Imperial Brake Repair Information


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Adjustment for normal brake lining wear should be made when the pedal goes more than half-way to the floor in making normal stop.  Foot operated parking brake requires adjustment when the pedal travels more than 41/2 inches.  Brake linings should be inspected for wear every 10,000 miles, when the front wheel bearings are lubricated.

 

Special Service Tools Catalog - 1956, Miller Manufacturing Co.

Some basics from Jim

Brake systems: Originally it was one chamber of a master cylinder that created the hydraulic pressure that expanded the "slave" cylinders at the wheels to force the shoes into the drums thereby increasing the rolling resistance and bringing the car to a stop. The problem is that if a leak develops anywhere in the system, the fluid becomes incompressible  and all brake action is lost. beginning in 1967 the federal government required a "dual master cylinder" type of brake system. When you push the pedal you are actually pressing one piston which compresses fluid to compress the second piston. Each piston compresses fluid for one half of the brake system. Some cars are separated front & back others diagonally, front & rear. There are actually two independent hydraulic circuits. If one brake hose failed, and could not hold pressure there would still be an intact system for two wheels allowing for a safe stop.  Adding a dual master cylinder to a car not originally equipped is a matter of physically bolting the dual cylinder (and power booster?) in such a manner that it can be actuated by the brake pedal. In some applications this may require changing the entire underdash (underframe?) pedal assembly. Then running new brake lines in such a manner that there are two independent circuits. Most manufactures used the front/rear format because it required the least amount of tubing.  One half of the master cylinder went to the front and another was routed to the rear.  The fluid was routed through a pressure differential switch. This was a spool valve that received pressure on each end from each side of the master cylinder. A finger from an electrical switch touched the spool valve and if it was slid in its bore because one half the system has pressure and the other does not, the circuit is made and the "brake system failure" light on the dash is illuminated. If the system is not bleed properly after repairs getting the light to go out can be difficult.

Disc brakes:

In a disc brake system there are some unique parts. They were all put there by the factory and should be by the vehicle modifier too, BUT folks have successfully added disc type brakes to the front of an all drum car and not included each component.  The master cylinder for a disc brake system has a bigger reservoir for the disc brake side. In normal use a disc brake will "use" more fluid than a drum brake. In order that the disc side does not need to be checked any more often than the drum side the reservoir is bigger.  People often ask which half of the master cylinder works the front discs? answer the side with the bigger "pool."

Metering valve: 

This valve does not allow pressure to go to the FRONT discs until it has built up over a predetermined amount in the rear.  This is to allow the drum brakes a moment of extra time to push out their pistons and begin their servo action. Disc brakes can begin dragging on the rotor faster than drum type brakes can. (drums have to push against the springs etc.) It doesn't take that long but there is a slight lag. Ford recalled the 1965 & 1966 Lincolns to change their metering valves.  They did not anticipate TWO FOOTED driving. On a drum brake car a foot pressed slightly on the pedal would not activate the brakes. (especially if the were adjusted slightly loose) Two footing these first disc brake equipped cars APPLIED the front brakes and caused premature pad wear and overheated the braking surfaces. The new metering valves required more pressure to activate the front brakes.

Proportioning valve:

This is a device that lowers the hydraulic pressure to the rear drum system. Kind of like a very primitive anti-lock device, it tried to keep the rear wheels from locking up during hard braking. Disc brakes can tolerate a lot more pressure with out locking, especially when they are on the front where the greatest need for braking action is.

Again, a disc brake conversion CAN be done with out adding these valves.  A new car has to be designed to operate in weather and loading conditions that no collector would take their baby out into today.  Recognizing that there might be a tendency for the rear wheels to lock more suddenly or minor differences in wear between the front and back when driving carefully and you may never notice a problem. 

But while we are talking brakes. Your car was designed with a brake system that worked fine when new. Why not just try giving it a good high quality repair? You will probably be very pleased with the results. High quality means all new components including springs and HOSES. Flexible hoses are often overlooked. they not only rot on the outside but became occluded on the inside as well. At least pull them off and see if you can blow through them easily. Good luck on restoring your brake system.


This page was last updated January 7, 2005.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club