Toploader Yoke side play and U joint side play
 

Working on the car to get it ready for Summer. I took the tunnel of and now will be calling Bob to get new carpets, not every pice but a least 5 pieces assciated with the tunnel. Somebody glued the carpet as if the tunnel was permanent.

Questions:
1) I have .050 " of yoke side play in the 14" tail housing measured at the U joint end cap.
2) My front U joint has .010" of side play. I can see it move. Is this too much?
3) I have 7/8" of slip yoke "clean machined metal" outside the rubber slip ring edge. Can that be reduced since I have the Jag rear end and there is no in and out. Hopefully to gain greater rigidity ?

I can feel a little drivetrain grunting going throught 2500 -3000 RPM, I wasn't looking for problems but working on the ERA Hurst shifter play.

It is Saturday and I am sure the drive shaft shops are closed.

Google searchs of the subject not real clear on the yoke side play issue

If you can see or feel any motion in a u-joint, replace it. A "loose" u-joint may be a contributor to your worn tail housing bushing.

When you reassemble it, make certain that your tailshaft and pinion centerlines are parallel (but not aligned).

I'm familiar with tailshaft wear in old Corvette Muncies. If you can feel lateral play in the yoke then it can create driveline vibration - the more play the worse the vibation. I can't relate it to .050 in play however.

It depends on a couple of things
 

Learjockey1 Being a short drive shaft, there is going to be a little vibration because you don't have the room for a dampener ring on the shaft. Have to remember that our motors are off centered and it is important to have the right angles from the trans to the driveshaft and driveshaft to the rearend. We also have a little right to left off center too. If you got your drive shaft from ERA they have grease fittings and only need a couple of pumps to remove any play in the universal cups. I use Amsoil hi temp grease in all my joints, upper and lower ball joints, inner and outter tie rod ends, inner and outter drive shafts between carrier and outter hub. Some hubs have grease nipples for the hub bearings, mine do.
You do need some play at the slip yoke. The problem may not be the yoke but the yoke bushing in the tail housing of the trans. Do you have a leak, wet spot, or any spray looking around this area? If yes, replace bushing and seal. You can add a little special grease inside the yoke that doesn't break down from the fluid. I will have to get you a GM number for it, comes in a kit. If you have a vibration at a certain rpm range, it could be any thing in the drive train from clutch to driveshaft to rearend yoke without a weight or may have a wobble. If it is really bad, take the drive shaft and have the balance checked. If it's not, than start with removal of the drive shaft and see if it happens in the rpm range without the rearend hooked to the motor and trans. If yes, start at shaft and then go to rearend, if not start at clutch and remove and go from there forward.
Do you have an ATI dampener on the motor?? I have had issues with it at times until the fluid warms in it and the weight moves.
As for length on driveshaft, IMO I like them with alot of spline in the yoke. I leave about 1" until bottomed out on tail shaft.
How many miles and is there any abuse done to the drive train? Where did the trans come from? It may be a simple as just needing a bushing and seal. Do basics first. Last thought and you need to be REAL careful. I don't recomend this to most garage mechanics because of safety.
Put the car up on jack stands, For the rearend have them as far out as possible to hold the weight of the car.
Make sure the tires don't rub
Have the tunnel out of the car
Start up the motor and run the car till you get the vibration
good light and a shape set of eyes will show it any thing LOOKS out of true spin. Start with that section for the vibrations. Wheels and tires get flat spots and have vibrations also after sitting on concrete floors for a couple of months. May need a balance for the tires. .5 oz could cause a vibration at a certain rpm range and not be felt at a high rpm.
If you can't find, send the car back to ERA. Let doug fix the problem. He's a top mechanic for finding these kind of problems and fixing them.
GM has a EVA machine that gets hooked to the chassic of the car and shows Hertz and helps isolate where the vibration is coming from. Doesn't work so well on a cobra. Good luck Rick L.

Thanks to all for the info. I think the tailshaft bush is worn and may be 90% of the problem. Grease on the joint will take up the .010" side play. I use the Dupont Krytox 215 grease on the yoke splines and I like the Amoil in the U joints. The vibe is not bad, I just notice it. I will do the simple stuff first. Again, to all, thank you for the analysis.