Rear suspension issue, I think
 

Under heavy acceleration with tires spinning in 2nd gear car goes to the left hard enough that I have to let off to maintain control.

67 LeMans
Tubular adjustable upper control arms pinion angle set to 2.5-3.0 degrees down
Boxed lower control arms with .75' sway bar
No Hop bars, 12 bolt posi 3.08's
All bushings are rubber and new
Measurements taken indicate housing is in proper position for and aft and even from side to side

Does anyone know why it is pulling to the left and is there a cure.

Sounds like the wheels are spinning at a different rate.

Is it a locked rear?

With no way for suspension adjustments, probably can't?


Might try stiffening the right rear shock compression if you had adjustable shocks?


:confused:

Its a new Yukon posi unit in a 12 bolt

Are your axle tubes welded to center section? If one let loose a car will want to swap lanes on you per my experience with a 1966 GTO

put jack stands under rear frame and floor jack center section looking at tubes for movement

I had it up on the lift and measured everything if there was any movement I think I would of found it.

they are fairly rigid even when roset welds are broken but the joint will flex under power then rear wheels dont track truely straight steering the car

supporting the frame and jacking the center punkin will make it visually flex if broken

if you say their solid then they are solid

Your rear end is gona try and rotate under accleration that's probly why your getting rear steer ajustable shocks or ajustable sway bar should help.

GT

I do have adjustable upper control arms

Adjustable sway bar?

Funny thing, I put in a rear sway bar and new shocks and it exaggerated the issue.

Without getting yourself killed, do a burnout on the other side of the road to rule out the crown of the road making the rear drift right pushing the car left.

I would say that the passenger wheel is exerting more downward pressure and during spinning it has more force to push the car left. Too much preload on passenger side or suspension binding keeping the passenger tire from traveling up the same amount as the left.

Is this when doing a burnout?


:confused:

Put an LS on it! :D

On hard acceleration, the pinion is trying to "climb" up the ring gear which reduces the effective weight on the passenger side tire. (Which is why an open differential usually only spins the passenger side tire) As a result, the driver side tire experiences a higher coefficient of friction, compressing the control arm bushings on that side and inducing a rear wheel steering effect that makes the vehicle want to go left. You might try running a few pounds more pounds of air pressure in the left tire to reduce the contact patch slightly to even out the tractive effort between the two sides.

Yes, tires spinning = burnout

I hammer it from a dead stop tires spinning shifts into 2nd tires still spinning car goes left pretty hard can't correct it and I let off.

LS???

Should've said put an LS in it... Not on it

I wouldn't worry about suspension if it's from a burnout.
Need to know how it's done.
Rolling burnout?
Linelock?
Have a trough to start burnout?
Back into water?

I also wouldn't start in 1st gear for burnout. (or 2nd really)

Then worry about same circumference tires, front to rear tires inline with each other, brakes hanging up on one side or other, so many things.

:confused:

When I was a youngster many years ago my dad had a 67 Oldsmobile Delmont 88 with a 425 and a two barrel. That thing would do a burnout for ever until you let off and it went straight as an arrow and this was with a non posi rear. My car has bigger tires, posi and more power but I still can't figure out why the aggressive turn to the left. I will put it up on the lift tomorrow and jack up the pumpkin just to see if there is any movement.