74 C10 front left disc locked

[elbpony]

Hi out there
Need to ask for ideas, I am running out of 'em.
My front left brake doesn't release after braking. It is power brakes and all stock material afaik
When the caliper is taken of the system the piston travels freely.
Changed so far are lines from prop. To Caliper, and the prop valve itself. I now attack the main cylinder next.

Any further ideas I miss here?

 

[Chevy 88]

Did you replace the rubber brake hose that comes off the caliper?

The hose fails internally and turns into a check valve.

Open the bleeder to confirm.

 

[fast 99]

When locked up open bleeder, does it release? If not bad caliper, stuck slides. If it does there is a restriction somewhere in the system as suggested above bad brake hose, ect.

 

[Ricko1966]

Hi out there
Need to ask for ideas, I am running out of 'em.
My front left brake doesn't release after braking. It is power brakes and all stock material afaik
When the caliper isc taken of the system the piston travels freely.
Changed so far are lines from prop. Caliper, line prop. valve to caliper and the prop valve itself. I now attack the main cylinder is next.

Any further idead I miss here?

A master cylinder will not cause this condition. So don't change your master.

 

[elbpony]

Thanks for the replies.
Lines are new and steel.
Caliper is new and piston is free traveling when not pressurized. I assume that is the same as open the bleeder?

I am puzzled. Is there a way to test the prop valve?

 

[elbpony]

A master cylinder will not cause this condition. So don't change your master.

I cant think if how, too. Yet i heard it happen. Explanation is that not all calipers, hoses, valves etc are equal in throughflow. Now, if the master is also rusty aged clogged it might just be enough to not release pressure enough on both break cylinders but, only on the easier one. My left side might be the touger one and Lock. Thats the theory

 

[Grit dog]

Id say probably the rubber line going to the caliper since you didn’t replace that. but you said the piston pushes back easily which sort of eliminates that.
Back to the symptoms. Is it push the brake pedal once when the vehicle is cold and it locks up or after driving and braking (everything is hot) that it hangs up a bit or does it lock up hard.
Does the bleeder release the pressure? That would be the first thing to do before throwing parts at it.
But you said all stock material, with the language barrier, you mean stock as in not some fancy aftermarket brakes or stock as in you think it’s original 50 year old parts? If the latter, it depends if you just want to make it roll and stop or if you want a reliable brake system?
We don’t know the condition of the truck or how it was treated but there’s about a 90% chance that the whole brake system needs replaced if original. Calipers, wheel cylinders etc.
How old and what is the condition of the fluid?
A lot of questions to answer or things to find out to create the right path forward.

 

[Grit dog]

I cant think if how, too. Yet i heard it happen. Explanation is that not all calipers, hoses, valves etc are equal in throughflow. Now, if the master is also rusty aged clogged it might just be enough to not release pressure enough on both break cylinders but, only on the easier one. My left side might be the touger one and Lock. Thats the theory

Anything is possible but that is not a very plausible explanation. If one side works and the other has issues 99% it’s not the master cyl.

 

[legopnuematic]

If the master cylinder was a drum-drum master or a disc-drum master, but plumbed backwards, there would be a residual pressure valve that would cause dragging on a disc setup.

But these trucks are 50-50 bias side to side, barring potential blockages or an imbalance down stream (mismatched piston sizes on calipers for example) what happens on the front left should be the same on the front right.

 

[elbpony]

Id say probably the rubber line going to the caliper since you didn’t replace that. but you said the piston pushes back easily which sort of eliminates that.
Back to the symptoms. Is it push the brake pedal once when the vehicle is cold and it locks up or after driving and braking (everything is hot) that it hangs up a bit or does it lock up hard.
Does the bleeder release the pressure? That would be the first thing to do before throwing parts at it.
But you said all stock material, with the language barrier, you mean stock as in not some fancy aftermarket brakes or stock as in you think it’s original 50 year old parts? If the latter, it depends if you just want to make it roll and stop or if you want a reliable brake system?
We don’t know the condition of the truck or how it was treated but there’s about a 90% chance that the whole brake system needs replaced if original. Calipers, wheel cylinders etc.
How old and what is the condition of the fluid?
A lot of questions to answer or things to find out to create the right path forward.

That line is changed and steel. No more rubber.

It started locking up hard after a regular drive. Ever since it locks hard immediately after only pushing the pedal - I can´t test it in hot as the truck won´t move enough.

stock as in no aftermarket stuff, yes. sorry for the language barrier.

I don´t know how old all that material is. I own the truck for a mere two months, only. I assume hoeever that getting that system refurbished is my step by step path anyway.

I´ll check what happens when i openthe bleeder with pressure applied. For now I had only taken the brake lines of and checked the piston for traveling back and forth - what it does. For that reason I did not figure opening the bleeder could also show me something.

so far so good, I got stuff to do for the next few days

 

[elbpony]

If the master cylinder was a drum-drum master or a disc-drum master, but plumbed backwards, there would be a residual pressure valve that would cause dragging on a disc setup.

But these trucks are 50-50 bias side to side, barring potential blockages or an imbalance down stream (mismatched piston sizes on calipers for example) what happens on the front left should be the same on the front right.

it came with discs from the factory. If not anaybody changed the master against the wrong one I can´t see how that might happen, But, everything was already seen, right?

 

[Ricko1966]

I cant think if how, too. Yet i heard it happen. Explanation is that not all calipers, hoses, valves etc are equal in throughflow. Now, if the master is also rusty aged clogged it might just be enough to not release pressure enough on both break cylinders but, only on the easier one. My left side might be the touger one and Lock. Thats the theory

It would happen to both fronts not just one. Look at what @fast 99 wrote to you. And you say no more rubber,that is very,very,unlikely please explain. If you have replaced the rubber front brake hoses with something else please tell us.

 

[elbpony]

It would happen to both fronts not just one. Look at what @fast 99 wrote to you. And you say no more rubber,that is very,very,unlikely please explain. If you have replaced the rubber front brake hoses with something else please tell us

the calipers are connected to steel lines.

 

[Ricko1966]

the calipers are connected to steel lines.

The front wheels turn, there has to be a flexible connection somewhere usually a rubber hose, without a flexpoint the lines will break when you turn the front wheels.

 

[legopnuematic]

the lines will break when you turn the front wheels.

Not if you go straight home…