Brake line question

[SuperBuickGuy]

I have a question about the C3 (Corvette) system. It is beyond my pay grade to understand why the front (which operates the front brakes) brake line from the booster to the proportioning valve is smaller to the front wheels than it is to the rear. I intend (unless some explains to me prior) to change the lines to the proportioning valve to same size (and let the valve, not the pipe size change the amount of fluid the front brakes get).

I think someone made a mistake at SS brakes because the front line/rear line orientation on a C3 is reversed of what is "normal." Normally, the front reservoir feeds the front brakes, and the rear the rear brakes; but on a true C3 Master cylinder the line from the front then crosses to the back of the proportioning valve.... however, as the fitting size is different front/rear, it's impossible to screw up from my end. What is odd, in all of that, is the smaller line feeding the front calipers since there are more pistons in the front than in the rear.

Or I could be complete full of crap.... but everything I've read points to what I just described.

Maybe it's supposed to be square line, and Chad will write an article about how it's stupid to have round line....

[Loren]

Not sure about the rear having more pistons, but...in the case of the calipers being equal front/rear, the way to have more pressure go to the fronts is to use a smaller area piston in the master, which is easier to do at the rear position (i.e. since some of the piston area must be used for the mechanical connection to the front portion of the m.c. and it's area is thus decreased).

As for the smaller diameter line to the front, I have no clue. Maybe they just want a faster response (it would be milliseconds) to the front and that's a way to do it.

[Deaf Bob]

Volume in res. Read piston stroke, needed to make a reaction, read displacement , The smaller line reacts quicker since it displaces less from the MC. If you were to go larger lines, you will need to press further on your pedal to get same stopping power.. You only need to react the caliper to stop.. If it was properly bled.. I'll have to look, but I'm sure the larger pot tends to work the rear brakes..which is usually in the front..

[STINEY]

I know GM (in the non-corvette production) used a larger line to the rear in order to control braking - I.E. not having the rears lock up first.

But you know this, and your issue is bass-ackwards from that. Weird.

[SuperBuickGuy]

Not sure about the rear having more pistons, but...in the case of the calipers being equal front/rear, the way to have more pressure go to the fronts is to use a smaller area piston in the master, which is easier to do at the rear position (i.e. since some of the piston area must be used for the mechanical connection to the front portion of the m.c. and it's area is thus decreased).

As for the smaller diameter line to the front, I have no clue. Maybe they just want a faster response (it would be milliseconds) to the front and that's a way to do it.

I have wilwood D8-4 brakes on my car - so there is a difference. the problem has been that either the rears hang and/or only the right front locks up when you stomp the brakes....


Bob, the front brakes generally have greater volume - thus, they'd need greater volume to move the same distance as the rears.

[SuperBuickGuy]

D8-4 Caliper Rear Piston: 4 Piston Area: 3.00 Pad Volume: 3.9 Mount Description: 5.16" Lug Mount Rotor Width: 1.25 D8-4 Caliper Rear PISTONS: Type: Stainless Finish Red Powder Coat Piston 1 Dia. 1.38 Piston 2 Dia. 1.38 Piston 3 Dia. - Piston 4 Dia. - MATERIAL: Aluminum FIT: Maximum Rotor Dia. 11.75 D8-4 Caliper Rear Caliper D8-4 Caliper Rear Caliper Drawing Brake Pad Plate # D8 D8-4 Caliper Rear Description D8-4 rear calipers are a direct bolt-on replacement for the OE factory rear calipers on all 1965-82 Corvettes. Forged billet aluminum bodies, stainless steel pistons, and high temperature seals put an end to the rust, bore pitting, and seal failures that plague the original cast iron caliper design. NOTE: PAD TYPES AVAILABLE: D8 Universal Black Powder Coat $350.99 120-10526-BK Call (805) 388-1188 Universal Clear Anodize $262.43 120-10526 Call (805) 388-1188 Universal Polish $371.99 120-10526-P Call (805) 388-1188 Universal Red Powder Coat $350.99 120-10526-RD Call (805) 388-1188

