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Testing McPherson struts - How to?

We had a recent discussion involving a lady who was told the struts on her '96 Maxima were “weak” (http://act… It later occurred to me that I have never heard either shocks or struts described as weak. I suspect a mechanic was merely concerned about his upcoming boat payment. Struts are typically described as either all OK or shot to hell. So how does one determine that struts are “weak” or otherwise test their condition?

Go to each corner of the vehicle and push down and release so that the corner begins to oscilate up and down, then release that corner. If the strut/shock is good, the corner should come up and stop. If the strut/shock is weak, that corner will continue to oscilate up and down a couple of times after it’s released.


Visual inspection and drop test. Though I haven’t seen that many shops with a drop test machine to be honest.

A drop tester simulates Tester’s push down test but drops the vehicle (one axle at a time) from a height of about 10 inches, it also plots a graph of the suspension drop reaction.

Some of those in-between ones are near impossible to determine. I’ve run across a number of them in which there appeared to be a ride problem but the car did not exhibit any pogo movement at all when pushed.

It came down to a barely educated guess and disassembly of the strut. When the strut was apart one could then move the shaft by hand and the “bad spots” could be felt. In some cases, it was even erratic.
It is irritating to have to go that far into them to know for sure because that smacks of guesswork. Of course if one is that far in then why not replace them at that point.

There’s the possibility that it’s a poor quality strut that gives a nasty sound when moving through the stroke, or while turning the steering. It’s like the shaft is binding in the cyliner, like a cheap office chair strut. I bought some cheap struts off ebay a while back and one of them started doing this soon after installation. Will finally get around to changing them this weekend - the sound reverberates all through the cabin and is driving me bananas.

In the old days the bounce test worked well. Today, while I might trust Tester’s opinion after using the bounce test, I would not trust mine. Of course if the left and right sides don’t match, you know for sure one or both are bad. Also if it bounces it is bad, but there are some that don’t really bounce but are not really good either.

As to the good or bad, it is not really all that simple, they can wear without wearing out.

I would suggest that if you have over 50,000 miles and have any reason to suspect them, it is time to replace them.

50,000 miles?? Maybe an American or Korean car that put those miles on entirely in a pothole infested city may need them that soon, but for the rest of the cars out there they should expect far better.

It’s not a big deal to determine if struts are bad. If the car floats on the highway they’re worn out. If the car skips over bumps in the road during turns they’re worn out. If you can press a corner of the car down and it stays there, they’re bad. If you’re in a performance car and the car rolls too much in aggressive cornering they’re worn out.

modified Mcpherson? or other?

This will not work with strut susp. Even with worn struts the car will not bounce enough to tell. A road test and tire inspection will benefit more.