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    1. #1
      Join Date
      Jan 2016
      Location
      Arizona
      Posts
      113

      Driveline shakes BAD

      For the past year that Iíve driven the truck since I got it finished, itís had a horrible shake past 70mph. So violent the car acts like it wants to come off the ground. Itís starts in the shifter, then the whole car shakes. Weíve changed pinion angles, tires, wheel balance, driveshaft balance (which I think wasnít done correctly) today I took the driveshaft out and this is what I found. Does this look normal for 3000 miles?Name:  D145FD5D-97FA-4069-B93C-1DF318747DD8.JPG
Views: 220
Size:  482.0 KB



    2. #2
      Join Date
      Jan 2021
      Location
      Tennessee
      Posts
      49
      Country Flag: United States
      I believe those grooves are an indication that the yoke is dancing around in the tail housing because of your suspected drive shaft imbalance. How are you checking the pinion angle? Don't just point the rearend up the same angle the engine/trans is pointing down. Gotta compute both U-Joints "working angles" and get them the same. With that kind of wear, inspect those front U-Joint bearings and caps closely.

    3. #3
      Join Date
      Aug 2004
      Location
      Jacksonville, FL
      Posts
      1,565
      Country Flag: United States
      When you made the driveline angle changes, how did you measure them?. Use the TREMEC smartphone app to see what your driveline angles are. That is a good starting point. What engine mounts, trans and and suspension are you running? Are your wheels square (front to back wheels measurement the same)?
      Chris
      1968 Chevy Camaro SS
      LS3/T56 Ridetech suspension


    4. #4
      Join Date
      Jul 2008
      Location
      Summerfield, NC
      Posts
      239
      Country Flag: United States
      I'm dealing with a similar issue in my car.

      One thing a lot of people overlook is critical speed of their driveshaft.

      What tires and rear gear are you running? How long is your driveshaft, what's its diameter, and what is it made out of.

      I have 25" tall tires, running 3.73s, and my shaft is 3" diameter, .083" wall, 54.5" long. I've hit the critical speed of the shaft and now it's bent.
      *Jeff*
      Project Salty - 1964 4 door Malibu, beaten, neglected, red headed foster child
      Cammed LQ4 / T56 Swap Project Thread <-click to read! 😁

    5. #5
      Join Date
      Jan 2016
      Location
      Arizona
      Posts
      113
      Quote Originally Posted by 130fe View Post
      When you made the driveline angle changes, how did you measure them?. Use the TREMEC smartphone app to see what your driveline angles are. That is a good starting point. What engine mounts, trans and and suspension are you running? Are your wheels square (front to back wheels measurement the same)?
      I had someone else do the install, I just provided the parts.

      -Stock towers with 1Ē back ls swap plates
      -Bowler T56 with energy poly mount
      -Hotchkis TVS Suspension
      -yes wheels are square 18x9 with the same back spacing all around

    6. #6
      Join Date
      Jan 2016
      Location
      Arizona
      Posts
      113
      Quote Originally Posted by Hotwire View Post
      I'm dealing with a similar issue in my car.

      One thing a lot of people overlook is critical speed of their driveshaft.

      What tires and rear gear are you running? How long is your driveshaft, what's its diameter, and what is it made out of.

      I have 25" tall tires, running 3.73s, and my shaft is 3" diameter, .083" wall, 54.5" long. I've hit the critical speed of the shaft and now it's bent.
      This is what Iíve been looking into as well. I have a 27Ē tall tire with 3:73ís. Driveshaft is 65Ē long and itís 4Ē in diameter and itís made out of steel.

      This is exactly what I was thinking it was.

    7. #7
      Join Date
      Jul 2008
      Location
      Summerfield, NC
      Posts
      239
      Country Flag: United States
      Is it 65" total length or 65" from center u-joint to center u-joint?

      I'd measured .020" runout in the middle of my driveshaft. Close to 60 you could feel it in the shifter, around 70 it felt like you had a DA stuck to your ass cheek.

