When to replace struts?

Question

I recently replaced my struts because the shop said the front driver side is leaking when I took it in to replace brake pads/rotors. But now that I am looking closely, I am not sure the struts need replacing. Yea, the boot is all torn and everything looks old/rusted but no alarming signs of oil? And the inner rod is so shiny!

This question from 10 years ago doesn't exactly specify tell tale signs beyond poor ride quality. My suspension felt fine so could I have kept my old struts?

Below are some pictures of the front struts.

Answer 1

Those look very worn to me. Of course it's your choice, unless your locality requires vehicle safety inspections, to keep driving on worn suspension parts but it's not the safe choice.

The fact that the boots are cracked and broken, the bushings are all cracked and distorted, and your mechanic says they are leaking oil tells me that these are end-of-life.

You have extracted the entire lifetime out of those struts. It's time for new ones.

Answer 2

The rod is not shiny at all.

It constantly moves, so it can't accumulate much of rust, but a sane inner rod will look like a high-quality mirror even after running around the equator 2 or 3 times.

Its main failure mode looks like this:

1. The rubber parts age and at some point tear.
2. Dust and sand adhere to the rod.
3. When the rod moves, the accumulated sand and dust grind the rod and the o-ring that keeps oil from leaking.
4. Oil starts leaking, attracting more sand and dust and accelerating the degradation of the other rubber parts.
5. After losing enough oil, damping function is gradually lost.

It is possible that it still retains some damping action, but at this point the degradation is self-accelerating.

Of course, depending on your tolerance to increased vibration, poor braking, poor curve handling, poor pothole handling, increased wear of the tires, bearings and the other suspension parts, your ability to drive safely a broken car, the available funds, your jurisdiction's tolerance to broken cars, etc... you may leave it as is, e.g. for an year or so.

But you probably shouldn't.

Answer 3

There are some very obvious symptoms of failure, like leaking oil, or that the vehicle doesn’t handle correctly, for example - it bounces over bumps.

How they physically look doesn’t really indicate whether they are working, or how long a life they have left. A broken rubber gaiter may not be a problem in some places, but will cause increased wear in others.

The only way to check if they are doing their job correctly would be to remove them, remove the spring and compare the compression and expansion qualities to a new strut.

You may well find that they are still performing well, but even then it would likely be more cost effective to just replace them, rather than putting the old ones back on. A simple shock absorber that is simply held on by two bolts may be worth removing just to test it, but a strut takes more time.

At least now that you have replaced them, you know you should be good for a few more years.