What does a steering do?

[Bill I.]

I've Googled it and it refers to preventing steering 'wobble' on motorcycles. Does the same apply to a 67 Corvette, no PS. Thanks, Bill

[Jean C.]

Re: What does a steering do?

Bill, did you intend to type steering damper?
Best regards,

[Bill I.]

Re: What does a steering do?

Yes Charlie, I did. Sorry, my screw up. What does a damper do on a non PS vette? Bill

[Brian M.]

Re: What does a steering do?

Probably makes it harder to steer.

Yes Charlie, I did. Sorry, my screw up. What does a damper do on a non PS vette? Bill

[Jim S.]

Re: What does a steering do?

With power steering the hydraulics tend to act as a damper. The C2 and early C3 manual steering Vettes had a seperate hydraulic damper (very much like a shock absorber.) Sometime in the 1968 model year the damper was eliminated from manual steer Vettes.

The basic Corvette chassis really didn't change from 1963 through the 1980s. The steering gear didn't change. The rubber disc in the flexible coupling didn't change. Changing to energy absorbing steering columns in 1967 really shouldn't have affected steering. Possibly tires changing from 7.75x15 to F70x15 in 1968? Wheel rim width increased from 6" to 7" in 1968 as well.

We probably will never know exactly what changed and allowed the elimination of the damper.
Jim

[Duke W.]

Re: What does a steering do?

Wobble is a high frequency (4-6 Hz) back and forth movement of the handle bars, which is a back and forth angular motion of the steering axis. The frequency is too high relative to human reaction time for us to be able to damp it out with bar pressure in severe cases. Some motorcycles have a hydraulic steering damper and IIRC my 1965 Honda CB 160 had a knob on the steering stem that was an adjustable friction damper.

A Honda factory tech I used to ride with taught me how to induce wobble on my '83 CB1100F. Wow! The amplitude was clearly rapidly increasing, and I was able to damp it out by putting full pressure on both bars before it got out of hand. It never happened to me in normal riding, but was a good training experience - like spin recovery in an aircraft.

Back in the early days of motorcycles, riders referred to severe wobble as "tank slappers." Most modern bikes are quite resistant to the problem due to frame stiffness, better tire damping, and better front end geometry. Bicyclists can also experience the phenomenon if they hit something in the road off-center of the front tire, and it usually results in a crash.

The other two-wheel vehicle dynamic response modes are weave and capsize, but I won't get into those.

The equivalent of wobble on a car is usually called shimmy. It was a real problem on early cars and trucks with solid axles, but modern cars that have high caster can also experience it.

Case in point. Once my '88 MBZ 190E 2.6 went into a violent shimmy. It scared the sh...t out of me as I had never experienced such violent shaking from a car - waaaaay more severe than even the worst wheel/tire balance problem.

The Merc has a high pressure gas (like Bilstein shocks) steering damper, and it was limp. A new damper solved the problem, and now I check the damper for oil leakage every time I'm under it because that car absolutely needs a steering damper.

I've always wondered why base C2 Corvettes had a damper because it was left off mechanical lifter SBs due to the larger oil pan - apparently to no ill effect. Possibly during GM's rigorous testing of the C2 a driver experienced shimmy, and it had relatively high caster for the era, so a damper was installed, but eventually dropped when they realized it wasn't really necessary.

BTW, the Merc runs about 10.5 degrees caster versus about 1.5-2 for C2s.

Duke

[Jim S.]

Re: What does a steering do?

The General Motors Milford Proving Ground and the Desert Proving Ground have Ride & Handling Loops that have washboard indentations on the inside edge of high speed right and left hand turns. By driving on the washboard areas at various speeds, you could sometimes hit it just right and the front wheels and steering wheel would start to frantically oscillate. It was called wheel fight. It was most pronounced on manual steered vehicles but it also showed up on some power steered vehicles despite the hydraulic damping.


The "fix" on manual steering vehicles was usually to add a shock damper to the relay rod. (I think the early manual steering Chevrolet Citations or possibly it was Cavalier vehicles that had a concentric silcone damper on the rack and pinion input shaft.)


On power steering vehicles it was determined that during wheel fight the rack piston inside the power gear would be forced back and forth by the oscillation of the tie rods. The motion of the rack piston would cause pressure pulses to be back driven into the pressure side of the gear valve. It was found that if a one way check valve was installed in the pressure port of the gear, the wheel fight could be greatly reduced. Saginaw Steering Gear developed a pressure port check valve that allowed relatively free flow of fluid into the gear but immediately popped back and checked the motion of the rack piston in the opposite direction. On power gears before 1980 you can look into the pressure port and see a small, spring loaded metal plate that is underneath the 45 degree brass seat. On the metric o-ring pressure port (1980 and later) there is a metal cartridge that has the same type spring loaded metal plate inside. It is a press fit into the port and can be a real pain to try and remove.
Jim Shea

[Bill M.]

Re: What does a steering do?

The equivalent of wobble on a car is usually called shimmy. It was a real problem on early cars and trucks with solid axles, but modern cars that have high caster can also experience it.

Duke

Duke:

I worked in truck chassis and thought you might appreciate what I learned about shimmy. There are two types of shimmy: classic and steering (my terms).

Classic is the solid axle shimmy. This involves a tramping motion of the solid axle. It is violent and you have to stop the vehicle to stop it. (There is a reference to this type in January 2010 Car Craft p.72: a '55 gasser with a solid front axle. )

Steering is an oscillation of the wheels in the steering direction only; no axle tramp. (I saw a tow truck that had this so bad that the tires squawked in each direction.)

The fix is the same: a steering damper.

Bill