Brake pedal "meh" thinking about braided lines.
#1594487
03/17/14 09:16 PM
03/17/14 09:16 PM
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Joined: Jun 2008
Posts: 10,847 Oakdale CT
gdonovan
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Converted my GTX over to 73-76 Dart/Duster disc brakes this weekend and the brake pedal seems like weak sauce. Rebuilt Autozone calipers, Wagner Thermoquiet semi-metalic pads, new rotors and new Wagner brake hoses.
Power bled the calipers with a electric vacuum pump and the old fashion way with an assistant. Clear bleeder hose shows nice clean fluid with no bubbles. Calipers are pointing the correct direction (bleeders UP)
Car has a '74 Disc brake master cylinder with no booster which was on the car when I was running the 11" drums and works fine. If I turn the line lock on and then hit the pedal its iron. If I heave on the pedal with the line lock off the pedal will go 5 or 6 inches down.
Driving the car is a pleasure, I can hit the brakes and the car doesn't dive about like it did with the old drum setup. The car doesn't lock up the brakes but I can stop in a hurry if I bury the pedal as hard as I can.
Admittedly, I only have about 40 miles on the brakes and perhaps the pads still need to be fully burnished in. I'll continue to drive the car and work the pads in but it seems to me even so the pedal could be better. I ran my Dart with the same setup decades ago and don't recall the pedal being this soft with a manual disc setup.
Inline Tube makes braided hoses for the front, good investment? For $60 shipped for the pair chump change that I don't mind spending.
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: RapidRobert]
#1594489
03/17/14 10:05 PM
03/17/14 10:05 PM
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Joined: Jun 2008
Posts: 10,847 Oakdale CT
gdonovan
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I'm 100% positive there is no air in the system, even went as far is to put 26 inches of vacuum on the caliper bleeders and pull a half quart of fluid out on each side.
And then manual bled them with an assistant for good measure.
The rears and master cylinder has already been eliminated as the issue, the line lock is on the front circuit after the master cylinder.
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594490
03/17/14 10:07 PM
03/17/14 10:07 PM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Posts: 36,041
Lincoln Nebraska
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when it acts up it will not pump up at all?
live every 24 hour block of time like it's your last day on earth
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594494
03/17/14 10:28 PM
03/17/14 10:28 PM
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Joined: Jun 2008
Posts: 10,847 Oakdale CT
gdonovan
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Like I said, its possible the pads are not bedded in. Maybe the compound is a bad match for the car without a brake booster. The rotors are new '78 big 11.75" rotors with the Duster slider calipers, one would have thought it will stop better. It did improve somewhat after a long roadtest with lots of heavy braking with cool down between applications.
P.S. the Master cylinder is the 1-1/32" unit if curious.
Last edited by gdonovan; 03/17/14 10:31 PM.
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594495
03/17/14 10:29 PM
03/17/14 10:29 PM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Quote:
but you have to really dig in to get the car to stop with authority and it feels soft.
Alright, I'd take off the front wheels & have a helper work the pedal as you checkout the hoses/pads/calipers for anything wonky. I did have the exact symptom on the stock car once & it was partial blocked flow to the front calipers from using the wrong braided hoses to the calipers that were bent at a bit too much of an angle & was restricting the flow. I had to stand on the pedal to get brakes. EDIT The more I think about it the more I think it's a mechanical hangup with the caliper/pad action
Last edited by RapidRobert; 03/17/14 10:44 PM.
live every 24 hour block of time like it's your last day on earth
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594498
03/17/14 10:45 PM
03/17/14 10:45 PM
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Joined: Sep 2007
Posts: 14,889 up yours
Supercuda
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About to go away
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I suggest you look into what the factory combination valve does before you dismiss having one or think just putting an aftermarket adjustable proportioning valve in is the same.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594503
03/17/14 11:46 PM
03/17/14 11:46 PM
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Joined: Jun 2005
Posts: 5,112 Western Md.
skicker
"The Champ"
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"The Champ"
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Western Md.
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Is it possible the 1 1/32" MC does not provide the volume of fluid needed to make the calipers more aggressive?? You said it used to dive with the drums, which to me means it had substantial front brake. Calipers do require more fluid volume than a wheel cylinder don't they? My 70 Satellite has the same issue. It has a long pedal on the first pump but it stops fine. Its been bled and bled with no difference. Makes my think maybe the M/C bore is the culprit. The line lock comment makes sense when mine is on and you touch the pedal there is nothing but hard line in the system and no way for the pedal to move whatsoever. This is normal.
...FAFO...
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Re: Brake pedal "meh" thinking about braided lines.
[Re: Todd]
#1594504
03/18/14 05:29 AM
03/18/14 05:29 AM
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Joined: Apr 2007
Posts: 4,233 petaluma,ca. u.s.a.
west
master
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master
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petaluma,ca. u.s.a.
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Quote:
Make sure none of the pistons in the calipers are retracting to far after the pedal is released. Had a brand new one do that. Turned out the seal bad and was pulling the piston back 1/8".
I would look into this as well. A residual valve would fix the problem. Either way, the braided lines won't correct the problem.
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Re: Brake pedal "meh" thinking about braided lines.
[Re: skicker]
#1594506
03/18/14 06:53 AM
03/18/14 06:53 AM
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Joined: Jun 2008
Posts: 10,847 Oakdale CT
gdonovan
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Quote:
Is it possible the 1 1/32" MC does not provide the volume of fluid needed to make the calipers more aggressive?? You said it used to dive with the drums, which to me means it had substantial front brake. Calipers do require more fluid volume than a wheel cylinder don't they?
Car already had a disc brake master cylinder on it for the last two years. It is a standard disc brake unit used in millions of Darts, Dusters, Valiants, 71-74.
A 1" bore would increase the pressure but at the expense of more pedal travel.
The pedal is not solid (unless the line lock is on) as it should be and its taking excessive pedal pressure and travel to get the car to stop quickly.
After sleeping on it I'm convinced something is flexing. Maybe one of the caliper slides are tweaked, seals are junk or hoses are no good.
I can swap parts off the Duster, heck I can swap the calipers, brackets, rotors and pads over if need be in an effort to isolate the problem.
"I think its got a hemi"
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