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I have developed a intermitten front end shimmey in my 1930, Model A, 7 Passenger SEdan under braking at speeds in and around 40 MPH. It does not happen all of the time and easily goes away if you release the brakes and maybe pump them one or two times. I would appreciate any insights that someone might be able to offer.
Sounds like steering linkage or steering box. Does a 30 have a kick shackle?
We have spoken about this situation a lot. My ’31 Model 42 had this problem. Proper front end alignment from a capable large truck shop stopped the problem immediately.
i am having a similar problem with my series 81 runabout. if i hit a small chuckhole i will start to violently shimmey until i come almost to a complete stop.
Tony is right. Shimmy is usually a symptom of caster being out of adjustment. A truck shop skilled in aligning straight axles can fix the problem.
Syd and George, I had the same problem some years ago with my 1930 Model C sedan, and like Tony, found it was an alignment problem, in this case too much castor. I picked up some shims at a local alignment shop, decreased the castor with shims on the U bolts, and the problem never recurred. Best article I ever saw explaining this was in Murray Fahnestock’s “Model T Owner’s Guide”” in the chapter on “”Steering Wabble””.”
He asked about shaking while using the brakes, not at speed. If it only happened under brake load it is not alignment.
It can be alignment even under braking. Depending on the condition of the components of the front suspension such as shackles and springs, caster can change under braking which can cause shimmy.
These cars need lots of negative castor. I have aligned hundreds and hundreds of cars and trucks at my modern shop. A shake under load will be worn components. Could be shackles, drag arm, bad ball and sockets on spindle, kick shackle on frame, steering box, or as I came across this last winter, wrong components in the car.
Actually these cars use positive caster. I.E. the top of the king pin laid back toward the car. Camber angle nomenclature is reversed. I.E. negative camber has the king pin toward the engine.
Neither is adjustable on a 30 Pierce. The caster can be changed with shims. To change camber one would need to bend the axle.
Happy Motoring,
Rick
Rick
Running negative castor will return the wheel to the center after a turn, unless my memory is fading, it negative, I’ll have to look it up.
I just checked the on line alignment site, confirmed rear wheel drive cars, bias tires, and non power steering box run negative castor to return the wheel to center after a turn. While slightly less stable at high speed, how often do you drive your car over 65 mph. Early and mid 60’s GM cars ran one degree negative untill power steering came in. I invite anyone to try and drive my 32 or 36 and see how they drive. Truth be told I have never driven better steering cars than mine, try mine and compare! Ed
This subject has been an ongoing discussion since day one of the PAS. A quick Question
Jak, I have been told by others of good results……I will try them soon. Happy 4th of July down under!
Jak and Ed,
If you search the Message Board by putting Dyna Beads / Balance Beads in the key word box, you will find a message by Peter Williams that discusses balance beads. It does not specifically relate to front wheel shimmy, but rather wheel balancing in general. As I recall, the discussion ended asking for follow-up from those who have used beads for balancing, but I don’t believe that anything further has been put up on the Message Board.
I have Dyna Beads in all six of the tubes in my tires. I believe that they help the balance. Of course the beads will not alter caster, camber, or toe, so if one or more of these is the basic problem, beads will not help.
For balance, one can estimate the weight of the beads to put in the tubes by first going to a shop that can dynamically balance tires and finding out how much weight would be required to balance each wheel assembly by putting weights near the rim of the wheel, as is conventionally done (but don’t actually install the weights). As an example, say that this weight is 2 ounces. Then measure (1) the radius from the center of the wheel to the wheel rim, which is close to where a conventional weight would be applied, and (2) the radius from the center of the wheel to the outer radius of the tube, which is where the beads would act. On my car, I have 6.50 / 7.00 x 17 inch tires, so the radius from the center of the wheel to the wheel rim is about 9.5 inches, and the radius from the center of the wheel to the outer radius of the tube is about 15 inches. So multiply 2 ounces by 9.5 and divide by 15 to find out that you should put about 1.3 ounces of beads in the tube to balance the wheel assembly. Of course this is the minimum weight of beads that you should use. if you add more beads than this, the wheel will still balance, but you are wasting your money and installation time.
Joe
Thank you Joe!!! This is what The Message Board is all about. I also have the beads in my other Veteran/ vintage cars. My Lancia Lambda having independent front suspension is particularly suseptable & the beads cured it. Your comments about castor etc are a good idea to get right at first & then use the beads for fine tuning. jak.
Thanks Ed for your good wishes & I hope you survive 4th July celebrations!!
I have experienced pronounced shimmy on our 1936 1601 over the past 19 years. Each time it was very speed and road condition sensitive. Each time it was immediately resolved by balancing my ancient tires with spin balancing – but ON THE CAR! I tried an add on steering stabilizer (shock) to no avail. I would try the Dyna Beads if the issue crops up again. I need to replace the tires and I’m curious whether it will reoccur with the new tires.
Dave
Dave
G’day Dave, In my experience Front Ends are a holistic beast. Changing any element usually requires a revisit of at least some aspect of the whole. Jak.
Ed,
Not sure where you are getting your information but, positive caster is what makes the steering heavier and also makes the car straighten after a turn. The only vehicles I know of using negative caster are large earth moving equipment.
At any rate those factors are not the problem. By adding positive caster we are trying to convince the wheels not the shimmy. As we increase the trail distance by adding positive caster to the the front wheels we can sometimes lessen or remove the shimmy. My personal opinion is as others have mentioned that it is a gyroscopic balance issue.
Happy Motoring,
Rick