Hoping for some help from someone who has had this same issue... It's very strange. I'm trying to chase down a 38-40mph hum/vibration that occurs only at float/cruise, When the drive line is loaded either accelerating or decelerating (it has 3.73's) there is no noise. So far I have had the 3rd member professionally serviced with a master install kit. No change in the noise. Then I had the axles professionally services with green bearings. Again no change in noise. I then bought the tool and tail shaft bushing. That moved the noise up a couple of MPH and changed the tone... so I "think" I am in the right spot now. Even with the new bushing the slip yoke moves quite a bit if you rock it... enough that you can make a audible "clunking" noise while wiggling it. I mic'ed the slip yoke and it does have a couple 2-3 thousands grooves in it. I ordered a 727 -7260 series yoke from Summit and it did not fit. The splines are visibly different. This morning I spoke to Brewer's and he tested his 7260 yoke before he sent it to me... guess what? It does not fit the 727 that he has sitting on his bench. I am lost as to what to do??? My 727 is a stock, late 60's unit (24 spline input) with what I assume is a stock driveshaft. The new yokes have splines that are cut more like V wedges and my original yoke and tail shaft have "squarer/ deeper" cut splines (if that make sense). Has anyone ran into this and has anyone found the correct, new slip yokes? I am not opposed to running a conversion U Joint if there is no other option... (however the conversion U joint would have to have a 7260 (the small one) on the one side for the fixed drive shaft yoke. Thanks for any help! Stay safe.