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Brakes drag after 10 minutes.
#1356995 Sat Apr 25 2020 01:42 AM
Joined: Sep 2011
Posts: 1,962
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Lugnutz Offline OP
Shop Shark
Right now I’m so frustrated I can’t think straight.
I just finished installing a new dual brake master cylinder and booster in my 1965C 10 I/2 ton. I was previously using a 1995 Blazer MC and brake booster. The brakes worked fine but I noticed that after 10 or 15 minutes of driving, the brakes would begin to drag. You could let off of the brake pedal on a slight incline and the truck would not coast backwards.
This new master cylinder and brake booster are doing the EXACT SAME THING. My 63 C10 has the exact same MC and brake booster with front disc and rear drums and I have absolutely no problems there.
I am certain that the brake pushrod is allowing the master cylinder plunger to completely return to the home position.
My next thought is that the pistons in the front disc brake calipers are not moving correctly. If this is true, then they do not pull the brake pads completely off the rotor as they should.
Anyone have thoughts on this matter?

Last edited by Lugnutz; Sat Apr 25 2020 01:43 AM.
Re: Brakes drag after 10 minutes.
Lugnutz #1356998 Sat Apr 25 2020 01:53 AM
Joined: Feb 2004
Posts: 20,371
H
Boltergeist
Once the brakes start to drag, stop the truck, chock a wheel front and rear, and loosen the bleeder screws on the calipers. It's possible you're trapping fluid in one or both calipers due to a flex line collapsing inside. If you get a spurt of fluid and the brake drag releases, replace the flex line on the offending side, or both of them if that hasn't been done recently. I've seen several examples of that problem over several years, one of which got so bad a transmission failed because the car owner was too stubborn to stop and call for a tow truck, and kept on driving with the brakes dragging.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Brakes drag after 10 minutes.
Lugnutz #1357002 Sat Apr 25 2020 02:01 AM
Joined: Sep 2011
Posts: 1,962
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Lugnutz Offline OP
Shop Shark
Thanks for your comment Jerry.
So if I understand you correctly, when pressure in the brake lines goes to zero (when I let off of the brake pedal), the flexible brake hose may be collapsing and preventing the fluid behind the caliper piston from going to zero. Right?

Re: Brakes drag after 10 minutes.
Lugnutz #1357005 Sat Apr 25 2020 02:22 AM
Joined: Feb 2004
Posts: 20,371
H
Boltergeist
Yep, I've seen it happen frequently. If the caliper doesn't release when the bleeder is opened and the wheel still drags (jack up the wheel to check that) then you have a sticky piston in the caliper.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Brakes drag after 10 minutes.
Lugnutz #1357018 Sat Apr 25 2020 02:59 AM
Joined: Apr 2005
Posts: 2,529
C
Shop Shark
Someone PLEASE come up with an answer for this. My 37 Buick worked fine for 30 years with a drum-drum dual master cylinder and power booster. Got caught in a dicey situation in Kansas City during a monsoon where the drums were under water so decided to put discs on the front. Put the disc-drum dual mc on and even the hubcaps are hot to the touch after ten miles. Decided the supposed to be 10# drum and 2# disc residual pressure seats in the mc were wrong so to test I put the old mc back on after drilling through the flare seats to eliminate ANY residual pressure. Same thing so replaced new hoses that came with the disc kit with two more new hoses. Same thing. Took some 3/16 steel line with a double loop and replaced rubber line for a (very) temporary test. Same thing. The link from pedal to booster is floppy loose when spring retracts pedal and have shortened the rod from booster to mc till the pedal has gone from near full height to 1.5 iches off the floor. When the car stops as soon as you leave up on the gas I jump out with a 10mm wrench and crack the bleeders which makes it completely free. Summary: NO rubber lines, NO residual pressure valves, rods NOT touching the booster or mc, what's happening? Oh yeah, used spare mc cap with two large vent holes in it for testing. Drove into shop while nearly sliding front wheels and cracked left bleeder--wheel spun free but right side was still nearly locked.