D8-4 Caliper Front Piston: 4 Piston Area: 5.56 Pad Volume: 3.9 Mount Description: 7.00" Lug Mount Rotor Width: 1.25 D8-4 Caliper Front PISTONS: Type: Stainless Finish Red Powder Coat Piston 1 Dia. 1.88 Piston 2 Dia. 1.88 Piston 3 Dia. - Piston 4 Dia. - MATERIAL: Aluminum FIT: Maximum Rotor Dia. 11.75 D8-4 Caliper Front Caliper D8-4 Caliper Front Caliper Drawing Brake Pad Plate # D8 D8-4 Caliper Front Description D8-4 front calipers are a direct bolt-on replacement for the OE factory front calipers on all 1965-82 Corvettes. Forged billet aluminum bodies, stainless steel pistons, and high temperature seals put an end to the rust, bore pitting, and seal failures that plague the original cast iron caliper design. NOTE: PAD TYPES AVAILABLE: D8

[NewEnglandRaceFan]

might be because of the engine set back, putting more weight on the rears than what a normal car would see.. and gm wanting the fronts to start braking first, but not as hard as a car that is nose heavy..

[Barry Donovan]

might be because of the engine set back, putting more weight on the rears than what a normal car would see.. and gm wanting the fronts to start braking first, but not as hard as a car that is nose heavy..

that is interesting.. I'd swear I had listened to an out loud conversation saying the same thing, corvette.

do whatever works, when they used lines to regulate, regulators were not good enough... today can do whatever you want.

I have 15/16ths all the way around in the master cylinder on a 2600 pound subaru. Needed alot more back brake.. they went equal giant somewhere along the line. A pun there..
inquire about modern proportioning valves.

[SuperBuickGuy]

that is interesting.. I'd swear I had listened to an out loud conversation saying the same thing, corvette.

do whatever works, when they used lines to regulate, regulators were not good enough... today can do whatever you want.

I have 15/16ths all the way around in the master cylinder on a 2600 pound subaru. Needed alot more back brake.. they went equal giant somewhere along the line. A pun there..
inquire about modern proportioning valves.

yes but there's one of the issues - is it how GM designed it, or is it how SS brakes messed up? if it's a mess up, could it be screwed up at the proportioning valve instead?

I'd really rather not fix this a 4th time.

weight bias is (IIRC) 52/48

[NewEnglandRaceFan]

knowing gm.. the big block and small block cars most likely have the same rotors/clappers/master.. and they balanced the braking between the two with a smaller line for the sbc..
a shop manual should tell you what the front line should be, or any of the venders that sell oem type parts.. eklers,mid America,etc

[SuperBuickGuy]

I wonder how you attach an .xls file here....

[Beagle]

RPM	4.23	2.53	1.67	1.23	1	0.79
1550	10.38020785	17.35505	26.29238	35.69779	43.90828	55.5801

paste the cells?

[SuperBuickGuy]

