|
Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: Stanton]
#1692689
11/01/14 08:25 PM
11/01/14 08:25 PM
|
Joined: Feb 2010
Posts: 1,645
Phila. Pa.
Mattax
top fuel
|
top fuel
Joined: Feb 2010
Posts: 1,645
Phila. Pa.
|
Quote:
Quote:
I would put in a correct MC for your application
Where's the fun in that ?!?!
He's probably close - The thing is, and what each hot rodder needs to figure out for their specific situation, is how much the brake system's balance has been altered. This is when it's worth getting a good book (like Carrol Smith or Fred Puhn's Brake Handbook) and going over scenario on paper.
For example, lets look at someone swapping front calipers. Lets ignore the disk diameter and just look at hydraulics. A stock '69 B-body would have come with Bendix calipers that had a total of 4, two inch diameter pistons. This equals 12.59 quare inches. Now how does that compare to the area of the calipers being changes too? How much difference in force applied from the stock system? This is the type of pencil and paper work that will reveal whether more or less master cylinder pressure may be needed to get the pad forces needed.
Back to the OP's Master Cylinder.
Hydraulic pressure = Force on piston from pushrod / Area of piston
1" piston, Area = .7854 sq inches
1 1/32 piston, Are = .8353 sq inches
1 1/8" piston, Area = .9949 sq inches
Therefore, for the same pedal force, we can see the effect of each of these on system pressure.
Lets say a gentle pedal puts 100 pounds force on all three piston sizes. The 100 pounds force in this example is at the pushrod, the foot is applying a lot less than that to the pedal. How much less depends on the pedal ratio - a number I don't have off-hand.
1" piston => 127 psi
1 1/32 piston => 120 psi
1 1/8" piston => 100 psi
You can see that changing to a 1" master cylinder from the 1 1/32 master that the OP already has, will make only a slight difference in pressure in the system for the any given foot pressure. Even if he stands on the brake pedal and puts 500 pounds into the pushrod, the difference in hydraulic pressure will be 600 vs 635 psi.
|
|
|
Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: Mattax]
#1692690
11/01/14 09:15 PM
11/01/14 09:15 PM
|
Joined: Jan 2003
Posts: 4,323
NY NY
340duster340
master
|
master
Joined: Jan 2003
Posts: 4,323
NY NY
|
Are the front and rear lines run from the correct ports on the master?
1966 Dart GT
...down to only 1 mopar for the first time in 15 years!
|
|
|
Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: 340duster340]
#1692691
11/01/14 10:02 PM
11/01/14 10:02 PM
|
Joined: Oct 2005
Posts: 8,869
Ontario, Canada
Stanton
Don't question me!
|
Don't question me!
Joined: Oct 2005
Posts: 8,869
Ontario, Canada
|
Quote:
He's probably close - The thing is, and what each hot rodder needs to figure out for their specific situation, is how much the brake system's balance has been altered. This is when it's worth getting a good book (like Carrol Smith or Fred Puhn's Brake Handbook) and going over scenario on paper.
For example, lets look at someone swapping front calipers. Lets ignore the disk diameter and just look at hydraulics. A stock '69 B-body would have come with Bendix calipers that had a total of 4, two inch diameter pistons. This equals 12.59 quare inches. Now how does that compare to the area of the calipers being changes too? How much difference in force applied from the stock system? This is the type of pencil and paper work that will reveal whether more or less master cylinder pressure may be needed to get the pad forces needed.
Back to the OP's Master Cylinder.
Hydraulic pressure = Force on piston from pushrod / Area of piston
1" piston, Area = .7854 sq inches
1 1/32 piston, Are = .8353 sq inches
1 1/8" piston, Area = .9949 sq inches
Therefore, for the same pedal force, we can see the effect of each of these on system pressure.
Lets say a gentle pedal puts 100 pounds force on all three piston sizes. The 100 pounds force in this example is at the pushrod, the foot is applying a lot less than that to the pedal. How much less depends on the pedal ratio - a number I don't have off-hand.
1" piston => 127 psi
1 1/32 piston => 120 psi
1 1/8" piston => 100 psi
You can see that changing to a 1" master cylinder from the 1 1/32 master that the OP already has, will make only a slight difference in pressure in the system for the any given foot pressure. Even if he stands on the brake pedal and puts 500 pounds into the pushrod, the difference in hydraulic pressure will be 600 vs 635 psi.
The later model calipers all have pistons that are about 2.75" diameter ('76 Cordoba), the area being roughly 6 inches ... half of the stock '69's !!
That said, using the same system but with the later calipers it would take less pedal to compress the piston BUT with less area it requires more pressure. Therefore, you'd want a smaller bore m/c which would take more pedal but be applying more pressure for the same effort.
