Mahogany Metallic 37

Shocks

Background

 

One of the more common questions these days  has to do with replacement shock absorbers for the Cosworth Vega.  NOS units are long gone from the dealer shelves, and have only appeared on very rare occasions on eBay.  Further, our cars are so old now that no manufacturer currently offers a shock absorber fitted for our cars.

 

 

What's an owner to do?

There's no easy answer to this question.  There's no magic solution for a number of reasons.  To understand this, we need to go back to the beginning.  The history hereinafter described is based upon rumor and hearsay, articles and intuition -- but we're pretty confident in it.

 

The Cosworth Vega was engineered with the Monza suspension, but parts weren't simply taken off the shelf.  The suspension was "tuned" for the Cosworth, presumably taking into account the aluminum alloy wheels, possibly the characteristics of the Goodyear Custom Steelguard BR70-13 radial ply tires, and undoubtedly the spring rates of the Cosworth specific front and rear springs.  The result, by all contemporary accounts and Duke Williams' early racetrack experience, was a suspension that provided "dead neutral" steering in hot lap racetrack conditions.  It also provided a firm but compliant ride on city streets, country roads, and Interstate highways.

 

 

If a little is good, more is better

 

It is a little known fact.  Aftermarket replacement shock absorbers are not simply copies of the original equipment pieces with identical construction and valving.  Rather they are engineered to be about 20% "stronger" than OEM shocks.  The shock buying public equates a stiffer, firmer ride with "better" performance.  Moreover, a stiffer shock helps reinforce the conclusion that the old shocks were indeed worn out and in need of replacement.  In short, making replacement shocks stiffer than the originals makes for happier customers.  It is simply good for business.

 

Cosworth Vega owners are in the mainstream when it comes to evaluating shock absorbers.  Their mantra is typically "stiffer is better",   up to the point where their fillings fall out.  Don't ask what it ACTUALLY does to the handling of their cars.  Just ask what they THINK it does for their handling.

There is occasionally a lone voice in the wilderness. Once such voice serendipitous appeared as this page was being edited. Pittsburgher Mike Rupert had this to say:

I have been daily driving the white Cosworth for about three months....Another item I realized as a serious drivability issue was the Spax shocks. Maybe I just got too old, but even at the softest setting I absolutely hate the "go-cart with no suspension ride". They were off the car within a week, never to return.

This author concurs. It is a function of old(er) age. Loud exhausts, once de riguer, are now a major annoyance. Stiff suspensions, however, still hold some charm for this author.

 

Yet owners chant the mantra: More is better.  More is better.  More is better.  Who was it that once said, "Repeat a lie often enough and it will be believed?" You might be surprised. But the point here is that shock stiffness is not the Holy Grail of suspension technology.

 

The FACT is that the best suspension is the one that keeps the tires in contact with the road surface the highest percentage of the time.  If a tire is lightly loaded or in the air, it is providing little or no traction.  A tire that follows the irregularities in the road surface closely will develop the maximum in cornering force.  Think about it.  Have you ever had your car's tail end skitter over a washboard gravel road as the tires skipped from the top of one rill to the next?  That's the result of a too-stiff suspension.  It may be the springs, it may be the shocks, it may be the combination, but more definitely isn't better here.

 

What about Spax shocks?

 

Well, what about them? You know what Mike Rupert has to say for a daily driver, but first some background for the uninitiated. "Spax shocks" as used here refers to a full set of   high quality gas charged Spax shock absorbers that Hutton Motor Engineering of Clarksville, TN, in partnership with the CVOA, had specially made for our Cosworths.  A mere 25 sets were produced, if memory serves.  Gas charged, stiff, expensive, and the ultimate in shocks for our Cosworth Vegas according to many owners.

 

They are high quality shocks.  Duke Williams' car sports them.  This author has driven several thousand miles in a heavily laden Cosworth with them.  They are "good" shocks if you like a stiff suspension.  But, in this author's opinion which coincides with Mike's; they are simply too stiff for the street in a lightly loaded Cosworth at the Duke Williams recommended settings of 14 front and 7 rear.  Remember those fillings?  They are at risk on those settings on all but the smoothest of highways.  They are way too much for the roads in and around Cleveland, and Pittsburgh as well.. Yet on a smooth racetrack, they can fall short.

 

According to Duke, "Only the front valving needs to be adjusted [stiffer!] the next time. Current max setting should be halfway. I have my fronts set at max (14 as I recall) and the rear is midway - seven.  These settings firmly control body rebound. The front shock needs to have more damping because the suspension works it through a lever arm. On the rear there is essentially no lever arm."

