Full Constant Mesh in New D.134 Gearbox
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ANEW David Brown five-speed constant-mesh gearbox will shortly become available to the industry.
Outwardly identical with the widely used David Brown No. 557 standard unit, the latest product embodies modifications which give constant mesh on all five forward speeds and in reverse. instead of on only third, fourth and fifth ratios. The gear-centre measurements continue as before and the ratios are unaltered. Single-helical gears are now emploYed throughout, and all gears are finishetr.by-shaving and -lapping. Engagement is by sliding dogs.
The box is intended for either unit or amidships location and forward-control equipment, with an operating rod having a universal joint at each end, is available for either type of mounting. As hitherto, direct drive is employed for the top gear and the standard ratios for the lower speeds are 1,565, 2.74, 4.68, and 7.92 to 1, and 1.92 to I reverse. An aluminium case encloses the gears, its ribbed design being a factor which enhances rigidity. The top half can be removed without disturbing the gear assembly.
An intermediate wall carries a centre roller-hearing for the layshaft, whilst there is a roller hearing and ball thrust on the input shafts, with a thrust race on the output shaft. Main-shaft gears are each carried on two rows of rollers, with the reverse shaft on one rollerand one hall-bearing.
An additional thrust-bearing has been provided to absorb end-thrust. The shafts throughout are generously pro portioned and where bearing! are located in the aluminium casing, steel liners are prdvided in order to prevent the possibility of creep taking place.
An auxiliary-drive gear, to operate a high-pressure pump for braking is taken off at the rear of the box so that pressure is built up whenever the vehicle moves, even though running in neutral. Also located at the rear is the speedometerdrive gear which has been designed for the modern type of electric speedometer. Both of these drives are ball-bearing mounted.
The D.B. 557 constant-mesh box has been incorporated in test units produced by well-known commercial vehicle manufacturers, and performance reports, covering a period of several months, show satisfactory and troublefree running throughout. -The test machines referred to have been employed mostly in hilly industrial areas where operational conditions arc extremely severe. Following these successful trials the new design is to be incorporated in a number of passenger vehicles which are being produced by a well-known maker.