C2 Steering Stabilizer (shock) Question

[Al P.]

I noticed that some small block 1967 Vettes w/o power steering have a "Steering Stabilizer installed between the center Link and the frame. It looks like a shock absorber right in front of the oil pan.

What it it's purpose?

Why were they not installed on non-power steering Big Block cars? All the mounting holes for it are there for one.

I know a person who installed one on his big block car and was wondering what benefits it provides on a big block car.
Does it enhance the steering stabilization?

Thanks!

[Duke W.]

Re: C2 Steering Stabilizer (shock) Question

It's a damper, and its purpose is to damp out any oscillations that develop in the steering system, like shimmy. It wasn't installed on big pan small blocks because the longer deep section of the pan occupies the same space, which is also why power steering was not available with the big pan.

It has little noticeable effect that I have ever experienced, however, I believe Chevrolet felt it reduced road shock that can transmit through the steering system, which would be more of an issue with "luxury equipped" models rather than "high performance" models.

My '88 MBZ 190E 2.6 has a similar damper. It is a high pressure deCarbon type (think Bilstein) so it can fail suddenly.

One day it did and the front end went into a violet shimmy the likes of which I had never experienced before. When I removed one end of the damper it was completely dead. The Merc runs a nominal 10 deg. of caster, and high caster can exacerbate shimmy - like "wobble" on a two wheel vehicle. Corvettes' much lower caster - about two degrees - is less likely to develop shimmy.

Someone should run an experiment by running with and without the damper over preferably the same rough road to see if they can detect any difference in road shock feedback through the steering. My guess is that the difference in the two states would be virtually undetectable.

Duke

[Jim S.]

Re: C2 Steering Stabilizer (shock) Question

Many C2 and C3 Corvettes with manual steering had a steering damper up until late in the 1968 model year. Most likely for cost reduction reasons, it was determined that a steering damper was no longer required. I would guess that both new and high mileage Corvettes were evaluated and found acceptable for steering and handling performance before they decided that they could remove it.

Now, the basic Corvette chassis didn't really change from 1963 through the late 1970s or 80s. So what changed from 1968 to 1969 that might have allowed the damper to be removed? Well probably nothing major. Possibly tire changes? Maybe something changed back in the middle 60s but removing the damper was never investigated at the time.

Steering dampers were never used on big block Corvettes because the damper would interfere with the oil pan. Maybe the experience with the big blocks keyed engineering into removing the dampers on the small blocks.

The General Motors Milford Proving Ground has a Ride & Handling Loop where some portions of the right and left hand turns have washboard indentations right on the inside edge of the track. By driving and turning on the washboard areas at various speeds, you could sometimes find the right speed to start the steering wheel to frantically oscillate in your hands. It was called wheel fight. All new vehicles (both cars and trucks) were evaluated at some point during their development for the tendency to wheel fight. On manual steer vehicles an expensive steering damper was sometimes required. On vehicles with hydraulic power steering, a check valve was developed that was located in the steering gear pressure port.

Jim

[Rich G.]

Re: C2 Steering Stabilizer (shock) Question

When I bought my 66 SB 10 years ago it had the original damper on it. When I would hit some bumps like RR track it would sometimes set up a shimmy. I replaced it with a new unit which fixed the problem. It is not a repro part in the sense that it would never pass judging. I don't even know if that is judged. Anyway, I kept the original one.

Rich

[John H.]

Re: C2 Steering Stabilizer (shock) Question

As I recall, when the steering damper disappeared in 1968, there was a minor increase in the nominal diameter of the relay rod (7/8" to 1"?).

[Mike E.]

Re: C2 Steering Stabilizer (shock) Question

Did cars that never had damper installed because they were BB, SHP/SB or FI/SB have the bracket on the frame anyway?

Mike

[John H.]

Re: C2 Steering Stabilizer (shock) Question

Did cars that never had damper installed because they were BB, SHP/SB or FI/SB have the bracket on the frame anyway?


Mike

Mike -

The plant would have had no reason to install the frame bracket on a car that didn't call for the damper.

[Mike E.]

Re: C2 Steering Stabilizer (shock) Question

That's what I thought....Thanks!


Mike

[Joe L.]

Re: C2 Steering Stabilizer (shock) Question

As I recall, when the steering damper disappeared in 1968, there was a minor increase in the nominal diameter of the relay rod (7/8" to 1"?).

John-----


1963-68 Corvettes used a relay rod that was 3/4" OD. 1969-82 Corvettes used a relay rod that was 7/8" OD. These sizes were for relay rods for both power and non-power steering applications. No 7/8" relay rod used in PRODUCTION had provisions for a steering shock absorber. However, I believe there was once-upon-a-time available in SERVICE a 7/8" relay rod that had provisions for a steering shock absorber. I've never been able to confirm it, though.

[Tom R.]

