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Pressure Points
Improve Brake Pedal Pressure with a
Remote Mounted Master Cylinder/booster.
text & photography by Jerry Slattery
For some street rod builders, creating enough pedal pressure to stop the car has always been a problem. It's usually due to an inadequate amount of booster space, a short pedal ratio, a too small booster. no booster at all, not enough vacuum or a master cylinder bore that is slighty too big or too small. In most street rods, the brake components usually are new and adequate enough to stop the car. The problem has been trying to create enough pressure to fully utilize these components. Many times the cam is too big with too much valve overlap to make at east 16 inches of vacuum needed to operate a booster (an electric vacuum pump or hydro-vac unit solves this problem) Detroit and the major brake component manufacturers for street rods make great brake systems so most rods have quality components at the wheels that can stop their cars.
For most street rods, where cleanliness is cool, holding a large enough booster and master cylinder within the 6 or 7 inch thick framerails, or having an unsightly 8-,10- or 12-inch diameter booster on the firewall, is out of the question. If a 7 inch-diameter, single diaphragm booster were adequate for all mid to large American brake component, Detroit car manufacturers would be using it. However, it's just the opposite. Detroit uses up to 12-inch diameter boosters with the same components used in street rods. In fact. most of the brake stories written are about trying to help create the maximum amount of pressure in the minimum amount of space, one way or another. The bottom line is that there isn't enough pressure to the wheels (in a lot of cases) to give a good pedal feel so the driver feels comfortable and in control. If alI the 7-inch diameter boosters on street rods could be replaced with 12 inch-diameter boosters, we'd hear a totally different story from most rodders with pressure problems. Often, builders don't even realize they have a pressure problem, and they start swapping components to find the problem. In many cases, greater pressure would solve most of their stopping problems, unless their brake system is out in left field.
Any (low) pressure problems, master cylinder bore diameter problems or most short pedal ratio problems now can be corrected and virtually eliminated with the new remote mounted master cylinder and booster from C.H. Topping Company in Long Beach, California
Since street rods have always been prone to having pressure problems, due to space and cleanliness, owner Vince Bunting now offers a custom-designed remote-mounted system (to work with your existing component bore diameters and pedal ratio) that can operate your brake system from wherever you have the room to mount it.
How is this possible? It's simply a marriage of two technologies that have been around a long time. Your existing brake system is plumbed to operate the remote unit. This is so simple that you're probably wondering why you didn't think of this. Yes, it's just a big exercise in replumbing your current brake system (and finding a place to mount the unit).
It doesn't matter if you have an existing manual or power-boosted brake system—either can operate the remote unit without having to change a thing, except the lines. So how does this work? Here's the part (to make it operate) we've all seen years ago, when we saw our first "juice clutch." A couple of small slave cylinders operate a pivot arm that pushes the booster rod into the booster. End of story. Get one and start plumbing. You'll be so pleased with how well your car can stop (using your existing components) that you'll wonder why this wasn't created years ago, when they figured out how to use remote slave cylinders to operate the clutch. Just ask Mike Keenan, owner of the beautiful '34 Vicky in this story or e-mail Vince at C.H. Topping Company.
The brake problem for Keenan's '34 Vicky was an extremely hard pedal. No matter how hard you pushed on the pedal, it didn't seem to make any difference in its ability to stop the car. There was no pedal feedback. The manual system had an unknown bore diameter (we think it was 1 inch) and a stock underfloor brake arm (a '39 Ford-style brake arm). The pedal ratio, about 5:1, just could not create enough pressure. Maybe, if it was 8 or 9 to 1, the car might stop better.
Since the car was built in the early 1970s, Volvo calipers and solid rotors were used on the straight-axle front end, while a Vette rear end with large, four-piston calipers stopped the rear wheels. That amount of brake capability should be able to stop the car quite adequately. Ideally, the big calipers should be in the front, with the same size or smaller calipers at the rear, with a pedal feel that has some predictable movement when pressure is applied. For better or worse, this was the braking problem that needed to be solved—not enough pressure could be applied.
This is the perfect scenario for the remote unit. It really doesn't matter what the existing bore diameter is, since the small slave cylinders operating the booster pushrod arm on the remote unit don't need much pressure. Since the remote unit can be custom built, the correct diameter booster and correct diameter master cylinder bore can be installed to coordinate with your existing brakes at each wheel. Bunting knew that more volume was needed to feed six pistons, so he used a 1-1/8-inch-diameter bore master and a (Ford) double-diaphragm 71/2-inch-diameter booster to provide plenty of pressure and volume. A good rule of thumb here is: A larger booster is always better. Another tip to remember when buying brake components is to always find out (and use) the same diameter booster that operated the disc/disc or disc/drum system on the car that those parts came from.
After the remote unit was installed, the pedal travel came back, and it was predictable how much leg pressure needed to be applied to stop. Luckily, this rod had a small trunk that opened at the top. In the photos, you'll notice that the trunk lid was removed for the installation. Keenan was so thrilled with how well the Vicky stopped, he actually said he'd be glad to tell any readers all about it!
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