Cadillac 1932 V8 - Front steering shaking issue

[47bigcadillac]

I have had the following issue on my 1932 v8, but it seems to be getting worse recently.

When hitting a small bump on the road, both front wheels start the shake very violentely sideways.

It feels like the front wheels are going to fall off anytime and the steering wheel cannot be held steady . The stearing wheel is shaking violently as well. The only remedy is to slow down to almost a halt, and the viration dissappears completely.

This happens only from  time to time, there is no vibration to be felt most of time or at highway speed (40 mph).
Car has period-correct ply-bias tires, and has been restored.

But Ssteering does have some play.

Any thoughts appreciated.

Thanks
Rob

[Otto Skorzeny]

Not an expert on cars of this vintage but I know where I'd begin my search.

First, check for broken springs and/or knee action shocks. A broken spring might not be easy to spot without removing the wheels and taking the weight off the suspension.

Of course perform the usual close examination of every piece of thesteering linkage and suspension system.

Put it on a lift and check each wheel for slop which might indicate a shot kingpin. Put your hands at 12 and 6 and try to rock it perpendicular to the body. If it moves more than a 16th inch or so investigate further.

Check your the balance of the wheels and look for damaged tires. If nothing looks out of place, switch wheels front to back and vice-versa and see what happens.

[Wayne Womble 12210]

This has been a problem with almost all solid axle cars.  You should check each joint that moves just to make sure everything is tight and adjusted properly.  I have found that even slight tire unbalances can set up harmonic vibrations so make sure the tires are balanced. Make sure that the rims run straight and true and check the wheel bearings and alignment. Cadillac had a damper built into one side spring shackle. Make sure the springs are not broken and it is adjusted correctly.

[harvey b]

Hi Rob,i have a similar problem with my 38-90 series,it is an independent front suspension car,but it is doing the same thing,they call it a speed wobble,very dangerous if you are going any speed at all,on my car i found the "wishbone" that the 2 tie rods bolt to in the center,one hole was wore egg shaped and this gave a lot of play in this joint,it looked like a bad tie rod end,but it was the hole that was wore not the end,this allowed the wheel to shake back and forth.I was able to get a washer in under the nut to tighten it up some,i do need a new part for it,am not sure what it is called?,i would look for a loose joint of some sort first.HTH Harvey B

[47bigcadillac]

Hi everyone, thanks a lot for the replies.

I will have the wheels balanced and see if the issue improves. This does seem like harmonic vibrations triggered by a small bump.
Rob

[The Tassie Devil(le)]

Now, that sounds like a badly worn part, or even a broken spring.

An out of balance wheel/tyre won't cause the trouble you are describing.

Bruce.

[Otto Skorzeny]

Right. An imbalanced wheel will give you trouble while you're driving. Like I said earlier, the first thing I would check for are broken springs or shocks.

[Mark Lowery]

Rob,
My vote is w/ Harvey's analysis.  The one thing I'd add is to test all your tie-rod ends with as much pressure as you can apply perpendicular to the threaded tapered shaft.  The trick is to figure out how to do this w/ the suspension in its normal position.  That is to say, if you jack the front end up and have the wheels dangling, the play may not be apparent.  Even though you feel it is in both wheels, it can easily be just one tie-rod end.  If they have never been replaced to your knowledge, they are a relatively cheap part to replace.  If you have the specific problem that Harvey mentioned (the hole going oval) let us know if you can figure out a way to repair it w/o simply replacing the part.  The tapered hole would seem to be a challenge to remedy for most machine shops, and the part (intermediate steering arm) is likely no longer available new.

Mark Lowery CLC #25216

[Wayne Womble 12210]

Rob,
My vote is w/ Harvey's analysis.  The one thing I'd add is to test all your tie-rod ends with as much pressure as you can apply perpendicular to the threaded tapered shaft.  The trick is to figure out how to do this w/ the suspension in its normal position.  That is to say, if you jack the front end up and have the wheels dangling, the play may not be apparent.  Even though you feel it is in both wheels, it can easily be just one tie-rod end.  If they have never been replaced to your knowledge, they are a relatively cheap part to replace.  If you have the specific problem that Harvey mentioned (the hole going oval) let us know if you can figure out a way to repair it w/o simply replacing the part.  The tapered hole would seem to be a challenge to remedy for most machine shops, and the part (intermediate steering arm) is likely no longer available new.

Mark Lowery CLC #25216

That's an understatement, nothing is likely available new.

