Technical The old beam axle shimmy at speed

Speedway coil overs were not adjusted at all. Easy fix for the bottoming out.
Took the drive shaft over and had it checked. The balanced the unbalanced shaft.
Will install it tomorrow and see what happens now!

 

Absolutely this. I had this problem on my coupe. It was a brand new Towel City front runner that was out of round. It shimmied like crazy at 45-50 mph.

A good tire balancer guy can check that for you.

 

Also air your tires to 35 lbs it is to little now!

 

I agree. Try the 1/32 tow OUT. I learned that trick from the T Bucket guys who ran those skinny Halicraft wheels. Every straight axle rod I build gets the tow out now. It works.

 

Do what now?

 

Technical is tire balancing (nowadays) There is static balance, (achieved thru bubble balancing) then kinetic balance.
Sophisticated machine (and operator) will correct dynamic balance, (the root of MOST tire imbalance) as when tire is balanced statically, it's 'in balance', right? WRONG.

A tire that's static balanced, (like 'bubble balanced') when subjected to spinning on an electronic balance machine, will tend to gyroscopically 'turn in', or out. This sets off the machine's sensors, negating weights applied with static (bubble) balancing.
Apply wheel and tire to the vehicle, and at 25, 30, 35 MPH (especially in that speed range) and the tire's tendency to gyro does just that, to the end of ANY movement in tie rod ends, king pins, or linkage quotient.
Then the inertia becomes apparent, as it's upset and rebounds. This is the 'vibration', or shaking at the steering wheel.
If components are excessively worn or loose, a 'shimmy' occurs. (bad shimmy is sometimes termed 'death wobble'...
A steering damper can disguise the symptom, but careful diagnosis and proper balance will be the answer.

'Toe out'? Actually, front end specs called for toe-in for a physical reason: the weight and rolling resistance of the front wheels/tires. When speeds above 30 MPH were reached, the force of wheels (widest extremities of rolling stock) were such that the toe changed to toe-out.
A static setting of 1/16"-3/16" IN was decided on for this reason.
Toe-out will result in tire scuff, ('razorlike tread' when scuffed across with hand)
'T' bucket toe-out may have been obviated by front installed tie rods...

 

Sorry John I already installed one. I'll do better next time.

 

As mentioned in post 10 & 32 , if the tires are out of whack , all the theorizing , changing parts , aligning & balancing won't mean squat . If you're poor like me & can't afford new tires right now , a $20 damper is a real good deal & in my case , cured the wobble

 

I’m driving my fifth hot rod I’ve built over the last forty years and have never needed a steering damper.
There’s either play in the system or a bad tire


Sent from my iPhone using H.A.M.B.

 

Well the drive shaft was way out. Good thing is the guys were able to balance it. So today the drive was much better!! But at 60 turning loose of the wheel the wheel moves back and forth.
So I come from bad to much better. Guessing I'll pull the rotors and have them turned a bit to see if they are outa round are wobbling. Tires are just over a year old. Been spin balanced. The dampner is in place. The axle is at 7 degrees. The tie rods are tight. The steering box is tight. The steering shafts are tight. Tire pressure is 25. Lug nuts are torqued to 75 lbs.

 

You have to do it all new or like new parts. Tie rod and drag link rod ends ( use Chryslers they are larger and stronger), King pins and bushings, caster 6 to 7 degrees (run the adjusters in and out til you have it), front spring shackles and bushings, front spring "U" Bolts and spring retainer ( make sure it is seated and has Square or round spring bolt thru the crossmember square hole) and is torqued evenly so the car doesen't sit crooked, wheels are not bent and are true mounting bolt surface to outer rim, no bead dents, new tires that are "Trued" on a machine and dynamically ballanced on the same machine, wheel bearings, races and brake drums new and true, new "Tube Shocks" (Houdale shocks don't work well), steering box adjusted with no slop, steering stabilizer, and finally do the rear wheels and tires, sometimes they are out and transmit shaking to the front end of the car Oh tire pressure light car 23 Lbs heavy car 28 Lbs. Too muck tire pressure can cause the tire hop.