This is all fine and dandy for disc to disc conversion but drum to disc conversions are a whole different ball of wax.
|
|
|
Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: Stanton]
#1692692
11/01/14 10:44 PM
11/01/14 10:44 PM
|
Joined: May 2005
Posts: 4,718
Florida
BDW
master
|
master
Joined: May 2005
Posts: 4,718
Florida
|
Quote:
Quote:
He's probably close - The thing is, and what each hot rodder needs to figure out for their specific situation, is how much the brake system's balance has been altered. This is when it's worth getting a good book (like Carrol Smith or Fred Puhn's Brake Handbook) and going over scenario on paper.
For example, lets look at someone swapping front calipers. Lets ignore the disk diameter and just look at hydraulics. A stock '69 B-body would have come with Bendix calipers that had a total of 4, two inch diameter pistons. This equals 12.59 quare inches. Now how does that compare to the area of the calipers being changes too? How much difference in force applied from the stock system? This is the type of pencil and paper work that will reveal whether more or less master cylinder pressure may be needed to get the pad forces needed.
Back to the OP's Master Cylinder.
Hydraulic pressure = Force on piston from pushrod / Area of piston
1" piston, Area = .7854 sq inches
1 1/32 piston, Are = .8353 sq inches
1 1/8" piston, Area = .9949 sq inches
Therefore, for the same pedal force, we can see the effect of each of these on system pressure.
Lets say a gentle pedal puts 100 pounds force on all three piston sizes. The 100 pounds force in this example is at the pushrod, the foot is applying a lot less than that to the pedal. How much less depends on the pedal ratio - a number I don't have off-hand.
1" piston => 127 psi
1 1/32 piston => 120 psi
1 1/8" piston => 100 psi
You can see that changing to a 1" master cylinder from the 1 1/32 master that the OP already has, will make only a slight difference in pressure in the system for the any given foot pressure. Even if he stands on the brake pedal and puts 500 pounds into the pushrod, the difference in hydraulic pressure will be 600 vs 635 psi.
The later model calipers all have pistons that are about 2.75" diameter ('76 Cordoba), the area being roughly 6 inches ... half of the stock '69's !!
That said, using the same system but with the later calipers it would take less pedal to compress the piston BUT with less area it requires more pressure. Therefore, you'd want a smaller bore m/c which would take more pedal but be applying more pressure for the same effort.
This is all fine and dandy for disc to disc conversion but drum to disc conversions are a whole different ball of wax.
That's a misconception, the 4 smaller pistons aren't 2x the single big piston.
You only use 2 of the pistons, they are pushing on each other.
4 piston Area = Pi*R^2 = 2*(3.14 x 1^2)= 6.28
Single piston = 3.14 x (2.75/2)^2 = 5.94
Less, but not 1/2 as much
|
|
|
Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: BDW]
#1692693
11/01/14 11:36 PM
11/01/14 11:36 PM
|
Joined: Feb 2010
Posts: 1,645
Phila. Pa.
Mattax
top fuel
|
top fuel
Joined: Feb 2010
Posts: 1,645
Phila. Pa.
|
Whoa guys! We're mixing my first two paragraphs about how changes in calipers etc can effect a system (side topic) with the rest of my post about the possibility that the bore of the OP's master cylinder could be the cause of his problems. All the bore diameters listed in the second part of my post refer specifically to the pistons in the Master Cylinders.
As far as the calipers go, I do agree that IF we were going to be considering a swap from a 4 piston Bendix caliper to Cordoba caliper, we'ld want to consider fluid at displacement. Now as far as force goes; If the MC stayed the same and the amount of force applied to the brake pedal stayed the same, the pressure applied to the front brakes would stay the same, athough there would be less pedal travel.
Then at the calipers, we have to reverse the calculation to figure the force applied to the pads.
The force on one pad using Bendix calipers is 6.3 sq. in. x Pressure.
The force on one pad using a Cordoba caliper with a piston of 6 sq. in x Pressure.
Not quite the same, but in the same ballpark. At say 500 psi the Bendix would be applying 3150 pounds force and the Cordoba pad would be getting 3000 pounds force.
A more complete braking force comparison should also consider effective radius and swept area...
I also agree that drum to disk is a very different animal to calculate and fortunately we don't need to do that here!
Last edited by Mattax; 11/01/14 11:44 PM.
|
|
|
Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: RapidRobert]
#1692694
11/02/14 12:33 AM
11/02/14 12:33 AM
|
Joined: Aug 2003
Posts: 643
Toronto, Ontario, Canada
plazomat
OP
mopar
|
OP
mopar
Joined: Aug 2003
Posts: 643
Toronto, Ontario, Canada
|
We're on to something with this (clarification). I would buy a pair of brass inverted flare male fittings to cap the MC & if it is good (& bled out) the pedal will be rock hard with virtually NO travel. Those "Edelman" fittings are cheap & you will reuse em. How about we get the MC cleared away as the culprit (I think it is guilty). It ain't the pads. with my (earlier mentioned) dart that is somewhat similar to your conversion there is a very slight bit of pedal travel & it's rock hard. EDIT If you have a MC fitting/line pigtail handy you might flatten the line end & install it in the disc port & see if the pedal is now rock hard/virtually no travel. OP post what it ends up being cuz we got bets on this one 
I just ordered up the fittings to block off M/C ports and will start there - also getting a residual pressure valve cause my M/C don't have em and not sure if my wheel cyls have the right springs.
it snowed today up here..so not sure how much I will get done before the car cover goes on til spring..
