Rear end "sway" at highway speed

[Roger P.]

I was cruising my '65 small block convertible on the highway yesterday at about 65 MPH and experienced some mild side-to-side sway coming from the back end of the car. I have owned the car for about 18 months and never had that strange sensation before. It didn't happen all the time, but I felt it on and off a few times during my drive (about 30 minutes each direction). I believe that the suspension is stock; although I am sure that many items have been replaced over the years. My 215/70R-15 Yokahama radial tires have only 1,500 miles on them and are mounted on knock-off wheels. When I had my clutch, tranny mount, and driveshaft universal joint replaced about 900 miles ago, the mechanic told me that I should replace one shock absorber, and that one of the rear yokes (half shaft) had a little too much play. However, he said that both would be fine for awhile and didn't require immediate repair or replacement. Could either of these be causing my sway issue, or might it be something else? I have noticed a crunching/squeaking sound when I get in and out of the car (or just push down on the car) as if something needs to be greased. I read through the archives, but didn't find a thread with my same issues. Duke and others have provided a lot of information about tires and shocks, but I want to know if shocks alone could cause my problem or if it might be another suspension component. It gives me an uneasy feeling when driving in a straight line on the highway and I feel the back of the car developing "the shakes" (gives me the shakes, too)!

Your thoughts are appreciated,
Roger (50141)

[Rich P.]

Re: Rear end "sway" at highway speed

Roger,

one possibility is not the correct toe in adjustment on the rear tires. Does the sway occour as you are driving straight or to you also notice a wandering of the rear as you go around turns?

Rich

[Christopher P.]

Re: Rear end "sway" at highway speed

Raise the car and check that the spinners are on correctly and fully and properly tightened down.

Even a small amount of play could give you the "sway" you are experiencing.

It's worth a check...loose knock-offs can be deadly.

[Joe C.]

Re: Rear end "sway" at highway speed

Make Sure That You Have The Knockoffs Mounted Properly. There Are 2 Sets Of 5-"Hollows" In Each Wheel. The Lugnuts Nestle Inside The Larger Set Of Depressions.

[Valeria H.]

Re: Rear end "sway" at highway speed

Wow, Now I feel a whole lot better about spending the extra money to have my original spinners rechromed!
Valeria

[Roger P.]

Re: Rear end "sway" at highway speed

Rich, Chris, and Joe,
Thank you for your prompt replies. I never had the car aligned since I bought it because it tracked straight on the highway; I figured if it ain't broke, don't fix it. However, I had my wife's car aligned a few weeks ago and spoke to them about possibly aligning my Vette. I printed recommended alignment specs from the CF and read threads about increasing positive caster to get better high speed stability (for the front wheels). Of course, my issue is related to the rear wheels. Does anyone on the TDB have recommended front & rear alignment specs for a small block C2? With regard to the knock-offs, I was thinking about the possibility of a loose spinner as I was driving. Before returning from my drive yesterday, I did a quick check to make sure there wasn't a loose spinner before returning. When I had the tires replaced, I gave the mechanic a lead hammer and the Chevy knock-off instructions, and returned a few weeks later with the KO pins and aftermarket spinner "torque wrench" that I purchased from Eckler's to re-tighten the wheels. I will check the spinners this weekend using the torque wrench, but I think my issue is something else. How should I proceed with diagnosing the problem?

Thank you,
Roger (50141)

[Gary C.]

Re: Rear end "sway" at highway speed

Roger, if the side sway happens on acceleration and de-acceleration some of the trailing arm shims could be missing. Check the knock-off's first to see if they're installed properly per the previous posts. Gary....

[Rich P.]

Re: Rear end "sway" at highway speed

Roger,

like I said the REAR tires also have a toe adjustment and if that is out it can cause this problem. Also with the fact that you are now hearing a new noise as you get into the car it could be bushings deterieating and that alone could cause the toe adjustment to change. BUT before I went out for a ride again I'd do a close inspection of the rear suspension.
Did you happen to notice if it only happend at certin locations? What I am thinking is that the tires could be getting caught in ruts in the road causing the swaying. The best way to make sure this is not the problem is to take the car for a ride on a freashly paved road with no ruts.

Rich

[Gerard F.]

Re: Rear end "sway" at highway speed

Rich, Chris, and Joe,
Thank you for your prompt replies. I never had the car aligned since I bought it because it tracked straight on the highway; I figured if it ain't broke, don't fix it. However, I had my wife's car aligned a few weeks ago and spoke to them about possibly aligning my Vette. I printed recommended alignment specs from the CF and read threads about increasing positive caster to get better high speed stability (for the front wheels). Of course, my issue is related to the rear wheels. Does anyone on the TDB have recommended front & rear alignment specs for a small block C2? With regard to the knock-offs, I was thinking about the possibility of a loose spinner as I was driving. Before returning from my drive yesterday, I did a quick check to make sure there wasn't a loose spinner before returning. When I had the tires replaced, I gave the mechanic a lead hammer and the Chevy knock-off instructions, and returned a few weeks later with the KO pins and aftermarket spinner "torque wrench" that I purchased from Eckler's to re-tighten the wheels. I will check the spinners this weekend using the torque wrench, but I think my issue is something else. How should I proceed with diagnosing the problem?