Evan
Re: Brakes drag after 10 minutes.
Lugnutz #1357023 Sat Apr 25 2020 03:28 AM
Joined: Feb 2004
Posts: 20,371
H
Boltergeist
Evan, have you tried swapping to a different caliper on the brake that drags? What's supposed to happen when the pressure releases after a brake application is the square O ring that seals the fluid is also supposed to retract the piston a few thousandths when it returns to "square" after being distorted slightly when the brakes are applied. At times, I have had to do some serious honing of the caliper bore so the piston is a sloppy loose fit. Otherwise, the piston can't retract enough to keep the pads from dragging on the disc. Back when Ford was using plastic caliper pistons, it wasn't a question of IF, but WHEN the brakes would drag. I can't count the number of chrome plated metal caliper pistons I swapped out on early 1980's Ford brakes!
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Brakes drag after 10 minutes.
Lugnutz #1357044 Sat Apr 25 2020 12:55 PM
Joined: Jan 2016
Posts: 557
S
Shop Shark
Along with the already mentioned fixes.........debris in the master cylinder that is blocking the return port with cause brake drag.

Picture is dual master so it shows two circuits.

Attached Files
Re: Brakes drag after 10 minutes.
Lugnutz #1357065 Sat Apr 25 2020 02:43 PM
Joined: Sep 2011
Posts: 1,962
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Lugnutz Offline OP
Shop Shark
UPDATE:
I just drove the truck for 10 minutes and the brakes have gotten really tight. I drove into the shop and put it up on the lift. The rear wheels turn freely with the transmission in neutral. No drag.
The front wheels are so tight I cannot turn them by hand.
So one possibility is simultaneous collapse in both front brake hoses.
The second possibility is that the caliper pistons are not moving smoothly.

Re: Brakes drag after 10 minutes.
Lugnutz #1357068 Sat Apr 25 2020 02:48 PM
Joined: Mar 2019
Posts: 736
G
Shop Shark
Replace all in front, calipers and hoses. Or unless theres a fluid issue of sorts from the master cylinder?

Re: Brakes drag after 10 minutes.
Lugnutz #1357070 Sat Apr 25 2020 02:52 PM
Joined: Feb 2004
Posts: 20,371
H
Boltergeist
Did you try opening the bleeder screws to see if the drag goes away? That's the best way to tell the difference in restricted hoses or sticky calipers.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Brakes drag after 10 minutes.
Lugnutz #1357073 Sat Apr 25 2020 03:00 PM
Joined: Sep 2011
Posts: 1,962
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Lugnutz Offline OP
Shop Shark
There was a squirt of fluid from the bleeder valve and I can now turn the rotor by hand, BUT . . . . there is still some drag on the rotor. So I’m not 100% sure I know which it is, or both.

Last edited by Lugnutz; Sat Apr 25 2020 03:10 PM.
Re: Brakes drag after 10 minutes.
Lugnutz #1357077 Sat Apr 25 2020 03:25 PM
Joined: Sep 2011
Posts: 1,962
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Lugnutz Offline OP
Shop Shark
I did not divulge every piece of information at the beginning of this thread. I did not want to complicate the issue since there were so many factors involved.
Here is what we now know to be true.
1. The front brakes get tighter and tighter. The rear brakes are fine.
2. When I open the front caliper bleeder valve, there is a squirt of fluid. This indicates that pressure is being retained in the front brake lines somewhere.
3. When I opened the opposite side front caliper bleeder valve, there was no indication of retained pressure. Both rotors now turn freely.

This would seem to indicate that the brake hoses are not collapsed. If both brake hoses were collapsing, I would think there would be a squirt of fluid from each caliper. Yet, both front wheels were too tight to turn by hand until I released pressure from one of the bleeder valves. Once I released pressure from one of the bleeder valves, both rotors could be turned by hand.

Now please don’t be mad at me for withholding the following information. (Or, you can be mad if you want, just don’t tell me).
I am using an adjustable brake bias on the rear brake line. I have it adjusted to the middle position. If this brake bias device is malfunctioning, perhaps it is not allowing the MC piston to return to the home position, even though the brake pedal push rod is loose and free. However, if that is the case, then I would think I would build pressure in the rear lines, since the two circuits are independent. Is it possible that the brake bias is hindering the MC piston from returning to the home position?

