Better Shoe Centralisation

When properly set up RM brakes are very good.  Sometimes however no matter how often they are checked they do not perform as well as they should.  The Workshop Manual covers most things but problems can arise which are not covered.  Before making any changes to the braking system ensure that they are properly adjusted and that the shoes and drums are clean.  The change described here has been found to work well but it is presented for information only. The braking system is one of the most important system on the car and it must be both reliable and efficient.  Do not make any changes to it unless you really understand what you are doing and are prepared accept any resulting consequences.

For brakes to work efficiently the brake linings on the shoes must make full face contact with the brake drum. Linings which are worn more at one end than the other are clear evidence that when fitted they were not making full face contact and have therefore worn unevenly. In this case braking performance will be poor until the linings have worn sufficiently to give full face contact.

Consider the system used on the RMF (above). The shoes are pushed towards the drum by the hydraulic cylinders. Assume that the shoes are not centred properly and one end of the lining contacts the drum before the other. The shoes are free to slide sideways at both ends so the end making first contact will push the shoes sideways until both ends of the linings are making equal contact.

Now consider the system used on the RMB (above). Again the shoes are pushed towards the drum by the cylinders but this time the other end of the shoes are constrained to pivot around a circular fulcrum. There is no provision for the shoes to slide sideways to ensure that full face contact is made. Even if the shoes are correctly positioned the end nearest to the cylinder will always move furthest so unless the other end of the lining started off almost touching the drum full face contact will not be achieved.

My prewar Riley had Girling rod brakes on all four wheels and even after careful adjustment they were never a good as I would have liked. I had a spare set of shoes which I was prepared to sacrifice so I decided to try an experiment

The picture above shows the overall layout for the rod system. The adjuster unit is at the top and the expander unit is at the bottom. At the adjuster end the shoes have a circular cutout which forces them to pivot around the adjuster thus preventing them from sliding sideways to centre themselves within the drum. I filed the cutout so that it was considerably wider and had a flat bottom so that the shoes could now slide sideways. I did this for all eight shoes. I then reassembled everything and adjusted up the shoes. I stamped hard on the brakes a couple of times and checked the shoes adjustment again before I took the car out for a road test. The improvement in the braking was immediate and very noticeable.

These modified shoes have been on the car for a few years now and the braking performance has remained excellent. I no longer fear the car in front with disk brakes stopping suddenly without warning.

I hesitate to recommend this modification to other Riley owners as should something go wrong the consequences could be very serious. All I will say it that it has made a big improvement to the brakes on my car.