Re: C2 Steering Stabilizer (shock) Question

Mike -

The plant would have had no reason to install the frame bracket on a car that didn't call for the damper.

However, it was my belief that all C2's did have the four holes punched into the frame whether there was power steering, a damper or had a 6-qt oil pan (SHP) engines that couldn't use a damper or Power. I's that correct?

[Jim L.]

Re: C2 Steering Stabilizer (shock) Question

and high caster can exacerbate shimmy - like "wobble" on a two wheel vehicle.

Why does this happen? I associate high caster with high self-centering forces and stability. Is there a caster value above which shimmy is likely and below which it isn't?

[Duke W.]

Re: C2 Steering Stabilizer (shock) Question

It's because of the high self-centering action with high caster that the propensity to shimmy can increase. A large disturbance that quickly rotates the tire about the steering axis creates a strong self-centering action that can then overshoot, or if the tire is hit by disturbances from opposite sides in quick succession close to the natural rotational frequency about the steering axis - like crossing RR tracks that are not perpendicular to the road -shimmy (or wobble on a two-wheel vehicle) can occur.

Actually, it's not the caster that creates the self-centering effect, but the "trail", which is the longitudinal distance between the point where the steering axis intersects the road and the center of the contact patch, and trail can vary with other design parameters of the suspension. "Scrub radius" the lateral distance between the point where the the steering axis intersects the road and the center of the contact patch also creates self-aligning torque. Tires are also a factor. For example, radials have inherently more self-aligning torque than bias-ply and tires provide most of the damping.

So one has to look at the suspension (including the tires) as a complete system, and like any dynamic system with multiple degrees of freedom, there is a lot of physics going on in control arm and multilink suspensions. Back in the day it was seat-of-the-pants engineering based on experience and intuition and then testing.

Nowadays, suspension behavior can be analyzed with computer simulation programs, and any bad dynamic response modes can be designed out or tamed with suitable damping. Designers have to juggle about a dozen variables to achieve the type of steering response and feeback that they consider appropriate for the type of vehicle. For example, a sports car should provide more steering feeback to the driver than a family sedan. Drive and old Porsche 911 back-to-back with a typical sixties sedan with power steering and you will experience the extreme ends of the spectrum.

Dynamic response modes of steerable vehicles are easier to understand if we limit it to two dimensions - like a bicycle or motorcycle. They have three dynamic response modes - capsize (about 0.5 Hz). weave (about 1-2 Hz), and wobble (3 Hz or higher). The speed of the human brain and nerve system limits our ability to control disturbances above 1-2 Hz, so suitable damping is required to mechanically damp out high frequency disturbances.

Then, with two-wheel vehicles there is "countersteer" - if you want to turn right you put brief forward pressure on the right bar to slightly steer the wheel to the left for a fraction of a second, which causes the bike to roll to the right. That's a whole other story, but once I fully understood two-wheel vehicle control and response, I became a much better motorcycle rider with much greater confidence and ability to control the machine with great precision.

Duke

[Joe L.]

Re: C2 Steering Stabilizer (shock) Question

However, it was my belief that all C2's did have the four holes punched into the frame whether there was power steering, a damper or had a 6-qt oil pan (SHP) engines that couldn't use a damper or Power. I's that correct?

Tom------


As far as I know, yes.

[Jim L.]

Re: C2 Steering Stabilizer (shock) Question

Actually, it's not the caster that creates the self-centering effect, but the "trail", which is the longitudinal distance between the point where the steering axis intersects the road and the center of the contact patch, and trail can vary with other design parameters of the suspension.

C4s (and maybe even C5s and C6s) locate the hub center of rotation behind the king pin axis and are specified to be set for several degrees of caster.... about 5 degrees (+/-) as far as I know. Lots of "trail", in other words.

What is it about the remainder of the C4 suspension design that prevents these models from having a tendency to shimmy?

[Duke W.]

Re: C2 Steering Stabilizer (shock) Question

Yaw damping can be designed into power steering systems, and PS is standard on all modern Corvettes. More precise understanding of suspension/steering behavior and modern simulations also contribute to more stable systems on modern cars while providing adequate feedback, though some describe modern Corvette steering as "too numb" - not enough feedback.

It's still a somewhat qualitative parameter that designers have to choose - something between that old 911 and and a '65 Impala with power steering, and not all will be happy with the engineers' choices. Maybe the day will come that drivers can actually adjust steering characteristics to their preference. The technology to achieve this exists, today.

The SAE book (PT-118) with all the Corvette SAE papers I referenced a few months ago has a number of papers on the development of the C5 suspension and steering systems. These papers are also in booklet SP-1282, which was published about the time the C5 was introduced.

There is no way I could briefly summarize these papers other than to say that a key design (and quantifiable) parameter was "yaw velocity damping". If you want to take a deep dive into automotive suspension design, reading these papers is a good way to do it.

Duke