Apologies for a non- Locost question. I asked recently about shortening drive shafts. I am putting a BMW diff unit in a RWD Skoda gearbox. On further investigation I can get the shaft shortened and re-splined for the Skoda outer CV joint to make compatibility no problem at both ends. Only thing is, the BMW shaft has CV's that are secured with circlips not allowing any increase and decrease in length as the suspension moves up and down. I need that to happen at one end. Can I rely on a spline to move back and forward within the CV if I dont fit circlips. There is no possibility that the shaft would come out of the spline on movement, I just need it to slide a bit, say 20mm at max. Is that acceptable with well greased splines? Hope I have explained this alright.

Hi, the front driveshafts on an early Polaris 4wd quad bike work like that, at the inner end is a UJ which is fixed to the "diff" & the outer end has a C.V. joint that only pivots, no sliding action. The sliding is all done by the spline between the shaft & the C.V. spider, there is a spring clip but it's only really there so keep the splines engaged while the shaft is not in place. I've never seen them have a problem, but obviously the mileage is much lower than with a car.
The only real issue I see is how well will the splines slide when under power? Was there not a problem on some Triumphs with the sliding spline of rear shafts sticking & locking the suspension if they wer'nt lubricated? Would'nt be a problem inside a C.V. boot.

There should be that much compliance in the CV's themselves. The spline is not usually designed to slide under load unless it is designed with square cut teeth and a greasing system.

Often splines will lock up under load causing whats known as 'spline lockup' under acceleration, anyone who has owned a TR5/6 will know what that feels like (very unnerving!)

Mmmm, looks like I could have a problem then as I am doing this mod on a classic trials car and the most movement and also power through the system will be when the splines are moving the most ie; on a rough, rocky, muddy, rutted, steep etc track. Were the Triumph splines not lubricated enough (design fault) to cause the problem or was it simply the spline geometry?

The tripod joint on the older Sierra push in shafts has wheels on one part that sit in a tripod on the other giving the movement you require, worth a look at that configuration, especially for the extreme suspension angles required in trialing