Seven Adjustable Dual Master Cylinder

Pictures and instructions by John Greeven

BG Developments (http://www.bgdevelopments.co.uk/bg-pedalbox.html) make a pedal box assembly which converts your braking system from a tandem brake master cylinder to a dual master cylinder set-up with balance bar for bias adjustment. As with many of these upgrades, it was not completely “bolt-on” and required a bit of custom work.

Issue – proper fit

The pedal box does mount directly where the tandem master cylinder was mounted. However, this places it very close to the clutch master cylinder (mine’s left hand drive although I imagine this would also be true for right hand drive). So, I enlarged the hole through which the clutch master is mounted to enable it to be shifted away from the pedal box. I fabricated an aluminum plate to place between the clutch master and the wall it mounts to in order to insure it was firmly held. Afterall, I had just enlarged the original hole significantly. The net results is that the clutch master is now about 0.4 inches further away from the pedal box. The main reason to do this is to give the balance bar mechanism sufficient room to operate without interfering with the clutch master cylinder. I shold also mention that I disassembled the pedal box initially and cut the balance bar threaded rod to be shorter on the side nearest the clutch master, again to improve clearance.

Issue – interference with steering column

Once installed, one of the master cylinders interferes with the steering shaft clamp (name?). I removed the clamp to make an alteration. I substitued 2 machines screws for the 2 main mounting bolts. I also countersink the two bolt holes to enable the machine screws to sit flush with the surface. It was the bolts heads of the original bolts which was causing most of the interferece. I also chamfered two of the corners of the steering clamp assembly for good measure. I’m not sure how much of a chamfer was necessary or even if it was ultimately necessary at all as I did this part by eye.

Workmanship

The four support rods which make up the pedal box fame were all of a different length. These were sufficiently different in length to notice
that the pedal box was not square. I disassembled the pedal box and milled the rods to be equal length.

General Info

I selected the flush mounted brake fluid reservoirs from AP Racing and these fit well under the bonnet. I had originally thought that the fit
would be close so I was planning to install remote reservoirs.

Performance

This is the best part. I am pleased thus far with the performance but it is early still and I need more time to get used to the feel of the new set-up. I will have better information after my next race later this Summer. My feeling so far is that the breaking power is significantly improved due to moving the bias rearward (my bias was much to far forward).

Once the desing is stable, my next plan is to install the 2-pot Hi-Spec rear calipers. I hope that my calculation of hydraulic ratios, selection of master cylinder bore diameters and the balance bar adjustor enable an optimal brake balance. We shall see… I also still need to mount the remote cable system to enable bias adjustment from the cockpit.