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800psi enough for manual disc brakes ?
#1290756
08/24/12 10:28 PM
08/24/12 10:28 PM
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Joined: Feb 2003
Posts: 1,646
Ontario,Canada
firefighter3931
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I've been fighting a braking problem for awhile now. Decided to measure the line pressure to my front calipers and came up with 800psi using the SSBC pressure kit. Basic rundown of the car : -original power drum brakes now manual disc -SSBC 4 piston 43mm calipers with 11in slotted rotors -Willwood 1in master cylinder -Hurst line lock to front brakes -proprtioning valve to 11in rear drum brakes *Heavy 68 Charger that sees some strip action...need better brakes  I was also wondering if there are different length brake pedals. Something along the lines of a longer brake arm to increase leverage at the master cylinder to increase line pressure and caliper clamping force.  Mine still has the stock brake pedal that came with the power assisted drum brakes. Thanks in advance for any input  Ron
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Re: 800psi enough for manual disc brakes ?
[Re: BergmanAutoCraft]
#1290759
08/25/12 10:15 AM
08/25/12 10:15 AM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
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Marysville, O-H-I-O
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I thought you needed 1200 for discs? 800-1000 for drums because of how they "self energize" when the shoes grab the drum and shift on the backing plates.
what size master cylinder are you running? you can step down a size in the master to soften the pedal feel and generate more line pressure.
Also, are you using a power brake pedal on a manual brake set-up? I thought there were different pedals with different geometry for power vs manual brakes?
**Photobucket sucks**
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Re: 800psi enough for manual disc brakes ?
[Re: firefighter3931]
#1290760
08/26/12 03:34 AM
08/26/12 03:34 AM
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Joined: May 2003
Posts: 6,566
Downtown Roebuck Ont
Twostick
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Still wishing...
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Quote:
I was also wondering if there are different length brake pedals. Something along the lines of a longer brake arm to increase leverage at the master cylinder to increase line pressure and caliper clamping force.
Mine still has the stock brake pedal that came with the power assisted drum brakes.
Thanks in advance for any input
Ron
You nailed it.
Power brake pedal not the hot ticket for manual brakes. The pedal ratio is a lot less. If you can find a manual pedal and a master with a 15/16 piston I will guess you would see around 1200 psi maybe more. 800 psi and discs must get a little exciting in a not so good way. There are some math formulas that you can calc out pressure for a given pedal ratio/pedal input/master piston size.
AndyF would be a good source for that info.
Kevin
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Re: 800psi enough for manual disc brakes ?
[Re: Twostick]
#1290761
08/26/12 05:20 AM
08/26/12 05:20 AM
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Joined: Jan 2003
Posts: 27,470
So Cal
autoxcuda
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So Cal
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Quote:
Quote:
I was also wondering if there are different length brake pedals. Something along the lines of a longer brake arm to increase leverage at the master cylinder to increase line pressure and caliper clamping force.
Mine still has the stock brake pedal that came with the power assisted drum brakes.
Thanks in advance for any input
Ron
You nailed it.
Power brake pedal not the hot ticket for manual brakes. The pedal ratio is a lot less. If you can find a manual pedal and a master with a 15/16 piston I will guess you would see around 1200 psi maybe more. 800 psi and discs must get a little exciting in a not so good way. There are some math formulas that you can calc out pressure for a given pedal ratio/pedal input/master piston size.
AndyF would be a good source for that info.
Kevin
I don't think every Mopar has a different ratio from manual to power pedel levers.
Years, models for that 
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Re: 800psi enough for manual disc brakes ?
[Re: autoxcuda]
#1290762
08/26/12 10:57 AM
08/26/12 10:57 AM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
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A bodies do not use different pedals, the leverage change is done via the linkage on an A. Not sure about a B though.
Before you get too carried away with anything, make doubly sure you have all the air out of the system.
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: 800psi enough for manual disc brakes ?
[Re: 70Cuda383]
#1290764
08/26/12 02:52 PM
08/26/12 02:52 PM
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Joined: Feb 2003
Posts: 1,646
Ontario,Canada
firefighter3931
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Quote:
I thought you needed 1200 for discs?
That seems to be what i'm reading online from several sources....1000-1200 is the number that comes up.
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Re: 800psi enough for manual disc brakes ?
[Re: Twostick]
#1290765
08/26/12 03:11 PM
08/26/12 03:11 PM
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Joined: Feb 2003
Posts: 1,646
Ontario,Canada
firefighter3931
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Quote:
You nailed it.
