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My drive to work involved entering a lot that has a fairly steep grade compared to the pavement. As such, in low riding vehicles, you need to enter it fairly slowly.

The thing is, recently, I can enter it at < 10mph, and it still sounds like I'm scraping something.

Now the Caravan is not a particularly low vehicle, so it really shouldn't be scraping anything. In addition I've inspected the underside for damage, and there doesn't seem to be anything.

Lately it's been happening more frequently, and I've also noticed the sound while entering my Apartment's lot, which is flat, but a little bumpy.

The front suspension has a lot of travel (e.g: bumps are fairly comfortable, but the car is 'rebounding' for a long while after the bump.)

How can I diagnose if the front suspension components are in need of replacement? I have no service history for this vehicle, so I'm not sure when they were last replaced.

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1 Answer 1

The front suspension has a lot of travel (e.g: bumps are fairly comfortable, but the car is 'rebounding' for a long while after the bump.)

I'm going to go ahead and call it: you've used up your shocks.

A lot of people forget that a shock (aka strut aka damper depending on your particular flavor) is a consumable part. It exists to damp out the cyclic motion caused by the springs holding up the car. When those parts wear out, they become less efficient at damping out that motion (which you have observed) and they usually present other symptoms.

For example, I just replaced the struts on my wife's Outback. Each one manifested the same issues:

  1. Insufficient damping (the bouncing continues and the suspension feels mushy).
  2. Noisy motion (scraping sound when going over a larger bounce at slow speeds).
  3. Leaking oil.

The expected lifetime of the parts used on her car is approximately 50K miles of normal driving. Considering that it had been more than 60K, she was right in calling her local mechanic (i.e., me).

Here's a simple confirmation procedure that you can use:

  1. Push down one corner of the car and release.
  2. Watch the motion: the corner of the car should start low, come up and return to rest. Any additional bouncing = bad shocks.

Edit: following-up on the question below

Almost all shocks have some sort of fluid (gas, oil or some combination) to assist in the damping of vibrations. If the shock is compressed, this fluid is forced to pass through a small passage (e.g., a hole) from the chamber under compression. The damper attached to the storm door in the front of my house illustrates this well: you can hear the air hissing as the damper allows the door to return closed slowly.

If you see oil on the outside of the shock, that's usually a bad sign. On my car, I would expect leakage to manifest at the top of the strut. This is where the moving piston arm enters the main body of the strut.

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You mention leaking oil as a symptom of bad shocks, which I do happen to have a fairly minor oil leak. What about bad shocks would cause an oil leak, out of curiosity? –  Robbie Nov 10 '11 at 22:03
    
@Robbie Often a seal or gasket will wear out over time, or the metal that passes through it will develop some kind of nick. If that fluid leaves, the damping ability is greatly reduced. –  Jeff Ferland Nov 11 '11 at 4:22
    
@Robbie, I set the struts that I removed from my wife's care to the side thinking "I need to take these to the dump later." Some weeks later, I look over and they're surrounded by a circle of oil stain (and I cuss). The leaks are slow but relentless. –  Bob Cross Dec 21 '11 at 14:18
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