Author Topic: Brand new brake calipers, pistons won't retract. 1976 c10  (Read 84 times)

Online DIG

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Brand new brake calipers, pistons won't retract. 1976 c10
« on: August 05, 2020, 01:17:30 PM »
I bought new remanned brake calipers and new brake hoses and replaced a broken driver's side metal line for my 1976 Chevy c10. I installed them, bled all the brakes but the caliper pistons do not retract. I can take the master cylinder cap off and push the piston back in using a screw driver or piece of flat steel and channel locks if I take the whole caliper off. I have brake fluid to both front and rear brakes. The mater cylinder is newish and I don't have a booster so that "shouldn't" be an issue. The rod for the master cylinder seems to be pulling out all the way releasing any pressure from the lines so the fluid can return. The proportioner seems to be working correctly (wouldn't I not get fluid to one end if it was blocked off?). I have bled and rebled the brakes several times and have used over a quart of brake fluid. I am pulling my hair out trying to figure this out.  I'm also a newbie and not a mechanic so keep that in mind. Any help would be appreciated.
1976 Chevy C10 250 I6 3 speed manual

Online bd

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Re: Brand new brake calipers, pistons won't retract. 1976 c10
« Reply #1 on: August 05, 2020, 02:14:34 PM »
You're having trouble solving the problem because a problem doesn't actually exist.  Disc brake pads do not retract from a caliper.  There is always ever-so-slight drag from continuous contact between the pads and rotors.  As long as the rotors spin with very little to no drag when the brake pedal is released and lock when the pedal is depressed, the brakes are working properly.  So leave your hair alone.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Online DIG

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Re: Brand new brake calipers, pistons won't retract. 1976 c10
« Reply #2 on: August 05, 2020, 02:20:34 PM »
No you don't understand. As I try bleeding the brakes with help of a pedal pumper person, the piston just keeps pushing out and never retracts at all or if it does its very slightly and the wheel can no longer be turned. Unless it somehow fixes itself as the truck drives, the wheels not turning is an issue. So basically no, the rotors do not rotate at all with the brake depressed.


« Last Edit: August 05, 2020, 02:22:37 PM by DIG »
1976 Chevy C10 250 I6 3 speed manual

Online MIKE S

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Re: Brand new brake calipers, pistons won't retract. 1976 c10
« Reply #3 on: August 05, 2020, 03:03:25 PM »
Two things come to mind. As bd says caliper pistons don't retract. They just kind of relax there grip on the rotor and will have a heavy drag that will slightly push the piston back as the wheel rotates from the slight runout of the rotor. That being said the later squarebody with the aluminum master cylinder has considerably less drag due to design of the system. The piston seal is designed to have more pullback on the piston causing less drag. The master cylinder has what is called a quick takeup valve built into it to push a large volume of fluid on initial apply of the pedal to make up for the caliper piston retraction so you wont have a low pedal. This was an attempt for better fuel mileage.  The other thing is that you could have the lines reversed on your master cylinder. If that is the case, then the drum brake side of the master cylinder would be applying the front brakes which would cause them to drag due to the residual check valve on the drum brake portion of the master cylinder.   
« Last Edit: August 05, 2020, 03:06:35 PM by MIKE S »

Online DIG

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Re: Brand new brake calipers, pistons won't retract. 1976 c10
« Reply #4 on: August 05, 2020, 03:10:30 PM »
How much drag are we talking about here? Like two hands all your might just to turn the tire or less than that? When the brakes are lightly applied as of stopping slowly at a stop sign the piston doesn't push out too far. But when pumping the brakes 10 times the piston pushes out really far and basically locks up the rotor. Requiring a lot of force to move. When I push the piston back in, with the master cylinder cap still on, I can turn the wheel with one hand but still hear the brakes dragging which I assume is normal. However if I "use" the brakes it becomes increasingly more difficult to move until its nearly impossible to do by hand alone.
« Last Edit: August 05, 2020, 03:15:01 PM by DIG »
1976 Chevy C10 250 I6 3 speed manual

Online bd

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Re: Brand new brake calipers, pistons won't retract. 1976 c10
« Reply #5 on: August 05, 2020, 03:21:45 PM »
Depress the brake pedal and then release it.  If the rotors are locked, briefly crack the bleeder screws open on each caliper and then close them.  After the bleeder screws are retightened, do the rotors release and spin easily by hand?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

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Re: Brand new brake calipers, pistons won't retract. 1976 c10
« Reply #6 on: August 05, 2020, 03:29:25 PM »
OK I tried that but they are still extremely hard to turn. The brake pedal is soft after I just push back the piston, so I pump the pedal about 10 times which makes it very difficult to push down and it doesn't go very far. It's at this point where the pistons are pushed so far out that it's very difficult to turn the rotor and impossible to turn with the brake pedal pressed down. Normally this would tell me that it's working fine but the resistance is just so high that I cannot believe it's correct. I am not in a good position to remove the truck from the jack stands as the only jack I have at the moment is a scissor jack from a 1996 Chevy express 1500. Shouldn't I be able to tell if the brakes are correct without having to drive the truck?
Also would having air in the lines somewhere on the truck cause this issue? Maybe the master cylinder needs bleeding? I have spent countless hours researching and trying different things to get them to work properly. Short of replacing all the brake line on the truck, which for the most part seems to be working just fine. I already replaced the rear drum brakes and they work great. I just recently replaced the front calipers because the drivers side caliper piston was sticking and I noticed that the rubber hoses and drivers side metal line was leaking. After replacing all of that, forcing the proportioner back open and bleeding the brakes I'm still with a non drivable truck and over $100 spent!
« Last Edit: August 05, 2020, 03:47:33 PM by DIG »
1976 Chevy C10 250 I6 3 speed manual

Online bd

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Re: Brand new brake calipers, pistons won't retract. 1976 c10
« Reply #7 on: Today at 10:49:51 AM »
Did you lubricate the caliper slides and pins?  When the pads are retracted into the calipers, do the calipers slide freely inward and outward on their mounts?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

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Re: Brand new brake calipers, pistons won't retract. 1976 c10
« Reply #8 on: Today at 10:51:38 AM »
Yes. They slide in just fine, however then never slide out due to the piston being permanently pushed up against the brake pad and rotor.
1976 Chevy C10 250 I6 3 speed manual

Online bd

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Re: Brand new brake calipers, pistons won't retract. 1976 c10
« Reply #9 on: Today at 10:58:00 AM »
What DOT specification brake fluid did you use?  Were they brand new sealed containers?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

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Re: Brand new brake calipers, pistons won't retract. 1976 c10
« Reply #10 on: Today at 11:01:14 AM »
Dot 3 and I just bought them.
1976 Chevy C10 250 I6 3 speed manual