Manky Monkey Motors

 First question , why ? Surely with a hard tail you can simply bolt it all together  using just the sliding front yoke coupled directly to the back flange via single u/j ?

I've often wondered that Kev -& you're certainly more qualified to know than me. Shortest I've ever had was the 2 UJs fitted back to back, as I still needed room for the seat between the gearbox & rear axle, plus a gearchange.

Mine's a bike trike of course - but the bike shaft (which is part of the original swingarm which is part of the trike build) is connected directly to the Relkiant shaft just forward of the diff.

Universal joints should be really be used in aligned pairs. A CV joint  between the sliding section and the axle flange would be better than a single UJ. In reality as long as the engine and the axle are carefully aligned a single UJ should suffice but don't expect the UJ bearings to last as they need angular movement to prevent wear and brinelling. If this  angle is introduced with a single UJ expect premature wear of axle, prop and gearbox, as the relative rotational speeds each side of the UJ will oscillate.

You could do away with the uj entirely though. I was only thinking of the one as it's the simplest way to make a connection. I've looked at the whole expected lifetime vs operating angles stuff on another project due to heavily misaligned operating angles ( just like hundreds of others the same but thought I'd actually look at the problem ) . The operating angle on mine reduced the life expectancy of the joint to 10%  which still worked out to something like 25k miles usage.:)


One reason I also asked is because in reality there is little difference to a torque tube application as on old Pops and many early Yank motors.

I used to work on line shafts in paper mills and factories, welding huge tubes to flanges. As technology and materials improved so did the speed of the machines. One of the down sides were the knocking out of the right angle drive gearboxes, bit like your diffs. To compensate we started installing the rubber doughnut, bit like Hillman imp and Lotus elan used but these are 20 inch diameter. The improvement was immense, the vibration level dropped and the gearboxes lasted forever. And the machine got faster. Now they use stainless steel shim type things on the star/Y joints with rubber inserts, amazing that they could improve even more, but they did. Any slight misalignment and vibration starts, causing wear on the diff gears.

I had 2 u/j,s together on my hardtail, solid engine mounded trike,for years, caused no probs,
I have now done a single u/j coupled with a bmw rubber doughnut,(and a small amount of slide) so far, it seems fine, I did some pics on this site somewhere, around 14cm long, in total

doesn't seem any better, its just that I thought the expension of the warm engine may cause load on the axle,?

As already mentioned I believe, an early Mk 2 Triumph GT6 I once had used inboard at diff. a standard U/J, whereas outboard at suspension end, a rubber/steel Rotoflex, which required shimming correctly, but once done they were fine, with reasonable life.Change the setup around for a trike prop. and, bingo The MK 3 GT6 system was somewhat different, so there you go, simples!....................... ;D  Morrag