[Roger H]

Hello
a couple more things ,  adjust the steering box  and check the toe in,  ( after fixing any loose items in the lynkage)
if you need help with either send an emai for detailed explabation.  Most older cars need 1/8 to 1/4 inch toe in. 

[Don Rundgren]

Rob,
The first thing I would check is the modulator assembly on the front end of the driver's side front spring. It contains four small springs, if they are broken it will cause the shimmy you describe. This has come up before on this forum, you should run a search. According to Johan Boltendal the shackle springs are available from Katy Springs, www.katyspring.com part number KC0921-0187 1500S. Good luck.

[47bigcadillac]

Hi Everyone, quick update:
I did all the checks and everything was fine, the damper springs are not brokern and nothing seems loose or has play.

But the 2 front wheels had no balancing weight fitted, as the car was moslty used as a "collection showpiece" not a driver, so I had those balanced.

On the balancing machine it clearly showed that the wheels were out of balance. They did a static balance with lead weights sticked to the center rim.

I then did drive quite a bit on that day and the violent shaking occurences have dissapeared.

Wayne was spot on, this was a harmonic virbration caused by wheel imbalance, amplifyied by the design of the single front axle.

Rob

[Jim Stamper]

     If your shake comes back when you hit a hole just right I vote for the king pins. I have had this exact problem and it was kingpins.

[The Tassie Devil(le)]

The Wheels being out of Balance usually only becomes apparent between the speeds of 45 to 50 Mph.

Bruce.

[Paul Ayres #5640]

Rob, et al - I recently wrote an article for the Classic Car Club of America Michigan Region's "Torque" magazine.  I will put the text here, and anyone who wants the complete article with illustrations can email me and I can send a Word document complete.  There are many reasons for shimmy, and some have been addressed in other replies, but the biggest reason is that solid axle cars with longitudinal steering links have an inherent design problem that initiates steering inputs when the car hits a bump.  Paul Ayres #5640

Why Does My Classic Shimmy (Pull Left, Pull Right) When I Hit A Bump (Hit the Brakes) â€" A Primer on Solid Front Axle Suspensions
By Paul Ayres

A discussion took place recently among several technically oriented CCCA Michigan Region members about the purpose of the steering modulator springs on the left front shackle of 1930 through 1933 Cadillacs and LaSalles.  To get the answer to that question is to delve into the geometry and engineering theory of solid axle front suspensions, with which most of our Full Classics® built before the mid 1930’s are equipped.

These cars, with a few exceptions, have two more-or-less parallel longitudinal front springs tying the front axle to the frame.  Some have a fixed mounting at the front with shackles at the rear, some are reversed.  The Cadillacs and LaSalles in question have a hybrid arrangement, with a spring modulator “cushion” on the left front mounting, and a fixed mount on the right side front attachment, with shackles at the rear of both springs.

The Cadillac Steering Modulator, with four coil springs, two in front and two behind the elongated left front spring shackle.  These were to be adjusted so that the adjusting nuts were just flush with the ends of the bolts.  It appears that this device actually allows for more axle movement, especially under braking, and might actually contribute to shimmy.  The writer’s experience with a 1931 Cadillac confirmed that best performance was had by tightening the bolts to strongly compress the springs, nearly eliminating the function of the modulator.


Why the differences?  What does all this have to do with pull and shimmy?  What introduces shimmy?  Most of us with these cars have experienced shimmy at some time when driving our cars.  There are many opinions about how to minimize it â€" add caster, subtract caster, tighten the steering linkage joints, add tire pressure, lower tire pressure, increase toe-in, decrease toe-in, etc.  In fact, strangely enough, any of these actions might reduce a tendency to shimmy in a particular car.

Perhaps the most knowledgeable individual in the field of suspension engineering in the 1930’s was Maurice Olley.  Olley was the Englishman in charge of Rolls-Royce’s Springfield Works in the U.S. in 1930, when he left Rolls Royce fro Cadillac.  He was a strong proponent of independent front suspensions for many reasons, including ride and handling, and control of unwanted suspension actions like pulling and shimmy.  His analysis and mathematic modeling of solid axle suspensions, front and rear, are the basis for the SAE publication Chassis Design Principles and Analysis by William and Douglas Milliken.

