Transfer box output shaft preload. And speedo drive.

[Gazzar]

I'm sticking a transfer box back together at the moment, am I right in that the loading on the output shaft is caused by the speedo housing pressing on the outer race at the back of the shaft?

So the shims are critical, too much tension leads to premature wear and too little leads to .....what? And new bearings + new thrust washer would suggest that more shims would be required?

Also, what drives the speedo gear? Surface tension on the shaft? Or is it trapped between the inner race and the flange?

The things that occur while you are awake in the night (damn dogs).

Thanks,

G.

[Snagger]

All correct - the shims set the preload - too many shims and the bearings will be loose, too few and the bearings will be tight and will wear faster and and also generate more ehat, scorching the oil (which gets pretty damned hot, even hotter than the main box because the main box spends most of its time in 4th and the gears are just idling, while the transfer box always ahs all torque running through gear wheels and shafts). They normally have four shims, though I had to reduce mine to three on rebuild. The preload is set by wrapping string arouns the output shaft and then pulling on the free end with a sping balance, much in the same way as setting swivel pin preloads.

The speedo drive is clamped between the drive flange and inner bearing race, as you said, so a loose nut on the back end will let the gear spin on the shaft, resulting in undereading and erratic indications and eventually no indication at all. Unfortunately, you can rarely set the exact torque specified on this nut because you need to align the slots with the shaft hoiles for the split pin.

[secondjeremy]

I suppose to get the correct torque you could replace the castle nut and pin with a suitable self-locking nut.

Often I find the nuts are nicely pinned but loose - so things crush up or shafts stretch over the years.

[Gazzar]

Thanks, all, the spring balance is working fine - I presume nylon cord is specified as twine will drop chaff into the gearbox.

All good.

G.

[ejparrott]

I suppose to get the correct torque you could replace the castle nut and pin with a suitable self-locking nut.

I did

[tacr2man]

Redline Shokpruf works well in T/B JMHE

[Gazzar]

That's good to hear.

I've always thought that the newer oils should help, but was afraid of them eating the bronze bits in the gearboxes.