2 speed gearbox strip

[Black Sheep]

My 1913 3 3/4 has started jumping out of high gear. I need to strip the gearbox. Any hints and tips on stripping and assembling the box? I don't want to cause any damage in my attempts. So far I have removed the 4 through studs but the box is reluctant to split. There must be a reason... 

[eddie]

Hi,
    It is probably just the good fit of the layshaft bearings that is preventing the cases from parting. Try warming the cases before applying too much force - the bearings are fitted into bronze figure '8' inserts that can become loosened by using excessive force. As you part the cases, there should not be any drag on the mainshaft bearings, as the sleeve gear should easily slide off the mainshaft. You will also find that there is a small brass/copper disc that blanks off the bottom of the hole for the gearchange shaft - try to keep the cases parallel, or this disc will drag and get bent as the cases part.

  Hope this helps,
                          Regards,
                                        Eddie.

[Black Sheep]

Thanks Eddie, I'll give it a go. I managed to buy a spare gearbox which I'm stripping as a practice run before taking the original one out. Hopefully between the two I should be able to build a fully functional one.
Gordon.

[RockDr.]

Sorry if this is a bit late but anyway....

[Black Sheep]

That's very helpful - many thanks.   

[Black Sheep]

The gearbox came apart easily once warm. It's in remarkably good nick. One of the gearwheels is stamped WD. Presumably a War Department item.
Now to get the box out of the bike and see what shape it's in. Won't be long until it's all back together and ready for more adventures.

[steveale]

Did you find the cause of it jumping out of high gear?  Mine is now doing it upon reassembly.  I've tried the linkage adjustment and when I get high gear stable it won't stay in low.  Similarly when I get low gear adjusted, high gear jumps out.  I have it in a compromise setting right now and just have to hold it into high gear until I am well underway then it stays there.

Anyone else with suggestions?

[Doug]

Steve,

The shift fork trunions and the the grooves that they engage in the bronze gluts are probably worn, resulting in lost motion. Also they are prone to wear where the shifter fork journals pivot in the gear case, resulting in even more lost motion. Usually new gluts solve 80% of the wear.

Besides losing motion, the clutch dogs on the gears may well have the corners worn down.

If the main shaft is worn (and/or the bores in the gears), things do not align as well as they ought and are less inclined to stay engaged.

-Doug