[Mgs] Drive shaft balanced

[PaulHunt73]

New driveshafts are balanced off car on a machine so should be capable of 
being fitted to any car and run true, but it does depend on the trueness of 
the shafts in the gearbox and diff of course.  It's easy to check the UJs 
yourself, grasp the shaft and flange and try and turn them in opposite 
directions and see if you get any play, also for sideways play along the 
length of each arm of the 'spider.

The Workshop Manual makes great play about marking the flanges if you remove 
a prop-shaft from a car in order to replace it in the original position.  A 
nice to have, but irrelevant as far as balance goes because of the off-car 
balancing that was done on it in the first place. What isn't mentioned, but 
is vital, is to mark the all four *UJ yokes* before dismantling, get those 
back wrong and balance will be compromised.  This will ensure that the UJs 
at each end have the correct orientation relative to one another, which is 
something else mentioned in the manuals.  However Haynes (my edition at 
least) shows the incorrect exploded orientation but the correct assembled 
orientation.  The Leyland Workshop Manual (again my edition) shows it 
correct in both cases.  You can check this, which will show if the sliding 
joint has been reassembled incorrectly, but either shaft yoke could still be 
180 degrees out with each other, and either flange yoke could also be 180 
degrees out with its partner.  There is some evidence that the each half of 
the sliding joint should have arrows to ensure correct reassembly, but not 
all prop-shafts seem to have the marks, and they can be very indistinct, see 
http://www.mgb-stuff.org.uk/propshafttext.htm#yokes

Even with that you can still get the flange yokes 180 degrees out unless you 
mark them first.  If the UJ came to you with the car then a PO may have 
dismantled it and got it wrong, it might be worth comparing the cost of 
testing/rebalancing against the cost of a replacement shaft (and hope *that* 
has been balanced correctly ...).

Note that prop-shaft vibration would normally be evident at a given road 
speed in various gears, not just one gear.

PaulH.

----- Original Message ----- 
> After some tests at several revs of the engine and speed I finally found, 
> that some vibrations between the speed of 50 and 70 m/h are caused by I 
> think an unbalanced driveshaft between the gearbox and the differential 
> gear.