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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).
Letter discussing brake squeak, 'Mechanical Fade', and the ordering of friction materials for testing.

Identifier  ExFiles\Box 141\1\  scan0251
Date  19th February 1937 guessed
  
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(7) Deterioration of the Ferodo causing squeak can immediately be achieved by heating to 300°C. several times.

(8) If the Ferodo never exceeds 200°C. and seldom 100°C. squeaks do not occur very easily.

(9) Fitting floating dampers to the shoes, which necessitates drilling two large holes in them, makes very little difference.

As a catalogue of experiments we have made, this list could be extended almost indefinitely.

Regarding the variations in the value of the co-efficient of friction, in which we are not primarily interested, the following points seem to stand out -

(a) Your type of test does not greatly resemble road use of a car brake.

(b) Our type of test is a closer approximation thereto.

(c) "Mechanical Fade" on our rig due to leverage changes is negligable compared to the torque variations we measure.

(d) "Mechanical Fade" on our rig due to bedding changes can be ignored as the Ferodo specimen occupies only 2½" in the centre of the shoe and therefore the pressure centre cannot be transferred from the 'toe' to the 'heel' of the shoe or vice-versa.

(e) That the fade we measure on either our servo or brake rig is similar when used with the same temperature limits and therefore if the fade is due to "Mechanical Fade", the mechanics of our servo and brake gear must be similar; and this is not so.

We will order two sets each of the following materials for test purposes, plus one set of rear only for rig tests, in Bentley sizes -

VM.20. VM.30. S.6860. S.6219. ML.

Your letter of the 12th inst. regarding our order for VM.30, came to hand on either Saturday or Monday and was on the writer's desk when he returned from your Factory yesterday, having been passed over by our Order Office.

Yours faithfully,

FOR ROLLS-ROYCE LIMITED.
  
  


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