Attached Files
C68CE1D7-A6B7-4081-AF4D-577051DFE3B1.jpeg (214.74 KB, 120 downloads)
F6C5EEC0-F526-454E-B545-8AAF6A834FC7.jpeg (200.23 KB, 121 downloads)
Last edited by Lugnutz; Sat Apr 25 2020 03:28 PM.
Re: Brakes drag after 10 minutes.
Lugnutz #1357086 Sat Apr 25 2020 04:04 PM
Joined: Mar 2019
Posts: 736
G
Shop Shark
Hmmm. Drive it again. Get em stuck. Open the rear bleeder at the master and see what if any thing happens. If not open the front at the master. To have both stuck and free up after only opening 1 side indicates that it has to do with a common denominator, master cylinder is all i can suggest without being there and experiencing it for my self.

Re: Brakes drag after 10 minutes.
Lugnutz #1357091 Sat Apr 25 2020 04:28 PM
Joined: Feb 2004
Posts: 20,371
H
Boltergeist
Expecting all the drag to go away is not realistic. The pads are going to remain in contact with the rotor. If opening one bleeder frees up both brakes, you're holding pressure in the front brake lines, probably all the way back to the master cylinder. Try loosening a line at the master cylinder and see if you get a pressure squirt there the nexct time the brakes drag.

I would be reluctant to use ANY sort of aftermarket pressure control device that the factory engineers didn't include in the original system- - - -chances are it was invented by some hotrodder who is going to solve all your problems by selling you something! P.T. Barnum would have been a good parts salesman!
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Brakes drag after 10 minutes.
Lugnutz #1357108 Sat Apr 25 2020 06:09 PM
Joined: Mar 2013
Posts: 176
Q
Shop Shark
Are you using a proportional valve in the system? That failing has been my experince with having both front brakes gradualy locking up and staying locked up. If you have one there and have replaced everything but that,then give it a whirl.

Re: Brakes drag after 10 minutes.
glenns towing #1357118 Sat Apr 25 2020 07:36 PM
Joined: Jan 2016
Posts: 557
S
Shop Shark
Originally Posted by glenns towing
Replace all in front, calipers and hoses. Or unless theres a fluid issue of sorts from the master cylinder?


Why would you ever start replacing parts with out finding the cause problem ?????

This could be as simple that the brake push rod is not returning completely or the five other things already mentioned,

Think it been already narrowed down to the master, proportioning valve and associated hardware.

Last edited by showkey; Sat Apr 25 2020 07:42 PM.
Re: Brakes drag after 10 minutes.
Lugnutz #1357125 Sat Apr 25 2020 09:15 PM
Joined: Sep 2011
Posts: 1,962
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Lugnutz Offline OP
Shop Shark
UPDATE!
I eliminated the rear brake circuit brake bias. I joined the rear lines with a union nut. No more brake bias.

Took it for a drive. Brakes tighten up within 10 minutes. Same as before. At least we know not to blame the brake bias.

My next step is to disconnect the front hard lines from the hoses and check flow back towards the MC. There is only one T junction block in the front circuit.

FYI: I’m using 1/4” hard line from the MC to the brake hoses with a 1/4” to 3/16” adapter nut at the front brake hoses because the hoses only accept that size thread. Most Chevy front disc brake hoses use a 3/16” hard line nut.

Attached Files
Last edited by Lugnutz; Sat Apr 25 2020 09:16 PM.
Re: Brakes drag after 10 minutes.
Lugnutz #1357131 Sat Apr 25 2020 10:31 PM
Joined: Apr 2005
Posts: 8,664
Grease Monkey, Moderator General Truck Talk & Greasy Spoon
I know you said the brake push rod was properly adjusted, but, just for funzies , back it off a couple of turns and try the test drive again. Don’t ask me how I know.🛠


Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne 4dr 230 I-6 one owner (I’m #2)
‘39 Dodge Businessmans Coupe
USAF 1965-69 Weather Observation Tech (got paid to look at the clouds)


"I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!