 

No one mentioned wheelbase? Measure your wheelbase on both sides of the car. They should be the same. One side longer than the other can cause shimmy

 

Straight axle “ shimmy” has been around since the invention of the straight axle! If your “ shimmy “ comes in at an exact speed every time, it’s your tires or wheels or rotors out of round or not balanced correctly.
If your “ shimmy” comes and goes at all speeds and tends to happen after hitting a bump, it can be many problems. As stated make sure all parts are tight and in good shape and the front end is aligned properly. If it continues, change the caster angle a little either way, till the shimmy stops. Once you get it to stop shimming then add the damper, for insurance.
This problem has been fought for years in the trucking business. Big trucks have the same basic axle as the t bucket, just mounted a little different.








Bones

 

These are not the only reasons. Read my post above yours.

 

Many things can cause problems. The most common by far on a shimmy, vibration, roar or sound at a certain speed is due to something that rotates. Tires, wheels, drive shaft, axles come to mind.
Over my career I have chased many problems such as these. From small to very large vehicles.
My post was written based on my experiences. During my time I’ve worked on brand new vehicles and vehicles that I wondered how they made into the shop.....and everything in between.
Other people may have different experiences. These are mine.








Bones

 

Hello,

Everyone has a way to stop different shimmy attacks on their cars. The old axle on my first 1940 Ford Sedan Delivery was somehow aligned well and did not cause me any unnecessary wear or driving/handling problems at any speed. If we could get any speed with that reliable, Flathead motor. But, 7 years later when we purchased a modified 327 powered 1940 Ford Sedan Delivery that almost looked like my first one, it had more power, but it was not correctly set up in the driving and handling department.

By this time, we had our own expert alignment service tech that had completely fixed the Impala, the first 40 Flathead Sedan Delivery, the 65 El Camino and now, sitting in his huge new alignment shop in the OC was our latest problem handling hot rod. A 327 powered 1940 Ford Sedan Delivery. He took it for several days and did almost everything he did on the other cars we owned. Lines drawn on the floor, measurements galore from front to back and side/side, each individual reading on his machines and calibration tools, etc.

It looked like a doctor with all of his tools splayed out on a nice blue shop drop cloth, along side his chalk and measurement devices. Since he had a new shop, he did have some new equipment. But, he did rely on his training in the old school ways and for the last thing he tried, was to balance the wheels and tires using an old “on the car” motor set up balancing machine.

The one thing he told me to do before I got to his shop, was to get the tires trued and round. Most people just don’t want to think that their tires are NOT round, so they skip this part of the fix.

https://www.jalopyjournal.com/forum...heel-wobble-is-to-much.1203519/#post-13718177

Then, the expert went to work doing his magic. After the long days, he told me the sedan delivery was fine and come back to his shop for a test drive. It rolled on the smooth streets in slow speeds and on the open highways past his shop at speed. No wobbles, shimmy motions or jerky handling. It drove like a sports car grabbing the road around corners and like a real car driving down the road with no external forces allowing the sedan delivery to sway or not. No, damper was necessary as the whole Ford front end was set up correctly, it just needed the fine tune by someone that had the expert skills to make it work.

Jnaki

His advice was to enjoy driving such a cool hot rod and that try to avoid going over pot holes or huge dips at speed. Well noted and for the next several years, he checked everything and it was the best handling hot rod we had driven. My wife liked it so much that somedays, I was alone at home looking at her 62 Corvair and she was out doing errands or visiting friends in the 40 Ford Sedan Delivery.

Most home builders have the techniques and knowledge, but someone who does it for a living just has those extra things that we normally don’t do or have the skills to get it done correctly. YRMV.

 

Yea , that'll work , throw a bunch of money at it , that always fixes everything

 

What does that video of a guy driving his T-bucket too fast for his skills have to do with a wheel shimmy?

