Enthusiasts' Directory: No.1 Shock Absorbers

A considerable proportion of Motor Sport readers derive enjoyment not only from driving fast or unusual cars but from doing their own maintenance of such vehicles and acting as amateur designers and engineers for the purpose of constructing fascinating “specials.” For this reason we have decided that there is a demand for information about various accessories and components applicable to sports-car operation. The first instalment appears below and will be augmented from time to time.—Ed.

Introduction

The shock-absorber used on Mors racing cars as early as 1899, is a very important item in the specification of fast cars. Races have been won and lost due to the efficiency or otherwise of these components and the breakage of a shock-absorber or its securing bracket is sufficient to retire a car from a race.

Although Mors pioneered with pot-type fluid dampers, the stiff suspension and limited wheel movement of the vintage era lent itself to friction damping and the original Bentley cars used D.B. dampers, while subsequently the Hartford scissors-type friction shock-absorber became almost universal in its application. Contemporary with it, however, was the Newton strut-pattern hydraulic damper, found on the Newton-Ceirano car and on certain American automobiles. Developments which followed embraced the single or twin dashboard knobs, akin to those of a radio set, whereby front, or back and front Hartfords could be adjusted by the driver through the medium of Bowden cables (Andrex feature this system today) and the use by Rolls-Royce, Bentley and Lagonda of two-stage supple or stiff suspension control in conjunction with hydraulic damping.

Present-day low-friction supple suspension permitting big wheel deflections is particularly suited to hydraulic damping, in which increased resistance can be arranged to occur towards “full bump” and in which different damping characteristics may be applied to upward as distinct from downward wheel movement. In spite of the small size of car-style dampers, those on a fast car may absorb work equal to some 2 h.p. per wheel. We follow with data on seven well-known makes of shock-absorber, hoping this will be of interest to enthusiasts mindful of good road-clinging, on which correct damping has a significant influence, and to builders of “specials” who seek shock-absorbtion for their cars.

Andre Hartford

T. B. Andre & Co. Ltd. was founded in 1903 and has been connected with many engineering projects, including manufacture, prior to the 1914/18 war, of the Marlborough light-car. The first Hartford, single-arm friction-disc shock-absorber was made in 1922 and became almost universal on British cars, being used in racing by such drivers as Segrave, Frazer-Nash, Count Zborowski, Ralph De Palma, Rene Thomas, and many others, almost from its inception. Incidentally, it was Andre who presented the enormous Gold Cup to the winner of the J.C.C. 200-mile race of those days. Down the years the design has remained largely unchanged, although detail improvements have been incorporated. The present version of the “triple Hartford” is known as the Multiplex-type, with triple arms and four Anduro friction discs clamped between non-corrosive stainless steel friction-plates. Dual control springs on each side give accurate pressure adjustment, variable as required, with a self-locking indicator. Dirt and moisture are excluded by a stainless steel ring and it is claimed that “stiction,” sometimes associated with friction shock-absorbers, is absent and that climatic conditions have no adverse effects. The Andre shock-absorber is attached to chassis and axle or suspension unit through the medium of Silentbloc bushes. These well-known bushes, which need no lubrication, were introduced by the Andre concern and are now made by a separate company, Silentbloc Ltd. The Multiplex models are identified by the letter M; the single arm versions by the letter S.

In conjunction with Andre shock-absorbers the Andre Telecontrol System was developed, whereby the driver can vary the tension on the pressure plates through the medium of hydraulic pressure, built-up by a regulator (one to each pair of shock-absorbers) with hand wheel and pressure gauge, drawing fluid from a small container and conveying it to the shock-absorber via solderless pipe lines.

