Interesting write up. Thank you!
Are you going to shoot the master cylinders later with cast iron look paint for aesthetics?
Update by Tim Suddard to the
Elva Mk VI project car
Nov 19, 2024
|
brakes,
wilwood,
Elva Mk VI
Photography by Tim Suddard
Could we upgrade the brakes while keeping things looking period-correct? That was our goal here.
Our Elva Mk VI sports racer was built in 1961. It’s nearly 2025.
Judging by the worn-out parts that came with the car, the master cylinders were 0.75-inch-bore units, likely from an MGA and MGB.
While Moss Motors still carries the needed replacement parts, we decided to modernize the heart of our braking system. The master cylinders are buried in the bowels of this car, so an upgrade to a modern setup with remote reservoirs wouldn’t visually intrude upon the car’s appearance.
While most racers would not even worry about the visual aspect of a race car’s restoration, we are trying to make this car look very original as we have some concours events planned plus some track work.
Thankfully, Wilwood Disc Brakes has duplicated the early Girling-style master cylinders with remote reservoirs and increased durability.
This is not a standard fitment–an Elva isn’t exactly as common as a Corvette or a Mustang–so Wilwood’s Mike Hamrick first had some questions for us.
[How to talk brakes: Ways to turn desires into hardware]
First, what did the rest of our braking system look like?
Our car came with early Spitfire calipers and 9-inch rotors. These brakes have two-piston calipers that measure about 2.125 inches in diameter.
While our car most likely originally had 9-inch drum brakes up front, by the end of the run of 30 cars, disc brakes were already being fitted. So we feel this is a period modification that would be allowable anywhere.
At the rear, inboard 9-inch drum brakes, similar to an early Sunbeam Alpine, Triumph TR3 or MGA, were used.
Mike noted that this 900-pound sports racer had more brakes than an early Miata fitted with Wilwood’s big-brake kit.
Second, what was the pedal ratio?
To determine pedal ratio, you need to measure the distance from the pedal's pivot point to the center of the pedal pad. This is measurement “A” in the diagram. For our car, that measurement is 6.25 inches.
You then measure the distance from the pedal's pivot point to the center of the master cylinder pushrod: In our case, 2 inches. (This is measurement “B” in the diagram.)
So “A” divided by “B” equals the pedal ratio. In our case, it came to 3.125:1.
We also needed to look at brake bias. Our car would have originally had a balance bar on the pivot point of the brake pedal so front-to-rear pressure could be adjusted.
While these parts were long gone, Wilwood also makes a balance bar mechanism that perfectly fit our brake pedal assembly.
“The bummer is the low amount of leverage,” Mike replied after looking at our entire system. “It’s going to be a balancing act: Generate enough PSI but still have enough volume for the rear drum cylinders.”
Mike suggested that we start with a 0.700-inch master front and rear. From there, he said, we may need to go to 0.750-inch on the rear or maybe a down to a 0.6258-inch in the front.
He sent us three different Wilwood master cylinders:
He also sent us a Wilwood balance bar that perfectly fit into our original brake pedal’s 1-inch diameter center hole.
While the balance bar perfectly fit and would allow us the adjustability that we would need, the master cylinders themselves were a different story–and we knew this before ordering.
The original masters were 1 inch in diameter, and the new Wilwood master cylinders mount into a 1.4-inch diameter hole.
While our master cylinder mounting brackets were wide and tall enough to accommodate a 1.4-inch hole, we were worried that might affect the structural integrity.
To solve this potential problem and add some structural integrity, we welded a brace to the outside of the bracket.
The final master cylinder we had to deal with was for the clutch. “On a push-type clutch pedal, we usually want to try/start at the same bore size as the push cylinder,” Mike said. “One to one.”
To that end, Wilwood sent us a 0.75-inch master cylinder.
So, while we have the cylinders temporarily in place, until we get the car finished, we won’t know if we have the correct ones. Fortunately we have some extras on hand.
Interesting write up. Thank you!
Are you going to shoot the master cylinders later with cast iron look paint for aesthetics?
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