 

2oldtoofast was bagging on me for saying you need to check and replace a bunch of stuff to stop wheel shimmy. He has a roadster very much like the one in the video so i was showing him a crash that could have happened with a bad frontend. You are the genius, go figure. An analog analogy, Eg: a picture is worth a thousand words.

 

Except the crash wasn't caused by a bad frontend. It was about an idiot showing off and driving way beyond his abilities with a car too powerful for him. So buying all new suspension parts for his T before the burnout wouldn't have done a single thing for him.

When trying to fix problems, I agree that sometimes it's easier to replace suspect parts. But you have to have a good idea on where to start. Not just replace everything. The OP is balancing, adjusting, and adding some new things, and he does seem to be fixing the problem a bit.

 

Try 35 go for a rip

 

I have no idea what the crash video was supposed to prove other than there's people who don't belong behind the wheel ..,..of anything
AFA my " bagging" on you ??? There are mechanics who are able to diagnose , then repair / replace , then there are parts changers ......unfortunately there seems to be fewer of the former & more of the latter.

 

Guys, we don't need a big argument here. All the parts on this car are new. My other 32 had no shimmy what so ever. This one the mentors that oversaw my coupe build are gone. I've run out of ideas and only ask for more opinions. I'll not drive much till I get it fixed.
Now do the hair pen radias bars lend to shimmy more so that's a four bar set up?

 

A friend is chasing a similar shimmy at about 70 mph on his 34 Ford. he said that with changing the front tire size to larger tires the shimmy would come in at a higher speed. We did some calculation and found that at 70 mph his 560-15 front tires were spinning at exactly 1/3 the rpms the engine was. ( I think it was 780 rpm for the tires and 2340 rpm engine speed). We continued to talk about harmonics and if they could induce a shimmy. Our next step would be to duct tape weights to the A arms ( MII on his 34) and to the driveshaft, just to see if and how this affects the shimmy.

Just an idea thrown out, but I agree that good alignment and a playless suspension and steering setup are mandatory.

 

As simple as straight axles are, they have some odd tendencies. I have seen a-frame style front ends in very sad shape and junk tires drive reasonably well with no shimmy. But a straight axle has to to be right! Or right for the vehicle it’s on. When you modify a straight axle suspension odd things can happen that can’t be “ seen”.
One experience I had in my career was with three identical , new , straight axle vehicles. One was prone to shimmy, the other two, not. Measurements were identical. Even swapped tires! One shimmed, the other two didn’t.
At wits end , I pleaded with the oldest tech at our best front end shop for help. He gave me two, two degree shims to go under the axle. I put them in and the problem went away! I went back and thanked him and told him how I put them in, he then, told me I put the in backwards! But the problem disappeared!
My point is, sometimes the problem will not show itself and shimmy on a straight axle is related to caster!
Since that experience, early in my career, I have solved many “ unsolvable” shimmy problems in, mainly OT vehicles, by changing caster, somewhat.
But, tires cause more problems than anything! And straight axles are touchy!
Just my experiences, in fifty years of vehicle repair.








Bones

 

Found one rotor was a bit wobbly. Had them both turned. Next I'll jack up the rear and run it in gear and see how the rear tires look.

 

I had an OT vehile when I was in school. I put new tires on it and couldn’t get the vibration out at a certain speed. Balanced them several times. Then made the tire company give me another set of tires......same thing! So I decided to live with it. My car was a light uni-body car and I could feel everything in it. About a year later it started to “ shimmy” when I hit the brakes, so I turned my rotors and like magic it quit vibrating at any speed. So... rotors can cause problems, even when not hitting the brakes.
Hope you found your problem.






Bones

 

Measured the wheel base as best I could using a steel tape it's about 106 1/8 on both sides. All tires balanced. Hits at 54 miles an hour. Didn't try to drive thru the shimmy. I don't know just how accurate the speedo is as I've not driven that much. All good 0 to 50. Turns good stops good and straight. Corners fine. Anybody got anymore ideas?