tailshaft

[graham7773]

This may sound like a stupid question but think about it for a minute before you flame me. Every irs car I have owned (except for front wheel drive models) has a 1 or 2 piece tailshaft with universal joints to accommodate movement of the differential. Every Commodore with irs has a diff bolted to the rear suspension cradle ie does not move as it fixed to the body. Why do they have universal joints? To my mind, they only need the center bearing which would look after any minor movement from mounting rubber blocks. Ideas, Suggestions?

[pablo]

With no uni joints every thing would have to be in perfect alignment. ANY variation would put a strain on the drive shaft or diff pinion. Eventually the bits would fatigue and fracture. Early cars had the diff housing ridgidly attatched to a steel tube which carried the drive shaft inside. This terminated at a slightly flexible joint at the rear of the g/box. The drive shaft would have a uni joint immediatelly behind the box, inside the flex joint to take up the missalignment and movement from the engine. The engines were bolted directly to the chassis, but still there would need to have that uni joint to stop the drive shaft from flexing.
Thats the best I can explain, but I know where you are coming from!

Pablo