what causes "darting" while heavy acceleration?

[protour_chevelle]

I have been having this darting issue ever since I have had some power in my chevelle(IE the 6.0l). Keep it mind its not a power house, but the car has no problem rolling in 1st, spinning them, and burning them into second.

It also feels like the car is shifting back and forth when traction is gained. Almost like a squatting but shifting back and forth at the same time type of feel.

It has 175lb rear springs, vari-shocks, panhard bar, heimed lowers with stock uppers. 12 bolt with limited slip 410s.(I had the same problem with the old 10 bolt 273 rear aswell but everything the else staying the same)

any thoughts?

[chicane67]

Rearend alignment or differential bias loading ??

[protour_chevelle]

what did you call me? could you explain some more.

[chicane67]

Rear end alignment = is it square in the chassis ?? Simple measurements can verify this and simple adjustments to your heimed lowers can correct this.

Differential bias loading = is the posi loose and/or wornout ?? If the clutch pack is loose or worn it can cause traction loading and unloading to turn the chassis. As one tires spins... and the chassis is unloaded, it then transfers load to the other, until it unloads and then subsequently spins. It is basically shifting back and forth between the two tires and it feels like it is 'steering' it. The solution to this, is to rebuild the clutch pack.

I mean it could be other issues... but this would be where I would start. The tires could be unevenly pressured, one tire could be physically older then the other... a freaky shock or weird suspension loading. But, take a look at the basics first. Nut and bolt the suspension and shocks, look for a shock leaking... are we even sure that the shocks are working correctly ??

I personally think it is a combination of the tire pressure and posi pre-load or clutch pack condition.

[shmoov69]

I agree.

[protour_chevelle]

alrighty, I will check with those. The rear end in the car is the springs and plates pushing out on the gears for limited slip. So not the posi style. What is the proper term for my rear end then.

Both the 10 and 12 bolt were that style. I will check the tire pressure thing. Shocks were sent back to varishock for a rebuild due to warrenty issues so they are apparently good to go. I'll measure the car up tomorrow and find out.

[chicane67]

"Limited slip" = posi.

"Plates" = clutches.



"Posi" was GM's coined trade mark name for a plate type limited slip differential.

[MrQuick]

...good stuff. Also check your front end alignment. Your toe can go crazy if something is off during acceleration. Loose or worn idler arm, etc.

I used set my toe with the front end jacked up 3 inches over ride height on my bracket Chevelle.

[jaybee]

How are your rear control arm bushings?

[Motown 454]

I was just going to post about the front control arm bushings that was what mine was doing they were warn out .

[protour_chevelle]

The front suspension is all brand new aside from the idler arm.

The rear uppers are probably quite old. they are being replaced over winter.

[Norm Peterson]

If the upper bushings are toast, the axle will move laterally. Probably worse if it's just those in one UCA that are bad. Since the lowers are also at some plan view angle, lateral axle motion will generate some geometric axle steer.

I didn't catch it the first time, but did it do this before you added the PHB? And is it horizontal with the car at rest?


Norm

[David Pozzi]

take a look at your rear bump stops, see if they look like the car has been bottoming out, the housing will look shiny and the rubber darker color where it hits.
David