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If you're accustomed to modern cars, pedal effort on any vintage car without power brakes, either drum or disk, can feel like "no brakes". You can increase the hydraulic ratio with a smaller bore master cylinder, but it will have more pedal travel and less pedal reserve.
The best solution is to add a power booster, which will make the system feel "modern" and reduce pedal effort by about two-thirds.
The front/rear caliper piston bore ratio is perfect and should not be changed. I recently helped a guy who put some aftermarket brake system on a gen one Camaro. The front and rear calipers have the same bore sizes, and the rears locked up on even moderate braking, even with the prop valve set at minimum rear brake bias.
Clearly the moron who "designed" this system knew nothing about vehicle dynamics or basic hydraulics.
I actually prefer the stock, manual discs, to the factory power system. I've always thought that the pedal "feel" was much better, with the stock manual brakes. Pedal feel for the power system seems numb to me, and lacks feedback.
We're required to use stock D-8 calipers, on the Corvette vintage racers I crew on. We've never used a booster on any of them. We get a better, and more consistent pedal, without power assist. We're always dealing with heat induced fade, and it's easier to deal with and compensate for, without the power assist.
I'd be a little careful about using DOT 5 in rebuilt, sleeved calipers. The following labels are coming on all Lonestar Caliper boxes now. Chemicals in the DOT 5 fluid, are causing premature seal failure. Since Lonestar does calipers for other Corvette brake companies, as well as many of the national parts chains, this may be an issue even if you didn't buy Lonestar branded calipers.
Can you clarify what Lonestar is referring to as "re-sleeved" calipers? Mine were stainless re-sleeved before I bought my project in 1999. I rebuilt all 4 using old fashioned lip seals and new pistons, not O-Ring seals, in 2002.
I filled my system with DOT 5 (silicone) brake fluid when I built my Corvette in 2002, because I liked the fact that DOT5 is not hygroscopic. Finally, after 15 years, I have had to rebuild all 4 calipers over this past winter and I found a lot of contaminants in the master cylinder, and all 4 calipers. My initial hope, in 2002, was that the DOT 5 being non hygroscopic, would not retain as much contamination as DOT 3 and 4 fluid.
I got 15 years life from a rebuilt system that I built in 2002 with DOT 5. I don't know how long the same system would have lasted with DOT 3/4. If I had it to do again, and considering that DOT5 costs 2x as much as DOT3/4, I would have used DOT 3/4.
PS: Another reason I prefer manual over power brakes is because early PB designs were too sensitive. Manual brakes allow much more modulation than older PB systems.
Last edited by 65tripleblack; 05-24-2017 at 05:03 PM.
Another reason I prefer manual over power brakes is because early PB designs were too sensitive. Manual brakes allow much more modulation than older PB systems.
Originally Posted by SWCDuke
If you're accustomed to modern cars, pedal effort on any vintage car without power brakes, either drum or disk, can feel like "no brakes".
The best solution is to add a power booster, which will make the system feel "modern" and reduce pedal effort by about two-thirds.
Originally Posted by gbvette62
I actually prefer the stock, manual discs, to the factory power system. I've always thought that the pedal "feel" was much better, with the stock manual brakes. Pedal feel for the power system seems numb to me, and lacks feedback.
Originally Posted by R66
R66 has factory manual discs that are fantastic as I feel I have more control over the braking than with power brakes. Pedal pressure is not excessive and the car stops very well. Keep in mind that I am use to older brake systems. I never liked the older power brake systems as they seemed touchy to me even though you can get use to them.
Originally Posted by DansYellow66
What was considered acceptable pedal pressure for brake operation in the 60s was greater than it is now. They will attain 1G stops but you have to tromp down hard on the pedal. I find they work well in conjunction with manual steering and transmission.
Originally Posted by CrossedUp
My '65 has stock manual brakes that work very well. No complaints.
Originally Posted by Kerrmudgeon
My 66 was standard discs with no power. Stopped great and not that much pressure required.
Originally Posted by MikeM
However, some have never driven a car without PB and think there is a design flaw in a manual brake system. But there isn't.
Originally Posted by Tom/99
I am running the factory non power disc brakes on my 65 coupe. It has a single chamber master cylinder. The pedal pressure is mot excessive. It stops well from any speed. the car does not need power brakes.
I was somewhat surprised to find so many that share my sentiments.
I grew up with non-PB cars and always found PBs to be far too sensitive, although they've improved over the years.
I find non-PBs to be easier to modulate, too, even though they take much more pedal effort to panic stop; however, I find that with good effort that they stop shortly and evenly, although clearly not as short or controllable as modern ABS.
With a high-compression engine, M21, and 4:10 rear gears, just lifting off the gas pedal does more to slow down my '65 than just lightly tapping the brake pedal with the effort similar to a PB pedal.
