RMB Pedal Stop Modification

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 worked well with several cars but is presented here 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 accept any resulting consequences.

On some 2½ litre cars with the hydro mechanical braking system it has been found that it is necessary to adjust the rear brakes very often if excessive brake pedal travel and a deterioration of braking performance is to be avoided. When everything is properly adjusted the driver's foot pushes the brake pedal forwards allowing maximum force to be applied to the pedal. When the pedal travel becomes excessive the driver's foot pushes the pedal forwards and down thus reducing the force the driver can apply to the pedal.

This can be improved considerably by allowing the brake pedal to start in a higher position and this can be achieved by cutting back the pedal stop on the chassis as indicated in the diagram. How much it needs to be cut back seems to vary from car to car but about 1/8 in. has been found to be a good start point. With the stop cut back it is necessary to adjust the rod which screws into the rear of the cylinder to restore the correct free play between the pedal and the front fork on the cylinder. The free play specified in the Workshop Manual is 1/32 in. This rod has a right hand thread at one end and a left hand thread at the other end. This allows the rod length to be adjusted by loosening the lock nuts at each end and twisting the rod to screw it further into the master cylinder and the fork end.