Resonance vibration in steering wheel at highway speeds
 

Greetings Club!
I've got a strange harmonic vibration that I'm hoping someone can diagnose. I've been at this one a while, so please excuse the wall of text.

Car is an 87 TII with 33k miles that sat for about 20 years. Current suspension is tokico blues and eibach prokit springs. The rest of the suspension components are original.

Symptom: When cruising at constant speed, there is a vibration in the steering wheel of about 1/4" in each direction at about 120 Hz, so it's very noticeable and unpleasant. The weird part is that it comes and goes in a dead consistent wave function with a 25 second cycle time. It is unaffected by turning, braking or coasting/accelerating but doesn't really affect how the car drives or transmit the same vibration to the chassis. It gets strongest at a particular wheel speed (75-80 mph, depending on the day), but the behavior is exactly the same above about 60. Since it comes through the steering wheel, I've been locked onto it being something in the front suspension/steering.


Since this began, I've done the following with no change:
-Different roads. Duh, but it isn't just one section of our terrible freeways
-3 sets of balanced wheels/tires
-3 different suspensions at significantly different ride heights.
-Wheel bearings seem good with no noticeable play. I replaced one side with no change. Waiting on parts and/or motivation to do the other.
-Tie rods and ball joints have been inspected and no noticeable play, although they did seem to have a lot more resistance than I expected.
-Alignment is set at zero toe. I tried messing with one side and then both sides to add toe out. No change. Currently on stock spring/shocks, so no other adjustments can be done.
-Replaced front brake pads

My only plan of action is a complete overhaul of wheel bearings, ball joints, tie rods and an alignment. However, I hate just throwing parts at it and praying.
If you've got any ideas, feel free to throw them out there. Thanks.

Control arm bushings would be my guess..

What kind of brake rotors do you have? I have seen cheap drilled rotors where the pattern was drilled offset of center. (non-concentric) needless to say regardless of how well balanced the wheel is. under this circumstance there would be vibrations. :icon_tdow

I also had a nasty resonance when my steering shaft u joints were bad and had a tiny tiny bit of play in them.

Are you using the same shop for balancing? Maybe try another that will take the time to properly road force them.

The brake rotors is an interesting point. I was also about to suggest that maybe the face of the hub needs to be ground flat, and the back if the wheel where it meets the brake disc may also need tending to.

Sadly, you could have a compounding problem as there are many variables that go into NVH.

Being that low mileage, having sat unused, can really take its toll on bushings and other things.

Thanks for the ideas. Also, the car has a manual rack.
That's a front runner at this point.

Currently running some newish Centric rotors. The behavior has lasted through at least two sets of rotors. I forgot to mention that I did change the rotors with the pads.

I'll take a look at the u-joints, but there isn't any noticeable slop in the wheel. It just seems that they would be worn out after so little mileage when they don't see constant load, like a wheel bearing.

I used different shops from chain tire stores to track-side tire shops. Rotating the wheels front to back also made no difference. The odds that they all made the same mistake on multiple wheels seems improbable.


Hub is a possibility. I don't hear about this being necessary very often, but we are well into the realm of weird ideas here.
I don't like my options of gambling on used parts, custom machining or new @ $550+ per side.


Agreed. Sitting may have caused some bearing somewhere to get a flat spot or rubber to age a certain way.
I would feel better if I could find it, but it sounds like replacement parts are coming soon.

I mean, take a die grinder with a prep disk on it and give the hub faces a quick clean. Could also clean, repack, and retighten your front wheel bearings.

Steering rack bushings are also not impervious to aging or dry rot.
At this stage in the cars life, you need new rack and control arm bushings anyway. So that's where I'd start.

Not sure if this will help as it's kind of a shot in the dark, but I seem to remember an old thread with a similar issue. IIRC the owner narrowed it down to a slightly bent fan clutch. Good luck, I hope you manage to figure it out. Problems like that drive me nuts.

I just noticed you're on stock suspension, and I'll safely assume it's as old as the car.. Perished strut mounts could also be contributing.

You're not really throwing parts at the car by refreshing the front end.. Being as old as it is, I'm the kind of person to recommend replacing it all so that you have a guaranteed baseline. Replace all four corners of dampers, with new shock and strut mounts, tend to at least your front end bushings, steering rack bushings, ball joints, tie rods, sway bar links, etc. It's just good standard practice to know that the components that keep you safely on the road have been replaced during your ownership. As I said, it gives you a guaranteed baseline... And the useful life of these components is so high that you won't need to worry about them for quite some time. It's a good investment!

Don't be tempted by poly bushings. The oe rubber ones will definitely give you the results you're looking for.

If after you've replaced these wear items, have tended to your wheel bearings, and maybe get the wheels and tires road forced by an experienced individual you still have a vibration issue, I'd be very surprised.

I'll keep it on the list, but I'm doubtful since it is very wheel-speed dependant.

The rubber mounts I'm currently using are the original ones with ~15k. I've tried other suspensions including tein coilovers that don't have any rubber and there was no difference.

I've had the car for 8 years and it is in great shape mechanically, other than this issue. So, replacing every 30 year old, 30k mile OEM part isn't going to get me much peace of mind. And like you said, they are parts that I shouldn't have to touch for a long time.

I'm proceeding with control arm bushings since I can't figure a good way to test those. Also, disconnecting one side of the sway bar had no effect. Maybe I'll try both sides.

