17" Wheels

18" Wheels

BRAKES

by Mr, D. ]. Punshon

Having spent many years building, modifying and generally fiddling with a CTD 40, I've come across tips and solutions to many problems, as most people have. However, as all cars are different, I would like to share my experiences.

I'm using a 351 Cleveland engine, which, as Ken Saunders has mentioned in a previous article, needs a lot of cutting, grinding and welding of the chassis to fit properly ( especially if it is fitted as low as possible ), but the biggest problem, apart from HUDDART ENGINES, has been the inlet manifold, as no-one makes one for downdraught DELORTO'S. I've had to make my own, so

if you are going the same route, either use WEBBER IDA'S, for which a manifold is available from Fast Freddy's, or be prepared to fabricate one,

The Cleveland's heads are completely different to the 302/351 Windsor engines ( excluding BOSS

versions ), but they can, with some small mods, be fitted to the small blocks as they are a very high flowing, big valve head, remembering of course the different inlet and exhaust manifolds needed.

With powerful engines come the need for better brakes, The standard Granada Scorpio based brakes are ok for the road, but are no use for any type of track work, Many people have changed to AP or similar discs and calipers which are a tremendous improvement. However they are expensive and require a lot of maintenance.

Personally, I don't like using servos, I've used them in the past, but a properly designed system without them can have the same braking effort with more feel ( important for those "OH SHIT" moments ). whether you use the latest dinner plate discs and multi Piston racing callipers or mass produced items, a properly thought out system is needed to bring out their best.

The standard GTD set for instance, uses a brake pedal ratio of around 2 . 5/3.0 : 1 because of the twin servo assistance . however, if servos are not used, the pedal ratio of at least 5:1 is needed, so a lot of cutting and welding is required, if a balance bar is to be used ( very useful if tyre or pad changes are made later ), the procedure is made more complicated. Another method is to use an adjustable proportioning valve incorporated into the rear brake system, you can even combine the two, depending on what the car will he used for. It's Possible to calculate the brake torque, pedal effort etc, needed or given for any particular system using simple mathematics. As an example, I will use the calculations for my braking system:-

Front Discs = 10.75 inch dia ventilated. Jaguar XJS

Front Callipers = 4 pot 44mm dia pistons. ( Rover SD1 )

Rear Discs = solid 11 inch dia. (Jaguar E type front )

Rear- Callipers = 4 pot, 38mm dia pistons. ( Austin Princess )

The following information and calculations were obtained with reference to the Brake Handbook,

by Fred Puhn,

GTD 40

I = wheelbase (95 inches)

Rft = Rolling Radius of Front Tyre ( 12 inches)

Rrt = Rolling Radius of Rear Tyre ( 12 inches )

FF = Vertical Friction Force On Both Front Tyres ( 1328 )

FR = Vertical Friction Force On Both Rear Tyres ( 1172 )

Weight Of Car = 2500 lbs

The following information is difficult to obtain so a typical or approximate value must be used -

N = Coefficient of Friction of Tyres = 0.75

dm = Maximum Deceleration = 0.75 G

Ycg = Height of Centre of Gravity = 21 inches

N1 = Coefficient of Friction of Pads = 0.3

Front Brake Torque = N x FF x Rft = 5976 inch lbs. / 2

Rear Brake Torque = N x FR x Rrt = 5274 inch lbs. /2

Front Calliper Piston Area = 8.547 sq.inches

Rear Calliper Piston Area = 7.065 sq.inches

Front Max Hyd Pressure=Brake Torque /N1 x Total Calliper Piston Area x Effective Brake Radius = 460.5 Pounds per Square inch (Pressure)

Rear Max Hyd Pressure = 553 pounds per square inch (Pressure)

Now, the maximum brake torque both front and rear is known also the hydraulic pressure is known and the calliper must be able to operate safely at these pressures.

Next, we have to determine-

1/ the pedal ratio,

2/ master cylinder size and pressure.

I'm using a pedal ratio of 5:1, it's a typical starting ratio and because of the pedal box design and foot well constraints it was the maximum practical ratio possible.

Note, if a balance bar is used the pedal effort is effectively halved to each master cylinder.

Pedal Pressure ( typ )= 75 lbs

Force on Cylinder Piston = 75 x 5 = 187.5 lbs / 2

Front, Master Cylinder Piston area = 187.5 = 0.427 sq.inches /438.5

Nearest Available Cylinder Diameter = 0.70 inches to 0.75inches

Rear Master Cylinder Piston Area = 0.30 sq.inches

Nearest Available Cylinder Diameter = 0.625 inches

I am using a 0.70 inch front cylinder, a 0.625inch rear cylinder and a .625inch cylinder for the hydraulic handbrake ( I also have a separate mechanical handbrake system using cables and Willwood mechanical calipers ). To help keep the cockpit as cool as possible and also to improve aerodynamics, I have installed the radiator further forward and panelled behind it to form a smooth air flow path from the radiator to the twin nostril outlets.

To improve access to the rear of the dashboard if needed, I cut the dash into top and bottom halves. I fitted brackets to the rear side of the mouldings so the pieces can be screwed together. The bottom half is painted and the top half is trimmed in leather cloth.

All I have to do now is to fit the sunroof, furry dice, tow bar and the car is complete, sort of.

To find out the Brake Pedal Pressure needed for the above calculations, without going to the expense of an inline pressure gauge.

1. Put a brick on the brake pedal.

2. Place your bathroom scales on the brick.

3. Stick your foot on the scale and press, then read off the pedal pressure.

Gulf Racing Colour paint codes

Thanks to Graham Endeacott for this information

045 RENAULT ORANGE
051 TRIUMPH POWDER BLUE
I have also been told the following are the same :-
Berger paints No 1125 standard triumph powder blue ICI no. 8013.
No 1456 triumph marigold ICI no 3393.