Thank you,
Roger (50141)

Roger,

If you are going to get it realigned, the rear camber for normal street driving should be 0d to slightly negative, basically straight up and down.
Excessive negative camber in the rear will cause that rear sway, and it is tough on the rear bearings.

For heavens sake, also have them check your rear bearings, for movement and play in the wheels side to side or up and down. If you ever hear that crunching sound from the rear wheels while you a driving low speed or high speed, just stop and get it towed home.

You don't want to wind up like this:




That's what you call excessive negative camber (with a broken spindle).

A few days prior to this incident, I had the rear end realigned and noticed on my trip that the shop had really put in some high negative camber.

Then on the trip I started to hear this clank clank clank and crunching sound. I convinced myself it was something else. The picture shows the rest of the story.

[Roger P.]

Re: Rear end "sway" at highway speed

Gary, Rich, Jerry, Chris, and Joe,
The sway issue appeared to come and go while I was driving in a staight line at a constant speed on the highway, not during turning. For most of my highway drive everything seemed fine. The problem only came up for short periods - roughly 20 to 30 seconds at a time, and only a few times during the drive. As I like to be proactive, I had a mechanic check the suspension bushings recently and was told that, although they aren't perfect, they didn't require replacement at this time. I will have a mechanic check out the suspension components this weekend, and have him check the wheel bearings and knock-off mounting. Chris, why do you recommend that I raise the car to check the knock-offs? Do the spinners have to be removed to check the wheel bearings and knock-off mounting, or can they be checked from the back? Is the concern that the lug nuts are loose, or that the spinners are loose, or both? I also thought about ruts in the road as Rich mentioned, and this would make sense since the sway was not consistent during my drive. Once I confirm that the knock-offs are mounted correctly, I will look for a newly paved road and take her out for a test drive - and will report back to you guys on Sunday or Monday. Jerry, I previously read the thread about your wheel bearing adventure... that must have been a very scary experience! I'm glad that it worked out OK for you, and that you got your car back together without more serious damage (or injury).

Thanks again for all your help,
Roger (50141)

[Michael B.]

Re: Rear end "sway" at highway speed

I have felt that "come-N-go" wiggle twice on my car. Once when the right side wheel bearings went out and once when the left side bearings went.

Raise the car supporting it with the trailing arm and check for any looseness. Sometimes they can last a while and sometimes they go pretty fast, but if it happens on the road they all look pretty much like Jerry's picture.

P.S. Note the closest phone in Jerry's picture. It seems to always happen that way.

[Jean C.]

Re: Rear end "sway" at highway speed

What Joe said.
Cheers,

[Gary R.]

Re: Rear end "sway" at highway speed

excessive side yoke endplay will also cause this to happen, had it on my 69 years ago. Driving 65-70 mph I could feel the rear sway in curves. After I blueprinted the T/A's and Diff it was on rails.

[Christopher P.]

Re: Rear end "sway" at highway speed

I can only speak from my experience and the sway came from just the spinners being loose (although I would imagine loose k/o wheel adapters might also feel the same).

I only suggested raising the car to make sure the weight of the car on the wheel didn't make the spinner feel tight when it possibly wasn't. If the car is in the air, you can wiggle the wheel to see if there is any play and you can push the wheel fully back onto the adapter before tightening it further.

Keep in mind that there are also right-hand and left-hand adapters and spinners so make sure those are correct as well. They are marked on the inside but I've seen professional installers get this wrong.

Lastly, proper tightening requires the spinners to be re-tightened every 100 miles for the first 500 miles.

Hope this helps!

[Roger P.]

Re: Rear end "sway" at highway speed

Gentlemen,
I really appreciate all your suggestions! I just returned from the mechanic and can now give you the 411. The knock-offs are on tight with no play, and the wheel bearings show no sign of play in any direction. That's the good news. However, as I mentioned in my initial post, the right rear yoke has about 1/2"-5/8" play, and when the car is on the lift, the right rear wheel moves like a gyroscope compared to the left rear wheel. This is most likely my problem. He also confirmed some deteriorating bushings; he said the leaf spring bushings and trailing arm bushings have some cracks and should be replaced - including one trailing arm bushing that was nearly non-existent! The mechanic told me that he recommends that I take care of these items sooner than later - especially the bushing, but that the yoke issue wouldn't create a safety concern if I drove the car for a while longer before making the repair. Do you guys agree with his assessment? Do you recommend rubber or polyurethane bushings? Would you suggest replacing the worn yoke with a new one or a remanufactured one? I don't want to spend a small fortune at one time, but I want to make sure my car is safe to drive for both my passenger and me. Jerry's photo scares me, so I want to make sure that I'm being proactive.

Thanks again,
Roger (50141)