From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Series of tests to diagnose and resolve rear brake groans on the Phantom II.
| Identifier | ExFiles\Box 12\5\ 05-page305 | |
| Date | 27th July 1931 | |
| To R.{Sir Henry Royce} etc. from GWH.{George W. Hancock - Head Chateauroux} RE : REAR BRAKE GROANS - PHANTOM II. We carried out a series of tests with the object of finding out the cause of the rear brake groans. The groans are entirely free from squeaks and should not be classified as squeaks. The groan is a period of slower vibrations with considerably more amplitude. There are occasionally squeaks from the rear brakes which are produced at a higher revolution of the drum. The period of vibrations per minute are quicker which gives off a note classified as a squeak. To find out which part of the brake mechanism was most susceptible to vibrations we carried out the following tests. We first tackled the anchorage of the brake shoes. 1st. New bushes were fitted with only a working clearance either in the bearing or endways. The result of this was nil. 2nd. Springs were fitted to prevent any chatter taking place in the toggle joints. The result of this was nil. 3rd. Springs of a considerable load were fitted to hold the half sections of brake shoes together to prevent any possible chatter. The result of this was nil. 4th. Steel ribbed brake drums were fitted. The result was groans at first were difficult to produce, but after approx. 1,000 miles they came as prevalent as previously, the difference being that the note was deeper and the revs. of the drums slower, i.e. the period of vibration was slower per minute. We jacked up the car and ran the transmission with the road wheels taken off. We were still able to produce the groans and by feel, we discovered that the back plate of the drums was the part that vibrated most. To damp these vibrations we procured a quantity of raw rubber, sand blasted the back plate of the drum and successfully vulcanised the rubber on to the plate. The result of this was most successful and after approx 1,000 miles with continuous braking, we were able to produce any groans. | ||