Types 502 S/2, 502 M/2, 506 S/2 and 506 M/2 are suitable for cars of various sizes and are priced at £4 14s.6d., £6 9s.3d., £6 12s.6d. and £8 0s.0d., respectively per pair with all necessary fittings. Special brackets are available for a wide range of cars and the charge for fitting four shock-absorbers is approx. £3. The commercial-vehicle Type 220 cost £14 per pair. The Telecontrol Type HC 23/2 car-size shock-absorbers cost £12 13s. per pair with fitting brackets and all hydraulic equipment, the Type HC, 33/2, for larger cars, £15 16s.3d. per pair. Each shock-absorber is guaranteed for one year. A fitting department is maintained at the address below, where technical advice is obtainable on mentioning Motor Sport. Competition Manager: L. W. Harris. Manufacturers: Andre (Components) Ltd., 38, Felsham Road, Putney, London, S.W.15 (Tel: Putney 5751).

Andrex

The Andrex, introduced a few years ago, is a totally-enclosed, fully-weatherproof version of the Andre friction shock-absorber, with the friction discs working in an oil bath. The friction unit is bolted to the chassis and the single arm to axle or suspension unit, via a drop-arm with Silentbloc bushes. Adaptor plates are available for almost every make of car. A pre-set screw enables the damping to be adjusted through a wide range of control from “hard” to “soft ” and it is claimed that once adjusted no further attention or topping-up is required and that tests in every quarter of the globe have proved the reliability and efficiency of Andrex shock-absorbers.

The Type TE 1/N, suitable for cars of up to 10 h.p., cost £7 15s. per pair, £8 10s. with adaptor plates, or £9 15s. with plates and brackets. This model is not available with Telecontrol. The Type TE 2/N, intended for cars, of all sizes over 12 h.p. (also for caravans and trailers), cost £9 10s. per pair, £10 10s. with adaptor plates, or £12 with plates and brackets. The Type TE 2/N is available with Telecontrol, when the price, complete, is £17 10s. per pair.— this version is sometimes suitable for cars of under 12 h.p. In some instances existing links can be used with Andrex dampers, when 10s. per pair can be deducted from the above prices. Competition Manager: L. W. Harris. Manufacturers : Andre (Components) Ltd.. 38, Felsham Road, Putney, London, S.W.15 (Tel.: Putney 5751).

Girling

In 1945 Girling Ltd. took over the manufacture of the Luvax damper, moving the plant from Acton to Grange Works, Cwmbran. With the Luvax background, and by intense research on the part of their own engineers, Girling produced a range of hydraulic suspension dampers capable of withstanding the severe road conditions encountered overseas and providing non-fade damping for long periods, at high temperatures, when used on racing and high-performance cars. The remarkable revival of motor racing was foreseen and a Racing Department was established, offering technical advice and servicing facilities to competitors at home and on the Continent. This competition service is continued, under the supervision of Girling’s Competitions’ Manager, Mr. C. E. Russell.

The Project Engineer, Mr. C. R. Stock, and the Chief Engineer, Mr. J. W. Kinchin, recently read an informative paper on Shock-Absorbers before the I.of Mech.E.

The present range of Girling dampers comprises their telescopic type and their piston-type dampers with single and double arms. Vane-type hydraulic dampers are still supplied as service-units on pre-war cars. The piston-type range consists of the types P, PR, PV, PVA and PVX. The P-type is the original version, providing dual action, a pre-set “bleed” taking care of small oscillations and h.p. relief valves the violent movements. Shim-type valves are used, satisfactory but sensitive to dirt. The PR-type is similar but has an additional recuperating chamber which ensures quick valve operation, absence of frothing and rapid recuperation at extreme temperatures and speeds. The PV is the latest development in Girling piston dampers. A c.i. body contains two pistons of the same material, linked flexibly together and actuated by a hardened-steel rocker-arm bearing on hardened-steel pauls. The recuperation valves obviate flexing shims and the h.p. relief valves are in a separate chamber and easily adjusted for accurate control of pressure. They are far less susceptible to dirt and at the highest speeds immediate fillings of each working chamber is assured. Spring connectors take-up wear between pistons and rocker, and cylinder-scaling is by steel plugs screwed into soft alloy discs. The PVA is similar but of larger bore. The PVAX and PVX dampers are similar to the PV and PVA internally but employ double-ended rocker shafts to accommodate wishbone linkage for use with i.f.s. systems. As greater stresses are taken by the body-casting this is sturdier and has four, instead of two, fixing holes.

