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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
L
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
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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: 8,662
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
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USAF 1965-69 Weather Observation Tech (got paid to look at the clouds)


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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
L
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.

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