      Check the chart below. The longer the shaft, the lower the critical speed. Think of a rope, when you spin it fast enough to turn into a jump rope, that's 1/2 critical speed. The point where you can spin the rope to make double U's, that's critical speed. That's exactly what your driveshaft is doing. At critical speed, that's when the shaft turns into a W, pretzels up, and spits out the tailshaft.

      https://pstds.com/critical-speed-chart
      Attached Images Attached Images  
      *Jeff*
      Project Salty - 1964 4 door Malibu, beaten, neglected, red headed foster child
      Cammed LQ4 / T56 Swap Project Thread <-click to read! 😁

    8. #8
      Join Date
      Jul 2008
      Location
      Summerfield, NC
      Posts
      239
      Country Flag: United States
      Sorry for the double, figure out what your shaft's critical speed is, then, assuming your T56 has 1:1 4th gear, look at your rpm vs mph. That tells you what your driveshaft is spinning. My 1/2 critical speed was around 70mph, have my cutoff set to 140mph, driveshaft would spin 7000 rpm! Luckily I'd only gotten to 132, it was sketchy enough for me.

      You can use this calculator to look at rpm/mph/shiftpoints, I love it, helped me visualize my downshifts/upshifts:

      https://www.blocklayer.com/rpm-gear.aspx
      *Jeff*
      Project Salty - 1964 4 door Malibu, beaten, neglected, red headed foster child
      Cammed LQ4 / T56 Swap Project Thread <-click to read! 😁

    9. #9
      Join Date
      Jan 2016
      Location
      Arizona
      Posts
      113
      Quote Originally Posted by Hotwire View Post
      Sorry for the double, figure out what your shaft's critical speed is, then, assuming your T56 has 1:1 4th gear, look at your rpm vs mph. That tells you what your driveshaft is spinning. My 1/2 critical speed was around 70mph, have my cutoff set to 140mph, driveshaft would spin 7000 rpm! Luckily I'd only gotten to 132, it was sketchy enough for me.

      You can use this calculator to look at rpm/mph/shiftpoints, I love it, helped me visualize my downshifts/upshifts:

      https://www.blocklayer.com/rpm-gear.aspx
      Thatís from cap to cap 65Ē. Thank you thatís awesome. Mines the same, the shifter starts shaking at 70 then if I keep pushing it the WHOLE TRUCK SHAKES BAD.

    10. #10
      Join Date
      Jul 2008
      Location
      Summerfield, NC
      Posts
      239
      Country Flag: United States
      Jack the rear of your truck up, idle it in 2nd and watch the shaft, check to see if it's out of round. That's when I saw mine wasn't right and put a dial indicator on it.

      You might need a new tailshaft bushing in the trans too once you get everything sorted out.
      *Jeff*
      Project Salty - 1964 4 door Malibu, beaten, neglected, red headed foster child
      Cammed LQ4 / T56 Swap Project Thread <-click to read! 😁

    11. #11
      Join Date
      Apr 2007
      Location
      Aurora, CO
      Posts
      389
      Country Flag: United States
      It looks like the driveshaft might be too short. The wear on the yoke makes me think you don't have enough engagement on the tailshaft of the transmission and that is causing the driveshaft to flop around. You can tell by reinstalling the driveshaft with jack stands under the rear axle to simulate it sitting on the ground. Grab the yoke right at the u-joint and push up and down. If it is too short you will see and feel the movement of the yoke rocking on the tailshaft. I don't know how to explain it better than that. Maybe someone else has a better explanation.
      Matt H.

    12. #12
      Join Date
      Jan 2016
      Location
      Arizona
      Posts
      113
      Quote Originally Posted by 2yellow69 View Post
      It looks like the driveshaft might be too short. The wear on the yoke makes me think you don't have enough engagement on the tailshaft of the transmission and that is causing the driveshaft to flop around. You can tell by reinstalling the driveshaft with jack stands under the rear axle to simulate it sitting on the ground. Grab the yoke right at the u-joint and push up and down. If it is too short you will see and feel the movement of the yoke rocking on the tailshaft. I don't know how to explain it better than that. Maybe someone else has a better explanation.
      I get what your talking about. The yoke has engagement where thereís only 1Ē sticking out, bowler recommends 3/4Ē so when I get my new driveshaft built tomorrow Iíll tell them. Hopefully they can just add 1/4Ē on to my old measurements. I think the driveshaft I have is past itís critical rpm. Itís 65Ē long.

