noisy half shaft

[alfred]

I'm just finishing off a full rebuild on my IRS and thought I would run the car a bit while it was still on the hoist. To my surprise I'm hearing a clanking sound once on every wheel rotation. Sounds close to or at the inner u-joint. But, when I loaded up the suspension (lowered the car onto jack stands at the rear hub) the sound goes away. So, is it just the limit of the u-joint at full suspension drop and am I Ok to test drive the car, or do I have to start removing things again

Alfred

[chrisfell]

UJ boots hitting the hub carrier?

[alfred]

I removed the boots earlier yesterday (they were grinding a bit as well), but the clacking sound remained.

Alfred

[JagWaugh]

Do the U/Js have grease zerks?

[alfred]

yes the joints have the grease zerks. It did not show any wear/hitting at that point.

[christopher storey]

Almost certainly caused by the angle of dangle. These are not constant velocity joints, and therefore at considerable angles there will be some point where the joint may " snap over" from one angle to the other

[alfred]

thanks fro the vote of confidence Christopher. I'm going to test drive the car today and see how it goes. Perhaps the rebuild suspension now allows a bit more travel and some u joint binding.

[alfred]

good news, after a short 20 minute test drive everything is running smoothly without extra clanking or other rubbing noises. (Other than the new brake pads need to wear in) Likely had the u-joint rotating beyond its working angle.

[Hugo]

The two u/j's should cancel each other out so the irregularity goes away. That's why u/j's must always be 'phased', so the input u/j and output u/j are a mirror image of each other. The yokes are fixed in the correct position on the Jag half shaft, so in theory the wheel should rotate smoothly no matter what the 'angle of dangle' of the suspension. The only way you will get uneven rotation of the wheel is if the output shaft from the diff is pointing an a different direction from the axle shaft. I would imagine there is a bit of camber on the rear wheels when the suspension is 'drooped', but I wouldn't have thought it would be enough to cause erratic rotation of the wheel. The drive shaft may rotate erratically but the wheel should not.

[christopher storey]

Hugo : constant velocity joints are exactly what you envisage - they create rotation at a constant speed. These are not CV joints and that is why at extreme angles they do not provide a constant velocity effect. Using opposite phases on the inboard and outboard joints will reduce the effect, but never eliminates it at significant angles. This is why CV joints are now universally used on FWD cars

[Hugo]

They must cancel out, surely? If you introduce an error in the first u/j, then take it out by reversing the process in the second u/j, the nett result has to be zero, doesn't it? Assuming the input and output angles are the same, of course.
FWD is different in that the angles between input and output shafts are going to be very different as soon as you turn the steering. I once had a BSA 3 wheeler with FWD and spider joints on the outboard side. You could certainly feel the unevenness when you turned the wheel.
Clever things, CV joints. Invented by some Greek bloke if I recall.

[christopher storey]

They don't cancel out altogether because the mathematics of the planes of motion involved are very complicated and beyond me , although there is a very interesting paper on the subject somewhere. They broadly speaking cancel out as long as the apparatus behaves as a double cardan shaft and the whole shaft is fairly straight , but as I understand it once you get significant angles on the joints themselves side loads start to appear on both the input shaft and the output shaft even though these to may be parallel with each other, and it is the reaction to these side as opposed to axial loads which starts to cause the UJs to experience friction which is beyond the design tolerances. The output shafts in a static state are probably near enough parallel to those in the final drive , but once drive is applied toe-in/ toe-out effects, coupled with squat etc under acceleration and dive under braking start to complicate the issue. It is probably unnoticeable in normal use, but if you have the wheels off the ground the angles are unusual. Having said that, I remember that on the Triumph 2.5 PIs I had now 45 years ago, there was a noticeable squirming effect one could sometimes feel under hard acceleration because of spline locking and/or Uj friction

I think the original inventor of the Cv joint was Rzeppa

[alfred]

Continued good news, several 1 hr trips in the car and all is quiet from the IRS/U-joints. An unexpected result of re-gearing the differential from 3.57 to 3.07 is the speedo is now bang on (it was reading 10-15 km/hr proud before the change).