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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).
Report investigating brake performance issues, specifically focusing on servo efficiency and temperature effects.

Identifier  WestWitteringFiles\T\2January1929-June1929\  Scan192
Date  19th April 1929 guessed
  
contd :-
-2-
a persisting feeling of sponginess.
(3) The front brakes appeared to be doing
far too much work as they started to squeak on all cars.
(a) Investigation of (1) shewed it to be
due to the servo. Our standard servo lining is 'Halo'. As
we have previously reported the µ of Halo falls with tempera-
ture. We find that on the S.S. the servo gets warmer than on
the Phantom for two reasons.
(α) By reason of the unit construction, the gearbox tempera-
ture is raised by conduction from the engine.
(β) The S.S. servo is over the silencer, on the Phantom
it was not.
Additionally, with a normal µ the servo on the
S.S. requires greater end thrust than the Phantom due to its
dimensions and as our tests of the servo shew its efficiency
falls as the end thrust is increased the effect of a drop
in the co-efficient of friction of the lining is comulative.
We admit the 20 HP. servo is operating under similar conditions.
Actually we find the difference between hot and cold can be
detected but is not so marked as we are asking the servo to
do less and have more in hand
(b) Our tests on the servo shewed that its
efficiency fell off with increasing output. Also our tests on
the efficiency of the brake linkage shewed that its efficiency
to the rear brakes fell off with increasing load, both servo
and direct braking. This accounted for observation (2).
contd :-
  
  


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