In it, he clearly defines the elements which contribute to shimmy and pull, with steering/spring geometry being the major culprit.  It boils down to understanding that the steering gearbox is mounted on the frame, but it controls the steering mechanism mounted on the springs, which move up-and-down and fore-and-aft with ride motions of the car.  Therein lies the problem:  how to maintain a fixed relationship between two moving elements.  A sketch from the Milliken book illustrates the geometry of the problem:



In an ideal situation, the relationship of the end of the steering drag link and the steering arm ball at point B would stay the same under all conditions.  In fact, they do, because they are fixed together.  But, since the drag link is also fixed at point C to the pitman arm, which is fixed to the steering gearbox, which is fixed to the frame, there is motion created when a bump is encountered in the road.  The spring and front axle move in an arc, shown dotted, that is different than the arc imposed by the drag link, shown solid.  Thus, every bump in the road causes some steering input.  Numerous devices were employed to minimize this, including unequal length front and rear sections of the springs, turned down spring eyes, modulating spring mounts ala Cadillac/LaSalle, and others.  None were completely successful, so no solid front axle car with drag link steering is immune from these steering inputs and consequent shimmy.

Cadillac published a 20-page manual in 1933 entitled Front Axle Alignment Manual, detailing all the requirements for maintaining good alignment, including the checks to control shimmy, which illustrates the seriousness of the problem in their eyes.

The problem is not only one of handling bumps in the road.  Under braking, the front axle reacts by moving rearward and rotating against the braking force, tending to wind the springs, again changing the relationship between steering gear and axle.  Thus, heavy braking can both initiate shimmy and in some cases, halt it once it has begun.

Likewise, the relationship changes when a car is put into a fast turn, which results in body lean.  Again the relationship between steering gearbox and axle changes, resulting in a tendency of the car to steer more or less than expected â€" over- or under-steer, to the point that some cars were actually unstable in high speed turns.

Caster and kingpin inclination, which provide the forces that give steering centering, or the tendency of the steering wheel to return to straight ahead after a turn, and keep the car going straight down the road, must be correct, or they can also contribute to shimmy.  Caster tilts the kingpin rearward at the top., meaning that the spindle moves slightly downward when the wheel is turned,  slightly lifting the front of the car.  Too much caster, and the car is difficult to steer, because the lifting is increased.  It can thus also initiate shimmy, since the weight of the car is directly involved in steering effort when the tire hits a bump.  Too little caster, and there is not enough force to keep the steering centered, which also makes shimmy harder to stop.  Unequal caster causes a pull to one side, another cause of shimmy.

Toe-in, where the front of the tires point slightly toward each other, counteracts forces from caster and kingpin inclination which tend to push the wheels outward at the front.  If it is not correct, and if tire pressures are not equal, the increased drag from the lower pressure tire can initiate shimmy.

Camber angle, or the tilt of the wheels, is likewise critical.  Unequal camber causes a pull to one side, again a contributor to shimmy.

So there you have it.  There is no single cause of shimmy and pull.  Everything must be to specification, every joint, bearing and bushing tight, tire pressures at specification and equal, brakes properly adjusted, all lubrication points properly greased.  And even then, you will probably occasionally encounter just the right combination of circumstances to initiate shimmy.  If it occurs, apply the brakes, GENTLY steer back and forth if possible, and slow until the shimmy stops.  In its most violent form, shimmy involves the entire front axle jumping up and down, with one tire after the other actually leaving the pavement and making a curved mark on the road when it hits the surface again, so it can do major structural damage if allowed to continue unchecked.

[TJ Hopland]

Are you running radial tires?  Radials on most cars require more caster than bias tires did.  I just recently worked on a car that had the same issue.  Alignment was set to factory specs ( which were all bias tires if the car was made before the 1970's).   If you are running radials a few more degrees toe will likely help a lot.   

++ edited to change toe to caster ++   
I was thinking caster but somehow typed toe.  I wonder if I could blame that on the computer somehow?

[The Tassie Devil(le)]

I was always under the impression that when fitting Radial Tyres to any vehicle, the Toe-in had to be less than with Bias-ply Tyres.

1/8" is what I set mine to.

Set it too much and problems will occur when turning.

Bruce.

[TJ Hopland]

OOps.... I was thinking caster but typed toe.    I will go back and correct that.   

On a solid axle I would assume this would be set by shims / wedges between the axle and springs?   I could imagine as the springs change shape over the years the caster also would change?     

[47bigcadillac]

Hi Paul, thanks for posting the article.
Balancing the wheels seemed to have made a big improvement, but I haven't driven the car much recently because of the rainy weather these days. If the issue re-appears I will try the wheel aligment/casting etc.. although steering was alwyas fine.
I might try tighetning the front end left spring modulator, but again, all seems in specs as per the manual.
Perhaps those springs are a bit tired though.

The car has the regular bias/ply tires

http://cadillac.gs/1932-2/ww9.JPG

I don't drive at more than 35mph even on the highway.

Rob