Technical Shimmy or Stablizer, Pick your poison.

I am working on a '26 T coupe hot rod. 4" drop beam axle. 4 bar. I replaced the Vega box with a Unisteer rack and pinion cross steering. All new parts. Parts slop is not a factor. I squared this car up before the body went on, personally. I know the front and rear supensions are square and centered.
This thing has a shimmy at 55 mph. (Of course it had to be at 55). It's not a death wobble, just a slight shimmy. Irritating, to say the least.
I have been working on race car front ends and suspensions of all types for more than 40 years. This problem just about has me whipped.
I have adjusted toe from 1/4" in to 1/4" out, in 1/16" increments, with a short test drive in between each adjustment. I have adjusted caster from 3 degrees positive to almost 10 degrees positive in about 2 degree increments, again with the test drives. I have tried 3 different sets of tires and 2 different sets of wheels in different combinations.
Some of the adjustments seemed to decrease the amount of shimmy, but none eliminated it.
It has always been my opinion that if you have to put a dampener/stabilizer in your steering to eliminate shimmy, then you have something wrong somewhere in the system. BUT, I think I have eliminated alignment and wheel/tire issues as being the problem with this one, and I still have a little shimmy.
I know So Cal doesn't build any cars without a dampner and they probably get the front end right to start with. But the reason they give for the dampner is that the straight axle front end was designed to go about 45 mph. Well, I have worked on straight axle pavement sprint car front ends that go 150+ without a dampner.
I hate to put a dampner on. To me it just looks like clutter on a clean front end. But I guess I will if that is what it takes.
I would like to hear your thoughts on my shimmy problem and the dampner issue.
It is possible I have overlooked something maybe someone else can shed some light on.
Thanks
(I posted this on another site and really got suggestions all the way from cutting it all off and starting over to resetting the toe, which I had already done 'til I'm blue in the face. Let's see what the HAMB experts have to say.)

 

I can predict that you will get a lot of statements like "a stabilizer is a bandaid" and things along those lines, it happens every time this subject comes up. But my opinion is, a stabilizer makes a good car even better.

My philosophy is that form should follow function, and I want to drive my cars like a car should be driven. We are running 3 cars in my family with SoCal stabilizers on them now and my current project rpu will have one too. They just give it a much more solid, safe feel going down the road. You can cross RR tracks and rough pavement without any wheel movement, and interstate speeds are so much more comfortable.

I can understand why some people hate them, but I don't.
Don

 

Could also be an out of balance drum or rotor.

 

Yes it could be a rotor out of balance. I wonder if adding balancing beads now would help? I wish the old spin balance on the car was still around.
I have ordered a So Cal stabilizer. The clamps will have to be modified to fit my application.
I still hate to put it on, but if I can find the solution, it can be taken off.

 

Check the run out on the wheels.
If u have a friend or a cool old school tire shop have them high speed check the run out, could be as simple as an out of round tire, or barely bent rim.

Yes, stabilizer will be a bandaid, but on the other hand lots of cars and trucks use/used them from the factory, VW, Jeeps, etc. up to you.

Its going to be the same ole thing, ask 700k members and get 700k answers.

My .02 cents.


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I rebuilt entire front end on 31' Chevy straight ax because of shimmy i couldn't seem to get out........then when installing driver side wheel i spun the tire around (don't really know why) and saw a wobble..........long story short, the tire was coming apart. New tires and she drives like a dream.................

 

Caster angles the same on each side? Camber angles close to the same each side, with maybe 1/4 more positive on the right to acct for the crown of the road? Check the scrub radius [with the different wheels if the backspacing/offsets are different]? Scrub shouldn't make that kind of difference at 55 [more commonly wandering at much higher speeds] but you never know.

 

Checked the runout on the front hubs and rear axles? Just a little might give you a shimmy, but not noticeable to the eye.

 

I had a small camper that would break rivets in the sides and balanced the wheels, tires with the brake drum, hub bolted up. The garaged used there modern balancer with cones in the bearing races to balance the whole ***embly and it stopped the vibration that was breaking the rivets. I then marked one stud and the adjacent spot on the wheel so it would get mounted in the same position.

 

So at 50 there is no shimmy,
It Starts at 55
Does it get better or worse at speeds over 60 ?

 

I had a shimmy at around 55 on my roadster and after tring basically the same things you have I bought a So Cal stabilizer,,it didn't help at all.

