Brake chatter does not usually arise in the early life of a Morris Car. Brake chatter or “brake pick up” is caused by the brake liners and shoes tending to resolve with the brake drums until the shoe pull-off springs exert sufficient tension to release them, when the process is rapidly repeated, producing a severe chatter.
This irregularity can be overcome by chamfering down the extreme ends of the liners, using a dreadnought or other coarse file. The brake-shoes should be removed from the car, and the liners dressed in this manner for about one-and-a-half inches at either end, tapering down from full thickness to nothing. The sides of the liners should also be filed so that they are flush with the sides of the shoes, as otherwise, when overlapping takes place, there is a tendency for the shoes to pull the other into contact with the drums.
In extreme cases of brake chatter, however, there may be one or more contributory factors which produce the irregularity, but in all cases the liners should be treated on the above lines as a first measure.
Weak brake-shoe pull-off springs would allow the shoes to be picked up easily by the revolving drums.
If suspicion is felt regarding their tension they should immediately be tested, and, if necessary, replaced.
(Extra strong pull-off springs arc available upon application to Spare Parts Department.)
Another factor to be investigated is the condition of the brake camshafts and bushes; cases have come to our notice where the camshafts were badly worn and excessively loose in their bushes, causing the shoes to fall and thus come into contact with the drums. It may not only be necessary to replace the bushes, but the shafts also, if they are found to be badly worn. Cases of this nature are generally directly traceable to inadequate lubrication. Bent camshafts could also allow the shoes to drop, but these can be straightened if care is exercised. If it is necessary to remove the shafts for any reason, care must be taken, when replacing them, to see that the shoes are left sufficient clearance for free working, quite independently of each other.
Assuming the above points are now in order, attention should be given to the condition of the drums, and if found to be dented, or perhaps eccentric, they should be either be skimmed up in the lathe, or if the defect is too severe they should be replaced.
A very important point to be examined in extreme cases of brake chatter is the condition of the brake flanges on the axle. If the rivets are found to be slack, enabling the flanges to turn or rock, re-riveting is necessary. That the rear hub ball bearings are loose either in the brake-drum or on the brake flange is another possible cause of brake chatter.
Bibliography and Photographic credits
Morris Motors Limited, Service Information No. G/3 July 1928