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Axles and Brakes

Internals of a typical pre-war Alvis made rear axle, from the TD 16.95 Silver Eagle Instruction BookAlvis used their own design of fully floating back axle for all pre-war models except the FWD, 12/70 and Silver Crest. Fully floating means that the halfshafts are only responsible for transmitting the drive, and have nothing to do with supporting the car or holding the wheel on. The benefit of this system is that a broken halfshaft does not result in the wheel coming off. On the other hand the splines transmitting the drive to the hub sometimes wear. Apart from a few Silver Eagles, the axle casing is cast aluminium, very handsome it is too, and surprisingly light. Various ratios were used, and most of the vital parts are available, including gears, halfshafts and bearings. Many owners nowadays opt to fit a higher ratio gear set for more relaxed cruising on modern roads at the expense of some top gear flexibility. Others fit an overdrive unit to give the best of both worlds but with added weight.

Alvis axles are very strong and will run for many tens of thousands of miles with no attention beyond lubrication. The 12/70 used a proprietary ENV axle of semi-floating design and this is more of a problem. The halfshafts are very strong, as is the steel casing, but the gears, crown wheel and pinion, and differential, can lose teeth. Spares are now available, with various ratios. Post-war, the TA 14 also used an ENV axle, hypoid this time, but parts from this do not interchange with those on the 12/70. The 14 axle seems to be stronger, and in any case there is a good float of secondhand parts for this model. A Salisbury axle was used on the Three Litre series, this is robust and parts availability excellent. It is possible to change the gearing to suit modern road conditions better. The automatic versions are rather higher geared.

From the Speed 25 instruction book, but this picture of a pre-war brake appeared many times from 1932, possibly earlier.Braking systems pre-war are rugged, simple and easily maintained ,as long as attention is paid to wear points. They are effective if in good condition, properly maintained and set up, but they require much more pressure on the pedal than is deemed normal nowadays. Compensation between different parts of the system, and consequently stability under hard braking, is difficult to achieve with mechanical systems. Drum brakes are also more prone to fade with repeated hard use from high speed. Alvis drum sizes are large, but it is important to use the correct (soft) grade of lining, especially in the non-servo systems. Modern asbestos-free lining material has been developed to match the old carcinogenic stuff. Nowadays linings are sometimes bonded to the shoes instead of riveted as originally. This allows the use of longer linings in the front brakes, with a gain in the swept area. Overhaul of Alvis brakes is easy using general engineering techniques and proprietary materials. The same remarks apply to the Bendix-Cowdrey brakes on the 12/70 and Silver Crest, also to the more complex Girling twin leading shoe system on the TA 14. The TA 21 and subsequent models have hydraulic brakes, and aside from a few early cars, the TD 21 moved to disc front brakes, then on the TE and TF 21 discs all round became standard.

The hydraulic systems on the later cars are easy to work on. It is standard practice to replace all the steel pipes and unions with corrosion-resisting copper or Kunifer. Some wheel and master cylinders are unavailable from time to time and substitutes may not match the originals in diameter. In this case restrictors may be necessary to maintain performance.

Controls of a Speed 25 as shown in the Instruction BookSteering boxes, rather that rack and pinion, are found on all standard Alvises. Up to 1927 an Alvis made worm and wheel box was used and new gears for this are available. All other prewar models, and the TA 14, except the Silver Crest, used Marles cam and roller boxes. Various sizes and types are found, with different bearing arrangements, and all can be overhauled relatively easily. Sometimes different and non-standard column lengths are found. Marles D2 and D3 units used in later 12/50s and early Silver Eagles are prone to cracking of the cross-shaft and MUST have this component replaced or ultrasonic tested before the car is used. The Three Litre box rarely needs attention, but cars with power steering need to be watched closely for leaks developing. Complete power steering sets are much sought after, which became available from the TE21 and were sometimes retro-fitted into earlier 3 litres by the factory. The Three Litre cars are considered by some to be heavy to park without it. There are modern discreet electric power systems available for those who find the cars heavy to handle. (The writer would point out that his late mother, a small woman of delicate proportions, cheerfully drove a non-power steered TE 21 and never complained!)

FootmanJames Insurance Longstone Tyres Chris Prince
Earley Engineering Fisher Restoration Hagerty Insurance
Tim Walker Restorations Peter Best Insurance Motor Wheel Service International Ltd.
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