Tightening Up Shock Absorbers (Without Crush Tubes)

Fitting a shock absorber to a truck or trailer may not seem an incredibly complex job but before you pick up that rattle gun, you should take note of the following.

Bushes are fitted to the shock absorber so that the shock absorber can articulate on the mounting point of the vehicle.

Over Tightening

By over tightening the shock absorber on the mount, this will excessively squash the bush reducing the amount of flexibility or articulation in the bush. This will lead to premature wear of the bush and possibly breaking the shock absorber eye or stud. Alternately the mounting bracket on the vehicle could also break.

Under Tightening

Under tightening the shock absorber can lead to the shock absorber coming lose stripping the nut off the thread or sliding on the mount. This will wear out the shock bush and the mount plus make a lot of noise in the process.

How Tight?

Many manufacturers do not have a recommend torque rating for tightening up a shock absorber. Powerdown recommend that shock absorbers should be tightened up with a spanner rather than a rattle gun to avoid over tightening.

When the tightening up a shock absorber with an eye mount, rotate the nut until you feel it make contact with the outside mounting washer and bush. Two full turns of the spanner clockwise should secure the shock absorber in place. Grab the shock and make sure it does not rattle on the mount and that there is still flexibility in the bush. If the bush is bulging over the outside of the washer the shock absorber is too tight. For a stud mount the same principles apply

Checking Height Control Values

I’m sure at some stage you had an irate customer at your counter, complaining that all of his air bags on his truck or trailer have deflated overnight. A common cause of this problem is a leaking height control valve. You can check if a height control valve is leaking by following this quick step by step guide:

Getting started:  ensure the compressor on the truck or trailer is operating, as there will be insufficient air in the tank to carry out the test properly. Un-bolt the linkage rod attached to the axle

  • Move the arm or linkage rod of the valve upwards, air should start flowing into the air bags immediately with an instant response valve. A delay valve should take approximately 5 – 7 seconds before it will begin inflating the air bags.
  • Return the arm back to the neutral position (horizontal) and the air flow should stop immediately.
  • Move the arm or linkage down and air should be exhausted from the air bags. A delay valve will take approximately 5- 7 seconds before it will exhaust air
  • Move the arm back to the neutral position (horizontal) and the valve should stop exhausting air

If at any stage during the step by step process the height control valve fails the test, it is a good chance that the valve needs replacing. Height control valves fail internally due to rubber seals perishing, moisture and contamination in the air system.


Air flow to suspension


Static Height


Dual Height Control Valve Set up

2K-500 Plumbing Diagram

Plumbing Diagram Height Control Valve Dump Horizontal Position

H01501 Plumbing Diagram-Horizontal

Plumbing Diagram Height Control Valve Dump Vertical Position

H01501 Plumbing Diagram-Vertical