Brakes

Installing an Updated Duel Chambered Master Cylinder

Thursday, August 16th, 2012

Warning:  When installing an updated duel chambered master cylinder under the floor of an older GM truck, a brake line modification may be necessary.

It is not acceptable to allow the modified brake line to touch or be very close to the exhaust pipe.  During long trips, the exhaust heat can cause a rise in the brake fluid temperature to near boiling level.  Modern master cylinders do not have a vented cap to release line pressure so fluid will be forced out through wheel cylinders.  The early single chambered caps are vented to prevent this.

Check your brake lines on non-original trucks.  Do not allow a safer system to leave you without brakes.

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1947-1948 Brake Release

Thursday, February 11th, 2010

The following article was released by GM on May 15, 1948. It was sent to all Chevrolet and GMC dealers and was to correct a problem with the location of the 1948 Brake release handle.

Brake Release Handle – Change of Location – 1/2 and 3/4 Ton Models

Some requests have been received for a method of changing the position of the brake release handle on the above models to prevent some operators striking their knees when entering the vehicle. The present location of the release handle is shown in Fig. 75.

1947-1948 brake release

In cases where it may become necessary to change the location of the handle, the position shown in Fig. 76 is recommended.

To re-operate proceed as follows

1. Remove the brake release handle, the release rod and the bracket at the instrument panel.

2. Drill two holes in the instrument panel for the new position of the bracket, 1- 1/2″ to the right of the original bolt holes.

3. Turn the bracket around so that the offset is towards the front and assemble to the new holes in the instrument panel, as shown in Fig. 76.

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Brake System Changes

Thursday, February 11th, 2010

Since the introduction of hydraulic brakes on trucks in 1936, Chevrolet and GMC had been using the Huck brake system. On light trucks and cars it can easily be identified by the existence of a pair of shoe adjusting holes in each backing plate. This system requires each brake shoe to be individually adjusted to the adjacent drum face by turning a cogged wheel on each side of the wheel cylinder. Thus the system does not use a primary or secondary shoe as in more modern types. Front and rear shoes in each drum are the same.

In 1951, light trucks and cars began using the Bendix brake system. Medium and heavy duty GM trucks converted to Bendix brakes in 1953. This system has a single adjuster on each backing plate and equally moves each of the two shoes. Thus the need for shoes with different amount of lining because wear levels are not the same on the primary and secondary shoes.

Brake System Changes

1936-1950 Huck Brake (above)

Brake System Changes

1951-1972 Bendix Brake (above)

Buy Parts for 1934 to 1946 Trucks

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Brake Drum Wear

Thursday, February 11th, 2010

Using a specialized gauge to show wear levels on brake drums is the best way to indicate wear, however there is a visual method.

Brake Drum Wear1

To give an easy indication of wear, GM builds a taper into their drums. The attached photos show this taper. When the drum is turned, the taper becomes smaller. Beware of drums that have been turned so much that the taper is no longer visible.

Brake drum Wear 2

Buy Parts for 1934 to 1946 Trucks

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Brake Cable

Thursday, February 11th, 2010

The common practice of replacing the original differential with a newer high speed assembly usually brings up another question: How do I connect the late model brake cable to the original brake system?

As the ends of most GM cables terminate with a steel ball, they can easily attach to a brake line connector as used on later GM vehicles. See photo. The other end of this connector attaches to a threaded 1/4″ hook found at your local hardware store. A nut on the brake’s shaft can be adjusted to eliminate excess looseness in the cable when the brake is not being used. This easy attachment will give years of dependable service!

brake cable 1

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