Radial play at gbx universal joint

[Glynh]

I have noticed an occasional clunk when taking up drive, so checked out the prop shaft. Everything looks fine but there is 0.5mm (measured with a dti) of radial movement between the front UJ and the gbx output shaft.

I'd appreciate some advice on this. 
 

[Gridgway]

Is this play between the two parts of the front UJ?  Or essentially play from the gearbox output shaft?

I'm no expert, but the former world worry me and I'd want to fix it.  The latter feels more normal.

[Glynh]

The play appears to be between the gbx shaft and the front yoke, so implies a sloppy fit between splines? 

[Gridgway]

That's a bit confusing, can you see the gearbox shaft staying still and play on the splines?

I would think it's more likely to be the output shaft turning slightly and showing the play.

[ScottR400D]

#4 I was wondering how you'd know exactly where the play was, you can't see the two shafts, the play could be elsewhere in the box. 

[Gridgway]

yes and that sounds like quite a normal amount of lash to me.  Again all from layman's knowledge