I changed transmissions and had to shorten my drive shaft after it was reinstalled the shimmy was gone,the guy that told me the drive shaft he cut down was out of balance. HRP

 

Keep everything fair and balanced(Fox News). Can we see pics of the coupe?

 

This is the car. HRP

 

I'd check the drive shaft first.

On my first Tudor, 350/350 8" rear with beam front and four bar / coilover rears, I had it at 55 as well.

Wheel and tires changes, drive shaft changes, alignments etc. I could not "shake it" hehe.

I started losing rear wheel axles, as in the shaft walking out the housing (scary on the freeway, four times!)

I even used a separate set of axle shafts.

The problem was solved when I cut the rear out and installed a 9".

I believe the housing was warped in a fashion that would give a toe out type position.

A week after the 9" went in it went on a 1000 mile trip.

 

as a rule of thumb a shimmy that comes in at a specific speed and goes away at higher or lower speeds is usually a balance problem.

 

Does the road surface type or condition have any effect?

 

Sorry guys, been away for awhile.

Squigy,
I have checked both axial and radial runout on the wheels and the wheel/ tire ***emblies. Don't get me started on trying to buy actually round and true wheel and tires. These are new wheels and tires that have been carefully mounted and spin balanced. I know, I stood and watched and made the tire guy remount and rotate any tire on the rim that had a visible runout. He was starting to get pissed. There is still some small runout, but it's the best it can be. I don't think you would feel it on one of my OT cars. I would say it is in spec. I really don't think its tires. Two different sets of new tires on two different sets of wheels.

alchemy, I have not checked hub runout front or rear. I would say that is next.

oldcars.acadia. yeah too bad the old 'on the car' spin balance is not still around.

31 vicky, shimmy is between 52 and 57, worst at 55.

A Rodder, you know, that could also be the problem. I very carefully and slowly welded the suspension brackets on. I guess it is entirely possible that I warped it. Never checked. Easy enough to check though.

HRP, you don't miss much. Thanks for posting the pic of my car. I just today put a stabilizer on the steering. Waste of time and $4o. It took the shake out of the wheel, but the car still had the shimmy. So now it is back to chasing the problem.
Now about this driveshaft causing a shimmy. I never heard of feeling a driveshaft vibration in the steering wheel. I never would have thought of it. I think that my driveshaft is good, bought it already balanced from a reputable builder. I guess that doesn't necessarily mean it's good. But, I do have a growling in the trans that could be the rear bearing. This might be causing the driveshaft to vibrate. The trans is coming out this winter for rebuild and I am trying to make it last the summer.
Dirty old man, yes the shimmy is worse on some roads than others. It actually feels worse on a fairly smooth road.
Thanks for the food for thought.
Thanks guys

 

Ok - so it Starts at 52 mph max at 55 mph and fades off at 57 mph.
And Different tires had no change.

The drums could be really out of balance ?
And or -
Wondering if you have a drive line harmonics issue at that rpm?
Did you try this :
Note the rpm range for 52-57 mph
Hit that rpm in second gear - observe shimmy
Hit 52 -57 mph in second gear - observe shimmy
Hit 60 mph and neutral, coast down to 57-52 observe shimmy

 

Thanks for the picture. Not to many full fendered T's look that good..................

 

31Vicky
I have not tried your experiment, but I will. This would go right along with HRP's experience. It may shed some light. I do know that it does it steady state, accelerating, or decelerating through that range.
I just have never heard of driveshaft problems causing a shimmy in the front end until now.

26hotrod, you'd have to thank HRP for the pic, but thanks for the compliment.

I just now checked rear end for toe. It is perfect, well, within tape measure accuracy, anyway.

 

I don't know that it will shake out an out of balance drive shaft, as those are usually (not always) an up and down vibration felt in the seat or floor pan.

But it will get you to nailed down to RPM drive line or Mph rotational.

I was next to a f 150 a few days ago. His left front tire looked like a basket ball. I looked at the drivers hand on top of the wheel and it was as steady as a rock. I was expecting to see at least some action. Maybe get someone to watch you ? Worth a shot any way. Gopro it?

You've made it clear that the normal suspects have been eliminated. So that puts you into either bad methods checking those or obscure causes. Some of those are flexing rim centers or frame, untrue axles, really bad drums, drive line harmonics, ****ty rear end, and maybe a driveshaft.

