Springs

Maintenance/Repairs
1

My son and I disagree on the cause of a rougher (“stiffer”) ride in his 2000 Jeep Wrangler. It has 90,000 miles on it and he thinks new shock absorbers would give him a smoother ride. I told him that the springs are getting older and stiffer due to “metal work hardening”. Only new springs would give him a softer ride. When I make the car bounce up and down at all four corners, the bouncing stops quickly within one or two bounces after I stop bouncing it (the old shade-tree mechanic’s test for shocks!).

Who’s right?

2

My vote is for bad shocks. Sometimes that bounce test is not entirely valid. When a shock is disconnected and worked by hand a problem may become very apparent.

3

If you live in Winter weather, the freezing has caused a lot of heaves in the road. See how it runs in May. The traffic will flatten the roads a bit. You have the wrong idea of what happens to metal with age. The springs don’t get harder.

4 
It is very unlikely springs in a 2000 car would need replaced at this time.  It is very likely that shocks with 90,000 miles on them do need replacement.
5

Spring steel is already very hard so I don’t think they will work harden to any degree. What often happens it that they take a set and your ride height isn’t what it used to be, resulting in more frequent bottoming out.
Work hardening is something that happens to mild steel. Constant cyclic loading work hardens the area where the most stress is resulting in that area becoming brittle. The metal then cracks there and the area of maximum stress moves to the adjacent metal, work hardening it until it fails and the crack grows and grows until the part fails. This is often called metal fatique.

6

good info!

7

Springs get SOFTER as they age. Work hardening is a different process. Springs also corrode and lose metal as they age, causing further softening. You probably have bad shocks and the very cold weather makes the SHOCKS a lot stiffer. Also check your tire pressure; too much air gives a stiff ride.

Most vehicles need new springs at about 200,000+ miles or so, not 90,000.

Jeeps are designed with very stiff springs compared to cars and vans.

I would do the bounce test (when the shocks are warm) to see if the shocks still have their damping function. If they do, you need to do nothing.

If you want a softer ride, you’ll have to buy another vehicle.