A driveline will feel like it's a rotational vibration -- kind of moving "around" the car...

Tires out of balance feel more like a "bouncing" vibration...

A bent wheel feels like a side to side vibration... or shaking side to side.


What we don't know is what kind of vibration you're feeling???

I know you've read these instructions/set up on driveshaft angles....


I've seen situation in FIG 7 -- many times.... and hope that you've loaded the rear axle and checked your driveshaft angle. I have a tool for that if you want me to bring it with me???

It's the same as it was before the gear and bushing change and it vibrates like a mother at 50-52.
Check......feels centered like the slight vibration that was present but magnified.

I jacked it up this morning but need taller jack stands to support the rear axle. Need to pick up a kid from school and grab taller jack stands then I'll confirm relations and angles best as possible with my little digital gauge. Then I'll loosen the shackles to snug and recheck angles. We'll see. :headscratch:

Engine trans -2.4*
Pinion +1.4*
Driveline -.6

2.4-.6 = -1.8
.6-1.4 = -.8
Uncancelled angle = 1.0

If the pinion goes up, that puts the driveline closer to 0 thus reducing the uncancelled angle..........Right? :headscratch:

None of Inlands examples show pinion down.....is there a reason?

Yes -- because engine trans are always DOWN.

Can you get the pinion angle up so it cancels??

Just running some rough numbers here, the vibration that was there occurred at 65 mph with a 3.31 ratio. With the new 3.73 ratio there is a vibration at about 52 mph. With a 275/40r18 tire, 65 mph is about 2700 shaft rpm with the 3.31. 2700 rpm of the shaft is about 45 hz. With the new 3.73 ratio, 52 mph is about 2440 rpm or about 40 hz. Might be the same vibration source that's now occurring lower in vehicle speed due to the ratio change. How well does the slip yoke fit in the trans. Any slop? U joints feel free to pivot?

Thinking about this ---- since the same issue was there - but got worse with the changes:


Major change was the improved bushings -- maybe stiffening the rear end as an assembly..... so just talking out loud now.... the pinion CLIMBS with force applied... maybe it used to (before new bushings) climb enough at speed to partly correct an out of angle driveshaft thus REDUCING the vibration (driveshaft working angles) and now it can't climb as much as it used to so is holding back and making the working angles out enough that it's increasing the vibration?

Yes, adding more wedge the front of the perch will rotate the nose up.
I had 5* up front at first I can add the 2* wedges I cut and see how it specs out.

My floor jack and those 1/2" u-bolts are kicking my butt! :lol:

Thanks for the math - much appreciated and the 65 mph is spot on. The intensity increase is alarming.

The trans, driveline, and u-joints have 3K 'relatively easy' miles on them. Ideally the driveline could be a 1/2" longer. Car in the air I can easily rotate the driveline by hand and don't feel any u-joint interference.

I you guys need me I'll be under the car doing shoulder and ab exercises. :D

I'd buy into that logic as the bushings made a noticeable effect on turn-in and cornering stability.