Drum brake assembly, brake shoes for same, and method

A drum brake assembly comprising a drum to be braked, a pair of brake shoe assemblies movable to engage said drum in braking relation, and means selectively acting on said brake shoe assemblies to move same to engage said drum, said brake shoe assemblies each having a pair of ends with one end of one brake shoe assembly being adjacent one end of the other brake shoe assembly with said means operatively engaging said adjacent one ends, each of said brake shoe assemblies including friction braking lining mounted thereon for frictionally engaging said drum in braking relation, said friction braking lining having a friction braking surface extending in an arc substantially symmetrical centered on the horizontal center line of said drum brake assembly, said arc being no more than 60.degree..

For use in a drum brake having a brake drum to be braked by friction surface engagement of friction material provided as a part of a brake shoe assembly, said brake shoe assembly comprising:

• a brake shoe, friction brake lining secured to said shoe and having a friction braking surface in position to be moved into and out of engagement with the brake drum, said brake shoe having a heel end and a toe end with said friction brake lining being secured to said shoe so that the transverse midpoint of said lining friction braking surface is located on the horizontal center line of the drum brake when assembled therein;
• said lining friction braking surface subtending over a total lining arc length of not more than 60.degree.;
• said brake shoe assembly having substantially the same brake effectiveness factor variation over the useful life of said lining independently of the friction braking material of which said friction brake lining is made.

A modification to a drum brake assembly on existing vehicles in which the drum brake assembly to be modified includes a wheel cylinder and a first brake shoe and a second brake shoe positioned to have adjacent shoe ends operatively engaged by the wheel cylinder so as to be acted thereon when the wheel cylinder is pressure actuated, said first brake shoe having a brake lining secured thereto provided with a friction braking surface which extends throug.h a predetermined arc length, and said second brake shoe having a brake lining secured thereto provided with a friction braking surface which extends through an arc length having a range of about 110.degree. to 120.degree. and being typically an arc length of about 117.degree., said modification comprising:

• changing at least the brake linings of the first and second brake shoes so that the friction braking surface of the brake lining of the first brake shoe and the friction braking surface of the brake lining of the second brake shoe each extends through an arc length no greater than about 50% of the original second brake shoe lining friction braking surface arc length of about 117.degree. and the friction braking surface of each brake lining is so positioned in the drum brake assembly as to be arcuately symmetrical about the horizontal center line of the drum brake assembly.

A drum brake shoe assembly having a shoe and a brake lining on said shoe, said brake lining normally having its friction surface extending through a lining arc length of about 97.degree. when adapted for use as a primary brake shoe and about 117.degree. when adapted for use as a secondary brake shoe, said brake lining having enough of its friction surface removed so that the lining friction surface arc length is reduced to about 50% of its normal arc length by removing portions of lining material from the heel and toe ends thereof, said lining friction surface arc length then being symmetrical about the shoe assembly installed horizontal center line.

The method of decreasing the variation in brake effectiveness of a drum brake assembly by a factor of about four in a drum brake assembly of the type normally having a first brake shoe and first lining segment thereon with a friction surface extending through an effective friction braking surface arc length of about 97.degree. and a second brake shoe and second lining segment thereon with a friction surface extending through an effective friction braking surface arc length of about 117.degree., said method comprising the step of reducing the effective friction braking surface arc length of each of said brake shoe friction surfaces to about 40% to 50% of the normal second brake shoe friction surface effective arc length.