The number following the type-letter signifies the size of the damper and further numbers—PVA 7/102— indicate the valve and bleed-settings (but not the pressures or timing employed). Obviously, this is not the place in which to describe the various settings available, but the Girling Technical Department can fully advise Motor Sport readers in this respect. The range of Girling piston-type dampers is as follows (the price, each, less linkages, is shown in brackets):

See table on page 43

The Girling DA-type damper is of direct-acting telescopic hydraulic type and is made in 1-in., 1½-in. and 2-in. working cylinder diameters. No linkage is required and, due to the long stroke, stresses are lower than in the piston-type, valve ports and restrictions are larger and therefore less sensitive, and as more fluid is in circulation pressures are lower. Maximum damping is provided on extension and compression damping can be varied between wide limits. Girling telescopic dampers are made in a wide variety of sizes, prices ranging from £2 5s. to £4 4s. each. Conversion sets to suit most makes of car are listed. The telescopic type requires no attention; the vane-type occasional topping-up with Wakefield-Girling thick oil, the piston-type occasional topping-up with Wakefield-Girling thin oil. Manufacturers: Girling Ltd., Kings Road, Tyseley, Birmingham, 11 (Tel.: Acocks Green 2831).

Newton 

Newton & Bennett, Ltd., were one of the pioneer manufacturers of direct-acting telescopic shock-absorbers and from 1925 up to the war they were the only makers of this type of damper in this country. It was they who introduced the method of replenishing this type of damper, whereby, to obviate over-filling, either the required quantity of fluid is measured out beforehand, or the level is ascertained by means of a steel rule, tables being provided to show the capacity of each size of damper.

The Newton hydraulic suspension unit functions on conventional lines, but it is noteworthy that the top gland is to all intents and purposes leak-proof, that its poppet valves (two in the piston controlled by a single spring) are of large dimensions and the “flap”valves lightly loaded. The piston-rod is chromium-plated and the piston and valve assembly is of zinc-base-alloy. The tubular members are of high-grade steel, copper furnace-braized.

To determine the required stroke, Newton recommend jacking-up the car by its chassis and measuring the distance between chassis and the top of the axle or spring when the wheel is just clear of the ground. The distance in inches will be the stroke unit needed, while to find the fitted dimension, measure between the centres of the fixing points when the road wheel is on the ground and add ½ in. to allow for compression of the rubber pad.

The Newton Suspension Unit is made in various sizes and types, of which the 14,000 is the universal car-size damper, although the Le Mans Replica Frazer-Nash, for instance, takes the SK.1662 damper, the Mk.V Cooper 500 the 11,250 at the front and the 11,240 damper at the back.

It should be explained that each damper is stamped with a code reference which tells the user its complete characteristics as well as its type. Thus 14,365 VE12C.2 is a 14,000-type damper with type 300 end fittings and a stroke of 6.5 in. U indicates normal constant leak (from the Code N  = no constant leak, U = normal constant leak, W = double constant leak. E indicates that extension setting No. 12 and C that compression or closing setting No. 5, are in use. S after the extension or closing setting code No. indicates that a special stop is fitted in the indicated direction of travel.

14,000 series dampers range from 3½ to 9½ in. stroke and 6 to 13.73 cubic in. fluid capacities. When it is remarked that the extension and compression settings available range from 10-30 lb. at 15 in. per sec. (Code No. 0) to 2,300-2,500 lb. at 15 in. per sec. (Code No. 21), the builder of a “special” car will appreciate that there is a Newton Suspension Unit for every need. The price of the type 14,000 is £6 per pair.

Manufacturers: Newton & Bennett. Ltd.. Valetta Road. Acton, London, W.3 (Shepherds Bush 3443).

