuilt . Typical autozone crap . Replaced it under warranty and it stopped the problem

Problem only happened when towing . The right front would get real warm as it was doing most of the braking and it did cause the ABS to engage in wet and sandy roads all the time .