motor boat sway on freeway bumps

[kensmith]

My 1978 124 spider on the freeway at 60+ MPH is fine until I hit large bumps. Then it acts like a boat going over a small wake. Not really bad but weird. Kind of goes from left to right but settles back. It has newer silver KYB shocks in the front. Not sure about the rear. Ideas on correcting? Stock size tires and wheels. All suspension looks stock and 133,000 miles.

[mdrburchette]

I would check for worn suspension bushings and check the rear trailing arms.

[kensmith]

All bushings look good. Shocks also look good. Has a front sway bar, maybe needs a rear sway bar?

[maytag]

A sway bar has nothing to do with the sort of problem you are describing. We need some additional diagnosis here.
When you say it goes from right to left then settles back down: is it mostly the rear moving from side-to side? And my suspiscion would be that it does that a couple of times, corresponding to the body going up and down?

This is important to really dial-in on the details of the symptoms. there are far too many opportunities with a handling issue to throw lots of money at the problem without improving the problem at all.... like throwing a rear sway bar on.

If you're like me, and you need a good escuse to rationalize putting-on a rear sway bar, we can help ya with that... but it won't help the problem youve described.

[kensmith]

Well, I just looked/eyeballed at the front wheels and it looks like there is a toe-out situation. Not sure if and when the previous owner had an alignment done. Maybe later when I have some time I will try and measure the distance in width front of front tires and rear of front tires to see. Would a toe-out cause this motor boat feeling over large highway bumps? I feel it at the higher speeds more than cruising around the neighborhood.

[So Cal Mark]

you might find the rear shocks seized if they are original

[kensmith]

you might find the rear shocks seized if they are original

Rear shocks are newer KYB silver shocks. I would almost bet the toe-out is the problem.

[kensmith]

Ok, so I drew some chalks marks on the ground at the same spot front and rear side of the front tires. Front portion is 1/2" wider than the rear portion. So it has toe-out. Would this cause the issue?

[v6spider]

It might allthough race cars are sometimes tuned with a little toe-out in order make it freer in the turns so I don't know if this is the cause of the sway... did you do a bounce test on the shocks? If it goes up and down than shocks are bad it should just go up... I would try all four corners... Set the alignment and see if that is the trouble... but there might be more.

Anyway just my two cents

Cheers!

Rob

[kensmith]

Shocks go down and back up and stop. No bounce.

[So Cal Mark]

1/2" toe out is WAY too much even for a race car. For a street car I set toe at 1/16" in. But it sounds like you also have bad rear arm bushings

[v6spider]

1/2" toe out is WAY too much even for a race car. For a street car I set toe at 1/16" in. But it sounds like you also have bad rear arm bushings

Mark, sounds about right to me too. Panhard rod or a combo of both.
Rob

[majicwrench]

Not quite sure how you are measing toe from your description, chalk on ground not gonna be very accurate, but 1/2' out would destroy your tires. Toe out would not cause issue you are describing anyway.

[mdrburchette]

Also check tire pressure. My Fiats hate uneven tire pressure.

[kensmith]

Also check tire pressure. My Fiats hate uneven tire pressure.

You were right on. R-rear tire has a slow leak. Fixed the leak and it fixed the problem!