How to find the right strut for your stuff

by Jim KerrBackyard Mechanic . Jul 27 2018

Question: I am looking at putting new struts into my car, and when I started shopping around I found a wide range of prices.

Some are listed as regular and others are called “heavy-duty.” Then the more expensive ones state they are “gas-filled.”

My question is, what is the difference in these strut assemblies, and are the more expensive ones worth the cost?


Answer: When you shop for replacement struts, there are different types of assemblies available.

Some come as only the shock absorber portion and require disassembly of the spring and bearing assemblies to install.

Compressing the spring assembly to disassemble it requires special tools and even experienced mechanics can find it tricky to do on some vehicles. A compressed spring contains a lot of force and I have seen one break free from a compressor and knock a cinder block out of a wall!

An easier but more expensive solution to this is to buy a complete strut assembly, which comes preassembled with the spring and bearings already installed.

These are fairly easy to install by the backyard mechanic, although you should have a wheel alignment done afterwards because you will be moving some of the settings.

There is also a difference in quality when it comes to struts or shock absorbers. I wouldn’t even consider buying standard units.

The heavy-duty units have bigger piston and rod assemblies and control wheel movement better. They also last longer than regular units.

The best units are gas-filled.

Pressurized gas is inside the hydraulic body of the strut. This pressurized gas does provide a little extra spring support for the vehicle but the big advantage is that the gas reduces the possibility of the oil inside the strut from foaming.

When a vehicle suspension moves up and down, oil inside the strut is forced through orifices in a piston that moves up and down inside the strut assembly with the suspension movement.

There are small spring-loaded valves that control the oil flow through these orifices. For example, when the wheel moves up, oil is allowed to flow quickly through the piston orifice.

When the wheel moves back down, oil flow is reduced through the piston so the tire doesn’t bounce on the road surface.

As oil flows through the orifices, it tends to foam and then the oil flow can’t be controlled. Gas pressure on the oil helps prevent that from happening.

If I had my choice, I would choose gas-filled strut or shock assemblies even though they cost more. The improved handling, especially on rough roads, is worth it.


Question: I have a question about my antique Ford that nobody at the dealership seems to be able to answer.

It’s a 1956 Ford Sunliner convertible and I have owned it for several years.

This spring, I noticed the gauge needles for the engine temperature and the gas gauge were moving back and forth slightly. Then a couple weeks ago both needles dropped to the bottom of their scales. Sometimes when I start the engine, the gauges read correctly but after a while, they start to act up again.

Do you have any idea what the problem could be?


Answer: It sounds like there are no “older” technicians around at your dealership. This problem was fairly common when these cars were new and is fairly easy to fix.

The temperature and fuel gauges operate on a lower voltage than the main electrical system. To provide a consistent reading, there is a voltage regulator on the back of the instrument cluster which provides this constant lower voltage. These mechanical voltage regulators disappeared in the 1960s as electronics replaced them.

This voltage regulator was a simple mechanical device, with a small bimetal spring and heating element. As the bimetal spring heated and cooled, it would rapidly make and break electrical contacts, regulating the voltage to the gauges.

The contacts inside your voltage regulator are likely pitted or dirty and therefore the gauges don’t read correctly.

It is a little cramped under the dash, but replacing the voltage regulator (it is about the size of a little finger) is simply a matter of unbolting it from the back of the cluster, exchanging the two wires to the new unit and bolting the new unit back in place.