 

Thanks 31Vicky, I will try your experiment tomorrow. My son has a go-pro camera to watch the shocks on his sprint car. I think I could try that easily. I have almost 50 years playing with race cars of all kinds with pretty good results. I hope my methods are good, but hell, I could have been doing them wrong that long, 'cause I sure have something wrong now that I can't get ahold of.

Ijust had a thought. I could put the go-pro on the driveshaft too. Might show something.

 

I have been trying to cure a similar vibration. After changing tires and a couple of balance tries, hub centric and lug centric, I went to a shop with the "old style" on vehicle balancer to see what might be going on.

They were able to get the tires and wheels to balance pretty well off the car, but when mounted and spun on the car one side was way out of balance. It seems the rotor is out of balance. The other complication is the steel wheels which have their own problems either being out of round vertically or too much run out sideways. We got it better, but so far the advice most involved give is alloy wheels. Hate to go there but I am tired of the battle and am concerned that more new steel wheels are not true enough.

Another thought to the O/P is engine balance or harmonics. Take note of what rpm range the vibration occurs. Then see if the engine does that when stopped, in neutral. All engines have harmonics at certain rpm and the manufacturers go to some extent to dampen them out.

 

Would maybe jacking the car up getting all 4 tires/wheels off the ground and running the car in place help to narrow the problem down to a drivetrain or tire/wheel/suspension problem ?

 

Sure read some good ideas],A note about drive shafts even if its not that,maybe handy for others to know;
If ya do a test like just posted by Andamo, be sure to not let the rear hang down out of it's norm spot for running. By the way a note about balanced drive shafts{ I built lot for race cars] being in balance on the balancer is fine,{ an yes I have an use a S.W. balancer] but a shaft can be out by the way it's mounted or ever made*,if both end U-joints are not very close to the same angle when running,or ****** tailshft bearing is ****,then it can vib.
If someone made it with out lining up both U-joint at each end=its wrong,can be inbalance on a tester,but as soon as it gets any flex in the u-joint it will vib when the ends are not made to match.........

If ya do the jacked up thing,check and see if spinning a wheel at a time shows anything werid you see,also take note if any always stops with one same side down{is a giveaway for out of balance drum or disk/hub.
I'll throw out one more odd thing,kingpins if old get some play that can an offten dose add to frontend wobbley,there is a old trick of taking kingpin wabble out temp before ya can replace,,, Temp Fix ;it's going to site a tow-out of around 1/2in. vs tow-in of 1/8in. when you have perfect pins an bushings,what that out siting really dose is load up the kingpin to ride on only one side of it's bushing keeping it from going sloopy=stops shake from that<

 

I been fighting the same problem,tried about everything except the rotors.

 

Glad to see this back up,
Looking for an up date-

 

Whenever I see threads about this, I'm can't help but wonder, why EVERY hot rod using a dropped axle and "bones" or radius rods, doesn't have the same problem? I've also read that it seems to not come up often in setups with 4 bars. It makes me think there just has to a problem with ***embly or bad products.

I have run a dropped tube and radius rods and now run a dropped "I" beam and radius rods. I had a shimmy with the tube axle, but it was cured by adjusting toe in. Was I, and a lot of other folks, just lucky?

 

Jaw22 has 50 years experience playing with race cars, so this probably doesn't apply here - but there's a lot of folks that don't know exactly what they are doing, another big section doesn't understand what they do know, and the folks manning the tech departments of the supply houses haven't got a clue. I had one tell me to just not tighten up the nuts on my shackles because their shoulders were too short. - idiots. I was expecting him to say "Oops we sent you the wrong parts. ". Scary thing is they sell a lot of them and they are wrong for the application they say they are for. That's just one example.

These things are simple but there are certain parameters that are especially critical because they are so simple. If that criteria is maintained then this stuff will work to land the space shuttle or remain stable at well over 200 mph. Do what you want anyway you can imagine while maintaining this and it will work.

The biggest problematic thing is king pins on old axles. Then alignment issues usually do to faulty methods.
The next is frame flexing with split bones and that changes squareness of the wheel base.

Why will 2 nearly identical cars react differently on the track? One launches hard and goes straight - the other acts like its racing on a icy road? It's in the details.

 

Thanks, 31Vicky. It just seemed to me, that a system so simple, would have only a couple things that would need to be checked. Your answer makes me think that perhaps the answer is just plain, old parts inspection. Looking more closely at what we buy or build. Not deviating too far from the normal usage and application.