114 Disc brake pad support arrangements

11.4.1 Swing yoke type brake caliper (Fig. 11.19) This is a lightweight, single cylinder, disc brake caliper. The caliper unit consists of a yoke made from a rigid steel pressing, a cylinder assembly, two pads and a carrier bracket which is bolted to the suspension hub carrier. The cylinder is attached by a tongue and groove joint to one side of the yoke frame whilst the yoke itself is allowed to pivot at

Fig. 11.18 (a-d) Automatic slack adjuster

one end on it supporting carrier bracket. The disc is driven by the transmission drive shaft hub on which it is mounted and the lining pads are positioned and supported on either side of the disc by the rectangular aperature in the yoke frame.

Operation (Fig. 11.19) When the foot brake is applied generated hydraulic pressure pushes the piston and inboard pad against their adjacent disc face. Simultaneously, the hydraulic reaction will move the cylinder in the opposite direction away from the disc. Consequently, as the outboard pad and cylinder body are bridged by the yoke, the latter will pivot, forcing the outboard pad against the opposite disc face to that of the inboard pad.

As the pads wear, the yoke will move through an arc about its pivot, and to compensate for this tilt the lining pads are taper shaped. During the wear life of the pad friction material, the amount of taper gradually reduces so that in a fully worn state the remaining friction material is approximately parallel to the steel backing plate.

The operating clearance between the pads and disc is maintained roughly constant by the inherent distortional stretch and retraction of the pressure seals as the hydraulic pressure is increased and reduced respectively, which accordingly moves the piston forwards and back.

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