Thanks for all the help - will post any findings.
Plaz
|
|
|
Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: plazomat]
#1692696
11/02/14 10:58 AM
11/02/14 10:58 AM
|
Joined: Feb 2010
Posts: 1,645
Phila. Pa.
Mattax
top fuel
|
top fuel
Joined: Feb 2010
Posts: 1,645
Phila. Pa.
|
Quote:
it snowed today up here..so not sure how much I will get done before the car cover goes on til spring..
Some good winter reading here about brakes and a lot more .
Enjoy.
|
|
|
Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: DoctorDiff]
#1692697
11/02/14 10:09 PM
11/02/14 10:09 PM
|
Joined: Jun 2014
Posts: 1,321
VA
dragon slayer
pro stock
|
pro stock
Joined: Jun 2014
Posts: 1,321
VA
|
Quote:
A 1 1/8" bore master cylinder was never installed on a factory equipped disc brake A,B or E-body.
All else being equal, a smaller bore master cylinder will yield higher line pressure at the caliper, with a longer, lighter pedal stroke.
I think this is wrong. The Bendix Disc Master Cylinder with Booster is a 1 and 1/8" piston.
I have a 70 B body with Bendix Booster, Bendix 1 1/8" MC, KH 2.75 calipers with stock B body rotors. The rear is a dana 60 which retained 11" drums. I have the 3 piece KH dist, proportioner and meter valve. My car brakes fine. When I switched to new rotors and was breaking in the new 11" rotors I could lock up the front wheels. This was with older pads.
Lots of folks have given wrong info in these post. We just converted a 70RR to a 73up 11" big bearing rotor set up with manual disc MC. So it can work.
I would make sure your brakes are bleed correctly, no collapsed hoses, use a MC with a residual valve for the rear and no residual valve for the front. It should be a Disc manual MC for your car otherwise the rod throw can be different which effects how the MC piston moves. Even with out Meter valve for front and proportioner for rear the brakes should work, just easier to lock up rear first.
The front meter valve (hold off valve) actually holds off front application until the rears start to gripe to prevent front locking up and spinning car when roads are slick/wet.
I think the MC is the issues based on what has been stated so far. G
|
|
|
Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: QuickDodge]
#1692699
11/03/14 01:16 AM
11/03/14 01:16 AM
|
Joined: Feb 2010
Posts: 18,493
Granite Bay CA
Kern Dog
Striving for excellence
|
Striving for excellence
Joined: Feb 2010
Posts: 18,493
Granite Bay CA
|
Quote:
I would test the brakes on a dirt or gravel road to make certain all four wheels will lock up. It may be the brakes on only one axle are working.
Good point.
When I was neck deep in my brake fiasco, MOST of the combinations wouldn't even allow me to skid on the dirt/gravel in my backyard!
|
|
|
Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: DoctorDiff]
#1692701
11/03/14 12:32 PM
11/03/14 12:32 PM
|
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
|
Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
|
Plaaaaaaz  . It ain't snowing that much up there
live every 24 hour block of time like it's your last day on earth
|
|
|
Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: plazomat]
#1875381
07/21/15 10:27 PM
07/21/15 10:27 PM
|
Joined: Aug 2003
Posts: 643
Toronto, Ontario, Canada
plazomat
OP
mopar
|
OP
mopar
Joined: Aug 2003
Posts: 643
Toronto, Ontario, Canada
|
Ok digging up an oldie here but just gettin around to this.
I am try to start at the top with troubleshooting before I put in a generic disk/drum hold off/prop valve and a residual pressure valve in the rear circuit.
I have the master cyl no lines attached but with both ports plugged. The pedal is pretty firm right after the pedal free play is used up. BUT if I push hard enough the pedal seems to sink a bit - I then stop pushing cause I don't wanna bust anything.
Is this normal? Do I need to bleed the master further or is it just a bad master?
Doh - looked hard again and it seems that one of the plugs in the front port was leaking a bit sinking the pedal. Once I gave the fitting a good tightening leak stopped and the pedal held high and hard.
Will get valve mounted and plumbed next and move on from there.
Thanks
Plaz
PLAZ
Last edited by plazomat; 07/22/15 02:34 AM.
|
|
|
|
|
