Driveshaft geometry question


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Sep 25, 2022
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Pulling my hair again. To pull driveshaft again for new front yoke, I put the car on blocks under the tires so I can get under. Yes, used to have a lift in a nice garage, but no more.....retarded. So, to gain just a bit of room for the rotundness, I used the bumper jack on rear corner to gain couple inches. Car on its feet with a little tilt. So, as explained below, I had some problem getting the driveshaft back in with new yoke.....slightly different from OEM. When the moded shaft went in, I had no extra length on the slip joint.....tight against the boot had to be careful in test runs. OK....all went well. Now, up under for a glance, and what do I see, but about an inch of shiny slip joint shaft out from the seal.....wth. Still on its feet, now on the ground, I jacked up the rear corner as before to see any change. Yes, about 1/4 inch less shiny shaft, but still over 3/4, not tight as when installed. I have checked by jacking up the corner again, checked motor mounts, rear spring mounts, and spring on the rear axle looking for what the heck is different. The singlular thing I have not done yet is to look at the rear yoke....but when istalling driveshaft the nut was in the right place, and no noise from the rear.....meaning to me that the rear yoke is not moving??? So, do any of you guys have any idea what the heck could be different, allowing the driveshaft yoke to show such a difference between install and after some runs. Got me drinkin.
Seriously, I suppose it can be explained to the nth detail including the weather barometric pressure, but I call it just settling in.
I'm not crazy about your severe lack of slip, tho.
I concur on your "raising methods", not near even "good", to me. Head to Harbor Freight and get a decent floor jack and jack stands when they come on sale next (which might be now!). The way you're doing it is three accidents waiting to happen! NO bumper jacks allowed!!!

In theory, the front slip yoke should be more in the middle of its splines, rather than not, if the rear springs have not sagged. If the rear u-joint is firmly seated in the rear yoke (which has minimal movement, in and out), the only movement the front yoke will have is from the action (raising and lowering) of the rear end moving it on its transmission output shaft splines.

Ran in to a similar situation with car on stands under frame. Yoke would not slip in far enough to allow rear u-joint to be installed. After a bit of head scratching, I put a jack under the differential and gained the clearance needed. The u-joint swings at the front of the drive shaft and the diff swings at the front spring eye. This difference allows the fore-aft movement. Lindsay
Thanks for comments. But, there is a bit of confusion on my methods. I use floor jacks, now on gravel with plywood under the wheels, to raise, but in some cases, instead of jackstands, I put the wheels on 6x6 blocks. Then, I will sometimes add some body lift, either with a small scissor under the frame, or in this case, I just added a few clicks with a bumper jack to raise the body a couple more....but I get your point on the bumper jack, but I am old.
Disconnect the rear u-joint from the rear yoke. Slide the shaft all the way into the trans. Mark the trans end yoke at the trans seal. Install the rear u-joint. Put the car on the ground. Jounce the car. Observe the mark on the front yoke. Measure the travel out.
If you don't see the mark, you definitely got a problem.