Slip Yoke Problem

Engine, Trans & Driveline

  1. HotRod777

    HotRod777 Well-Known Member

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    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.
     
  2. R/T Boy 67

    R/T Boy 67 Well-Known Member

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    Must be a bad batch of yokes. I would try other places, and make sure they try it first. If you explain the problem they should be willing. OF Course the big parts slingers won't have a trans laying around. Dr diff has 7290 yokes and conversion joints.
     
  3. Fran Blacker

    Fran Blacker FBBO Gold Member FBBO Gold Member

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    Is your driveshaft the right length? Clearance on bushing a couple thousands. Mine rattled at 3200+ rpm had .010 or .012 wear.
     
  4. chignikred

    chignikred Well-Known Member

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    One item often neglected on service , is changing the trans rear housing babbit bushing where the yoke slides. They take all the abuse of driveshaft mis-alignment.
     
  5. Daves69

    Daves69 Well-Known Member

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  6. Fran Blacker

    Fran Blacker FBBO Gold Member FBBO Gold Member

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    If your yoke rocks you have a problem. How about a picture of end of trans to front u-joint and if the weight is or isn't on rear suspension.
     
  7. HotRod777

    HotRod777 Well-Known Member

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    Here is a pic. This is at ride height with full weight on the suspension.
    I just replaced the tail housing bushing and seal on Saturday with a Timken set (the bushing is brass colored inside).
    I bought the pair of tools for $80 off the company in Texas to remove and install it correctly. Even after the new bushing the yoke rocks a lot (in my opinion). That is why I am now looking for a new yoke to try. As far as overall driveshaft length, when removing the shaft it will slide into the tranny about 1.75” overall before bottoming out and give about 1” of clearance on the differential yoke to remove the shaft.
    My driveshaft is original and I think to-spec. It necks down on the diff end and still has the tone ring up front. The length from U joint centers is exactly what the FSM calls for for a 1966 B body.

    1F934C06-B26C-4321-A9BC-57B96B2217BD.jpeg
     
  8. Fran Blacker

    Fran Blacker FBBO Gold Member FBBO Gold Member

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    Mine looks the same with the shorty seal. On the left edge of picture is that the u-joint cup hanging out?
     
  9. HotRod777

    HotRod777 Well-Known Member

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    The u joint caps do hang out like that but they are installed correctly. These are the smallest, 7260 joints with the C clips on the inside of the yoke.
    Here is a link to a vid of the slip yoke play, this is WITH the new bushing installed. This is why I’m think I should try a new yoke.
     
  10. Fran Blacker

    Fran Blacker FBBO Gold Member FBBO Gold Member

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    That in my opinion is to much play. Wonder what others think.
     
    • Agree Agree x 1
    • Fran Blacker

      Fran Blacker FBBO Gold Member FBBO Gold Member

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      A year or two ago some members had problem with the shape of the splines on some yokes.
       
    • mopar 3 B

      mopar 3 B Well-Known Member

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      Mic the yoke near the universal and at the bushing. If the same its not the yoke.
       
    • Mick56

      Mick56 Active Member

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      Have you checked the driveshaft for balance?
       
    • Fran Blacker

      Fran Blacker FBBO Gold Member FBBO Gold Member

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      Did you measure what Mopar3B said? While your at it take a picture of trans splines. Would be nice to know if splines in yoke or in trans are worn? Got a 7260 yoke I used as a plug, can measure OD if you want? It has light rust in some areas. Can take a picture if your interested. I'm house bound until 5/1 at least, high risk group. Oh was your new bushing tighter than the video before you installed it.
       
    • AR67GTX

      AR67GTX Well-Known Member

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      I agree - way too much movement. I may be dreaming this but seems a year or two ago I found out the yokes with the tapered splines are for newer 727 variations and their output shaft. But Brewers should know that if that's the case. I bought a new yoke for my 68 727 a couple years ago that is tight and works fine. I'll try to find the invoice as to where I purchased it.
       
    • 1967coronet

      1967coronet FBBO Gold Member FBBO Gold Member

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      Call me nuts but I think you need a 30 spline, get on https://www.dennysdriveshaft.com/ you deal with them they will get you set up at what ever price range you wish to be.
       
    • Fran Blacker

      Fran Blacker FBBO Gold Member FBBO Gold Member

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      Was thinking it was you with yoke problem but couldn't think of your complete screen name.
       
    • AR67GTX

      AR67GTX Well-Known Member

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      Well, this may help. I ordered a yoke from Summit first and I think it was too short. I ended up with a yoke from Mancini Racing #SY7290-8335. As you might suspect from the part number it's for a 7290 u-joint instead of a 7260. My drivetrain is a mix of parts with a 68 transmission, 67 driveshaft and I forget what year rear. I think I have combination u-joints front and rear to make it all work. But Mancini has a SY7260-8330 that may be what you need. All the specs are on their website. It is 30 spline.
       
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      • Fran Blacker

        Fran Blacker FBBO Gold Member FBBO Gold Member

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      • Fran Blacker

        Fran Blacker FBBO Gold Member FBBO Gold Member

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        Here's the yoke I have, if your interested? yoke8.jpg
         
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