    13. #13
      Join Date
      Mar 2015
      Posts
      80
      Country Flag: United States
      Awesome thread. My fairly new (just hit 1000 miles) Chevy II wagon LS swap has a similar issue. Not as bad but definitely there.

    14. #14
      Join Date
      Apr 2007
      Location
      Aurora, CO
      Posts
      389
      Country Flag: United States
      Glad I made sense to you. I would also call the driveshaft shop before you go and ask them how they want the measurement. I have seen the way some driveshaft shops online ask for a measurement but the local shop I use wants it measured differently. They have me go from the end of the output shaft to the flat where the u-joint cap sits in on the rear yoke.
      Matt H.

    15. #15
      Join Date
      Jan 2016
      Location
      Arizona
      Posts
      113
      I took my driveshaft to a local shop here in town and explained my problem, and they checked it for balance and it was out of balance on the transmission side, the differential side and the center badly. They couldnít even get all the way up to speed on it. So I have them building me a 4Ē aluminum driveshaft thatís just a tad longer to get a little more yoke engagement. Itíll be done tomorrow. Hope this ends this problem.

      He explained my driveshaft was over the recommended length for the steel, and with the horsepower in making, its pushing the limit of the aluminum. But he thinks if I keep my power where itís at itíll be just fine.

    16. #16
      Join Date
      Jul 2008
      Location
      Summerfield, NC
      Posts
      239
      Country Flag: United States
      Glad to hear you got validation on the shaft being bad. I got seriously lucky and found an 03 crown Vic shaft is 55.5" center to center, 3.5" aluminum. Just got one from the pull a part for $35, hopefully will be a bolt in for me once I swap the slip yoke. Mine's also stamped POLICE, internets saying that's the best version to get. Old shaft is 21.2lbs, Vic shaft is 15.6lbs.
      Attached Images Attached Images  
      *Jeff*
      Project Salty - 1964 4 door Malibu, beaten, neglected, red headed foster child
      Cammed LQ4 / T56 Swap Project Thread <-click to read! 😁

    17. #17
      Join Date
      Jan 2016
      Location
      Arizona
      Posts
      113
      Quote Originally Posted by Hotwire View Post
      Glad to hear you got validation on the shaft being bad. I got seriously lucky and found an 03 crown Vic shaft is 55.5" center to center, 3.5" aluminum. Just got one from the pull a part for $35, hopefully will be a bolt in for me once I swap the slip yoke. Mine's also stamped POLICE, internets saying that's the best version to get. Old shaft is 21.2lbs, Vic shaft is 15.6lbs.
      Thank you, that is a super awesome find, let me know how it works. Iíll check back on here this weekend to let you know if itís completely gone or not.

    18. #18
      Join Date
      Jan 2016
      Location
      Arizona
      Posts
      113
      Name:  IMG_0012.JPG
Views: 135
Size:  596.1 KB

      4Ē aluminum driveshaft with a sonnax yoke and 1350 u joints

      Hopefully this fixes most of it

    19. #19
      Join Date
      Jul 2008
      Location
      Summerfield, NC
      Posts
      239
      Country Flag: United States
      Quote Originally Posted by Cshenker1121 View Post
      Name:  IMG_0012.JPG
Views: 135
Size:  596.1 KB

      4Ē aluminum driveshaft with a sonnax yoke and 1350 u joints

      Hopefully this fixes most of it
      Have you been able to run the new shaft?
      *Jeff*
      Project Salty - 1964 4 door Malibu, beaten, neglected, red headed foster child
      Cammed LQ4 / T56 Swap Project Thread <-click to read! 😁

    20. #20
      Join Date
      Jan 2016
      Location
      Arizona
      Posts
      113
      Quote Originally Posted by Hotwire View Post
      Have you been able to run the new shaft?
      Yes all of the problems are now fixed!!!

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