Can someone educate me... do ALL rear shocks have oil in them? I know some are charged with Gas. The newer ones have an oil well that can be drained and may also have gas in them... What about the older ones (eg FZR)? Gas only? I can't find anywhere you'd put oil in my rear shock, for example.
Yes, all shocks have oil in them. Many also now have nitrogen under pressure. OEM shocks are usually not serviceable
So... if it's not serviceable how do you know if it's leaked? If there's no residual anything on the shock (could be dirt etc anyway)? And I'm assuming if it has leaked the oil couldn't be replaced...
You have to remove the spring and physically try to move it. Shock specialists, like RAD in Brisbane, can modify and rebuild many OEM shocks. Dr @Murdo might know something about this.
All shocks use oils of varying weights as the dampening medium. This is pushed through small holes and valves to give the resistance (or dampening) to slow down the movement of the wheel. Modern shocks have pressurised nitrogen gas to keep the oil under pressure and so prevent cavitation (or gassing) of the oil and give smooth operation throughout the stroke of the shock rod. RAD can rebuild your shock for about half the cost of a new one. Any shock can be opened and re-oiled/re-gassed to make it work again, but I would not be spending money on rebuilding anything that does not have damping adjustment (compression/rebound) as the rebuilt ones do not last as long as an original one, and will need to be adjusted to compensate for wear.
Awesome stuff. So how do you tell if it has leaked the oil out? does the shock bottom out terribly or something? I'm just trying to figure out if my old shock (I got @Moo 's replacement and used it for the RW) actually has a problem or not. It cleaned up nicely with some degreaser, but not being able to open it up, I wonder how to test it?
If your OEM shock needs replacing, why not take the oppotunity to replace it with something better! I have an 06 R6 shock in my fizzer and man did it make a massive difference! Fully adjustable for preload, compression and rebound and all for $100 (with some minor fiddling). If you look around you could probably pick one up for the same or even cheaper!
Yep, that is high on my Fizzer priority list! Hey Generic... what did you do to your front forks/shocks?
When you fit a shock from another model check the travel. Spring rates are often different too. There is a shock length and travel spreadsheet at www.eurospares.com/graphics/suspension/shock_length_chart.xls The 2006-2007 shock that Generic used is listed as having a length of 300.5 +0/- 6 mm and a stroke of 62.5 mm One of the members on the 400Greybike forum reported "The R6 has a standard spring rate of 9.8kg/mm or 547lb/in in old money. The standard 3TJ shock has a spring rate of 5N/mm - 5.9kg/mm - 330lb/" The spring rates do not actually mean that much because you cannot simply compare from one bike to another; the different leverage ratios make that impossible. You need to setup your shock for sag and the right spring to suit your weight etc. Obviously if the spring is too hard then you won't be using the full travel. Lots of docs are available online for this type of information just google motorcycle suspension setup.
I've replaced the stock springs with racetech linear .85kg/mm FZR400 springs. http://racetech.com/ProductSearch/2/Yamaha/FZR400/1988-90 I used the calculator in that link to figure out about what spring rate I needed. The calculator came back with .80kg suggested but after having some further chats with Terry from shock treatment (racetech supplier in aus) he suggested the .85kg would be more beneficial to the track bike. Next for me will be to get some valve emulators. @maelstrom, you are bang on! me at ~73kg makes the oem spring in the r6 shock near perfect! preload is set at halfway (can't remember how many clicks) which gives me 23mm with heaps of room for movement either way. Do also need to be careful as the stock Fizzer shock length is 310mm so you end up messing with the geometry of the bike and make it squat in the rear. Can be fixed by pushing through the front forks, but this lowers the whole bike and reduces ground clearance or as I did you can make some shorter dogbones. There is a link to the writeup that I used to figure out how to do it all... http://www.fzr250.com/viewtopic.php?f=22&t=3554&p=27985#p28046
So... unless it's dirty around the shock, there doesn't seem to be another way to tell that it's leaking without diassembly of some sort?
