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Here are some of the more interesting highlights of a few hours with an old Moog catalog.

Front Coil Springs

By Rob Smith

Appended by Jeff Davidson with permission.
 

As you can see by the added numbers, there are numerous springs of the same spring rate available. This allows the spring to be matched to the weight of the vehicle since, depending on options, the ride height would vary if only one spring was available. If you know the weight of the front axle of your car, you could pick a spring that would give you the ride height you desire.

Example:

Let's say you want to use the 5658 S-10 spring in your Monte to gain some spring rate. Assume you already have 5606 springs in your Monte. Let's install a set of 5658 and see what happens. We know that we already have a front end weight of 2142 pounds (assumed) or, 1530 pounds at the spring, but if you look at the installed height weight capability of the 5658, you can see that it can't support that weight, at that height, so it compresses until it can. In this case, it compresses about .5" further than the 5660 does for the same weight vehicle.

The following chart shows the various spring forces generated by the different springs. As you can see, the stiffer springs lose much of their "push" at heights greater than their Installed Height. The 5606 produces almost twice the force at a 12.00" loaded length than the 5658 does. This should help handling as there will be less weight transferred when cornering. The stiffer spring will decrease body roll as well. One interesting comparison is the 5606 and the 5658. These two springs would have similar ride and produce the same force at around 9.00" height, but the 5658 force drops off rapidly under rebound conditions when the spring height gets above 10.75". This should prevent the vehicle from rising too far in the front in response to a rise in the road and get rid of the "floaty" feeling of excessive rebound. But, the 5660 will provide more spring rate if the spring is going to be shortened to attain a custom ride height. You already get around a .25" drop, but that really depends on the actual weight of the vehicle involved. If you want an even stiffer ride, the 5662 springs have been used with good success by several members of the Monte Carlo Mailing list. This spring will really resist the tendency to bottom the front suspension and is needed if you choose to lower the front end by two inches. If you only want to lower by one inch, trimming a quarter or half coil off of the 5660 would probably sufficient to give the ride height you desire and not bottom. The 5662 is strong enough to resist almost .75" of further travel compared to the 5658 and about .5" compared to the 5660.

Stare at this chart for a while and you will see how different springs function. Interesting!

Blue highlighted ( and bold) fields indicate design installed height. Notice that the 5658 would drop the front end almost an inch compared to the 5606. Cells with red borders indicate the installed height relative to the 5606 (around 1500 lbs spring force). Yellow highlights indicate spring force closest to 2400 pounds.

So, you can see that swapping in a 5658 spring in place of the 5606 would drop your front end about a half inch, if nothing else is changed! If you wanted a little more drop, then the spring could be trimmed, but only a little, instead of putting in a spring with way off dimensions and having to cut off a lot of coil. Since the design installed height of the 5606 is 11" and the installed height of the 5658 is 10.75", you would get an immediate .25" drop IF the 5658 could carry the same weight at that height, but we have seen that it doesn't, so it compresses until it can. The 5662 springs would give a normal ride height compared to the 5606 springs. If you trim coils off, you can re-measure the Free Height, but, the spring rate goes up a little when you shorten the spring.

The math:

To get the compression force on the spring at the installed height (meaning-car sitting on its wheels), take the Free Height and subtract the Load Height from the above charts. Then multiply that result by the spring rate for that particular spring. I assumed a relative wheel rate by multiplying the spring force by .7 to simulate the lower control arm. I based it on some simple measurements of the lower control arm, but .7 is close enough for our purposes. You can then multiply the last number (force at the ball joint) times 2 to see what the front end weight is. If you know the weight of the front end, you can work backwards through the math.

Free Height minus Load height equals distance spring is compressed when installed and holding up vehicle.

This distance times the spring rate equals the amount of force the spring is exerting on the suspension at the point where the spring contacts the lower control arm.

Rear Coil Springs

Note: The style 19 is double pig tail and style 17 is single pigtail, open coil top.

The following chart shows the spring included in the chart above, but with spring forces at various heights added. It's interesting to note that at least four of these springs would supply the stock ride height for a Monte SS, even though some were not intended for that application. The rear springs seem to have more variances than the front springs. It looks like at least two of them are intended for station wagon use (5391, 5461). The 6377 spring for the Monza would lower a Monte about a half inch and has the open coil style at the top so it could be trimmed slightly to lower the rear further.

The aqua color represents the design installed height. Note that the two F-body springs are designed for a 10.25 installed height, so they don't appear on the chart. The red outlined squares indicate the height that spring would sit at at the same load as the 5379 spring.

After doing some investigation, I have determined that a load height of 10.25 for the rear springs is more realistic. One list member said that is where the stock Monte SS should sit. The spring loads match better using 10.25 as a reference, also.

updated: 03/22/2001 at 3:30 EST