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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).
Braking performance, servo equality, chassis weight reduction, and lever modifications.

Identifier  ExFiles\Box 16\3\  Scan030
Date  12th December 1928 guessed
  
contd :-

-3-

SS.{S. Smith} servo has only 56% of the power of the old 40/50. This is rather the impression that is given on the road.

To bring the servos on equality, therefore, we have fitted 30° cams. The other noticeable feature of the SS.{S. Smith} brakes was a slight absence of firmness due to the increase direct braking augmenting the effect of any spring in the linkage. The direct units on Expl: cars have been :-

V.{VIENNA} series 25
EAC.14. 24
SS.{S. Smith} 28.5.

Now we have saved 500 lbs. on the chassis since V.{VIENNA} series and bodies are being made lighter so that we find cars are about 15% lighter than they were at the beginning of V.{VIENNA} series. Under the circumstances, it seems reasonable to reduce the direct braking by 15% to reduce the necessity for adjustment and to increase the feeling of solidity. This we did by increasing the length of lever G.76811 from 1.375" to 1.725" making the direct braking 21.5 units.

[Handwritten note above 'to reduce']: from V.{VIENNA} series

[Diagram of lever G76811]

The actual effective μ on our servos from various tests previously appears to be from .15 to .2. Assuming the lower figure on the SS.{S. Smith} servo due to the reduced driving pin radius we have the brake distribution on 18-EX to be :-

contd :-
  
  


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