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Diagnosing a worn out strut

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Old 01-21-2018, 09:38 AM
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TangoAlphaZulu
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Default Diagnosing a worn out strut

I have been told by an auto mechanic that the struts on the g/f's 350z need to be replaced. Looking at the struts I see no sign of leakage. What other symptoms would there be to indicate the strut is worn out?

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Jeff
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Old 01-21-2018, 10:31 AM
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dkmura
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Crap- for the umpteenth time, the Z33 does NOT use struts! The shocks are not used to locate any suspension pickup points, and perform dampening duties only. So call them shocks from here on out.

Other symptoms of a worn set of shocks include excessive drive under braking, wallowing in the corners or leaning back on acceleration. You could try the bounce test, of putting your body weight on the front or back of the Z and see if once you get it bouncing to see if the shocks stop the oscillation as soon as you stop. But in my book, mileage is a factor, and anything in excess of 80K means the OEM shocks have likely exceeded their useful lifespan.
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Old 01-21-2018, 03:07 PM
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Whoa. did not realize it was such a sensitive subject. Fine. A shock. A shock trying to look like a strut.

The car has about 200k on the odometer. Not sure when the shocks were changed, though. Her mechanic told her the shocks needed replacement. Being the trusting soul I am, I started replacing them. Once I got them off of I noticed the distinct lack of leaking, etc. Unfortunatly, it's kind of hard to do the ol' bounce test right now....
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Old 01-21-2018, 03:31 PM
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MicVelo
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Originally Posted by dkmura View Post
Crap- for the umpteenth time, the Z33 does NOT use struts! The shocks are not used to locate any suspension pickup points, and perform dampening duties only. So call them shocks from here on out.

Other symptoms of a worn set of shocks include excessive drive under braking, wallowing in the corners or leaning back on acceleration. You could try the bounce test, of putting your body weight on the front or back of the Z and see if once you get it bouncing to see if the shocks stop the oscillation as soon as you stop. But in my book, mileage is a factor, and anything in excess of 80K means the OEM shocks have likely exceeded their useful lifespan.

The "bounce test" is a myth. It tells you about as much about the condition of a shock as pushing down on a spring. Meaning, it tells you NOTHING about the condition of the spring (hence, shock) because of the very high rate of the spring (beyond what a human can compress). There are really only two ways to tell if a shock (of the type design on a Z) has or is about to fail:

- dkmura summed it up above; brake dive, excessive lean in corners and under hard acceleration. Also, excessive stiffness or a sharp, jolting ride (riding on uncontrolled springs with no spring control) under the dynamics and weight of a moving vehicle, bad shocks will show up easily. These - and mileage - are telltale signs.

- The other way is removing the shocks completely and test them by hand (or ideally, on a shock dyno but that's not something available to most people). They should be very difficult to rebound or compress by hand. If you can move the shafts with a small amount of force, replace them. Gas shocks are even harder to compress from their extended positions.

What you should do as a back-of-the-hand-test: Bleed the shocks (extend/compress a number of times in the vertical position, let them rest a few minutes vertically leaning on a wall) then give it a really good compression shove. If you can compress them all the way with one hand, they're weak.

OE shocks typically don't last much more than 50k (or less if operated on a lot of bad roads) and they rarely show signs of visible leakage. AT 200k, unless you know they've been replaced at some point, I'm going to give even odds of their demise.

Last edited by MicVelo; 01-21-2018 at 03:34 PM.
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Old 01-21-2018, 04:31 PM
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MicVelo,

Thanks for the response. I checked the shocks and both the old and new shocks are pretty tough to compress with one hand. The one I pulled off of the car will not re-extend on it's own, though I can extend it by pulling on it.

The new one will extend on it's own, though slowly.

I don't know exactly how old they are, but I bet they are not OE.

Thanks,
Jeff
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Old 01-24-2018, 09:49 AM
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In Tango's defense, for guys like me who were selling and installing cheap-*** Monroe suspension components back in the 1980s, we basically had shocks, struts and strut inserts. Even today, I think most of the wandering public simply sees anything with a spring attached to it as a strut and anything without a spring as a shock. Struts up front, shocks in the rear.

It's like trying to tell a person (or Kia) that the "e" in the word Forte is silent. Forte' (pronounced for-tay) is a musical term meaning loud. Forte (pronounced fort is a French word describing something a person excels at. Understanding the differences between a strut and a shock isn't going to be everyone's forte.

Here's how an online suspension parts retailer defines it:

This is a common question that we receive as the terms shock and strut are often used interchangeably. A shock and a strut do the same basic job on a vehicle, damping the movement of the spring and stopping oscillation and bounce. Even though they do the same thing, shocks and struts are completely different parts. A shock cannot be used to replace a strut and a strut cannot be used to replace a shock. A vehicle will have either a shock or a strut at each wheel, never both. Every vehicle was designed with either shocks or struts and your vehicle's suspension cannot be changed to use the other.

The major difference between shocks and struts is that a strut is a structural part of the vehicles suspension system where a shock is not. A strut is also crucial part of the vehicles steering system and greatly affects alignment angles. Camber and caster angles are usually adjusted right on the strut itself. A strut is also a pivot point for the vehicles steering system and contains a coil spring. Because of this an alignment is always needed when replacing a strut. This is also the reason that struts are typically more expensive than shocks.

People often call in saying they have been told they need shocks and struts. This is usually a friendly neighbor with a less than perfect knowledge of suspensions trying to be helpful. Because the terms are used interchangeably, customers often get confused as to which they need. To add to the confusion, some vehicles have struts on the front axle and shocks on the rear.


Strut:



Shock:

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Old 01-29-2018, 05:56 PM
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^^ Agree!
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