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73-87 Chevy _ GMC Trucks => Brakes, Frame, Steering & Suspension => Brakes and Braking Systems => Topic started by: DIG on August 05, 2020, 01:17:30 PM
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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.
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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.
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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.
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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.
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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.
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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?
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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!
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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?
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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.
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What DOT specification brake fluid did you use? Were they brand new sealed containers?
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Dot 3 and I just bought them.
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Well, if releasing the hydraulic pressure at the calipers by cracking the bleeder screws doesn't release the rotors, then either the calipers are binding on the slides or the caliper pistons are binding in the caliper bores.
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Ok, so add lots more lube to the slides. Would brand new caliper pistons bind? Should I add lube to them?
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Don't goop a large amount of lubricant onto the slides or you will risk transferring it to the friction surfaces as the brakes heat up, causing more problems. Smear Permatex Silicone Ceramic Extreme Brake Parts Lubricant (P/N 24129) or equivalent disc brake lubricant onto the slide surfaces and the pin o-rings after the slides have been wire brushed, thoroughly cleaned and/or burnished, and rinsed with brake cleaner. Don't allow any lubricant to land on the pads or rotor faces. Rinse and wipe all friction surfaces down with some aerosol brake cleaner before seating the pads against the rotors after assembly. Don't try to lubricate the pistons as it won't accomplish anything useful and will make a huge mess, compounding issues.
Any new or recon caliper may impose slight rotor drag that should decrease with normal use. A problem exists when the drag is excessive, as you have described.
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Alright thanks for all the info. The reman calipers came with new pins and lube, and I applied a moderate amount to them already and they slide nicely. I dont want to buy all new brake lines but I am also tired of burning my money on quarts of brake fluid hoping its just air in the lines. I am lost as to what to do now. From what Ive read it seems that they should just work, but of course as with everything else in my life its a huge pain!
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So I just put the tires back onto the studs to check if that made any difference, and I can move the tire with just one hand and moderate effort. The tire doesn't spin around freely but it's not nearly impossible like when I was trying to turn the rotor using my hands on the studs. Is this what you would consider normal resistance?
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Are you trying to turn the rotors with the wheels bolted on or just trying to turn the rotors by just grabbing the wheel studs. Even with the wheels bolted on it won’t freewheel but it would be easier to tell. Like bd says, if you open up the bleeder screws and you feel that they are still to tight the problem would not be upstream of the calipers. You would be relieving all hydraulic pressure so none of the other brake components would would affect your problem.
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I know you've only mentioned the brakes being replaced and no maintenance to the hubs or bearings. However, just for narrowing down the issue and making sure the light is on the actual culprit. Use a pry bar in the vents of the rotor tod force the caliper to move on the slides. Do not push the brake pedal. Now remove the caliper and attempt to rotate the rotor. If this is difficult you may have to much preload on the hub bearings or bad bearings.
If the hubs move without the caliper and with slight resistance(preload) the I'd investigate the rubber lines. It is common for them to corrode internally and allow pressure to the caliper due to applied force but without any counter acting force the pressure will not bleed off. I had this problem on a '69 panel and it was a pain to diagnose because the lines were fairly new and we always doubt new parts are bad.
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Originally I was just grabbing the studs and I couldn't rotate it. Just now I just put the wheel on the studs, without bolting it and it was much easier. I will attempt moving the wheels with the bleeders open to see if I can move them even easier. I'm about to just bleed the brakes and go down my private dirt road to see if I notice any bad dragging.
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I know you've only mentioned the brakes being replaced and no maintenance to the hubs or bearings. However, just for narrowing down the issue and making sure the light is on the actual culprit. Use a pry bar in the vents of the rotor tod force the caliper to move on the slides. Do not push the brake pedal. Now remove the caliper and attempt to rotate the rotor. If this is difficult you may have to much preload on the hub bearings or bad bearings.
If the hubs move without the caliper and with slight resistance(preload) the I'd investigate the rubber lines. It is common for them to corrode internally and allow pressure to the caliper due to applied force but without any counter acting force the pressure will not bleed off. I had this problem on a '69 panel and it was a pain to diagnose because the lines were fairly new and we always doubt new parts are bad.
I just bought new rubber lines and with no calipers/brakes on the rotors spin freely easily. I may at some point repack the bearings etc but for now I just need to get it moving so I can do other stuff. Trying to save up for tools and parts. Currently the truck will not be driven on the road until at least next year and that's only if I get my drivers permit and fix the floor pans which entails me buying a $400 welder which will take half a year to save up for. I'm 23, disabled and cant receive disability. So my wealthy friend charitably gives me $100 a month so I can buy things and fix my truck.
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OK so just to fill you all in, I did a final bleed of the brakes and put the tires on. Went for a test drive and didn't notice any dragging or pulling and they stopped nicely. After the very small test drive of less than a mile with very light brake use, I checked the calipers and rotors to see how hot they were. They were moderately warm but I could easily leave my finger on them for a while. Before I changed them they pulled to the left and dragged hard, as the drivers side caliper was siezed and the rubber hose was leaking. Replacing the calipers was on the list of things to do but I was trying to budget towards getting it running and moving first. Stopping was already covered by the locked up rear drum brakes. Well now I hopefully have both done and dusted. My biggest issue is that the truck will not go over 25mph and struggles to take off or go up inclines. I believe that would be the clutch. We have guessed that the clutch plate has been bad for quite some time and it was supposed to be fixed but the ppl that were going to do it never did. So now I am at the dilemma of either fixing it with a clutch kit for around $100 or buying and installing a th350 or some other automatic transmission instead as I don't know how or want to drive manual. As the truck will be for daily driving, towing and light offroading. So my next forum excursion will be to figure out which trans is the best for my needs and what will fit with the least amount of modifications. Thanks for all the help! Close thread.