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Technical Driveshaft slip yoke questions

Discussion in 'The Hokey Ass Message Board' started by Squablow, Aug 4, 2019.

  1. Squablow
    Joined: Apr 26, 2005
    Posts: 14,400

    Squablow
    Member

    So I'm working on a '57 Chevy, it's got a newer Turbo 350 (1980ish) in it with the original rearend. I found a driveshaft that is almost the perfect length, maybe just a bit short.

    You can see from the slip yoke on the unknown driveshaft that it originally had about 1" exposed and the other 2 1/2" inside the tail of the transmission, the barrel is 3 1/2" long total. When I put this shaft into my car, I get about an 1 3/4" exposed, almost 2"

    I'm not experienced at all on drivelines, so I have two questions.

    1. Can I assume that I should not run this with only 1 1/2" to 1 3/4" of yoke barrel in the tranny tailshaft? It's clearly not ideal.

    2. Can I remedy the situation with a slightly longer yoke? I see the aftermarket offers a yoke that has a 5" long barrel length, which would give me about 3" in the tailshaft and 2" exposed, maybe 3 1/4 in/ 1 3/4" out depending. Would it hurt the car at all to have the U joint an extra inch away from the tailshaft? or is 3 1/4" too much to have in the tailshaft?

    This is a relatively low horsepower car with stock leaf springs/suspension travel.

    Here's a pic of the current yoke which you can see the witness mark on from whatever car it originally came from, and a pic of it installed in the car with a tape measure for scale. The car is standing on it's suspension with all of it's weight on the wheels, minus the seats, doors, side glass, and a driver, so I suppose it could compress a bit more once those things are added back in.

    20190802_161234.jpg
    20190802_161525.jpg
     
  2. A Boner
    Joined: Dec 25, 2004
    Posts: 5,573

    A Boner
    Member

    Seems a little shaky. Speedway sells a longer yoke.
     
    Last edited: Aug 4, 2019
  3. Get the longer one,
    It’s not the Ujoint but the tailshaft bushing that will get whipped
     
    loudbang, Hnstray and Mark Yac like this.
  4. BJR
    Joined: Mar 11, 2005
    Posts: 6,335

    BJR
    Member

    It is too short, it will whip around and cause a vibration and take out the tail shaft bushing and seal. You need a longer yoke or a longer driveshaft.
     
    loudbang likes this.
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  5. WB69
    Joined: Dec 7, 2008
    Posts: 1,226

    WB69
    Member

    Need longer.
     
    loudbang likes this.
  6. DDDenny
    Joined: Feb 6, 2015
    Posts: 13,428

    DDDenny
    Member
    from oregon

    Waaay too short!!!
     
  7. The cold, hard fact is that you need a longer driveshaft.
     
    loudbang likes this.
  8. Alter wheel base or put an Olds Pontiac rear under it. ;)
     
  9. blowby
    Joined: Dec 27, 2012
    Posts: 6,589

    blowby
    Member
    from Nicasio Ca

  10. 56premiere
    Joined: Mar 8, 2011
    Posts: 1,445

    56premiere
    Member
    from oregon

    The splines on the tranny only go so far, a longer yoke may bottom out. I used a longer one on mine, but had to take out the splines in the yoke.
     
  11. OLDSMAN
    Joined: Jul 20, 2006
    Posts: 2,424

    OLDSMAN
    BANNED

    The correct fix is to use a longer driveshaft. Get the shaft to someone who can replace the tube with a longer one.
     
    choffman41 likes this.
  12. Squablow
    Joined: Apr 26, 2005
    Posts: 14,400

    Squablow
    Member

    I get that the ideal solution would be a custom made driveshaft at the correct length, and I'll do that if I absolutely have to, but I'm really hoping to avoid it due to the cost. I understand that currently there isn't enough barrel length in the trans, but if I had a longer yoke, so the trans would have the proper 2 1/2" in it, would the tailshaft bearing really get destroyed by having the U joint slightly further away than stock? Not talking about a lot here, it's about 3/4 of an inch extra.

    Also, anyone know how to determine the ideal or maximum amount of yoke that can be slid into the back of the trans? The aftermarket long yoke adds quite a bit and I don't want it to bottom out. The 2 1/2" measurement is just a guess based on the wear indicated by the yoke on the unknown driveshaft, it's not original to the car or the transmission. I'd hate to have this driveshaft reworked and then find out the yoke I'm trying to use is not the correct one. Was every TH350 yoke from GM the exact same length?
     
  13. DDDenny
    Joined: Feb 6, 2015
    Posts: 13,428

    DDDenny
    Member
    from oregon

    Nikes' tag line says "Just Do It", you should too, believe me (all of us), it's the smart thing to do, the cost of a new driveshaft pales to the carnage from not heeding this advise.
    Maybe not this week or month but it will have to be dealt with!
     
  14. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 6,214

    56sedandelivery
    ALLIANCE MEMBER

    The longer yokes are designed to be shortened, if necessary, to your needed length. Although a driveshaft of the "correct" length would be ideal, you can probably get by with the longer, modified, yoke. What you DO have to worry about when using a longer yoke, is that it's not too long, and pushes the speedometer drive gear forward, thereby disengaging it from the driven gear. It's what I did in my D.D. truck when I swapped to a short shaft TH-350 from a 9" extension housing TH-350 and a 700R4 before that. Truck should have had a TH-400 from the factory! I am Butch/56sedandelivery.
     

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