I have had to let people driving mine for the first time (admittedly a small population) to get on the brake pedal with some energy. The first time my wife drove it, she was absolutely sure that the brakes had failed.
Last edited by Easy Rhino; 05-24-2017 at 08:13 PM.
I replaced my manual shoe brakes on my ’63 in the early 70’s. I did not change the master cylinder but did need to remove the valve to release the pressure. Not sure the name of this valve but it is in a plastic bag in my garage. I think it is called the residual valve. In 2005 I replaced all the rotors, calipers (stainless) and pads. Very little pedal travel is required to brake and there is no drag on the car from the brakes. Since I have never driven a power brake Vette I have no feeling for how they are. I do know that my Vette has turned over 300,000 miles since the conversion with no brake related issues. Also I have never felt like I needed more braking than what I have. Another note is that I pull a trailer (600 pounds empty) with no trailer brakes and still feel the brakes are adequate. I do not have silicone brake fluid in my braking system.
Steve Stone (original owner ’63 triple black convertible, 550,000 miles)
My bride's track car runs manual four wheel discs and stops very well without requiring unusual pedal effort. It uses the stock C2 pedal assembly and therefore stock C2 pedal ratio.
Consider the overall leverage ratio which includes not just the pedal arm ratio but also the ratio of wheel cylinder piston area to master cylinder piston area. Too, the radial location of the caliper and the friction coefficient of the pad material affect the pedal effort.
When I was designing the brake system for our track cars, I put together a spreadsheet so I could tweak individual parameters until the numbers made sense. If you aren't using a spreadsheet in the design of your brake system, you should consider doing so. Set your design goals.... maximum pedal effort, overall deceleration at that effort.... then massage the parameters over which you have control until you meet your goals.
Jim,
I agree with everything you've stated, and yes I'm running an ever growing spread sheet in order to see all of the numbers on one page.
I'm looking for a system that can build 3400-3700 lbs of clamping force with 80 lbs of force applied to the pedal. Based on my research, thats roughly mid way between the original manual brake systems and a modern boosted system as far as pedal effort.
Running that math, with the 4.54 pedal ratio, and a 7/8 in bore master cylinder, you can generate 3328 lbs of clamping force with the Wilwood D8-6 front caliper, or 3793 lbs of clamping force with the Wilwood D52 caliper.
The basis for my statement about the factory pedal ratio of 4.54 is that with that relatively low pedal ratio, you need to reduce the master cylinder bore size, and increase the piston area...both of which will increase pedal travel...in order the achieve the same clamping force that could be achieved with a more traditional manual pedal ratio of 6 or 6.5 to 1 and a larger master cylinder bore with a smaller piston area...thus less pedal travel.
As you stated, I can mess with the numbers on the spread sheet, essentially leaving pedal force and pedal ratio a constant, so see what master cylinders and piston areas will provide the clamping force I'm looking for, but its difficult to determine how drastically those variables will affect pedal travel.
I'd be a little careful about using DOT 5 in rebuilt, sleeved calipers. The following labels are coming on all Lonestar Caliper boxes now. Chemicals in the DOT 5 fluid, are causing premature seal failure. Since Lonestar does calipers for other Corvette brake companies, as well as many of the national parts chains, this may be an issue even if you didn't buy Lonestar branded calipers.
The folks at Muskegon Brake don't seem to have a problem with it.
We have been selling DOT5 silicone brake fluid for over 20 years and recommend it for C1, C2, and C3 Corvettes without reservation.
My 65 Coupe with stock manual disc brakes stops just fine including panic stops. I have not done anything to the brakes but I believe they were rebuilt sometime before I got the car 10 years ago.
BTW, my 62 with stock drum brakes also stops fine.
Last edited by ohiovet; 05-24-2017 at 11:25 PM.
Reason: add info
I actually prefer the stock, manual discs, to the factory power system. I've always thought that the pedal "feel" was much better, with the stock manual brakes. Pedal feel for the power system seems numb to me, and lacks feedback.
We're required to use stock D-8 calipers, on the Corvette vintage racers I crew on. We've never used a booster on any of them. We get a better, and more consistent pedal, without power assist. We're always dealing with heat induced fade, and it's easier to deal with and compensate for, without the power assist.
I'd be a little careful about using DOT 5 in rebuilt, sleeved calipers. The following labels are coming on all Lonestar Caliper boxes now. Chemicals in the DOT 5 fluid, are causing premature seal failure. Since Lonestar does calipers for other Corvette brake companies, as well as many of the national parts chains, this may be an issue even if you didn't buy Lonestar branded calipers.
I can't help but wonder if that notice is for some liability issue.
I just want to add that my corvettes have dot5 since the early eighties and never a problem.
I will say that the calipers on my 67 have been overhauled twice but I believe the leaks in the calipers were due to rotor run out and just plain sitting for long periods without normal brake use.
