Automatic and semi automatic gears [loss of]

[Jonathan]

If you lose gears with an automatic gear box such as an epicyclic gear box, try the following;

1. Switch off the engine and turn off the battery master isolator. Swith the isolator back on then restart engine. Gears should resume.

2. If having tried 1 above you still cannot engage a gear check the fuse to the gear box.

[BruceH]

Jonathan, I'd like your advice. What is the likely cause if such a fault is *intemittent*? On my bus (Daimler Fleetline, fully automatic gearbox), the reverse in the new transmission works as normal for serveral cycles, then for no apparent reason fails to engage. The trick of cycling the main battery isolator switch on and off seems to work and restores the reverse function but then it fails to work again after two or three or four cycles.

__. Any ideas? Thanks, Bruce Henderson, Wallace NC USA

[Jonathan Smith]

Hi,

There are two main areas to look at;

Gearbox and Electrics.

Usually you need a power supply to the gear box controlled from the cab which engages and holds the gear as selected. Normally reverse gear has an interlock requiring two separate actions to engage reverse gear.

On the electrical side I would be looking for a loose connection, faulty or dirty switch contact.

As far as the mechanical side of things go I would not know where to start.

Often there are switches on doors and lids which can cut out the transmission to prevent the vehicle being moved inadvertantly.

[BruceH]

__. Thanks, Jonathan. There is a separate lock-out knob for reverse on the shifter selector (there are only "R" and "A" positions on an upside-down "U" quadrant, neutral is at the top of the "U" with a spring-load to move the selector to the right, above the "A" position) and this seems to work OK. I'm pretty sure that there is no interlock on the doors since I've driven with them open for visibility when manuvering in tight spots.
__. But your description of the interface between electrical selector and the pneumatic shift system sounds exactly like the place to start looking for problems. I have a copy of the workshop manual for the chassis, but it goes into detail only for the four-speed semi-automatic -- but the fully-auto box must work in a fairly similar fashion so the info there should be generally helpful.
__. Thanks for your input. B Henderson, Wallace NC USA

[Jonathan Smith]

As far as I am aware the semi auto and fully auto are the same gear box. They just add the bits you need for the electronics to "decide" when to change gear.

I went to view a DMS fleetline near Oxford that was for sale, the batteries were flat and it needed jump started. We could engage the gears when the good batteries were connected, but as soon as the batteries were disconnected the gears disengaged.

As you fault is intermittent I would be looking at the wiring to the reverse gear. Does it work alright in all the forward gears?

[BruceH]

__. Interesting info on the low battery effect. I'm not sure exactly about how it works now (the bus is at the transmission shop) in the forward gears but I think it's OK. I'll send this info to the mechanics who are working on my bus -- I'm sure it will be helpful.
Many thanks, Bruce