1936-46 Rear Brake Line Protection

Friday, November 11th, 2016

For those that have not looked under the differential of an early Chevy / GMC truck, the following may be of interest.

Protection of the metal rear brake lines are shown in the attached photos from a 1939 Chevrolet ½ ton. They are separated by a brass division block (gray in photos) which is on the right side of the differential.

The result is a much shorter brake line section on the right side that connects to the wheel cylinder. It is interesting to see how GM protected the lines from stumps and rocks in the field. The line reaches from the top of the axle housing down to the wheel cylinder it is run behind and above the shock attachment arm and spring attaching bracket. It is kept away from incoming materials as the truck is driven in very rough terrain.


Full View

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.

Brake Pedal Pads, True or False?

Thursday, February 11th, 2010

The rubber quality on Pre-World War II vehicles was fair at best. Its useful life was limited. Thus, GM engineers did not add rubber pedal pads to early trucks. They were aware of the heavy abuse so many commercial vehicles would receive. In an era of limited income, GM knew few truck owners would never replace their pedal pads.

The solution was to add rows of bumps on the pedal surface. The leather shoe soles of the driver then prevented his foot from sliding across the pedal while driving. These bumps usually outlasted the life of the truck.

Brake Pedal Pads

Brake drum Wear 2

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

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

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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