Brake pedal "meh" thinking about braided lines.
#1594487
03/17/14 09:16 PM
03/17/14 09:16 PM
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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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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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RapidRobert
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when it acts up it will not pump up at all?
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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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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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RapidRobert
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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.
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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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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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skicker
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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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west
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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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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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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594507
03/18/14 09:48 AM
03/18/14 09:48 AM
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Joined: Jan 2003
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therocks
oh wait.but hey.lets see.oh yeah.
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oh wait.but hey.lets see.oh yeah.
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get a reman master for a 70 C body with disc/drums.They are all we run.Pedal is always right there.That and make sure the rears are adjusted up.Rocky
Chrysler Firepower
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594521
03/18/14 06:51 PM
03/18/14 06:51 PM
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gdonovan
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Pulled the pads off and it looks like they had uneven contact with the rotor, will head out to take a pic.
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594522
03/18/14 07:03 PM
03/18/14 07:03 PM
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gdonovan
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You can clearly see three spots on the pads where they were not making full contact. Either the pads were not flat out of the box or the caliper and or slides are not totally square to the rotor face.
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: Twostick]
#1594524
03/18/14 08:07 PM
03/18/14 08:07 PM
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gdonovan
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So I'm digging around further and here is what I found- When there is two chunks of steel in the calipers I can clearly see the pistons move out 1/8" and then back in about the same amount when the pedal is released.
This jarred a memory- Is there not suppose to be a residual check valve built into the master cylinder that leaves a pound or three of pressure in the lines for disc brakes? Or do I have it backwards, for drum brakes?
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594525
03/18/14 09:00 PM
03/18/14 09:00 PM
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gdonovan
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In for the night, I can't get a good seal on the banjo fittings. Try again tomorrow..
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594526
03/18/14 10:20 PM
03/18/14 10:20 PM
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can.al
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no check or residual valves for discs...
Last edited by can.al; 03/18/14 10:21 PM.
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Re: Brake pedal "meh" thinking about braided lines.
[Re: west]
#1594529
03/18/14 11:54 PM
03/18/14 11:54 PM
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Quote:
Quote:
no check or residual valves for discs...
That is incorrect.
I'll agree but the OP appears to have all the answers having done thousands of brake jobs throughout his professional career. "NOT his first RODEO". OK I'm done here.
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594533
03/19/14 07:30 AM
03/19/14 07:30 AM
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gdonovan
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For those leaning towards the prop valve, here is the section where the manual clearly states its for metering pressure to the rear brakes to prevent lockup.
I have done this swap several times with great success, I'm starting to think I have a defective master since the rest of the system looks to be up to snuff. Stranger things have happened. I have a lightweight manual master with adapter on my Dart, I'll try swapping it and see what happens.
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594535
03/19/14 08:05 AM
03/19/14 08:05 AM
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slantzilla
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Don't be surprised if your Otterzone rebuilt calipers are junk. I had the same issue on my old Duster and ended up changing calipers.
Had the same experiences with an AZ master. Took 3 of them to get a good one.
"Everybody funny, now you funny too."
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594539
03/19/14 12:03 PM
03/19/14 12:03 PM
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RapidRobert
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Gdonovan you sure are handling the haters on here much better than I would (or have) . It's always a pain when peoples' Mammas dont tuck em in at night then we have to deal with their attitudes. After rereading your OP, with the line lock in the line to the front discs when it's on the pedal is rock solid which tells me that the M/C is good (& it was before) & the rear drum half is good & that the problem is downstream from the line lock which is the front discs. I bet it is the calipers & rebuilt ones are cheap. Keep us updated
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: can.al]
#1594544
03/19/14 08:22 PM
03/19/14 08:22 PM
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Todd
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Quote:
yes,1/8 travel seems far too much.perhaps using a spacer position those pistons further out and re assemble?
Spacer??? Maybe your forgetting how a disc brake caliper work If your pistons are retracting 1/8" that's way to far. Like I stated before the seals are pulling the pistons back to far. They should only retract far enough to let the rotor spin without touching.
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Re: Brake pedal "meh" thinking about braided lines.
[Re: Todd]
#1594545
03/19/14 08:40 PM
03/19/14 08:40 PM
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gdonovan
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Swapped the calipers from Duster <---> GTX, noted the Duster had steel pistons while the GTX had the phenolic resin units. Both calipers had 3699963 part number cast into the back of the drivers side unit.
No road test tonight, have to be up at some ungodly hour of the morning to pull a third shift fire drill. Dinner, Justified and bed!
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: skicker]
#1594548
03/19/14 11:31 PM
03/19/14 11:31 PM
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can.al
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let me explain.. take the calipers off the rotors and using a "spacer" narrower than the rotor,force the pistons further out. re assemble such that they are only about 1/32" off the rotors. now there will be almost no travel.
Last edited by can.al; 03/19/14 11:32 PM.
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594553
03/20/14 09:39 PM
03/20/14 09:39 PM
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gdonovan
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A quick recap, since it looks like I found the problem.