Power brake pedal not the hot ticket for manual brakes. The pedal ratio is a lot less. If you can find a manual pedal and a master with a 15/16 piston I will guess you would see around 1200 psi maybe more. 800 psi and discs must get a little exciting in a not so good way. There are some math formulas that you can calc out pressure for a given pedal ratio/pedal input/master piston size.
AndyF would be a good source for that info.
Kevin
Oh it's exciting allright...trying to stop 4100lbs at 125+MPH sure gets interesting. The car should pick up substantially with the new Tq converter so this has me concerned.
Kevin, I've searched and haven't been able to find a manual brake specific brake pedal. Might have to make my own   
From what i've reserched so far : the power brake ratio is 5:1 and the manual brake is 6:1. When i converted mine i remember having to redrill the brake pedal arm to align the pushrod to the master...moved it lower which i'm sure had a negative impact on the ratio. The manual master sits lower in the engine bay and uses a different firewall plate....hence the requirement to redrill a new hole for pushrod alignment. I may be at less than 5:1 ...need to disassemble and do some measurements 
Using the calculator @ Mark Williams racing i came up with a 6.32:1 pedal ratio requirement for 1200 psi using a 1in bore master and 150lbs of foot pressure on the pedal.
Going backwards, i come up with a ratio of 4:1 to achieve 800 psi with 150lbs of force so that's probably what i currently have. 
Ron
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Re: 800psi enough for manual disc brakes ?
[Re: Supercuda]
#1290766
08/26/12 03:13 PM
08/26/12 03:13 PM
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Joined: Feb 2003
Posts: 1,646
Ontario,Canada
firefighter3931
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Quote:
A bodies do not use different pedals, the leverage change is done via the linkage on an A. Not sure about a B though.
Before you get too carried away with anything, make doubly sure you have all the air out of the system.
The brakes have been bled multiple times....over and over and over.
Trust me, there is NO air in that system 
Ron
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Re: 800psi enough for manual disc brakes ?
[Re: autoxcuda]
#1290767
08/26/12 04:34 PM
08/26/12 04:34 PM
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Joined: May 2003
Posts: 6,566
Downtown Roebuck Ont
Twostick
Still wishing...
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Still wishing...
Joined: May 2003
Posts: 6,566
Downtown Roebuck Ont
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Quote:
Quote:
Quote:
I was also wondering if there are different length brake pedals. Something along the lines of a longer brake arm to increase leverage at the master cylinder to increase line pressure and caliper clamping force.
Mine still has the stock brake pedal that came with the power assisted drum brakes.
Thanks in advance for any input
Ron
You nailed it.
Power brake pedal not the hot ticket for manual brakes. The pedal ratio is a lot less. If you can find a manual pedal and a master with a 15/16 piston I will guess you would see around 1200 psi maybe more. 800 psi and discs must get a little exciting in a not so good way. There are some math formulas that you can calc out pressure for a given pedal ratio/pedal input/master piston size.
AndyF would be a good source for that info.
Kevin
I don't think every Mopar has a different ratio from manual to power pedel levers.
Years, models for that
Well that's what assume gets me.  I know C-bodies have a power and a manual pedal. It seemed reasonable to assume a B would too for the same reasons. Has anybody got a pedal from a manual car and a power car to compare? Then we would all KNOW.
Kevin
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Re: 800psi enough for manual disc brakes ?
[Re: firefighter3931]
#1290768
08/27/12 12:14 AM
08/27/12 12:14 AM
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Joined: May 2005
Posts: 723
Houston Tx
Uhcoog1
super stock
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super stock
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What pads do you have on the car?
Normal "street" pads have a coefficient of friction of .3-.4. Race pads might have as high as a .5-.6, almost doubling the friction, which almost doubles the stopping with the same pedal pressure/ line pressure. Keep in mind some may not have a good coefficient until warmed up.
It is definitely worth finding out what the coefficient of friction of your pads are, though I agree that 800 is low.
-'02 Dodge Viper Ex-World Challenge racecar
-'73 Duster, 6.1 based 392 hilborn hemi, tko600, full floater rear 9", Hellwig custom bars, viper brakes, built for road course
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Re: 800psi enough for manual disc brakes ?
[Re: Uhcoog1]
#1290769
08/27/12 08:05 AM
08/27/12 08:05 AM
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Joined: Feb 2003
Posts: 1,646
Ontario,Canada
firefighter3931
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Quote:
What pads do you have on the car?