I'd be a little careful about using DOT 5 in rebuilt, sleeved calipers. The following labels are coming on all Lonestar Caliper boxes now. Chemicals in the DOT 5 fluid, are causing premature seal failure. Since Lonestar does calipers for other Corvette brake companies, as well as many of the national parts chains, this may be an issue even if you didn't buy Lonestar branded calipers.
I just scanned the entirety of that EPA regulation looking for anything which discusses seal failure. Didn't see it.
The regulation affects manufacturers of certain chemicals, among them triethylene glycol dimethyl ether which does have some use in various consumer products, including brake fluid.
Manufacturers are required to notifiy the EPA at least 90 days before commencing manufacturing, importing, or processing this and six other chemicals (none of which relate to brake fluid).
I don't know (and don't care to know) enough chemistry to positively say this relates only to DOT 3 and DOT 4 brake fluid, but the word "glycol" makes me strongly suspect that to be the case.
If I'm right, there is nothing here about DOT 5 fluid at all and it's a bogus shield to hide behind when saying not to use DOT 5.
Chemists, feel free to tell me where I'm wrong.
Jim
Edit: Read the entire eye-glazing regulation for yourself here:
I read through the same thing and came to the same conclusion but I am certainly no chemist either nor do I know what all those chemicals are.
I have read there are new types of material being used for brake seals and boots but they still must comply with the various SAE, DOT, FMVSS compatibility requirements that have been on the books for quite a few years.
Of course, it'd be easy to miss something in all the muck and mire of all the various federal regulations that could possibly be at odds with one another.
I'll continue to use my Dot 5 until I see a reason not to.
I agree with everything you've stated, and yes I'm running an ever growing spread sheet in order to see all of the numbers on one page.
I'm looking for a system that can build 3400-3700 lbs of clamping force with 80 lbs of force applied to the pedal. Based on my research, thats roughly mid way between the original manual brake systems and a modern boosted system as far as pedal effort.
Running that math, with the 4.54 pedal ratio, and a 7/8 in bore master cylinder, you can generate 3328 lbs of clamping force with the Wilwood D8-6 front caliper, or 3793 lbs of clamping force with the Wilwood D52 caliper.
The basis for my statement about the factory pedal ratio of 4.54 is that with that relatively low pedal ratio, you need to reduce the master cylinder bore size, and increase the piston area...both of which will increase pedal travel...in order the achieve the same clamping force that could be achieved with a more traditional manual pedal ratio of 6 or 6.5 to 1 and a larger master cylinder bore with a smaller piston area...thus less pedal travel.
As you stated, I can mess with the numbers on the spread sheet, essentially leaving pedal force and pedal ratio a constant, so see what master cylinders and piston areas will provide the clamping force I'm looking for, but its difficult to determine how drastically those variables will affect pedal travel.
Any input would be greatly appreciated!
My instinct is that the target clamping force is waaay high.
That's at each front caliper, yes? So how much braking torque at each front wheel can you develop with that much force? And how much torque would the wheel/tire develop at 1G deceleration or the limits of adhesion, whichever is lower?
If I'm right, the brakes can generate far more torque than the wheel/tire can use.
BTW, I've found my old spreadsheet and, when I get time, I'll review my old numbers. If I learn anything I'll post again.
On my 65 I replaced every thing. with all stock calipers, disc, lines, I do use breaded flex lines, but I did go with a split master cylinder Dot 5 and I could not ask for a better stopping car. after I did it all the car sat for 7 years with very little use and when I got back to it no break problems at all. for the last 2 years been using it a lot it works as good now as when I first did it.
My instinct is that the target clamping force is waaay high.
I wasn't as right as I thought.
I've blown the dust off my ancient spread sheet and have run some numbers. I assume 7/8" master cylinder, 4.54 pedal ratio, .48 pad coefficient of friction.
Using your target pedal force of 80 lbs, I find that, with 26" diameter front tires, the Wilwood D8-6 brakes can generate approximately 2450 lbs of decelerative force.
That's a decent number. Add another 800-ish lbs of decel force contributed by the rear brakes and you are looking at 1 G decel (assuming tire grip is adequate to support 1G).
Too, with about 800 lb contribution from the rear, you're looking at about 75% front brake and you'd be unlikely to lock up the rears before the fronts lock up.
Jim
Last edited by jim lockwood; 05-25-2017 at 12:08 PM.
I've blown the dust off my ancient spread sheet and have run some numbers. I assume 7/8" master cylinder, 4.54 pedal ratio, .48 pad coefficient of friction.
Using your target pedal force of 80 lbs, I find that, with 26" diameter front tires, the Wilwood D8-6 brakes can generate approximately 2450 lbs of decelerative force.
That's a decent number. Add another 800-ish lbs of decel force contributed by the rear brakes and you are looking at 1 G decel (assuming tire grip is adequate to support 1G).
