Author Topic: 68 brake issue  (Read 1030 times)

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Offline smines80

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68 brake issue
« on: February 09, 2019, 07:26:12 pm »
Need help, I cannot get enough pressure to the LF caliper on my 68.  It bleeds, but provides little pressure. I can still turn it by hand.  I'll list everything thats been done.

1.  Original booster that was rebuilt in Oct by Daves.
2.  Original calipers just rebuilt by me with kits from NPD.
3.  All new brake lines from NPD.
4.  New distribution block from NPD.

  I've pulled the caliper, hose and line several times hoping to find something wrong.  Caliper bolt isnt blocked.  Other three bleed fine and have good holding pressure.  Perhaps I got a bad distribution block from NPD?  Thanks.

Shannon
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Offline Coralsnake

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Re: 68 brake issue
« Reply #1 on: February 09, 2019, 09:12:57 pm »
There are left and right calipers, do you have them on the correct sides?

Offline Brian Conway

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Re: 68 brake issue
« Reply #2 on: February 09, 2019, 09:16:02 pm »
First guess would be a stuck caliper piston.  Pull a pad/s and check how much movement you get pressing on the brake pedal ?  Brian
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Offline smines80

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Re: 68 brake issue
« Reply #3 on: February 09, 2019, 10:31:10 pm »
The calipers were mounted correctly.  I've pulled the caliper off several times, and gone through it, the piston does stick some.  But I've also tried another caliper, from OReillys.  It had the same problem, bled but didnt provide much holding pressure.

Offline 6t8-390gt

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Re: 68 brake issue
« Reply #4 on: February 09, 2019, 11:08:17 pm »
You stated the "lines" were replaced, did that include the hoses?  Brake hose may have collapsed if you did not replace them.

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Offline Kent

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Re: 68 brake issue
« Reply #5 on: February 10, 2019, 04:42:40 am »
How did you bleed the brakes?

Offline dragpack

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Re: 68 brake issue
« Reply #6 on: February 10, 2019, 05:55:18 am »
Sounds like a defective brake hose



Offline smines80

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Re: 68 brake issue
« Reply #7 on: February 10, 2019, 09:09:22 am »
Brake hoses are new, so doubt that's the issue.  Wondering if I can take the RF caliper off and put it on the LF, bleed and see if it hold. Then I can determine if its a issue with the caliper(s) or the distribution block.  I know the bleeder will face to the back instead of straight up.  FYI, I did not bench bleed the master cylinder, but everything else has bleed just fine and is still holding good pressure.  Went back around again just for the heck of it.  Just the dern LF. 

Offline rhjanes

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Re: 68 brake issue
« Reply #8 on: February 10, 2019, 10:01:55 am »
Just guessing/thinking out loud.  You didn't bleed the master before installing?  The one time I did that, was a mess (but more than one brake wasn't clamping much).  I'm wondering if since he LF is closest to the master (shortest line run), a lot of the air from the master went to the LF? 

Wonder if you took that caliper off, took it apart checking for torn seal and smooth bore.  Maybe some way to let gravity just allow the brake lines to drip for say a pint of fluid (watch to keep the master full).

Just some thoughts. 
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Offline RoyceP

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Re: 68 brake issue
« Reply #9 on: February 10, 2019, 10:11:14 am »
You can't do that because it will not bleed if it is swapped with the other side. When the calipers are installed correctly the bleeders point to the rear of the car.

If fluid comes out of the caliper when bleeding then it is not an issue with the distribution block or master cylinder. Maybe the caliper is incorrectly assembled to the bracket? Brakes are pretty simple, it is likely an installer issue rather than a defective part in my experience.


Brake hoses are new, so doubt that's the issue.  Wondering if I can take the RF caliper off and put it on the LF, bleed and see if it hold. Then I can determine if its a issue with the caliper(s) or the distribution block.  I know the bleeder will face to the back instead of straight up.  FYI, I did not bench bleed the master cylinder, but everything else has bleed just fine and is still holding good pressure.  Went back around again just for the heck of it.  Just the dern LF.
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Offline 69cobrajetrugae2

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Re: 68 brake issue
« Reply #10 on: February 10, 2019, 07:04:20 pm »
1. 1500 PSI gauges with a bleeder valve.

Take the pads out and install shims or worn pads and check for a bind.

If a brake line is crushed but not completely then the pressure should equalize across the restriction but might take 5 minutes of hard brake pedal effort to so and lock the rotor.

If this is the issue then conversely it might take a few minutes to relieve the pressure so that the rotor will release.

If there is a kink in the line then it might be hidden on the back side of a 3/16 line next to the frame.

The master cylinder might be bad, the disc piston seal might be bypassing or there is a casting flaw.

The proportioning valve is used for a switch or pressure delay or both to the rear brakes.  I would clean the original or source an OEM one if required.

In my opinion never use new brake parts because issues like this are par for the course.

The new lines should be flow checked there might be a bee or wasp or chunk of material from the manufacturing process in there, if the part is new I assume it's bad unless I can prove otherwise.

If all else fails see number 1.  Good luck.


Offline smines80

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Re: 68 brake issue
« Reply #11 on: February 10, 2019, 07:57:15 pm »
When calipers are installed on correct side, bleeders face up, not back.  The proportioning valve on the distribution block is new.  All one unit on this car.  The RF caliper and rear wheel cylinders have plenty of pressure.  The LF bled fine, just doesnt have much pressure.  Maybe a air lock in the block, I'll keep bleeding.  NPD said they'd swap it out if it doesnt work.  But dern, taking those things in and out with everything else is a pain!     

Offline Brian Conway

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Re: 68 brake issue
« Reply #12 on: February 10, 2019, 09:09:14 pm »
Your left front caliper/bleeder looks like this ?  Brian
« Last Edit: February 10, 2019, 09:36:19 pm by Brian Conway »
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Offline smines80

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Re: 68 brake issue
« Reply #13 on: February 10, 2019, 10:15:56 pm »
Whoa, thats how the 69s are?  I thought I read and was told to have the bleeder going up on my 68.  Maybe thats all I have wrong, sure hope so.  I'll look into that again.
« Last Edit: February 10, 2019, 10:30:50 pm by smines80 »

Offline smines80

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Re: 68 brake issue
« Reply #14 on: February 10, 2019, 10:30:09 pm »
My LF.  Reckon I got them on wrong.   I'll swap them out tomorrow, everything will probably work just fine.