Re: Brakes drag after 10 minutes.
Lugnutz #1357134 Sat Apr 25 2020 10:39 PM
Joined: Feb 2004
Posts: 20,371
H
Boltergeist
Since a dual chamber master cylinder has a piston for each circuit, it's possible that one relief port is getting uncovered and the other one isn't. I can remember one incident where it took three master cylinders before I found one that didn't cause a set of front brakes to drag.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Brakes drag after 10 minutes.
Justhorsenround #1357139 Sat Apr 25 2020 10:54 PM
Joined: Sep 2011
Posts: 1,962
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Lugnutz Offline OP
Shop Shark
Originally Posted by Justhorsenround
I know you said the brake push rod was properly adjusted, but, just for funzies , back it off a couple of turns and try the test drive again. Don’t ask me how I know.🛠
“Been there, done that, got the T-shirt“ as they say. I will do as you ask. That was my first thought BEFORE I swapped out the old MC and booster for a new one. The reason I wanted a new MC and booster was so I could go back to my factory air intake and filter. My Blazer booster was too big and in the way. I’ve already done this same setup in my 63 and I love it.

Attached Files
Re: Brakes drag after 10 minutes.
Lugnutz #1357142 Sat Apr 25 2020 11:25 PM
Joined: Apr 2005
Posts: 8,664
Grease Monkey, Moderator General Truck Talk & Greasy Spoon
As Jerry just mentioned, you could have a bad M/C, I too have had that issue.


Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne 4dr 230 I-6 one owner (I’m #2)
‘39 Dodge Businessmans Coupe
USAF 1965-69 Weather Observation Tech (got paid to look at the clouds)


"I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!

Re: Brakes drag after 10 minutes.
Lugnutz #1357146 Sat Apr 25 2020 11:35 PM
Joined: Sep 2011
Posts: 1,962
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Lugnutz Offline OP
Shop Shark
Justhorsenround,
I backed the pushrod up 1/4” and went for a drive. About lap 3 around the block I began to panic because I sure I was gonna have to eat humble pie. But by lap 6 I began to feel the drag again. You had me sweating big time. The push rod is sloppy loose and the brakes are tight as a tick right now.
So I’m back to looking at a problem with either the MC or something in the front lines that restricts return flow to the MC.
I even ran the engine at idle in the driveway until it got hot under the hood. The exhaust downpipe was 250* but the brake hard lines were 150* at the level of the frame where they are closest to the downpipe. I pumped the pedal repeatedly but could not get it to tighten up like it does when driving.

Attached Files
Last edited by Lugnutz; Tue Apr 28 2020 01:33 PM.
Re: Brakes drag after 10 minutes.
Lugnutz #1357151 Sat Apr 25 2020 11:42 PM
Joined: Aug 2000
Posts: 1,372
D
Shop Shark
Maybe I missed you saying, but are you using a 2# residual valve on the fronts? If so, maybe it is failing? Or, there is a 10# one there?

Dennis


40 Chevy 1/2 ton
Re: Brakes drag after 10 minutes.
Lugnutz #1357152 Sat Apr 25 2020 11:51 PM
Joined: Mar 2019
Posts: 736
G
Shop Shark
Do you have a known good master cylinder? If not, buy one, it wont goto waste. If you eliminated the rear, and cracked the front bleeder like i mentioned a while ago, and the brakes loosened. Bingo.

Re: Brakes drag after 10 minutes.
Lugnutz #1357172 Sun Apr 26 2020 01:23 AM
Joined: Sep 2011
Posts: 1,962
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Lugnutz Offline OP
Shop Shark
I just had a thought. The current set up consists of a 1970’s Corvette style master cylinder. I’ve seen lots of cars and trucks use these when they upgrade to disc brakes. The MC piston has a place for the pedal pushrod for applications when a booster is not used. With a booster, a short piece of steel rod is inserted in the back of the MC piston to fill that hole and provide a place for the booster pushrod to push on to move the MC piston. If the steel rod is too long, then the master cylinder would never be able to fully retract to the home position but on the bench, the MC would work normally during the bench bleed. What do you think?
You can see the steel rod in question in this picture. Am I crazy?

