Robin Allum - Brake Modification

The brake system on my 1956 3 litre Lagonda has always needed a lot of effort when applying the brakes and every year the handbrake would fail the MOT. According to the inspector, as the car has a single circuit system, the handbrake is also the emergency brake should the hydraulic system fail. If it had a dual system the handbrake is then a parking brake and in theory the handbrake should pass at a lower figure.

I checked out the wheel cylinders and found that the rear ones were not compensating correctly and needed freeing off until they would slide satisfactorily. The Clayton Dewandre servo had been serviced by a previous owner but there was never the feel of assistance from it. I had the idea of changing the drum brakes to disc brakes and fitting a combined servo and master cylinder with remote reservoirs from an early Jaguar XJ6.

A disc brake conversion would be difficult but a dual circuit system would be easier. Unfortunately I could not get the Jaguar unit to fit in place of the existing one as it would not clear the cross member channels fitted to the underside of the floor. If remote servos were fitted, then two are needed. I spoke to a classic and vintage brake supplier who advised using 1.9:1 servos but he could not help with dual circuit master cylinders as these were too modern for him. I found that the American company Wilwood make a lot of equipment for race cars and that they do a 1 dual circuit master cylinder that would fit. I went on the web to find a Wilwood agent who had one in stock and the kit contained reservoirs for remote fitting. On Ebay, I also found some servos but the prices varied so much even though being sold by the same company MGBHIVE. I spoke to them and they explained that the prices were different because of the different ratios. They had a pair of 1.9:1 servos so I bought them. They are brand new Powertune units and appear to be the same as the old Lockheed ones even down to the instruction sheet.

The Wilwood dual circuit master cylinder.

Two Servo Kits.

On removal of the old combined servo and master cylinder it became clear that the new master cylinder would need a new support bracket making. I made this from 3mm steel and had to fit it nearer to the pedal. The operating rod supplied with the Wilwood unit has a 5/16 UNF male thread and the clevis bracket that needed to fit on has a 3/8 BSF male thread. I had some 5/8 hexagonal bar so I made an adapter.

Master Cylinder Bracket and support.

Master cylinder assembled with adapter to the clevis bracket.

Master cylinder in position.

The site for the servos was limited. Both would have to fit to the rear of the cruciform in the chassis. The one for the front brakes was fitted forward of the fuel pump. They come with a couple of brackets and only some small modification was needed to fit them on the main chassis rail and the tube rail. The rear brake servo is on the other side but the silencer is close. They need to be a certain distance from the exhaust system and I could just about get this but a heat shield needed fitting as well as a dirt shield.

Front brake servo fitted to the near side chassis.

Rear brake servo fitted between the off side chassis rails and behind the vacuum tank.

The size of the original pipe work for the brakes is with 7/16 UNF thread and the new equipment uses 3/8 UNF or 10mm threads so this would present a problem. Fortunately I found nuts with 7/16 UNF thread for 3/16 pipe that would be needed for the new equipment. Two of these nuts would be required, one for the banjo fitting on the rear hose and the other on the tee for the front brakes.

I used cupro-nickel 3/16 brake pipe as it does not rust like steel pipe or suffer cracking that can happen with copper pipe. I have a flaring tool so making up pipes was not a problem and to get the pipes to fit first time I used a length of wire, 1.5mm single electrical cable to be exact. I ran the cable along the route bending it to conform to all bends etc and then laid it along the pipe and cut the pipe 10mm longer for the flares. My one problem with the pipes was on the master cylinder as they fit to the bottom of it and turning them in to the master cylinder would be too close to the exhaust pipe. This is not a problem with an original engine but I have a V6 Ford unit fitted and one pipe is too close and I also needed the shield to fit. The problem was solved by fitting banjos to flexible hoses and the other end being fitted to plates on the chassis so the 3/16 pipe could couple up.

Master cylinder pipes connected and the dirt and heat shield fitted.

The vacuum pipe was connected to the existing tank but now there were two pipes. The connection to the tank is 3/8 BSP thread. I made up a manifold from 15mm brass rod with two spigots soldered to it and the end is turned down to 3/8 for the pipe union nut and olive to enable it to fit on the vacuum tank.

Vacuum tank manifold for hoses to servos.

Servo hoses connected to the vacuum tank.

The reservoirs are fitted to a plate and then fitted to the original mounting points. I would have liked to retain the original reservoir but I felt that this would be a safer option.

The new reservoirs.

Once the system was bled came the road test. The brakes have a totally different feel now and the effort is certainly less. Light braking is as before but heavier braking requires much less pushing on the pedal. Before under heavy pedal pressure one felt that the car would not stop but now I have much more confidence when applying the brakes. In my mind it was a good modification to the car. The disc brake conversion I wanted to carry out proved to be too complicated. New hubs would have had to be made if the original wheels were to be retained.

Shields covering servos.

Robin Allum