Many mods on the undercarriage. Discs all the way round, 700 T/M, boxed control arms, original sway bars, 15" rims, modified steering box (less turns), rear air shocks @ 20 lbs., etc. Stock 350, no mods. Think that's about it. Before ANY of that, car held road very, very well. Since all mods, when driving at 70 MPH can feel (in my butt, for lack of a better term) something just "wiggles" a bit. Was going to take it to the shop this morning and have Monroe coil-overs installed, but concerned about harsh ride and raising the rear end. Wondering if I go to 40-50 lbs in the air shocks, that would eliminate the wiggle. Responses very welcome. Going to postpone installation of the coil-overs until I get some more ideas.
THANKS!
Aron

 

Try less air in the shocks first.

 

You might consider changing from boxers to briefs. That has worked for me in the past. Just firms things up in the rear and eliminates any wiggle and jiggle!

 

I hate air shocks because they do weird things based on how they are hooked up and the amount of air you have. If they are T'd together they tend transfer air between each other based on weight transfer. Since the shock itself is not gas charged, temperature plays a part in how they perform and they become bouncy. If your rear suspension is sagging without the air shocks, I would suggest installing new springs. I've run coilovers and station wagon springs and will admit it really stiffens things up, but I liked it.

 

Aron, did you replace the U-joints at the same time? It is possible one of the joints has a needle that slipped down and only show any out of balance at speed. Or maybe one of the u-joint straps isn't centered.

 

I would suggest to get a 4 wheel alignment since you changed the rear lower control arms. Be sure the car is tracking down the road correctly. I don't know what tire pressure you use but double check all tires and if you are following the factory pressure settings, I would think about increasing it a little. I would think around 30 psi for wider radials and see if that does anything. Also, try rotating the tires to see if that matters in the event a tire may have a problem. Tire problems will usually cause a vibration too but it's worth a try.

Another thought is what differential do you have? Is it a Chevy style differential with C clips on the axles? If so, double check that you don't have a lot of play in the axles by seeing if the wheel/axle moves in and out more than it should.

Brian