74 C10 front left disc locked

[Sad Sack]

the calipers are connected to steel lines.

IMO ...That is not a good thing..

 

[elbpony]

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.

I guess I need to talk to the shop...
and yes i was absolutely not thinking about that. just took the information i got for granted. feels kind of stupid

 

[DoubleDingo]

I guess I need to talk to the shop...
and yes i was absolutely not thinking about that. just took the information i got for granted. feels kind of stupid

It's steel lines to the frame (inside the frame rails), then a rubber hose to the caliper (outside the frame rails). In the back it's a rubber hose to the axle, then steel to the wheel cylinders. There has to be rubber between the frame and the calipers and the frame and the axle, otherwise the steel lines would bend immediately and break from suspension travel, leaving you without any braking whatsoever.

 

[Ricko1966]

I guess I need to talk to the shop...
and yes i was absolutely not thinking about that. just took the information i got for granted. feels kind of stupid

If your shop doesn't know this info,and already have the problem figured out,sounds like you need a different shop.Is this a legitimate, real shop with a credit card machine and employees?

 

[fast 99]

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.

Agree can never say never, however I can't remember a master alone causing unequal side to side brake issues.

edit, OP don't overthink it. Whatever fixes it will be logical and you will say why did it take so long to figure it out.

 

[Grit dog]

I guess I need to talk to the shop...
and yes i was absolutely not thinking about that. just took the information i got for granted. feels kind of stupid

Nah it’s just learning bud. I thought you were working on this yourself.
But any real repair shop, regardless of being in Germany with an American truck, should know the basic principles of braking systems.
AFAIK they’re all about the same and anything that old is literally just hydraulics and a brake light.
As always more info for interweb diagnoses is important. And we haven’t heard the history or condition of the vehicle.
For example: Brakes leaked and pedal to the floor. Hard lines from Mc to prop valve and wheels replaced because one was rusted through. Now 1 corner locks up. And I tried A B C things to fix it.
And yes there is a rubber hose going to each wheel and/or axle because the brake lines are mounted to the frame and the brakes are on the other end of the suspension so there has to be a flexible line to account for suspension movement.

 

[Grit dog]

the calipers are connected to steel lines.

I didn’t see this post before my response above. Confirming what I and others said. There is no way to hook a solid steel line to a brake assembly (on the front brakes) not allowing for any flexing.
Rear axle a bit different. 1 flex line from the hard lines to the axle and then hard lines along the axle to the rear brakes.
It’s obvious you are unfamiliar with basic vehicle mechanics and brake systems. Would be worth doing a little self training. Especially if you still suspect the shop did what they did that is wrong, so you can speak more knowledgeably to them.
Best of luck

 

[SlickGTP]

Unless they were telling him that it was steel braided hose, but it would still be rubber from the frame to the caliper, just wrapped in steel braid. I had a similar issue awhile back and it was the rubber line from the frame to the caliper.

 

[pduffyd]

I had this happen to me on my 76 C20. RH caliper would stick on, I could release it to get me home by cracking the break bleeder on the caliper. Replaced the flex hose to the RH caliper and all was good.

 

[elbpony]

Truck still won't move.
The rubber hose, and yes there is one each side, is not the problem. They switched the hoses left right. Left brake still locks, right still operates well. Changing back again did again not change snything.
Another round of bleeding at the caliper bleeding screw shows the piston travels back and the wheel rotates until steping on the brake pedal again.

 

[Scottgenex]

May sound like a broken record here; but when you say the lines have been replaced, are you referring to the hardlines that come from the prop valve all the way to the rubber (or steel braided) flex line to the caliper? If so I didn't read well enough. If you replaced the caliper and flex line then I'd imagine the blockage is in the hardline that is on the frame. Not sure what else it would be if the piston moves freely when not pressurized.

Just to get some clarification I've added photos. Maybe this can help breakdown what you mean when things were replaced.

Below is a steel braided flex line.

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Hardlines at the prop valve

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Hardline on the frame to the caliper

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[77Dmax]

If the master has been replaced there could be a mismatch with the pushrod. This usually just causes a drag, but if its wrong enough I suppose the wheel could lock up. Lots of variables with different combinations of boosters and masters out there. A seasoned tech will always check the piston on the new master with the old one to verify the correct depth, and same for a booster change.

A quick check is to loosen the master cylinder and see if it sits flush against the booster with no effort. If it'll only seat when tightening the nuts than that is your issue..

 

[fast 99]

Another round of bleeding at the caliper bleeding screw shows the piston travels back and the wheel rotates until steping on the brake pedal again.

When the brakes are locked what happens when bleeder is opened? To get anywhere with this need to follow suggestions and report back. Shouldn't be a hard problem to isolate.

 

[elbpony]

Lots of yes.
Scottgenex, the hardlines from prop valve to caliper are new, that because of corrrosion. The prop valve us new, that was done as thought of reason for the lock.

The rubber lines, flex hoses, are not new but were interchanged left vs right and back. No change, whell still remains locked.

The lock occuref during the last owners last drive, no parts changed begore that. The mc is still that gool old one.

77Dmax, i'll pass that on the shop.

 

[elbpony]

When the brakes are locked what happens when bleeder is opened? To get anywhere with this need to follow suggestions and report back. Shouldn't be a hard problem to isolate.

Fluid comes out and piston travels back. So i was told