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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).
Customer complaints regarding brake noise and analysis of a proposed servo modification.

Identifier  ExFiles\Box 30\6\  Scan154
Date  17th January 1924
  
R.R. 403A (40 H) (SL 42 12-7-23). J.H.,D.{John DeLooze - Company Secretary}
-3-
EXPERIMENTAL REPORT. Expl. No. 9940 REF:Hs{Lord Ernest Hives - Chair}4/LG17.1.24.

it has been complained of by everyone who has tried these brakes.
There is also a chunk when the brakes are applied going backwards, if it happens that the rear brake ropes are at all slack This means that the servo is not pulled back on to its stop.
Knowing how our customers complain of the least noise in the operating of the car, we feel that we shall get complaints with regard to this point.

Da.{Bernard Day - Chassis Design} suggested a scheme for pulling the servo round with the first movement of the brake pedal. We found this took considerable pressure.

It would be difficult to get this scheme to operate satisfactorily owing to the following conditions.
(1) With the standard leverage as on the 40/50 four wheel brake system, the pull in the rod operating the servo toggle amounts to .56 pedal pressure.

The pull required to rotate the servo (with shoes not in contact with drum) to take up the rear brake clearance is found by experiment to amount to approx. 80 lbs. at 3.35 radius which is the radius to which the pull rod is attached.

If the pull rod could be so arranged that it rotated the servo at this radius it would require a pedal pressure of
80 / .56 = 143 lbs.

The servo shoes would have to be separated by a spring of sufficient stiffness to prevent the shoes pressing on drum below a pull of 143 lbs.

This also would result in an appreciable amount of front braking before rear brakes came into operation. contd:-
  
  


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