Rotoflow

The Rotoflow damper has one moving part only and employs a special-filling material, being intended to retain the desirable aspects of the hydraulic damper without recourse to large numbers of small parts which have to be manufactured to precision limits. Consequently, it requires no maintenance. The Rotoflow damper is made in two main styles — the “A”-type, which provides a rapid build-up of damping on reversal which enables it to absorb the energy of comparatively small movements and the “G”-type, which is more suitable for soft suspension and large wheel movements, as it gives progressively greater damping with movement, in either direction. All the “A”-types and the ” G1 ” are adjustable, small movements of an adjuster screw affecting the power considerably. The “G3” is not adjustable, but is available in different strengths. A “D”-type damper is being developed which will give a degree of resistance, different in “bump” to that on rebound, this degree of difference being variable with the design.

The characteristics of some popular sizes of “A”and “G”-type Rotoflow are :

See table

Carding diagrams are available to those interested. The “A1” damper measures 3¼ in. in dia., is approx. 3½ in. wide to end of shaft, 2½ in. between fixing hole centres and 2 ⁵/₁₆ in. wide from base to inner end of spline on shaft. The bolts required are ⅜ in. and two spline lengths, ⅝ in. and ¾ in. are available. Equivalent dimensions for the “A2” are: 4 in. dia., 4 in. to 4½ in. wide to end of shaft, 4 in. between centres and 2 ¹¹/₁₆ in. to 3 ¹/₁₆ in. wide, spline lengths being ¾ in. or ¹¹/₁₆ in., and of the “G1”: 3¼ in. dia., 3⅜ in. wide to end of shaft, 3⅜ in. between centres and 2 ⁵/₁₆ in. wide, spline length ⁹/₁₆in. These dimensions should enable constructors to choose a damper to suit individual suspension systems, remembering that the Rotoflow is a replacement for existing lever-and-link dampers but may replace strut-type, integral or scissors-type dampers if special linkages or brackets are made and the chassis drilled to suit. Various linkages are available, including those for old-type Austin Sevens, and special parts can be made to specification by the Rotoflow people at short notice. Anti-roll bars can usually be dispensed with when “A”-type Rotoflow are fitted.

The units themselves, which incorporate a patented shock-absorbing principle, cost £1 10s. each for size “A1,” £2 10s. each for “A2” and £1 12s. 6d. for “G1.” Manufacturers: Universal Dampers Ltd., Cranmore Boulevard, Shirley, Birmingham (Tel.:Shirley 2278).

Telaflow

This is a strut-type teleseopic hydraulic damper made by the Rotoflow people. They claim even-cooling because the working chamber is largely unshrouded, further temperature reduction due to a large working chamber, as no recuperation chamber is used, and low weight. The main aluminium tube is ribbed for cooling and rigidity and the piston-rod is of high-tensile steel, protected by-rubber bellows against wet and dirt. The resistance medium is a solution of synthetic rubber in mineral oil. A rubber ball forms the recuperation medium and thus no free air or gas is in contact with the resistance medium, eliminating frothing and aeration. In the average car-size Telaflow the internal dia. of the working chamber is no less than 1½ in. Manufacturers: Universal Dampers Ltd., Cranmore Boulevard, Shirley, Birmingham (Tel.:Shirley 2278).

Woodhead-Monroe

Woodhead-Monroe strut-type telescopic hydraulic dampers, product of the famous spring manufacturers, are made in sizes ranging from those suitable for 500-c.c. racing cars, to dampers for diesel locomotives. The same principle is used for all types, a chromium-plated piston-rod reciprocating in a pressure-tube concentrically contained in a reserve tube. A compression valve is situated at the lower end of the pressure tube and a rebound valve is incorporated in the piston. Damping characteristics can be varied without recourse to excessive increases in oil pressure by altering the size and number of holes in the piston-valve. A feature of the Woodhead-Monroe strut is its ability to operate effectively at rapid rates of operation. The model “B,” suitable for cars of up to 35 cwt., has an internal bore of 1 in. and a maximum external dia. of 2 ¹/₃₂ in. The Technical Information Section is at your service with data, advice, blue prints, etc. on mention of Motor Sport. Manufacturers: Jonas Woodhead & Sons, Ltd., Kirkstall Road, Leeds, 4 (Tel.: Leeds 20814).