Trials Australia Forums

Photo sequence showing a Falcon Trials Classic shock coming apart in case anyone wanted to see inside one

Hi David,

Geoff rebuilt his Falcons the day before the NSW championships; shafts, seals & piston rings (plastic ones). He didn't have access to nitrogen gas, so tried compressed air at 70psi. This resulted in the shocks topping out quit badly.

What is your plan with regard to re-gassing?

Steve

I use compressed air at about 70 psi. Can't see what the type of gas has to do with topping out problems. The only thing that using air should do compared with nitrogen is to cause the oil to degrade a bit quicker, due to the oxygen and trace amount of water in the air. Was there anything else different after the rebuild compared with before ie oil weight, oil quantity, spring preload? I would be interested in what is found with Geoff's shocks when he works out what went wrong.
The shocks in these photos went back on the KT with 100ml of 10wt fork oil in each and got a severe hammering this afternoon on my practice sections and they worked fantastically.

I will see if I can get Geoff to post his process.

Hi all.

I pulled mine apart very much the same as Dave did, only i replaced all components. (Oil seals, Dust seals, shafts, guides and piston ring)

I didn't bother measuring the amount of oil that was drained (1 shock was totally empty). When i put them back together i followed instructions given from Robin from Falcon UK, for the alloy bodied light weight action shock.

Use 5 weight oil
fill to 65mm from top before adding components
70 PSI gas.

I did all this and as Steve said they were topping out way too quick, so for a quick fix i just dumped the gas and they worked fine for the state titles but i know its not right so i will have to investigate the issue further. ( probably the night before the next trial )

The spring tension was set the same, the oil is now heavier than the last rebuild as there was a mix of 5 and 2.5 weight oils previously,
so if i had to guess what is wrong, i would say iv'e put the valves in the wrong way around ops!!!

Just something i noticed in your pics Dave, the dust caps had some marks on them from the tool you used to remove them, I used a very fine chisel almost like a bread and butter knife and popped em off with hardly a mark, no biggy just thought id mention it for others thinking of embarking on the falcon rebuild journey.

Geoff

Geoff.
Can you tell me which way up you have the shocks on the bike?

Body to the top, shaft at the bottom.

Geoff

Hi Geoff I'm thinking the same as you about the pistons being the wrong way around, causing reduced rebound damping
Thanks for the idea about using a chisel on the dust seal holders. I wish they made them with a recess to make it easier to get them off

You will find using air instead of nitrogen, that you will get quite a wide pressure margin relative to ambient temperature and also surface temp of body ( sun on black shock body ) nitrogen reduces this problem to "almost" no change in pressure.
Being the gas chamber is so small amplifies change quickly! ie surface area is high % of volume.
But this would only matter to an A grader, not my wobbly riding.

I forgot to mention that I would "suspect" that any inert gas would do ( say Argon, Argo shield ) so anyone who has gas mig or tig should be able to fix u up!