Too, with about 800 lb contribution from the rear, you're looking at about 75% front brake and you'd be unlikely to lock up the rears before the fronts lock up.
Ive been using a vehicle weight of 3180 lbs, a weight distribution of 48/52, a CG height of 16.5, wheel base of 98 inches, and a 1.2G max braking force.
Based on those numbers, a 25.7 inch tire, (245/45/17), you would require 2785 lbs of force on the front axel and 1300 lbs of force on the rear.
As you assumed, 4.54 pedal ratio, 7/8 master cylinder, and 80# pedal input, I can generate 3177 lbs of force on the front axel by using the Wilwood D52 caliper due to the 6.28 sq. in. of piston area.
I can generate 1570 lbs of force at the rear by running the Wilwood D8-4 replacement rear calipers.
This is using 11.75x1.25 discs front and rear with pads of .48 coefficient of friction.
Please correct me if something looks off, but I would think this would make for a very drivable manual disc brake set up with excellent performance for a street car, and a pedal feel somewhere in between the factory disc brakes and the squishy modern boosted stuff.
The calculator also spit out a pedal travel of 3.141 inches....not entirely sure what factory is....I suppose i could go downstairs and measure.
I converted my 65 vert to a dual chamber master cylinder w/ no power and it brakes just fine . the only problem i encountered was that i wasnt aware that there was a bleeder on the outboard side of the rear calipers , i bled those brakes for a month cause the pedal kept getting soft after a couple days . Finally called the place where i bought the dual mc and they told me about the bleeder on the outboard side .After bleeding that one they are working great.
I'm looking at that calculator. Right off the bat, it's producing goofy numbers for me. It's telling me the front line pressure in my vintage racer is 258 psi when I'm standing on the pedal with a 100 lb force.
The correct number should be in excess of 500 psi.
Anyway... new question: What is the use of the car for which you are designing these brakes? Reason I ask is that the 1.2G decel is probably right about what my vintage racer can do on sticky Hoosiers. Are you building a car for racing?
I'm looking at that calculator. Right off the bat, it's producing goofy numbers for me. It's telling me the front line pressure in my vintage racer is 258 psi when I'm standing on the pedal with a 100 lb force.
The correct number should be in excess of 500 psi.
Anyway... new question: What is the use of the car for which you are designing these brakes? Reason I ask is that the 1.2G decel is probably right about what my vintage racer can do on sticky Hoosiers. Are you building a car for racing?
Decidedly not. I'm building what I can best describe as a 4-wheeled Harley Davidson. Something you COULD commute in if need be, but whats true purpose is taking out on the weekends and beating on for long hours through the Smokey Mountains. Hot Rod Power Tour, Rally North America, and just spirited weekend road trips are where this car will live.....with very occasional track and autox outings (Im terrible, but I have fun).
I'm 100% committed to a manual brake system, and I think that through adequate research, I can assemble a system that requires moderate pedal pressure (somewhere between a full manual race system and the squishy over-boosted BS on the roads today) while providing excellent feel and feedback.
I understand that when dealing with any calculator, as the one I posted earlier, BS in = BS out. I came up with that 1.2 G figure and 80 lbs of pedal pressure as a target approximately half way between the original, street going C2 at 120 lbs of pedal pressure to generate a 1.0 G stop, and the advertised 50/50 street/race car on some of the pro-touring forums (I hate that term BTW) where the suggested figure is 80lbs of pressure for a 1.5 G stop in an un-boosted brake set-up.
Anyway, I welcome your input....I want to do this right the first time, which is why I'm asking all of these questions now.
I'm looking at that calculator. Right off the bat, it's producing goofy numbers for me. It's telling me the front line pressure in my vintage racer is 258 psi when I'm standing on the pedal with a 100 lb force.
The correct number should be in excess of 500 psi.
Are you inputting Master Cylinder bore instead of area? Initially I was making that mistake and entering .875 for the 7/8 master cylinder instead of .601, which resulted in some extremely low numbers.
Are you inputting Master Cylinder bore instead of area? Initially I was making that mistake and entering .875 for the 7/8 master cylinder instead of .601, which resulted in some extremely low numbers.
Weeeeeeelllllll, this is what it says:
Front Master Cylinder Diameter (inches):
.... and that is bore. It's not asking for area.
Something else I question is the usage of the entry for pad radial height. The torque generated by pad force and friction varies along the radial height of the pad being a function of both radial height and pad shape. The calculator doesn't have a way to account for pad shape.
However, the calculator does try to account for weight and weight transfer, something I addressed with my spread sheet only slightly.
I'll fiddle with the calculator a little more to see why I'm getting goofy results. If I learn anything, I'll report back.
05-24-2017, 11:28 AM
My '65 has stock manual brakes that work very well. No complaints.