Comparing solid metal strut mounts to 30 year old rubber ones is not a valid comparison, but whatever. Clearly I'm wrong here... I suppose it depends on how much NVH you are willing to deal with.

It's completely your choice, of course. Good luck with your problem.

Edit: Don't take my advice out of its appropriate place.. At this age, especially having sat unused for as long as a 30 year old 30k car has, your rubber has degraded significantly. Just because it might not all have gotten to the point of causing a problem that you are capable of noticing does not mean it's still perfectly normal.

What that bit of advice is meant to be applied to is that replacing bushings, steering and suspension components, brakes, etc will indeed give you that guaranteed baseline I continue to talk about that then allows you to know with absolute certainty those components will not have to be tended to for many years and miles. Whereas leaving in service perished parts is definitely a toss up on when you'll be forced to replace those parts.. Sometimes at inopportune times.

The first RX7 the I've owned was an 86 Sport that I purchased new in Cincinnati, OH. The Sport model came with 15" directional wheels and tires. I remember always having problems with front end vibrations. Had the shop balance my wheels a couple times without success. After a couple failed attempts, the mechanic suggested balancing the front wheels while they were on the car. The shop had the equipment to balance the front while they were on the car. They jacked up the front end, put the wheels on rollers, spun up the wheels and put on the balance weights as required. That solved my front end vibration problem! Apparently, the rotors and/or hubs were causing my vibration problem.

Currently, I'm the original owner of a 90 RX7 GXL with nearly 345k miles. In my many years owning this car, I find that vibrations in these cars are sometimes a bitch to diagnose. I remember once going to a shop to have my wheels balanced. Had a vibration after leaving the shop. Took it back, had the wheels rebalanced and to no avail the problem still persisted. Being the stubborn SOB that I am, I took it to another shop, had the wheels rebalanced and my vibration problem was solved. Few days later, I got a call from the original shop asking me to bring the car back because they found their balancing machine was broke. So, I would suggest going back and rechecking everything that you already checked. I would especially take another look at your inner/outer tie rod ends, struts and upper mounts, and control arm bushings. Good luck and please keep us informed of your progress!

i got to drive this car yesterday, and i've never seen anything quite like it.

when you're just cruising along, it'll be fine and then it gradually starts vibrating the steering wheel only, it gets kind of bad, and then starts going away until it isn't vibrating anymore, and then repeats. the cycle is completely regular. we didn't time it, but its regular enough where you could predict it with a watch.

the road doesn't matter, we went ~50 miles to a car meet. vehicle speed matters somewhat, it always does it, but for it to be noticeable you need to be going 60mph+

it vibrates the steering wheel only too. if you're in the passenger seat its remarkably smooth.

stuff that has been replaced for no change:
tires, thrice
wheels, thrice
front brake pads and rotors
strut assemblies, so shocks, springs, and mounts, for no change x3


car is red btw

Painting the car would be my gut diagnosis.

Applying Vulcan mechanical logic trees would lead Spock to investigate the steering system, from the tie rods all the way to the column bearings if necessary.
It's such a localized phenomenon, only manifesting in the steering wheel...seems like all the areas you've addressed would have been more globally noticeable, especially by the passenger.

Update: Tried swapping the nut behind the wheel. No change.
I'm currently tracking down a tiny 'click' in the steering system. It can be felt in every component from the column down to the individual tie rod ends, but it's not specific to any joint. If you turn the wheel and let it go, it will click as it all settles back into the resting position.
I'm focused no the inner tie rods or excessive lash between the rack and pinion gear. Not sure when I'll have time to work on it, but at least I'm chasing something.

Well, I can't prove that it isn't not causing the vibration...

Spot on as usual Number 1.

i should say my friends BMW does this exact same thing, except it goes from as bad as RXSpeed's car to we're going to die. passenger can definitely feel it.

so yeah i like steering. the click went away in my FC when i tightened the bolt on the column slip joint

Welp here I am again. Lots of activity to report, but very little progress. I usually enjoy this investigation, but this one just sucks.

Front control arms were replaced for ones with new urethane bushings. No change.
Swapped ball joints with other used, but seemingly good condition units. No change.
Replaced one wheel bearing and re-packed the other. (Welder issues prevented removing the second race) No improvement and no issue suspected here. There is no play in the wheels even with everything else detached.
Swapped entire steering rack with a powered unit, including outer tie rods. Alignment was off, but some issue was present. Couldn't tell if it was exactly the same, but definitely wasn't good.
Inner tie rods don't have any play, but they refused to come off and I wanted to keep at least one functional rack.
Removed both sway bars to eliminate a variable.
No play in steering column links and all are tightened.
Tried messing with rear toe to see if it was causing some weird tracking issue. No change.
Engine, trans and front diff mounts look good. Steering rack bushings are in excellent shape.


Where to go from here:
I suspect there is an issue with the pinion lash setting on the car, but I there isn't a good way to measure it. So I can play with that via guess and check.
Maybe a full rebuild of the rack, but I'd have to farm that out.
After that, another round of wheel and suspension mix and match to rule out the rubber/wheel balancing suggestions.
Then paint.

If anyone has experience adjusting the pinion lash, I'd love to hear some success stories.

Bad bearing in the column?

Adding it to the list!
It's possible, since I haven't checked yet. It makes sense for the clicking, but unlikely to be the cause of the vibration tied directly to wheel speed. Also, strange that it would fail after only 30k, but this isn't the first part I've replaced.