Attached Files
B9B92FEB-B2B3-44F2-8129-33EBF6E292A1.jpeg (106.91 KB, 120 downloads)
Re: Brakes drag after 10 minutes.
Lugnutz #1357181 Sun Apr 26 2020 02:12 AM
Joined: Feb 2004
Posts: 20,371
H
Boltergeist
Get a piece of cold rolled round stock the same diameter as the spacer, and cut off a piece about 1/8" shorter, and try a test drive with the short piece installed. You won't be making any sort of permanent modification that can't be reversed by simply reinstalling the original part.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Brakes drag after 10 minutes.
Lugnutz #1357202 Sun Apr 26 2020 03:05 AM
Joined: Sep 2011
Posts: 1,962
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Lugnutz Offline OP
Shop Shark
Ladies and gentlemen! I am happy to bring this story to an end.

The problem was the intermediate pushrod between the booster and the MC. It was approximately 1/8” too long. This was not noticeable when bolting the MC to the booster during assembly. However, once the MC was bolted to the booster, the piston in the MC was pushed in 1/8” and no longer at the “home” position. That means the MC piston was never able to properly release pressure from the front lines. So pressure in the front brakes would just keep building.

I removed the intermediate rod and functionally shortened it by drilling out the center about 1/8” so the nipple on the booster rod had more room. Put it all back together. Test drive and NO MORE DRAGGING OF THE BRAKES!

Time for a HAPPY DANCE!

Attached Files
31C85DEF-61E8-49B9-8316-1067B2280BD6.jpeg (125.76 KB, 107 downloads)
5F87245D-1D20-4798-9AE4-50CC529D288A.jpeg (191.12 KB, 111 downloads)
2CA6A5BF-040B-42DB-BC08-7E9D321015F2.jpeg (266.25 KB, 105 downloads)
Re: Brakes drag after 10 minutes.
Lugnutz #1357209 Sun Apr 26 2020 03:52 AM
Joined: Feb 2004
Posts: 20,371
H
Boltergeist
Look at your photo of the booster- - - - -that looks a lot like a bolt and a lock nut where the plunger pushes the master cylinder. Dimpling the adapter accomplished the same thing, but in case you need to make any further adjustments, you can fine tune it in either direction without doing any more drilling.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Brakes drag after 10 minutes.
Hotrod Lincoln #1357212 Sun Apr 26 2020 04:15 AM
Joined: Sep 2011
Posts: 1,962
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Lugnutz Offline OP
Shop Shark
Originally Posted by Hotrod Lincoln
Look at your photo of the booster- - - - -that looks a lot like a bolt and a lock nut where the plunger pushes the master cylinder. Dimpling the adapter accomplished the same thing, but in case you need to make any further adjustments, you can fine tune it in either direction without doing any more drilling.
Jerry
Yes, I tried to adjust that first while my wife patiently held the MC so it wouldn’t bend the brake lines. No matter what I did, it didn’t seem to change the booster rod tip length. So I resorted to drilling the spacer for the same result.

Re: Brakes drag after 10 minutes.
Lugnutz #1357231 Sun Apr 26 2020 12:39 PM
Joined: Apr 2005
Posts: 8,664
Grease Monkey, Moderator General Truck Talk & Greasy Spoon
Don’t you just love it when a plan comes together. Good job.🛠


Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne 4dr 230 I-6 one owner (I’m #2)
‘39 Dodge Businessmans Coupe
USAF 1965-69 Weather Observation Tech (got paid to look at the clouds)


"I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!

Re: Brakes drag after 10 minutes.
Lugnutz #1357262 Sun Apr 26 2020 04:19 PM
Joined: Mar 2019
Posts: 736
G
Shop Shark
Congrats. Glad you found it.

Re: Brakes drag after 10 minutes.
Lugnutz #1357682 Wed Apr 29 2020 01:58 AM
Joined: Jun 2008
Posts: 1,394
S
Shop Shark
Great diagnostic work! Congrats!!!


Chuck
1950 Chevy 1/2 ton (original)
1951 Chevy 1/2 ton (future streetrod)
1941 Chevy coupe
1938 Chevy coupe streetrod
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