Mono-Leaf vs. Multi-Leaf Springs
From Eaton Detroit Springs, Inc
The following opinion is from someone who has actually been making springs for nearly 30 years for a company that has been making springs for 70 years.
Now, just don't skim over this, read it, pay attention and learn It may save your life!
Before we can answer whether mono-leaf springs are safe, let's look at the make up of both mono-leaf springs and the multi-leaf springs they attempt to replace.
A multi-leaf spring is not just a bunch of pieces of steel put together. It is an engineered system designed to provide support, stability and safety to a vehicle. In a multi-leaf spring the length and make-up of each leaf is important because each leaf is designed to carry a proportionate amount of load and stress.
Mono-leaf springs consist of one plate of spring steel that is thick in the center and tapers out to the ends. The amount and length of the taper is critical to the durability and safety of the spring.
Contrary to what has been written in magazines by people who only sell springs, not make them, mono-leaf springs are inherently dangerous.
Remember, all springs have a finite life, that is one day they will break.
When designing a leaf spring this eventual breaking must be taken into account.
What will happen to the spring and the vehicle should this failure happen when a vehicle is in motion?
A correctly designed multi-leaf spring is designed so each leaf carries a proportional amount of load, is stressed equally, and will provide support to the vehicle when it fails.
The main leaf of the spring attaches the axle to the vehicle.
A multi-leaf spring consists of a main plate and several supporting leaves.
A mono-leaf spring is just a fancy main plate without the supporting leaves.
Should the main leaf break, dire things could happen.
When the main plate of a multi-leaf spring breaks in front of the axle, the axle may shift rearward.
When the mono-leaf breaks in front of the axle, the axle will shift rearward.
When the main plate of a multi-leaf spring breaks behind the axle most multi-leaf springs will provide enough support to keep the body of the vehicle from dropping down onto the tires.
When a mono-leaf spring break behind the axle, the body of the vehicle will drop down onto the tires. probably bringing you to pretty quick stop.
Now, what about the axle shifting rearward? This might be a concern.
Shifting of the axle causes a change in the control of the vehicle. This change of control can vary from slight to a complete loss of control.
In the case of a multi-leaf spring, it is extremely rare that the axle moves enough to cause a loss of control of the vehicle.
However, in the case of mono-leaf springs, there is nothing to stop the axle from moving backwards.
The number of leaves, their stepping, the placement of the rebound clips, whether or not a wrap leaf is used, and the type of axle attachment are all items that should be considered when designing a spring. A correctly designed multi-leaf spring will provide support to the main plate upon failure. With the correct placement and style of rebound clips, a main plate can be broken without any, or very little, shifting of the axle.
In most cases a vehicle with a broken multi-leaf spring, can be safely driven to the repair shop.
Aftermarket mono-leaf springs are either designed to have an even taper, which is not necessarily the correct taper to keep stress and load distributed evenly, or they are overbuilt, resulting in springs which are too strong for the application. Too strong of a spring will not only cause a hard ride, they can fail sooner than a correctly designed spring.
But more importantly they provide none, repeat, none, of the safety features built into a multi-leaf spring - stepping, rebound clips, backing leaves required for support and even distribution of loads and stresses.
While it is true that GM spent millions of dollars designing, testing, building, and using mono-leaf springs on the F and X body (Chevy II, Nova, Camaro, Firebird) cars of the 60's and early 70's, they have not used a steel mono-leaf spring since.
One must ask - Why?
GM, with their drive to reduce costs and weight and with all the resources to design and test the latest and greatest , is no longer interested in steel mono-leaf springs. Nor has any other OEM has used or is interested in them either.
Could the reason be safety?
Do not compare the current composite (fiberglass) mono-leaf spring being used by GM and others to a steel mono-leaf.
The composite mono-leaf spring is a completely different animal in its composition and it works. It is extremely rare for composite springs to suffer catastrophic failures.
Now that you know our opinion about steel mono-leaf springs, do we offer them?
Our mono-leaf springs are direct replacements for the F and X body GM cars. Our Chevy II, Nova, Camaro, Firebird mono-leaf springs are made directly from the original GM blueprints and match GM's design.
Do they fail? Yes. But recall one of the considerations used in designing a spring is the axle attachment.
Every broken GM steel mono-leaf spring I have seen, which has been less than 5 out of the thousands we have sold, have been broken at the axle.
GM encased these springs in thick rubber pads at the axle. This encasement holds the broken spring in place.
Another factor is the spring's taper. GM perfected the taper profile which eliminated breakage between the axle and the spring ends.
So now you think you are stuck with crummy riding multi-leaf springs, right?
Don't forget, we manufacture springs and everyday we make multi-leaf springs that lower and greatly improve the ride of just about any vehicle.
So give us a call and let us do our magic for you.
The last thought on this subject - like steering and braking systems, springs should be considered a safety item.
Need more info on Springs contact the people at Eaton Spring.... they’re the EXPERTS and they’re great people ... always willing to help.
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