Normal "street" pads have a coefficient of friction of .3-.4. Race pads might have as high as a .5-.6, almost doubling the friction, which almost doubles the stopping with the same pedal pressure/ line pressure. Keep in mind some may not have a good coefficient until warmed up.
It is definitely worth finding out what the coefficient of friction of your pads are, though I agree that 800 is low.
Thanks for the response Wade. To answer your question ; the brake set-up currently has whatever SSBC provides with their conversion package and there's not much information on their website. I suspect that the pads are nothing special....
I've purchased a set of Hawk HPS pads and will have the rotors resurfaced a few thou for cleanup before reassembly but want to address the low line pressure as well.
Ron
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Re: 800psi enough for manual disc brakes ?
[Re: firefighter3931]
#1290770
08/27/12 03:57 PM
08/27/12 03:57 PM
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Joined: May 2005
Posts: 723
Houston Tx
Uhcoog1
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super stock
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Houston Tx
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As stated above, you could also go with a smaller diameter MC. The amount of foot pressure required is a result of both the pedal ratio and the MC piston size; there is no real advantage to one over the other. The calipers won't care which one you change to get more leverage. That's assuming your pedal wasn't close to bottoming out as-is?
-'02 Dodge Viper Ex-World Challenge racecar
-'73 Duster, 6.1 based 392 hilborn hemi, tko600, full floater rear 9", Hellwig custom bars, viper brakes, built for road course
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Re: 800psi enough for manual disc brakes ?
[Re: firefighter3931]
#1290771
08/27/12 09:12 PM
08/27/12 09:12 PM
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Joined: Jan 2003
Posts: 2,836
Detroit boy in Saugerties, NY
BrianShaughnessy
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master
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Detroit boy in Saugerties, NY
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Ron,
If you can pull a pad out and check for any codes on the back you can probably figure out what they sent by googling.
Aerospace sent dirt track racing pads with their rear disk kit... they made horrendous noise and absolutely sucked on the street. I changed them out for Hawk HPS also. Much better.
Black Betty: '69 Charger RT: 440 6 pack, TKO600 5 speed, 3.73 Dana.
Sinnamon: '69 Charger RT: 440, 727, 4.30 8.75. High School Sweetheart.
El Grande: '98 Grand Cherokee 5.9 Limited.
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Re: 800psi enough for manual disc brakes ?
[Re: hooziewhatsit]
#1290773
09/03/12 05:53 AM
09/03/12 05:53 AM
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Joined: Feb 2003
Posts: 1,646
Ontario,Canada
firefighter3931
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Thanks for the feedback so far  I've looked at the pedal ratio and taken some measurements ; the pedal ratio is 6:1 which seems OK from what i've been reading I was mistaken in my previous post about lowering the pin on the brake pedal when the conversion from power to disc was completed several years ago. I did have to enlarge the brake rod hole slightly for the adjustable pushrod hardware but the hole is still in the original location and the pedal ratio is intact. Next step is going to to be installing the guage directly to the output port on the master and measure line pressure there. This will at least confirm that there are no issues downstream of the master. At this point there is a linelock between the master and calipers so it's possible that the issue lies there but it doesn't seem likely. Ron
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Re: 800psi enough for manual disc brakes ?
[Re: firefighter3931]
#1290774
09/03/12 09:14 AM
09/03/12 09:14 AM
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Joined: May 2005
Posts: 723
Houston Tx
Uhcoog1
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super stock
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Houston Tx
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Do your lines still go through the factory distribution block?
-'02 Dodge Viper Ex-World Challenge racecar
-'73 Duster, 6.1 based 392 hilborn hemi, tko600, full floater rear 9", Hellwig custom bars, viper brakes, built for road course
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Re: 800psi enough for manual disc brakes ?
[Re: Uhcoog1]
#1290775
09/03/12 09:39 AM
09/03/12 09:39 AM
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Joined: Feb 2003
Posts: 1,646
Ontario,Canada
firefighter3931
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Quote:
Do your lines still go through the factory distribution block?
No sir....the rear (large) chamber from the master is plumbed into the Hurst linelock and from there the left and right calipers are plumbed in. Using the Hurst unit as a "T" because it has multiple discharge ports. The factory distribution block was deleted.
Rear brakes go directly to an adjustable proportioning valve that has a residual pressure valve installed.
All brake lines, hardware, wheel cylinders are new.
Thanks, Ron
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