“SUN” SERVICE STATION

Sun (Auckland), Volume III, Issue 906, 25 February 1930, Page 6

“SUN” SERVICE STATION

THE '•Motordom*' section or The Sun includes in Its service to readers a Queries and Answers Department, the object of which Is to give accurate information regarding mechanical and touring subjects. Whatever the particular puzzle may be in either diagnosing irritating troubles or motoring information of any kind. ‘"Headlight' will endeavour to help, or refer the point to men who are recognised automobile experts in their respective lines. _ _ All communications must De accompanied oy the inquirers name and address (not for publication), and sent to THE SUN “Service Station, Motordom” THE SUN, Auckland. Answers will appear weekly in this column.

H.E.F.— Could you please inform me through your S.S.S. columns what fluid is usually used in hydraulic shock absorbers. Is it ordinary lubricating engine oil? This is a special fluid and may be obtained from garages or dealers. A.M.F. —My car is a Plymouth, and I’m supposed to get 25 miles + o the gallon; but the best is 19 to 20. One mechanic advised me to get extra air fixture on, while another advised a duo vaporiser. The car pulls and runs all right, and idles well. I would like to hear from readers who have tested these gadgets which is the netter fitting and where to obtain them. We do not recommend any attachments as being likely to reduce petrol consumption. The writer considers that if these devices were of any real utility, they would have long ere this have been standard equipment on all well-known American cars. It is impracticable to guarantee petrol consumption on any car, as a lot depends on the method of operation, etc. * * * “Old Timer." — l have an 11-h.p. old model Citroen tourer, and I am having trouble with the hand-brake, which works on the two back wheels. The brakes go on suddenly when applied and lock the wheels, and will not act smoothly. I have had it to two garages, and they have made no material improvement in it. Could you with experience of this trouble suggest a remedy?

(1) Ensure that brake cams move freely, and are a reasonably good fit in the bushes. (2) The liners of the shoes must be tapered off to nothing at the ends. (3) Shoes must be carefully balanced, meaning that the shoes must move at the same time when the brake cam is operated. This can be tested by the following process: Chalk the shoe liners and fit on drum temporarily. Put slight pressure on cam, then move drum round one turn.

still retaining the slight even pressure bn the cam. Remove drum, and examine the chalk indications. If one shoe should operate before the other, an adjustment can be made by fitting a small metal shim between the cam and the offending brake shoe. This operation must be carried out until the shoes function together. Check tension springs to ensure that they are strong and not stretched.

A.K.S.—Would you kindly answer the following question through the “S.S.S.”? I have been driving an Essex car for a good while, but don’t seem to be able to get the knack of changing down into second gear when going uphill, and also when coming down hill. What is the really correct way of making these two changes? I would rather try to teach you by demonstration than to put the method into words, for gear changing essentially is a matter of timing, and the more familiar a driver is with the note of his engine the easier the task should be. Remember that gear changing is merely an alteration of driving ratios. You have a top gear ratio probably of 5.25 to 1. and a second gear ratio of about 7.5 to 1. When driving in top gear your engine makes 5-25 revolutions for every complete turn of the rear wheels, so that to get the same road speed in second gear your engine must turn over 7.5 times. That is, it must, be sped up to half as much again if second gear’s driving shaft is to cleanly pick up the driven shaft, which is rotating at the equivalent speed of the road wheels. That is the basic principle of gear changing. When ascending a hill at 15 m.p.h. and you wish to change down, disengage top gear in the usual way by declutching and pushing the selector into neutral. Your foot is off the? accelerator, so the engine speed drops abruptly, but the road wheel speed

continues to be the same, or very little less. Obviously, then, the engine speed must be increased to the ratio of 7.5 to 1 revolution of the road wheels, which means that you tread sharply on the accelerator, rev. the engine up, then, as you take your foot off the accelerator again, declutch and push the selector gently into second gear. The process for changing down when descending a hill is the same, except that the car gains—instead of loses—speed when you disengage top gear, so that the engipe needs to be revved to a greater extent to co-ordinate with the speed of the road wheels. The easiest way to learn to change down is to practice on the flat at very low speeds, and to go through the operations very slowly and carefully. Don’t try to do it quickly until you are familiar with the engine’s note at various speeds. Once you master the motions you can do it at any speed and on any grade noiselessly.