1) Car was pulled into the garage with functioning 4 wheel drum brakes with a .960 manual disc brake master cylinder. No pedal problems.
2) In less than three hours the spindles were swapped out, new lines, rotors, reman calipers and pads were installed. The system was never allowed to bleed out.
3) Pedal quality was poor, multiple efforts to bleed out system with both helper and electric vacuum bleeder tool to no avail.
4) Swapped calipers from known good vehicle, pedal the same.
Tonight I installed a cast iron master cylinder with plastic reservoir and 2 to 4 bolt adapter from my '67 Dart (patiently waiting in the wings) which had manual disc/drum when I purchased it and it worked great. Don't even have an idea what year it is off, former owner mentioned late 80's truck and Autozone.
Did a half ass bleed with the unit in the car and then hooked up the lines. Bleed the master out again by cracking open the lines at the master with a helper.
Now I have an awesome pedal.
So, whats up with that?
Can't wait to road test, hope the ground is froze in the morning and I'll buzz it to work. Been raining here for several hours, driveway is mud pit.
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594556
03/20/14 10:01 PM
03/20/14 10:01 PM
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Todd
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Re: Brake pedal "meh" thinking about braided lines.
[Re: barracuda7199]
#1594558
03/21/14 12:07 AM
03/21/14 12:07 AM
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Quote:
A new aluminum 1 1/32 master cylinder with adapter from doctor diff fixed your same problem on my car. Stops far better than it ever has and has the best pedal it ever had. His masters are going on all our cars from here on out.
Nailed it earlier! Glad you got it straightened out. I will say again that The good doctor diff has the best deal on the new lightweight masters with adapter.
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Re: Brake pedal "meh" thinking about braided lines.
[Re: skicker]
#1594559
03/21/14 07:38 PM
03/21/14 07:38 PM
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gdonovan
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Road test was very successful! Was a riot banging through the gears and then heaving on the brakes watching the twins plastered against the seatbacks.
Would not mind a little more aggressive pad or a master with more pressure, might look into one of the Dr.Diff units!
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: Telvis]
#1594560
03/23/14 08:29 PM
03/23/14 08:29 PM
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gdonovan
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So I have a question while we are still on the subject of brakes- If the St.Regis rotors and caliper adapters work on the A-body spindles does it follow the pads do as well?
Under A-body part numbers there isn't much for good pads but under St.Regis there is several police and taxi pad sets listed.
I was out road testing today and it felt like on the last application of the brakes it felt faded, I don't think the Wagner premium semi-metallic pads I have on there are going to cut it.
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594567
03/23/14 09:47 PM
03/23/14 09:47 PM
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RapidRobert
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I used 2.75" calipers with ceramic pads & they were adequate around town & I never needed to challenge em so I dont know how they'd be under performance conditions. The R calipers are all 2.75" & the bleeder location would likely be different on em & not sure how they interchange & reportedly (by Andy) Andy's bible covers that subject very well. If I wanted more I'd get some 11&3/4" horseshoe adapters/ 11&3/4" rotors. They take the same calipers & I'd do a bed in procedure with some performance pads
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]
#1594569
03/23/14 09:54 PM
03/23/14 09:54 PM
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can.al
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you have increased .140" (more than 1/8") i think 1/16" is about 12% increase in volume...and leg, and will explain the hard pedal with a lot less travel.
Last edited by can.al; 03/23/14 09:55 PM.
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Re: Brake pedal "meh" thinking about braided lines.
[Re: can.al]
#1594573
03/29/14 09:05 AM
03/29/14 09:05 AM
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gdonovan
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Bigger calipers will be here today and the pads have already arrived.
Pads are Wagner SX84/SX7017 severe duty pads.
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594574
04/03/14 10:59 PM
04/03/14 10:59 PM
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gdonovan
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Just an update- Swapped the calipers and pads over last night and bled the system out. Drove the car for about 1/2 hour and worked on bedding the pads in. As expected there is more pedal drop than before due to the larger pistons (2.75" vs 2.60") but the brakes seem to work better. I'm going to drive the car this weekend for a few hours and see where everything settles out. I think the current master is going to stay as with the current caliper and pad setup the pedal drop to pressure ratio if you will seems good to me.
Next step is to move to the rears and get them where they belong with 11 x 2.5" brakes again. Already have two brands of shoes on the way along with new wheel cylinders from e-berg.
Thanks to everyone who chimed in! The car is much more fun to drive with some proper brakes and not diving about.
"I think its got a hemi"
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Re: Brake pedal "meh" thinking about braided lines.
[Re: gdonovan]
#1594575
04/04/14 06:11 PM
04/04/14 06:11 PM
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gdonovan
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Rock Auto strikes again!
I ordered the first set of heavy duty pads and they came in correct so I went ahead and ordered a second set to have on the shelf.... and they are generic junk pads in a generic Big A Automotive box.
sigh.
"I think its got a hemi"
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