Black Jack: Fixing torque steer

Good question and advice, Bullitt. I'll look into it and report back.

Finished up the rear-end today. Test drive demonstrated that the vibration has not changed. I guess for the $60 this cost (bearings, seals, gear oil + the 2 days I had to spend messing with it, it feels a bit defeating to have not found the source of the vibration. I guess the best way to frame the effort in a positive light is that I crossed another possibility off of the list, did a little preventative maintenance, didn't pay someone else to fail to fix the vibration, and have a shiny black diff cover instead of a rusty one. I had just about had enough when I was done, so I didn't mess with the pinion flange nut or swap the tires back around. I'll have to come back to those items later.

The charcoal canister & purge solenoid have arrived, but I'm still waiting on the purge's wiring pigtail, vacuum lines and adapters before I can install that stuff.
Bullitt, here's a pic that both shows the shiny diff cover and the LCA mounting points a little closer. You can also see the stock location's bolt. There's a 3rd hole between where the LCA is currently mounted and the stock mounting point, which I could use to raise the mounting point of the LCA. If I determine that the pinion angle is the culprit, I will do it and see if it alleviates the vibration to some degree.

Trogdor said:

Do you have a pinion angle tool? They are not too expensive and could tell you if the angle is wrong before you go in and spend a bunch of time moving the control arms.

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I have two angle cubes. I didn't know they had a special tool for pinion angles.

Bullitt347 said:

Usually dropping the real lower control arm mounting point by 1 inch or so is sufficient to change the Instant Center enough to be advantageous for helping the car hook.
If more than 1 inch, then you should certainly check your pinion angle.
On average, with stock bushings in the rear upper and lower control arms, having 1.5-2.0* pinion down angle is needed due to bushing deflection under acceleration.
If you have Urethane bushings then only .75 to 1.0* pinion down angle is required as there is less deflection in the control arm bushings.
With Heim Joints or solid bushings, then near 0* down angle is required as no real deflection is taking place.
Ideally you want the driveshaft at 0* front and rear when under acceleration as this provides the least amount of friction in the drivetrain.
If you have more than 2* of pinion angle, then I suspect that this is the source of your vibration.

Typically, U-joints are designed to work with up to 1.5* of angle each. So 2 U-joints should handle 3* of angle total. This is why double cardan joints are used in some applications to accommodate more severe driveline angles..................................................^^^^
Should is the key word.

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I think I've got a strong candidate for the vibration, now.