Manual vs. Power Brakes

rbohm said:

a power brake booster doesnt decrease stopping distances, or increase braking efficiency, so much as it multiplys the force you put on the brake pedal which makes it easier to get the line pressure up on a disc brake system. you can apply the same pedal pressure without a power booster, it is just alot harder to do so, and that is where the illusion of shorter stopping distances comes in with a power booster.

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While in theory I agree, you're not factoring in "time for the human factor." It takes a certain amount of time for you to physically apply the pressure to stop fast.

If the pedal is harder to push, it will take you a little longer to depress it as hard as a car with a booster. I'm confident side by side you will find the booster car will stop faster just because it has immediate pressure when depressed.

mdjay said:

While in theory I agree, you're not factoring in "time for the human factor." It takes a certain amount of time for you to physically apply the pressure to stop fast.

If the pedal is harder to push, it will take you a little longer to depress it as hard as a car with a booster. I'm confident side by side you will find the booster car will stop faster just because it has immediate pressure when depressed.

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that is true in a panic stop situation, but remember that you gain in one area, but lose in another. power brakes are nice for the average person and for daily drivers, because you dont have the pedal effort needed to for manual brakes. but manual brakes are easier to modulate, especially in slippery conditions.

liken the panic stop situation, when comparing power and manual brakes, to a drag race where the only change is rear gears. power brakes lets you apply maximum pedal effort quickly, like lower gears allow you to accelerate more quickly, so you get the illusion of having better brakes, but in reality, there is no change in maximum braking, and there is no change in maximum braking distance, assuming a driver that knows what they are doing. the difference is "feel", and that is why the average person thinks power brakes help the car stop faster.

my old F250 had power brakes, but it had a bad power booster as well, talk about and extra disadvantage, but i could out brake lighter cars with equal brakes anytime i wanted.

I'm not so sure that you can say definitively that power will help you stop faster. Power brakes are going to be more difficult to modulate.

If you are trying to stop as quickly as possible, you want the maximum braking force without locking them up. If there is a smallest incremental force that you can easily apply, that is the amount of braking lost when compared to antilocks. I would argue that given that the smallest incremental amount of force you can easily apply doesn't change - with higher force manual brakes you can get closer to lock up without actually locking up the brakes.

It's possible in my mind that some people can stop faster with power, some with manual. For instance, a small woman probably is better suited with power whereas a large and athletic man might stop more quickly with manual brakes. I'll keep my manual brakes.

I read an online article a while back that made me think. It was written by a Wlwood dealer, and basically it said that if you chose the correct master cylinder, you can have an easy pedal AND great brakes without a vacuum booster. While most disc systems use a 1 1/6" bore master cylinder (my wife's manual disc 'vette uses a 1" bore) the article said that Wilwood offers a true dual master cylinder that uses two side by side 3/4" pistons. One goes to the front and one goes to the rear brakes and it's supposed to give you the best of both worlds. Rather than a proportioning valve, it uses a balance bar to physically adjust the brake bias. I'm not sure how easily it would adapt to early Mustangs, but I'm sure it couldn't be too hard. I've always thought that sounded like a great idea, since I know full well that a disc brake system doesn't need a power booster to be effective. My last couple of streetbikes could be stood on the nose with a gentle two-finger squeeze on the lever.

Which is exactly why you have some people swearing the dual MC that JMC sells is the chit. Maybe someday I'll have a few bucks to prove it...

zookeeper, the wilwood dual m/c with balance bar works great. i crewed on a circle track car that had it installed, and it made bias changes very easy, even from the cockpit with an adjuster.

I have the JMC set-up on my car, I can leg press over 800 lbs and this pedal is too stiff for me!

Maybe I'm just getting old and lazy

I'm not sure laziness has anything to do with it, Jay. You sound like a pretty stout guy so I think we can rule out puny legs, but it sounds like your master cylinder bore is too big. Look at it this way: the Nextel Cup cars weight something like 3400lbs, right? They also use 15" wheels (like lots of our Mustangs) so it stands to reason they use small discs. They also use manual brakes, yet the brakes are so sensitive that it's hard not to lock the wheels on road courses. I remember a TV show a few years ago on ESPN where the host drove a Cup car at Road Atlanta and one of the remarks he made were that the brakes were so powerful, it was hard to keep from flat-spotting a tire on the entrance to a corner. Now I realize that they use ultra-rigid calipers, and such, but physics is physics, regardless of how much you spend on brakes, the performance is largely determined by the amount of fluid being moved and the force used to generate the movment of the fluid, right? If the master cylinder piston/caliper piston relationship is wrong, you get either a soft pedal that goes to the floor without stopping the car, or a rock hard pedal that you can't depress without a booster. My point is, I believe that there is a perfect manual disc setup with the right sizes that works as well as any boosted brake setup. The person doing the installation may have to try a few master cylinders to get the bore size right, or be willing to do some research before laying out your money, but isn't doing it the hard way and making it work what this whole hobby is all about?

i hear ya zoo. i'm not against trying different masters with this set up but i really liked the booster. it use to make your eyes want to pop out of your head.

I went from a ssbc booster/dual master set-up to the jmc set up when i swithced to the tremec tko 3. it went from an effortless stop to pushing on a brick. now i can stop the car fast, but it takes a "major" effort.

I'm in no hurry so we'll see where it lands

mdjay said:

i hear ya zoo. i'm not against trying different masters with this set up but i really liked the booster. it use to make your eyes want to pop out of your head.

I went from a ssbc booster/dual master set-up to the jmc set up when i swithced to the tremec tko 3. it went from an effortless stop to pushing on a brick. now i can stop the car fast, but it takes a "major" effort.

I'm in no hurry so we'll see where it lands

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I'm hoping to do brakes this year and really wanted to use the JMC MC. What brakes and which JMC MC are you using?

I planned to use the JMC MC with the cobra front and rear brakes.

Does anyone have a list of master cylinders with the various bore sizes that fit the classic mustangs? I have a 1969 stock power disc/drum (1", I believe) and I'd like to find a 7/8"s that fits the car without line rework.
Thanks

There are two points/opinions I'd like to add to this:

1. Those Nextel Cup cars must have something different going on in the world of pedal leverage than we have. I bet their pedals provide much more leverage than our Mustang pedal boxes.

2. I think the "initial time to hard engagement of discs" is lower on a power brake setup than manual. It takes me less time to provide a light push to the pedals than a hard stomp, and with more modulation. And there is less or no flex in the pedal box with power brakes than with manual brakes.

Parts

caveeagle said:

My '67 Conv is a 289 4-speed car that still has the original non-power 4w drums. I have most of the parts aquired to put 13" cobra/PBR disks on the front and '86 SVO disks on the 8" rear axle.

I am now trying to decide what MC / booster combo to use. I am also looking for advice on prop valves.

I have been told that I can go with a manual MC from an SVO or a granada and stay manual. MC bore must be 1" or less.

I would really like to go to a power booster, but I don't want to deal with pedal swapping or hacking up my firewall. A couple of the Mustang suppliers (NPD & Laurel Mt Stang) sell an upgrade booster that they say will bolt to the original pedal / mounting holes. Only concern is using an aftermarket MC that may not be available in the future.

Has anyone used the NPD conversion booster?
Any other advice on the conversion?

Thanks..... CE

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I've got a 67 coupe I wanted to upgrade like your doing where did you get your parts?? Did you find a kit??