What about GM A-Body car shocks?

 

Well, what about them?  They fit the 71-84 Monte Carlo and Buick Regal models.  They will physically bolt in too.  But, and this is a big BUT, they are too long.  This isn't a problem in the front, but is potentially disastrous in the back. 

 

The key to understanding the danger is a simple fact.  The rear shock absorbers limit the downward travel of the differential.  If the shocks are too long, the springs can be lifted out of their spots when the car is on the lift.  You could lose a spring during spirited driving on a whoop-de-doo, with possibly tragic consequences.  But that isn't the worst of it.

 

Think about what happens when the differential hangs down.  Think about what keeps it from hanging WAY DOWN.  Yep.  That's right.  THE REAR BRAKE HOSE!  Imagine going over that same whoop-de-doo and ripping the brake hose apart.  No more rear brakes, a brake pedal that goes almost to the floor, and, if your are lucky, no other damage other than a need for a quick trip to the laundromat.

 

 

So what are the key dimensions of our shocks?

 

We're glad you asked.  Monroe has published the following information:

 

Front:

Upper Mounting End: thread 3/8-16"

Lower Mounting End hole size 5/16"

Lower Mounting End hole spacing 1 7/8"

Compressed Length 8"

Extended Length 11.750".  Note:  This Monroe shock is described as a Bumper Stop Unit.  Dimension shown at Bumper Contact.

Length Traveled (Inches): 3.75"

 

Rear:

Upper Mounting End hole size 5/16"

Upper Mounting End hole spacing 2 7/8"

Upper Mounting End hole configuration Closed (note that stock is Open)

Lower Mounting End hole size 7/16"

Lower Mounting End  hole spacing   7/16"

Compressed Length 12.125"

Extended Length 19.125".  Note:  This Monroe shock is described as a Bumper Stop Unit.  Dimension shown at Bumper Contact."

 

 

So what should we be looking for?

 

Here is the best explanation that I have found so far regarding compression and rebound settings.

 

The function of the shock absorber dampening is to control the spring's reaction to input. This is done using a special piston called a dampening piston. It is attached to the end of the shock shaft inside the shock body. The dampening piston has special through passages or "ports" that allow fluid to pass from one side of the piston to the other. On either side of the piston there is a series of tuning washers or "valve shims", which seals off fluid flow in one direction and restricts or "dampens" fluid flow in the other direction. When the shock is compressed or retracted, the dampening piston moves through the shock fluid, forcing the fluid through these passages. Dampening is thus regulated by the assembly of the valve shims on either side of the dampening piston. Compression dampening regulates how fast the spring will compress, and rebound dampening regulates how fast the spring returns after being compressed. 

 

The compression dampening should be taut, firm, but not harsh. Too much compression dampening and the ride will be stiff and choppy. Too much compression dampening could also cause the shock to become solid or "hydraulic". This causes a number of undesirable effects, two of which are blown seals and bent shafts. Too little compression dampening and the ride will be spongy and vague. Not having enough compression dampening will also cause you to blow through the travel too fast.  The rebound dampening should be on the slow side, but not too slow or the shock will "pack up". Pack up means that after the shock has been compressed, the speed at which it returns is too slow to reach proper extension before the next compression stroke. With a gradual loss of shaft travel at each compression stroke, the shock could eventually run out of shock travel and bottom out. Not enough rebound dampening, the ride becomes springy with a buoyant feeling. In either case, not having the correct rebound dampening prevents the tires from not staying planted on the ground, causing them to skip, wander and bounce, which results in loss of traction and control."

 

www.yellowdogracing.com/springs.htm 

 

This explanation relates to another bit of information that I have learned--that the starting point for designing an appropriate shock for a particular application is the springs. Makes sense to me.

 

 

One owner's observations

According to Gary Darien, "Dynamic driving conditions rely on shock damping far more than springs. Springs set steady state behavior, a long corner or driving straight down the road. Everything else depends on shock damping.  Cars ride much better when the compression damping is softer than rebound. Race only cars use close to 50/50, but at what piston/wheel velocity? Road cars are closer to 30 compression/70 rebound.  It depends on the setup."

A lowered car needs stiffer compression to prevent bottoming out. This hurts the ride and when it does bottom, [the resulting jolt to the suspension] hurts the handling. 

Pushing and pulling by hand a shock only tells you the very lowest speed damping. The valves "blow off" when certain pressures are reached. For bump, the blowoff is set fairly low to absorb road impacts. For rebound, less blowoff is used because most of the rebound force comes from the springs.

 

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Cosworh Vega Owners Association - Created 2017