February 2012 Newsletter - KDA132

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Twenty Topics by Dr David Davis (Reprinted from Præclarvm 12-1 with the permission of the Author and Editor) The NZ Rolls-Royce & Bentley Club Magazine 11-6 has an article about fitting 4 wheel hydraulic brakes to an early 20hp GA69. The story of how it was done is fascinating. A later front axle has been used with the internals replaced with wheel cylinders hydraulically linked to the brake pedal. Two separate master cylinders with slave cylinders operate the rear brakes through the existing levers. The installation required a lot of meeting problems as they arose including the lubrication arrangements for the front axle. I wonder if the hydraulics would lock the rear brakes especially in the wet which is the main objection to 2 wheel brakes. I suppose it would be a matter of balance between the front and back. The modification passed compulsory certification. There are two other front brake conversions that I know of being 76A5 which has had motor bike disc brakes fitted to the front which involved machining new hubs. I understand that the pads wear quickly due to the weight of the car. The other conversion is Jim Kelso’s GRK81 which now has vacuum assistance applied to the brakes including the RR front axle fitted many years ago by Patrick Kane White .GF8, has vacuum assistance applied to its 2 wheel brakes which work well in dry weather but readily locks the wheels in the wet. Early in my ownership of 42G1, I asked Bert Ward should I fit An excuse to publish photographs of three “Twenties” active here: (clockwise from above) Philip Eilenberg’s Hooper bodied GEN39; Mulliner Weymann Saloon with Division GFN49, cared for by John Ferguson; and GTM28, James Young Drop-head Coupé from 1934 replacing the 1928 Melhuish Tourer body, owned by Vicky Ellis front brakes to the car. Bert’s response was that, properly adjusted, 2 wheel brakes were more than adequate. After I had driven two Silver Ghosts with 2 wheel brakes namely 45NA and 56 AG both of which were great, I appreciated that he was right. Early cars with A steering, such as Jim’s, have a special problem as the forward seating position necessitates downward pressure on the brake pedal rather than outward leg pressure as is the case with D. The seating position on the latter is further away from the pedal under the lower raked steering wheel. Clearly, nowhere near as much comfortable pressure can be applied to the pedal in the case of A steering as can be in the case of D. I can understand, then, why there is a perception that A steering cars have a problem. There is no doubt that the fitting of front brakes to a Twenty, involves assistance as the pressure required to operate 4 brakes effectively, is beyond leg strength which is a point raised by Bert. I have always been wary of the RR servo system as reversing can be unpredictable as can ahead, unless holding the wheel firmly. There is a full discussion on the RR servo system in Fundamentals of Car Performance by Hives etc including these issues which relate to adjustment. That book also comments on the differences between 2 and 4 wheel brakes noting that 60% of braking in the servo system is taken up by the rear brakes the performance of which in both systems is directly related to the proportion of the car’s weight over the rear wheels. The book points out that, in the end, it is all about tyre adherence to the road surface. The book notes that the greatest retardation achieved in tests was 20ft/second, squared and that the limit for personal comfort of the passengers in the rear of the car was 12ft/second, squared. The vacuum assistance fitted to Jim’s car is effective and I would say is more predictable than the RR servo. Of course the engine has to be running for it to work which is not the case with the RR system. It is interesting to note that the Springfield Factory retrofitted vacuum brakes to Silver Ghosts, and a Canadian owner of both Rolls-Royce and vacuum types, commented to me that he preferred the vacuum. The fitting of front brakes to an early car involves other considerations besides assistance including whether king posts and struts should be added to the bottom of the chassis frame to counter braking stresses and whether changes need to be made to the front springs to counter windup under braking which affects steering. There is a discussion of the latter in Fundamentals of Car Performance which explains why 4 wheel braked Twentys have longer front springs. Looking back over my ownership of 42G1, as Paul Samuels commented when he owned the car, the brakes were hopeless. The issue was the brakes seeming to not work at all followed by lock up. Replacing the heavy body helped matters but a significant improvement resulted from mounting the spare wheel at the back which stopped the wheels from locking up especially in the wet. Curing a differential oil leak followed by a complete overhaul including softer linings which have a more progressive action, has resulted in effective brakes in which I have every confidence. David G Davis 42G1 NSW NZRR&BC Issue 12-2 16
FOR SALE: 1960 Rolls-Royce Silver Cloud II Chassis SVB331. Good condition, imported new, always garaged. Present owner for 35 years. Comes with spare new windscreen, full set of tools (including some special), original handbook and set of workshop manuals. $38,500 o.n.o. For more details phone Merv Warner (06) 751 2414 FOR SALE: 1972 Corniche Convertible, 73000 miles, owned last twenty years. Original owner famous fashion photographer Terence Donovan. Receipts for $80,000 spent recently with Burkes Metals, and much more spent in Hong Kong prior to 1999. Body all done with DVD evidence and prepared for re-spray. Engine has leak to block. A good project, car presently with Bruce McIlroy, and looking for a good offer. Barry Donovan (03) 351 2600 dragonfly88@xtra.co.nz FOR SALE: Rolls-Royce 20/25 Rolling Chassis GRW51. Has been dry stored for the last 30 years; motor seized and no instruments, but otherwise complete, and with bonnet and scuttle. I have some history. Just one project too many. $19,500 1920s Maddox (coach-builders of Huntingdon from 1905) alloy panelled barrel sided tourer body originally on Minerva chassis, but fits 20/25 Rolls-Royce. $9500 Call for more information. Alan (03) 215 6383. 027 656 4632. alanfbryce@hotmail.com FOR SALE: Bentley R Type parts: brake linings, reproduction handbook and more. Phone Michael 0274 148 145 FOR SALE: 1993 Bentley Continental 111 Convertible, in pristine condition. Chassis SCBZDO2A8MCH 30587. Colour Brooklands Green. Serviced by Colin Gray annually. Original Avon Tyres replaced 5,000 km ago. Toolkit untouched. Owned for 10 years. One previous Bentley enthusiast owner. I’m coming on 86 and think its time to see another enthusiast in ownership of a wonderful low km irreplaceable Bentley. Could help with finance if required Bob Cleave, 29C The Parade St. Heliers Auckland 1071 Phone: (09) 5758 115 e-mail: rcleave@ihug.co.nz THE REAL CAR COMPANY North Wales Specialists in Rolls-Royce and Bentley Motorcars, 1920 to 1970s. Around 30 to 40 cars in stock, ranging from restoration projects to concours. We are always looking to buy similar vehicles, especially pre 1950. Highly experienced in the Ocean Shipping of these important cars. Web: www.realcar.co.uk Phone: 0044 1248 602649 Please contact Bernie Snalam for further information. e-mail: bernie_snalam@hotmail.com NZRR&BC Issue 12-2 17
Page 1 and 2: New Zealand Rolls-Royce & Bentley C
Page 3 and 4: Well, it’s that time of year agai
Page 5 and 6: (left and above) John King’s phot
Page 7 and 8: B166FB, engine H5BY, Park Ward Salo
Page 9 and 10: Dr Ian Johnstone’s image of B118L
Page 11 and 12: en route in the Carmargue, was aske
Page 13 and 14: trip of three more or less equal da
Page 15: The Opening of the Rolls-Royce Show
Page 19 and 20: Provenance The Rolls-Royce Motor Ca
Page 21 and 22: COLGRAY MOTORS Rolls Royce & Bentle
Page 23 and 24: BRUCE MCILROY LTD Authorised Bentle

February 2012 Newsletter - KDA132

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