Driveshaft length Question

Discussion in 'Got gears?' started by nick21, Oct 15, 2017.

  1. nick21

    nick21 Active Member

    Hi all!

    I'm in the process of changing my torque converter in my 71 skylark. The car has the original 350 and th350 transmission. To get the driveshaft out of the car I had to remove the caps off the rear u-joints and could just barely maneuver the u-joint out of the rear-end. (The car is sitting on 4 jackstands). The torque converter has been changed and the transmission is back in the car. I also changed the yoke because I was concerned that something was wrong with the original one. I'm trying to reinstall the driveshaft, but it just seems to be too long. I'm just wondering what I'm missing. All the main components of the car seem to be original. I don't know why the driveshaft would be too long. When I push the driveshaft into the transmission there is still about 1/2 inch sticking out when it bottoms out into the transmission (see attached picture). Is this normal? The overall length of the driveshaft is 56 1/2 inches. Any suggestions are appreciated.

    Thanks, Nick
     

    Attached Files:

  2. Bens99gtp

    Bens99gtp Well-Known Member

    I would think that should slide in farther, not sure why it won't go in any farther........but if everything is as should be sounds like the shafts just needs shortened
     
  3. 64 skylark mike

    64 skylark mike Well-Known Member

    Are the jack stands under the axles or the frame? If under the frame, the rear end might be hanging at an odd angle possibly causing the pinion yoke to move forward. Not sure on this being a possibility, but it does move with torque on acceleration, maybe causing your problem.

    Hopefully others will chime in here.
     
  4. hugger

    hugger Well-Known Member

    You should have about an inch of movement before it bottoms out in the trans with the suspension loaded
     
  5. nick21

    nick21 Active Member

    Thanks for the responses so far. I have all 4 jack stands under the frame. I tried jacking the rear end up (load the suspension) and that seems to help a little, but I still can't get the u-joint in without removing the caps and maneuvering the u-joint into place. Once in place with the u-joint caps on and the rear end sitting on a jack the driveshaft can move back and forth around 1/16th of an inch. This is the same amount of movement I had during disassembly. So moving forward should I have this driveshaft cut? Just to verify with the suspension loaded i should be able to unbolt the rear u-joint and slide the driveshaft around 1 inch forward?
     

    Attached Files:

  6. knucklebusted

    knucklebusted Well-Known Member

    The rear end needs to be where the drive shaft is straightest. That tail shaft pic looks like you should have a little more play in the yoke. I would slide it out and look at the splines in the yoke and the tail shaft. On a Turbo 350 you can remove the tail shaft housing with 4 bolts and see if there is something mechanically stopping you from going further. It could be just some build up/gunk/varnish in the splines. If so, you can use the drive shaft to lightly slide hammer it on further to clean them out.

    Also, when you take it off and put it on, do you twist the ujoint all the way to one side, slip that cup in from the side and then set it on the rear end yoke? It helps to have the trans out of gear and the e-brake off so you can turn them to find an optimal angle. All of mine are tight but not so tight I have to remove the cups.
     
  7. buick64203

    buick64203 Just plum crazy Staff Member

    The 1971 assembly manual says the driveshaft length should be 55.144
     
  8. 64 skylark mike

    64 skylark mike Well-Known Member

    My understanding is that there should be 3/4" to 1" slide movement with the suspension loaded. My brother in law had a drive shaft tight like you describe on a 70 Skylark. He had 2 transmissions destruct before he figured out what was happening.

    The rear end rolls slightly under hard acceleration, and the pinion will raise up towards the floor board. When that happens, it pushes the drive shaft towards the transmission. That is where the 3/4" slide on the yoke comes in. Plus it allows you to install the drive shaft and then slide it back that 3/4" to mate up the u-joint at the pinion.

    It's possible in 46 years somebody changed the drive shaft.
     
  9. Bigpig455

    Bigpig455 Fastest of the slow....

    I've got my 65 up on a two post lift, lifted by the frame and with the rear axle hanging it is tough to get the driveshaft out.. I've got maybe a 1/2 inch of play and I have to sneak the caps around the yoke..
     
  10. Mark Demko

    Mark Demko Well-Known Member

    Question: Is your current driveshaft one piece?
    The original shaft was two piece with the rubber sleeve joining the two.
     
  11. hugger

    hugger Well-Known Member

    Yes you need an inch of movement with the suspension loaded

    If there is enough room outside the tail housing but it's Bottomend out inside the trans, unlikely but I have run into that on a th400 I just trimmed the yoke about 7/8 and moved on. just make sure you have a full spline yoke , I've never seen a th350 yoke that wasn't fully splined tho. You need at least 1.5 to 2in of spline engagement
     
  12. BrianTrick

    BrianTrick Brian Trick

    It is easier to remove the shaft with the suspension under load. When the rear is hanging,it actually moves forward,pushing the yoke further into the transmission,leaving you little or no room to move the shaft forward to unseat the u-joint from the rear yoke.
    The rear is actually the furthest from the transmission when it is under load,and almost in a straight line.
     

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