Manchester bus gearboxes
Page 66
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I write to point out two errors in a recent article — "Transmissions: a period of change" (CM December 6).
First, the Allison 41540 transmission fitted to our Seddon Midi buses does change clown during deceleration. Under foot-off conditions, without the brakes applied, the vehicle does run on, but as the speed drops so it changes down through the gears. The changes are more noticeable with the brake applied when changes occur at 19, 12 and 5mph.
Secondly, our two Mercedes-Benz 0.305 buses are fitted with The Daimler-Benz W3 D080. This is a three speed torque converter transmission with four stages. The first stage is, of course, torque converter in bottom gear. The second stage is lockup in bottom gear. The third stage is second gear and the fourth stage is third gear. Lock-up occurs at a comparatively low road speed and from then onwards all upwards changes are in lock-up.
This is a very efficient transmission which is noticeable in fuel consumption and very good road performance in comparison with the power available. It has other advantages in that there are holds in both first and second gear, but although these gears can be selected at any speed, engagement will occur only at the correct road speed to prevent mechanical damage. Both upward and downward changes, regardless as to how the vehicle is driven, are extremely good.
HARRY TAYLOR, Group Development Engineer, Greater Manchester PTE