F/O A.M.R. Mallock, R,A.F., supplies some useful Austin Seven conversion hints
Much informiition has beenpublished in the past on the subject of Austin Seven tuning and conversions – some of it good, but most of it, unfortunately, confused, if not inaccurate.
All my facts, therefore, are based on first-hand knowledge unless otherwise stated.
(1) Lowering a standard chassis. – The rear end of a standard chassis may be lowered by removing the rear springs and flattening them or by substituting already flat springs, such as “Ulster,” “Nippy,” or post-1934 standard types. The transmission line, braking arrangements, and shock-absorbers need not be altered.
(2) Track road clearance. – Some lowered front axle conversions employ a very deep bend in the track rod which leads to steering trouble. If the steering arms are changed over from left to right and inverted, an extra clearance of about 2″ can be obtained, thus allowing a standard track rod and steering arms to be used on an “Ulster” or similar axle, providing, of course, that dropped “Ulster,” “Nippy,” or W. special-type radius rods are used.
(3) Adjustment of castor action. – Oversteering is not an inherent feature of the Austin Seven suspension as sometimes suggested, and it is, in fact, adjustable to personal requirements.
To increase the castor action, slacken off the nuts securing the front end of the radius rods and twist the rods down and outwards with a wrench. Without allowing the rod to twist back, tighten up the securing nut. The alteration in castor angle can be clearly seen as the rod is twisted.
Under heavy braking torque this adjustment will probably slip back, but with “Ulster” radius rods this can be prevented by taking a strap from the rod to the shock-absorber securing bolt. Increasing the castor angle in this way tightens up the front brake adjustment, while apparently hopeless cases of steering instability can be cured in this manner.
(4) Fitting a 4-speed gearbox. – When a 4-speed gearbox is fitted to a 3-speed chassis it will be found to foul the near side body-mounting bracket. This bracket should be unrivetted, reversed, and bolted back in place. When a 4-speed gearbox is fitted to a 3-speed chassis, either the prop. shaft must be shortened or the engine moved forward. The latter has the advantage that the normal speedometer drive can be used, which is not possible with a shortened prop. shaft, but, on the other hand, moving the engine may lead to difficulties with fan-clearance, etc. In any case, a pre-1929 self-starter must always be used, as the 1929-30-31 type will not clear the gearbox top, and even with the older type starter some “carving” is necessary before it can be fitted.
If a 4-speed engine and gearbox unit, either “Standard” or “Nippy,” is put into a 3-speed chassis, no alteration need be made to the prop. shaft length, and there is clearance for the speedometer drive.
In general, 3-speed or “Ulster” speedos. cannot be used with a 4-speed gearbox, although I believe that some of the very earliest 4-speed boxes may be an exception to this rule; the reason is that the gearbox reduction ratio is different.
The reduction ratio of the 1934 standard 4-speed is the same as the 1936 “Nippy” close-ratio 4-speed.
(5) Interchangeability of front universals. – I have “swopped” over the engines and gearboxes of a 1936 “Nippy,” and 1934 standard chassis, which was possible because the front part of the spider on the 1934 fabric universal was splined on to its gearbox in the same way as the Hardy-Spicer universal of the 1936 “Nippy.” This combination of 1936 “Nippy” engine and gearbox with 1934 spider was later fitted to a 1928 chassis.
I am told, however, that the 3-speed spider is not splined on to its shaft in this way, so that anyone wishing to install a Hardy-Spicer equipped gearbox in a 3-speed chassis must first obtain a 1933 or 1934 Spider.
(6) Interchangeability of crown wheels. – It would be possible to write a whole article on this subject alone, due to there being nearly a dozen different types and variations of back axle. Unfortunately it is a subject on which I have no firsthand knowledge. The following is, however, from a “reliable source.” It is only a most general survey, and. is not guaranteed infallible in every case.
The 5.67 to 1 “Ulster” crown wheel requires an extra large case, and can only be used in its own axle. In general, all crown wheels and pinions having a thread on the rear end of the pinion shaft, just in front of the pinion, are interchangeable. This includes most crown wheels and pinions made after 1930.
The 1931 axle is of this type, and is therefore a valuable acquisition because: (a) a 5.25 or 5.625 to 1 crown wheel and pinion can be fitted, thus giving a choice of three ratios in a narrow axle; (b) its crown wheel and pinion can be fitted to a wide axle, thus giving a higher ratio (4.9 to 1) if desired. The 1931 type is believed to be the only 4.9 to 1 axle of this description.
(7) Banjo joints and transmission lines. – The Austin Motor Co., Ltd., seem to think that flattened rear springs require a raised transmission line. The “Ulster,” “Nippy,” and post-1934 standard engines have a higher transmission line than the older standard motors. This necessitates the use of an extra long “banjo joint” between the rear universal and chassis ball joint. Therefore indiscriminate swopping of engines may require modification to the transmission line.
Altering the wheel-base alters the transmission line, but some adjustment of the effective banjo-joint length can be made with packing pieces which will compensate for this.
A few examples will demonstrate my point: I started out with a 1928 “Chummy,” and fitted a 1934 engine and 4-speed gearbox. These went straight in with a little adjustment. I later swopped this unit for a “Nippy” engine and gearbox, and found the transmission line was a long way out. I could cure this by raising the front of the engine about 3/8″ on blocks, but this introduced snags with the radiator clearance. I removed these and tried fitting a standard 1936 long banjo-joint, which is approximately 1 1/2″ longer than the old ones. This was very much too long, so I cut it down by 1″, which served the purpose.
A similar effect could be obtained by inverting the chassis-mounting ball-joint bracket, as the ball is mounted eccentrically on the bracket. Similarly, if a 1927 engine is put into an “Ulster” chassis it is necessary to pack up the rear end about 3/8″.
(8) Interchangeability of back axles. – All back axles of the same width are interchangeable provided the correct length prop. shaft is used. There are two lengths of short prop. shaft, one being 3/8″ longer than the other. I was under the impression that the 5.67 to 1 “Ulster” was the only axle requiring the shorter shaft, but I recently found one fitted to a 1930 saloon. The 1928 “Chummy” and 1931 saloon use the longer “short” shaft. The 5.67 to 1 “Ulster” axle has a very large casing, which may foul the body.
(9) Exhaust manifold. – When fitting an “Ulster’s exhaust manifold, make sure that the centre manifold stud hole is properly blocked up. I was once somewhat shaken, when filling my radiator, to observe water pouring from the exhaust pipe!
If anyone has any queries, or requires further information, I shall be glad to be of what assistance I can.