Need help with driveline vibration!

[Thomas Fournier]

Ok, so I have a 77 k20, sbc350, th400, drivers drop np241, new balenced driveline, new 1410 ujoints installed professionally, fully rebuilt axle and a newly installed anti-wrap bar. It has new engine bushings, and new trans bushings. I have a pulsing vibration at 65mph not lower and goes away If you go alot faster like 75ish. My t-case angle is down 6 degrees, my driveshaft is down 10 degrees and the rear pinion is up 7 degrees. It's operating angle is is -4 at the trans and -3 at the pinion. The total if I'm doing the math right would be -1 wich is suposably close to perfect. What am I doing wrong?

 

[obijuank5]

Are you sure it's driveline? Check the tires. Does it only do it under load or when coasting? Constant?

 

[Bent77]

Does said new driveline have a CV?

And yes tires. I just changed tires and my vibration went away

 

[Kain]

mine did this and the tires where out of balance. and just cause its new doesnt mean it cant be bad.

 

[Thomas Fournier]

Tires freshly balenced and no cv joint, it has a slip yoke at the t case.

 

[Thomas Fournier]

And it only vibes when going fast, under load or not. Since I have the antiwrap bar nothing is moving.

 

[Blue85]

Sometimes these harmonic vibrations go away when you shift into 4th gear because then the driveline is not at the same speed as the engine, but with TH400, you'll never know. (EDIT: although without the torque converter locked, the speeds are a bit different, especially with high load).

I think the possibility of tweaking the pinion angle with the anti-wrap bar is interesting. You could change the shackle length a little or play with spacers on your crossmember - hopefully there's an easy way. There may be a pinion angle that works better. And like you said, it won't twist (much) under load, so you don't really need the pinion 1 degree higher than the T-case.

Could also be a worn output bushing on the slip yoke. How far is the yoke engaged into the T-case at ride height? What are the tires?

 

[Thomas Fournier]

It has about an inch more on the output to go in. I have falken wild peak ats on 17 inch alloy wheels ballenced by America's tire. Im worried that I have the pinion the wrong way, maybe it should be down not up, idk maybe I should tack some perches on and move them around until it stops vibrating. The t-bar is totally adjustable I have hiems on all connections so if I move it around it will be okay

 

[Blue85]

I was suggesting that for troubleshooting you leave the perches alone and put just a bit of an S in the springs with the traction bar. If there's a better angle you can find it before making any real changes.