Design your braking system: sizing the master cylinder(s)
Vehicle weight	2500	lbs
Front weight split	45	%
Wheelbase	95	"
CoG height	14	"	Puhn suggests sports cars just above wheel center if not otherwise determined (pg 92).
Max deceleration	0.80	g	0.8 street tires, pg 93
Brake pedal input force	75	lbs	75 lbs to 100lbs recommended, pg 101
Brake pedal ratio	4.85	:1	wilwood dual master swing mount
Number of masters	2	cyl	1 tandem, 2 for dual
Pad coeff of friction	0.50		0.3 typical according to Puhn, pg 99. 0.4 for modern OEM street pads, Wilwood catalog page 37
	Front	Rear
Wheel rolling radius	12.45	12.95	loaded wheel				185x60 on 14", guess at rolling radius, 11.25
Effective braking radius	5.492	5.666	measure, or use (discDiameter-pistonDiameter)/2				front: GTS 9 1/8" = (9 1/8-2)/2, Previa 9 7/8" = (9 7/8-2 3/8)/2, rear: GTS 9" = (9-1.375) / 2
Brake calliper type	1	1	1=fixed, 2=floating
# of pistons	6	4	per calliper, pg 99
diameter (")	1.279	1.062	of each piston
effective piston area	7.709	3.543	area = #pistons * calliperType * pi * (pistonDiameter/2)^2
Maximum Conditions	Front	Rear
weight per tire	710	540	weight plus weight transfer / 2 tires, pg 94
friction force per tire	568	432	weight * CoF == weight * deceleleration (assuming front CoF == rear CoF), pg 94
ideal force balance (%)	56.8	43.2
brake torque per wheel	7070	5596	frictionForce * wheelRollingRadius, pg 94
hydraulic pressure needed	334	557	brakeTorque / ( padFrictionCoeff * totalCalliperArea * effectiveBrakeRadius), pg 99
master cylinder area	0.545	0.326	masterCylinderArea = pedalForce * pedalRatio / numberOfMasters / hydraulicPressure, pg 101
brake torque ratio	6.245	4.752	brake torque ratio = (pistonArea / masterCylArea) * (effectiveBrakeRadius / wheelRollingRadius), pg 99-103
Ideal master diameter	0.833	0.645	ideal = 2 * sqrt(masterCylinderArea / pi)
Ideal Balance	56.8	43.2	%
Choose closest match	0.813	0.625	======>	Available Master Cylinders
master cylinder area	0.519	0.307		Bore Size	Diameter
resulting brake torque ratio	6.550	5.053		5/8in	0.625	<-- available from wilwood
Resulting balance	56.5	43.5		11/16in	0.688
movement / wheel / 1/64"	0.232	0.180		3/4in	0.750	<-- available from wilwood
pedal force	35.8	35.3		13/16in	0.813
	see notes below			7/8in	0.875	<-- available from wilwood
				15/16in	0.938
				1in	1.000	<-- available from wilwood
				19mm	0.748
				20mm	0.787
				21mm	0.827
				22mm	0.866
				23mm	0.906
				24mm	0.945
Notes:
Ideal is to have the rear locking force just higher than the front locking force
If using a tandem master cylinder, wheels with the lower required pedal pressure will lock first. If the rear force is lower a proportioning valve will help to prevent instability under braking.
If using dual master cylinders through a balance bar, pedal force is the sum from both masters. A balance bar is used to adjust the pedal force to lock front wheels just before the rears.
Pedal movement is masterMovement * pedalRatio. Master movement is the sum of front & rear movement for a tandem master. For dual masters, use the cylinder with the most movement.
Balance Bar	55	%	toward the rear
Proportioning Valve
valve setting	550	psi	wilwood proportioning valve 260-2220, 100-1000psi
slope	57	%	wilwood proportioning valve 260-2220, 57%
						Braking Torque			Hydraulic Pressure
	Weight					Front	Rear		Front	Rear
braking force (g)	xfer (#)	Front (#)	Rear (#)	% front	% rear	Ideal	Actual	Ideal	Actual	Balanced	Proportioned
0	0	1125	1375	45.0	55.0	0	0	0	0	0	0	0	0
0.1	37	1162	1338	46.5	53.5	723	866	558	34	86	56	61	61
0.2	74	1199	1301	47.9	52.1	1492	1685	1151	71	168	115	126	126
0.3	111	1236	1264	49.4	50.6	2307	2456	1780	109	245	177	195	195
0.4	147	1272	1228	50.9	49.1	3168	3180	2444	150	317	243	268	268
0.5	184	1309	1191	52.4	47.6	4075	3855	3143	193	384	313	344	344
0.6	221	1346	1154	53.8	46.2	5028	4483	3878	238	447	386	425	425
0.7	258	1383	1117	55.3	44.7	6026	5063	4648	285	504	463	509	509
0.8	295	1420	1080	56.8	43.2	7070	5596	5454	334	557	543	598	571
0.9	332	1457	1043	58.3	41.7	8160	6081	6295	386	606	627	690	610
1	368	1493	1007	59.7	40.3	9297	6518	7171	439	649	714	786	651
1.1	405	1530	970	61.2	38.8	10478	6907	8083	495	688	805	886	694
1.2	442	1567	933	62.7	37.3	11706	7249	9030	553	722	900	990	739

[SuperBuickGuy]

as you can see, this is quite the page.... but why I'd like to post it up is it'd be useful to others to calculate master cylinder sizes.... but again, with no ability to post .xls or attach a file... sol

[Loren]

Neat chart. That Puhn guy they refer to was who I learned from via his book...really turned the witchcraft into science. I have followed your build so I should have known what calipers were in there.

I guess I'm confused about whether the lines in your new setup are same as stock and you're wondering why, or different than stock and you're wondering why. In any event I think it can be figured that smaller lines are used to tune in faster response in general (imagine in a corner, near the limit, with any little panic stab you'd want the fronts to hit first) and can be used as very little fluid actually moves through with a disc system. The larger front caliper bore size surely is the result of some formula Wilwood has proven...problems such as differing behavior front/back or one side locking before the other are surely something more basic. Do the discs have any runout ground into them to push the pads back, and is it the same side-to-side up front (dial indicator check, and might as well do the rears also)? With the front lifted in the air, with the pedal pushed then released do the wheels then turn with the same effort, showing the callipers not hanging up? Really, even with Wilwood's great rep, I wouldn't automatically trust their stuff more than anybody elses without checking. Not saying I'd know what's going on, but maybe another methodical going-through...