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A note about squeaky shocks

  • Posted: 04-30-2009 12:54 PM
  • 1 Comments
  • Suspension

I get asked from time to time about squeaky shocks so I thought I'd make a post about it.
 
Why do shocks squeak? Well there are a number of reasons. And trust me when I say it is really not a brand-specific issue. I spend a lot of time on Acurazine where people tend to complain about Teins squeaking. Well, they don't really buy anything else there with any great volume so of course more people have noises with Teins! Really though any shock can develop a squeak and I will give a few reasons why!


I will preface the following by mentioning the "science of a squeak." Sqeaks are caused when there is a moderate pressure-force over a small cross section. Usually the ideal squeak would involve a rigid item encounters some flat surface with minimal abrasiveness (IE, more smooth surfaces provide higher friction). Like nails on a chalkboard, right? Or rubbing your finger on a dry slip-n-slide. You need some pressure and some friction to make a squeak.


* Worn shaft seals or shock shafts.
As the seals wear they can become firm and loose lubrication. As shafts wear they can heat and become harder than normal. The seal provides the pressure, and the movement of the shaft against the seal provides the friction. Hence you can get a squeak. This noise can be remedied by applying some light liquid silicone spray lube to the shaft. Try to not use anything with petroleum in it as it can break down the seal further and/or attract dirt causing a leak!
 
* Bubbles in shock fluid.
More prevalent with street-use twin-tube dampers where there is high pressure nitrogen gas in direct contact with shock oil. Vibration and heat can cause the gas to emulsify into the oil. When you get bubbles in the fluid and it passes through the small orifices in the shock piston you can get a noise. Pressure is caused when the oil forces the bubbles through the piston. The friction is provided by the variance in coefficient of friction of material going through the piston (is oil then air then oil then air as bubbles pass through). The system can be designed to minimize sounds from one material, but not both. This situation is a lot less prevalent in mono-tube shocks as the oil and nitrogen are divorced.
 
* It's a performance shock. Compromise is built in.
To a certain degree you need to expect that if there were no compromise in noise or ride the automotive engineers would have put a superior handling system in the car from the get go! Therefore you must expect that part of the reason you are getting squeaky shocks is because they work better in other ways than non squeaky shocks. One instance is that the viscosity of the fluid in performance dampers is thicker than stock and the piston orifices many times are smaller, or adjustable in size. Thicker fluid through a tighter hole: Pressure = hydraulic pressure of the oil forcing through the holes. Friction = higher viscosity fluid inherently "sticks" to the surfaces it contacts greater a greater resistance to flow...stick, resistance....FRICTION caused by the fluid itself! ---- To add to this point, many people notice more squeaking as temperature drops and with some ability to warm up it goes away. Lower temps increase viscosity which only enhances this effect of fluid friction causing noise. Drink warm water through a straw then drink a cold milkshake through the same straw. You won't only need to suck more, you'll hear that shake sucking up the straw! Now try cold water with a smaller straw...you can hear that too! Mr Wizard lives on!
 
 
So I am sure there are a number of other reasons why a suspension system might make sound. Loose fasteners, worn bushings, etc. But assuming all else is normal the noises you are hearing from the shocks are not really much to be alarmed about!
 
Marcus


About the Author

Marcus di Sabella Marcus is the founder of Heeltoe Automotive. He's been working with cars (mostly Honda cars) since 1996, and has been providing enthusiasts with excellent products, services, and web experiences since 2002. He's been published in Honda Tuning, and holds a degree in Engineering Technology.

1 Comments


 
Carolyn
08-07-2013 11:28 AM at 11:28 AM
My car is a 98 ford escort had new shocks put on last year a family member, a little later I noticed a squeak it got worse and worse couldn't fix it job went over seas so I'm still in that boat pretty much it gets worse when the weather is hot.

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