Left front brake locks up and releases after pumping pedal lightly?

[RichLo]

My Friend just dropped off his truck asking me to look into it quick since he is actively trying to sell it.

1989 K2500 350TBI ECLB Auto trans, 6-lug truck, vacuum brake booster.

OK, Lots of recent history with this truck and he is just trying to get the front brake to unlock and drive like normal so he can sell it. I'm just looking for quick checks to look into. I cant work on it until tomorrow night so asking for input tonight and tomorrow. If it was my truck I would go about the situation much differently but he needs cash quick so just trying to help him.

Recent history related to brakes: His Pop replaced rear brake lines from the master to the wheel cylinders and also the proportioning valve right next to the master, then tried to bleed the rear brake lines. He said the left rear couldn't bleed at all. He got the proportioning valve lock-open tool so he could bleed the rear, still didn't quite work apparently. I looked into the master and the rear reservoir is fresh and clean and the front is dirty.

He told me to not mess with the rear, its 'good enough' unfortunately. I'll still bleed that rear properly because its somebody else's safety. But that's just showing where his mind is at right now.

OK, history done, now onto the problem that he asked me to fix: This is a new problem since the rear brake lines and proportioning valve were replaced. (and fronts probably haven't been bleed). When you step on the brakes to shift from park to drive or reverse and try to go, the front drivers side is LOCKED SOLID. After he left, I tried to move it in front of my garage and it just spun the rear tires in either Drive or Reverse, non-directional. Then lightly tap the brake pedal dozen times and it drives like normal. Come to another stop like sitting at a stop light, same thing... tap it a dozen times and drives like normal.

My first step was going to be just bleed the whole system properly tomorrow but please any other ideas welcome!

The front rubber 'looks' ok but that would be my 2nd suggestion to him to replace. But ballooned rubber wouldn't let loose by tapping the brake repeatedly, right? Those just hold pressure and gets the rotor hot from my experience. These rotors weren't hot when he got here (30 min drive)

I've never replaced a proportioning valve or had to use a special tool to bleed it, could something be out of adjustment with it?

The left front was the worst but it could very well be both fronts locked up.

 

[Orpedcrow]

Sounds like hoses to me. They can kind of check valve them selves as they’re deteriorating. The quick little pumps moves the fluid back and forth quickly, dislodging the “check valve” therefore releasing some of the pressure.

Black fluid with black particles in it helps to verify that.
They’ll usually start to swell towards the inner diameter before the outer.

Could also be a chunk of dirt or something that got dropped in the line when the prop valve was replaced. I’ve also seen plumbers thread tape that clogged a line. (You don’t need thread tape)

 

[454cid]

My first thought would be the pins in the calipers and then the pistons themselves, but the hoses mentioned by Orpedcrow sounds reasonable, too.

Maybe lock them up purposely, and then see if cracking the bleeders open frees them up?

 

[HotWheelsBurban]

That's kinda what my Burb did when the brake hoses collapsed on it. Locked up the right front, then after it cooled off, it worked normally (till it heated up and locked up again).

 

[Orpedcrow]

Maybe lock them up purposely, and then see if cracking the bleeders open frees them up?

That’s a good idea. If they relax when the pressure is released, that would mostly verify the pins and pistons working and would at least point further up the hydraulic system.

 

[Erik the Awful]

If he's selling the vehicle, you're opening yourself to liability.

I looked into the master and the rear reservoir is fresh and clean and the front is dirty.

Start there. Siphon out the master cylinder and then wipe it clean. Put an inch of fluid in it, take the lines loose, and pump the fluid out of the master cylinder fittings. Reconnect the metal lines and top off the master cylinder. If the hoses aren't new, I'd strongly suggest replacing them. Pull them off, bleed the lines until the fluid comes out clear, and then install the new hoses. Finally, bleed at the wheels.

 

[Schurkey]

If he's selling the vehicle, you're opening yourself to liability.

I am not a lawyer.

NORMALLY, I'd say that if there's no work order, no written or e-mailed receipt, no money changes hands for labor charges, there's no liability to the current owner, and even less to whoever he sells it to.

In today's world, where the courts have gone insane...be careful.





I have heard about--but never seen or experienced--brake hoses acting as check-valves, where the fluid can apply the brakes but is then trapped keeping the brakes applied. My actual experience is that hoses plug--you can't push fluid through them at all. The hoses are tighter than a bull's a_ss in fly season. I've personally had three of those--both front hoses on my Parts Toronado, and the rear hose on my 'Camino. I'm not saying this can't happen...just that I've never seen it.

Most everything I can think of that would keep the brake locked-up, (problems "farther up the hydraulic system") would affect both front brakes not just one. So maybe a failing hose acting as a check-valve really is the most-likely possibility.

I'd pull the caliper and see if the piston, or the caliper mounting was sticky, before I condemned the hose.

And deliberately "locking" that brake, and then opening the bleeder valve to release hydraulic pressure is a GREAT idea.

 

[Erik the Awful]

I am not a lawyer.

NORMALLY, I'd say that if there's no work order, no written or e-mailed receipt, no money changes hands for labor charges, there's no liability to the current owner, and even less to whoever he sells it to.

I'm not a lawyer either, but if you wrenched on the brakes and a couple days later the brakes fail and someone dies, you're at least going to be making a court appearance that you don't want to make. We live in a country where you can sue anybody for anything, and as chaotic as that sounds, it helps keep people from trying to make end runs around the law. You can follow the letter of the law and still end up in a civil suit because what you did hurt someone.

My point was simply that you don't want to do the bare minimum in this case. RichLo already stated the master cylinder was dirty. Fix it right so that no one has a reason to question your work.

 

[0xDEADBEEF]

Have him sign something to the effect that he acknowledges brakes are not road-worthy, dangerous, and potentially life threatening. I am not a lawyer either.

 

[RichLo]

So Last night I induced the lockup and cracked the bleeder and it released right away. So I'm 90% sure its the rubber hose now, the other 10% is that he received a faulty proportioning valve. I talked him into re-bleeding all 4 corners and replacing the rubber hose and replacing all 4 bleeders since they are crusty and stripped and the drivers rear is probably plugged up which is why his Pop couldn't bleed that corner very well.

And for the liability I totally get it, that's why I talked him into doing it right instead of 'good enough.' A few extra bucks for a big jug of brake fluid and new bleeders is peace of mind that your not going to hurt somebody else.