Ferret Gearbox issues (stiil) !!!!!!!!!!

[Chris Preston]

Greetings All,

 

So far so good (with this forum - I actually managed to get the photos posted). The two photos are from the Ferret I'm working on - under strict supervision of course. Our Ferret will start on the first turn but will not move when the gear-change pedal is depressed. We've gone through all the pre-start checks as per the manual, as well as the "manual adjust" with 30 depressions of the gear-change pedal, with no luck. We're able to move the gear selctor lever with no problem, as well as the forward/reverse lever, but the vehicle will not move.

We removed the cover plate over the tranmission brake bands, and saw that the transmission appears to be stuck in 4th gear, as per the photos below. Any thoughts on what's wrong (and how to fix it)?

 

Cheers,

 

Chris Preston,

Victoria, BC

[Richard Farrant]

Chris,

When you work the gear change pedal, do you see an movement of the 4th gear toggle? I am wondering if it is an issue with the gear change linkage that the pedal is not pushing the bus bar down enough for 4th gear strut to release. When I worked on these for the army, we had levers to fit directly to the gearbox (removing the short lever) then we could work the box without the pedal linkage inhibiting movement. Once a box was set up correctly, the pedal linkage could be adjust accordingly. For you, you could find a good fitting length of pipe to slide over the short lever, then drill it to fit a bolt to secure it to the lever.

 

Richard

[robin craig]

Richard,

 

what a sensible and simple idea.

 

R

[Fugly]

I stripped my ferret gearbox down and posted a thread on here somewhere. Its all purely mechanical inside the box, and very simple concepts . I did not do a full rebuild , but did reline the bands and had the selector mechanism to pieces.

 

If its stuck in 4th gear, the vehicle wont want to move because the stationary weight of the ferret is too much for the fluid flywheel to overcome. It will do this in 1st gear or emergency low but I reckon 4th is too highly geared . If you try too hard it could overheat the flywheel.

 

The selector mechanism is operated by the linkage so initially drop the lever linkage off the selector mechanism ( forgive me if you have already done that) . By hand try and move the gear selector lever ( not the gear change lever that's connected to the pedal) backwards and forwards. Its should move fore and aft. It should move easily by hand and wont select a different gear unless the lever is in the appropriate position AND the gear change pedal is depressed. Pressing the gear selector pedal releases the band tension on the gear brake bands AND allows the strut on the desired gear to move into position and when the gear change pedal is released , pressure is reapplied to that brake band because the strut that has just been moved into position. The struts normal resting position is away from the band mechanism, and by moving the gear selector lever this engages each strut. It sounds like the selector mechanism is not doing its job, perhaps because ( As previously mentioned) the gear change pedal is not moving enough to release the strut out of engagement , or there is a breakage or failure in the gear selector mechanism inside the gearbox.

 

If the gear change pedal is doing its job , when applied, it compresses a very large spring inside the gearbox that normally ( when not compressed ) applies the clamping force via the brake bands. You do have to be really careful with this spring as if there is too much free play in the selector mechanism , the gear selector linkage can go (over centre) for want of a better word, and send the pedal flying upwards, hence the need to regularly adjust the auto adjuster up by operating the pedal in each gear. You can release the spring pressure by removing the spring cover but be careful and follow the EMER - replace two of the bolts with extended bolts or studs and use the to slowly take pressure off the spring.