shock test without spring, shock fault diagnosis

[ccubed]

I bought a spare rear shock on Ebay for my L3 ZXR400. The new (to me) shock is from a J1 ZXR400 with green spring, remote gas and rebound adjustment only.

The original one is a sealed unit also with rebound adjustment only.

I have taken the spring off both units.

1. The J1 unit has good damping which is adjustable - but the adjustment seems to affect both rebound and compression. (I am simply pulling and pushing the rod with no spring in place. Seemed like a good test to me)

2. The original one bounces back when it is pushed in. Not particularly quickly but it seems like it has a spring inside it or compressing a gas.

Which one is faulty? Both faulty? Both acting correctly?

I am interested in understanding what is going on. I expected that the spring, (when put back on) would do all the returning force with the rod staying in position but resisting movement according to the damping setting. Compression damping constant - rebound adjustable. Any enlightenment gratefully received.

[Mori Man]

The way I see it is,

When you set the rebound / rising rate its the same effect you have dialing up a steering damper so the effect is felt both ways.

The gas is meant to add compresion dampening so sounds like your 2nd one is doing its job but the rebound isn't.

Think I got that the right way round

Pushing it in is acting on compression = Gas

Pulling it out or it springing out is acting on rising rate = bottom adjuster

But the spring is doing a hell of a lot of the work on both.

Take it as red the thing is 20yrs old and hasn't been overhauled and get it done. I am using a M3 shock without overhauling it and happy enough about the performance but I am fairly sure when I fit the overhauled J2 shock there will be a stepped improvement - 20yr old oil is no better than water and gawd knows what the gas pressure will be at compared to original. It will then get sent off and have the same treatment done, although a Gold Nitrate damper rod would be nice too

MM!