ccubed Posted February 28, 2011 Report Share Posted February 28, 2011 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. Link to comment Share on other sites More sharing options...
lorenzo Posted February 28, 2011 Report Share Posted February 28, 2011 Your adjustments on one will affect the other, so compression adjusting will change the rebound, just not as much. The shock should, I think, push back up slowly. Link to comment Share on other sites More sharing options...
Superdunc Posted February 28, 2011 Report Share Posted February 28, 2011 Most dampers, even quite exspensive ones, affect the rebound damping when you adjust the compression damping, and vice versa. The damper should have a small volume of gas in it to allow for the varing displacement of the damper rod as it extends and compresses. The gas, nitrogen is pressurised even when the damper is fully extended, to prevent the oil cavitating when it is forced through the orifices on the damper piston, so the damper should spring back when compressed without a spring fitted. The only exceptions are the Ohlins TTX series dampers which are a through rod constant displacement design, like a steering damper, they still have pressurised gas in them but only to prevent cavitation. Link to comment Share on other sites More sharing options...
ccubed Posted February 28, 2011 Author Report Share Posted February 28, 2011 Thank you guys, it is starting to make sense. I suspect the ebay shock needs re-gassing. Link to comment Share on other sites More sharing options...
lorenzo Posted February 28, 2011 Report Share Posted February 28, 2011 Easy way to tell is to pump it up with a bike pump, the nitrogen only means it's stable at various heats. Just let it back down and refill with nitrogen if it's OK. Give it about 80psi. Link to comment Share on other sites More sharing options...
Kin Useless Posted March 1, 2011 Report Share Posted March 1, 2011 Is there any information anywhere that tells you how much oil should be in the rear shock? Not sure my workshop manual tells you that sort of info Link to comment Share on other sites More sharing options...
ccubed Posted March 1, 2011 Author Report Share Posted March 1, 2011 On the zxr400 there is no detail at all about dismantling the rear shock in the repair manual. Not even taking the spring off which is real easy Link to comment Share on other sites More sharing options...
blow_away Posted March 1, 2011 Report Share Posted March 1, 2011 Chris, take the shock to Bill and he will sort it for you http://www.whitecrossmotorcycles.co.uk/ Link to comment Share on other sites More sharing options...
ccubed Posted March 1, 2011 Author Report Share Posted March 1, 2011 White Cross looks like the dogs. That was the idea to have a spare so I could get one properly re-built. Are they around the zumerzet arial? Link to comment Share on other sites More sharing options...
blow_away Posted March 1, 2011 Report Share Posted March 1, 2011 Yes, Bill is round by the lakes somewhere - East Harptree or West Harptree I think. Tell him Alan says hello and butter him up for a cheap price on the Team South suspension! Link to comment Share on other sites More sharing options...
ccubed Posted March 26, 2011 Author Report Share Posted March 26, 2011 I took Lorenzo's advice and tried the shock with bike pump air. It seemed to work OK, it certainly felt more compliant and controlled than the original, so I took Al's advice an took it to Whitcross. He recharged it to 180lbs with Nitrogen. He also confirmed that is should ease back on its own after compressing. It is sticking very slightly but not enough to feel a resistance. So it is good to go now. It was slightly embarassing taking my manky 20 year old shock to the pristine Ohilin's draped bike workshop at Whitecross. It was tidier than our kitchen. - I am fairly sure he thought the best place for my shock was the dustbin. Also he suggested it would blow up if I pumped it with air instead of nitrogen. I suppose he means it would terminally overheat if it was ridden hard with air in it. sorry Al he was about to close when I arrived. I did not engage him in charitable donations talk. Link to comment Share on other sites More sharing options...
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