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Help with vibration in 78 d100

Chase Marose

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Aug 5, 2015
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Hey there I have been working on this truck of mine and I recently swapped my 8 1/4 out for a 9 1/4 with 4.11 and posi, I have a 727 with a 3000 rpm stall in her, and I have noticed when I get on the highway at around 3200 and up rpm, I get a really intense vibration, and even when I'm driving in town it seems like it's wobbly, I put new u joints in when I did the swap and the only thing I can think of is the front tires are older about 8 years now and getting warn, could the front tires be out of balance? And I noticed a small nick on my driveshaft as well, I just want to fix the vibration issue so I can take it to the track and test my 1/4 mile time!! Scared the shit out of me with the vibration and I don't know where it's coming from!! Any help would be appreciated!!

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Could be anything . Can you feel it in your steering wheel or is it more under were you sit ? I did notice one thing you said about a nick in the drive shaft . Does it look like you might have lost a weight off your drive shaft ? That would cause bad vibes .
 
Doesn't look like there's weight missing but I feel it in the steering wheel and under the cab
 
Rule of thumb . If you feel something in your steering wheel then your problem is in your front end . If you feel it in your floor boards the problem is either in your front end or your drivetrain under you . If you feel it in your butt then your problem is in your rear . I should have asked you this first . Did you have any issues before you did the rear end swap and did you do anything else to it before you started have the bad vibes ?
 
When you did your swap did you test everything by spinning it by had to make sure you got everything in alignment and nothing was binding? Does it do it more under load versus not under load?
 
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