1968 Firebird Rear Suspension Question

[Zyman]

My 1968 Firebird has SpeedTech control arms, SpeedTech Front sway bar, Viking Coil overshocks & springs front; DSE 3" drop leaf springs & shackle kit w/Delrin bushing, Viking smoothbody rear shocks. The chassis has Pro Touring F-Body – Solid Body Bushings and GEN II Sub-Frame Connectors.

When proceeding from a stop and turning under acceleration, the 4L60E tranny shifts to 2nd in mid turn and the rear end wants to unsettle.

Would adding a rear sway bar address this? If so, any reason to consider any particular brand over another, I would lean to a SpeedTech rear since I have theirs up front and DSE does not make a leaf spring rear sway bar.

[79T/Aman]

Delin bushings in the leaf springs can cause a lack of articulation causing snap oversteer, do you have Delrin in the front leaf spring bushing?

[Zyman]

Dave - front and rear of leaf springs are using polyurethane bushings.

[Zyman]

Bump - All the expertise on this site and no one is able or willing to provide advice?!?!

[dhutton]

I guess in order to help folks would need to know if the issue is understeer or oversteer versus unsettled.

Don

[Zyman]

Don - It is neither. The rear end has what feels like lateral movement within the suspension while the rear wheels do not oversteer. Perhaps the rear end slides to the outside of the turn ever so slightly. But since I am aware of the issue and not fully accelerating the car does not go out of control. If I did accelerate harder, I am sure the rear end would swing out and oversteer at the point of the auto tranny shifting to second.

[dhutton]

Try sending David Pozzi a PM. I’m sure he can help you.

Don

[stab6902]

I still don't have a great understanding of the problem, but adding a rear sway bar will increase the car's tendency to oversteer (i.e. make it feel "looser"). You'd normally add a rear sway bar to balance the car if the front end understeers (i.e. pushes or plows) around corners. Rear sway bars have no affect on keeping the rear end from moving laterally.

If everything is put together correctly, there should be no perceivable lateral rear end movement, especially with your upgraded parts and what sounds like street driving. Are your shocks adjustable? If the valving is way off/unbalanced (either front to rear or even left to right) that may result in the type of behavior you're describing. Does it act the same way regardless of if you're turning right or left?