Author Topic: 68 GT500KR Brake Woes  (Read 389 times)

EmeraldMC

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68 GT500KR Brake Woes
« on: October 05, 2019, 03:02:27 PM »
So here's what I've got: The car has been in the family since new, from my uncle to my dad to me.  It's got under 46K on it.

I went thru the brakes last year, changing the fluid, replacing MC, calipers, and rotors, and adjusting the shoes, and bleeding it.  Stopped pretty decent.  Then a few weeks later the booster went out, so I had it rebuilt and the proportioning valve and distribution block rebuilt as well. After reassembling everything and bleeding it there's a good pedal feel when the motor is off. 

As soon as I start it, the pedal goes waaaay down, and then sinks a little further.  It stops, but pulls to the right.  When I start checking things, there's no flow to the LF caliper, explaining the pull tot he right.  It has good flow on all other three wheels, the rear brakes are properly adjusted, the bleed screws on the calipers are in the right position, I bench bled the MC.

I've bled a couple of gallons thru it, and I'm stumped - its as if the piston in the distribution block is going all the way to the front, blocking the LF port.  I even got a repro distribution block and proportioning valve assembly from Tony Branda to see if the rebuild of my originals was not up to snuff.  Exact same behavior.

Any ideas on what to check, as I'm out of ideas, and frustrated over not being able to drive the car.

Thanks for any help,

Eric Mullins

Coralsnake

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Re: 68 GT500KR Brake Woes
« Reply #1 on: October 05, 2019, 03:07:38 PM »
Did you put the caipers on correctly?

Can you share a picture of them installed?
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acman63

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Re: 68 GT500KR Brake Woes
« Reply #2 on: October 05, 2019, 04:18:23 PM »
did you have the special tool in the junction block when you bled the brakes. Theres a shaft in there and you take the plastic switch out  and if the hole is empty,  insert the tool,  bleed the brakes then put the switch back in

NPD  has em  $10
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EmeraldMC

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Re: 68 GT500KR Brake Woes
« Reply #3 on: October 05, 2019, 04:26:12 PM »
yep, I've got the tool. 

It'll be Monday before I can get a picture of the calipers.  I'll do it then, anything else that would be helpful w a pic?

Coralsnake

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Re: 68 GT500KR Brake Woes
« Reply #4 on: October 05, 2019, 05:44:36 PM »
Lets start ther, as installed from the inboard side so we can look at the bleeders
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Corey Bowcutt

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Re: 68 GT500KR Brake Woes
« Reply #5 on: October 05, 2019, 07:10:08 PM »
acman63,

What happens if you bleed your brakes and did not use this tool?  I have never heard of this tool before and I have bled my breaks twice.  I do have an issue with my brakes but sounds significantly different from what the OP has.  My breaks feel nice when you press lightly on the pedal.  But if you push harder the brakes to not get any better and is seems the peddle bottoms out.  I could never lock up my brakes if I wanted to.  Would this be the result of not using this tool when bleeding the brakes?  If not any idea what the issue is? Master cylinder? Power booster?...

Corey

TLea

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Re: 68 GT500KR Brake Woes
« Reply #6 on: October 07, 2019, 06:39:22 AM »
Calipers installed backwards nor not using the lock tool will isolate left side from right. The tool keeps plunger from shifting front to back if brake failure but not side to side.
You say no fluid to LF caliper but yes to right. Start there. Loosen hose from LF caliper slightly and step on pedal. If flow caliper issue, if no move back to cracking brake line from LF at distribution block. If flow line problem. If no problem with distribution block.
As a sidebar I have seen many times calipers installed backwards (left and right) In correct position bleeder points towards rear of car not up

69 GT350 Vert

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Re: 68 GT500KR Brake Woes
« Reply #7 on: October 07, 2019, 09:26:05 AM »
Calipers installed backwards nor not using the lock tool will isolate left side from right. The tool keeps plunger from shifting front to back if brake failure but not side to side.
You say no fluid to LF caliper but yes to right. Start there. Loosen hose from LF caliper slightly and step on pedal. If flow caliper issue, if no move back to cracking brake line from LF at distribution block. If flow line problem. If no problem with distribution block.
As a sidebar I have seen many times calipers installed backwards (left and right) In correct position bleeder points towards rear of car not up

Great information in this thread.  I didn't know about this tool to replace the shaft.  What if the hole is not empty and the mechanism is not centered in the hole?  How can I re-center it?  After I replaced all my brake lines and rebuilt the entire system, I left my brake light harness connector disconnected because it always turns on.   

shelbydoug

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Re: 68 GT500KR Brake Woes
« Reply #8 on: October 07, 2019, 09:33:58 AM »
I didn't read the entire thread but if it wasn't already suggested, you probably just need to change out the bleeder valves in the calipers. Those things freeze closed in time.

Donmo

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Re: 68 GT500KR Brake Woes
« Reply #9 on: October 10, 2019, 09:15:27 PM »
What's the chance of a collapsed brake hose to the LF caliper?