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Armstrong shocks are remarkably reliable and long lasting. However, once they start to leak, usually from the shaft, they can degrade quickly.
They will leak because the packing (1/2" think ribbed washer)that is retained in the zinc body has become hard, or has gotten contaminated with grit salt, or whatever from the road. Oil or tar can attract the grit and also grind away at the shaft allowing a faster leak. If things get too dry, the shaft may start to wallow out the shaft bore in the zinc body, as there is no bearing. If it gets really dry and empty, catastrophic things happen, like splines on the rocker stripping, or pistons blowing their poppet valves. That's when you suddenly get no damping.
Something that I preach in my tech seminars is that there is a downside in overfilling the shocks; namely that eliminating the necessary air space will cause the shock to leak as the oil needs to expand when hot.(in use) In the early small shock (TR3, 4) the filler plug is on the side of the body. Oil should be below that, and above the level of the shaft. On the later big shocks (TR4A, 250, 6)the filler plug is on top of the lid, but has a boss to prevent overfilling. But, some people work real hard at getting the shock full, and that's where the problem lies. Essentially, if the shock is not leaking, then it doesn't need to be "topped up", as there is no oil being used.
Briefly, what we do (aside from cleaning, etc) is pull the arm with shaft from the shock, pry out the packing and retainer. We bore the body and install Delrin/nylon bushings (bearings) and bore for and install a radial lip sprung oil seal. To restore the shaft, we install our custom made stainless steel sleeve. Of course everything, pistons, valves etc. are all inspected, and repaired or replaced. There is some labor in each shock. There are other details that I can supply if you want. Thanks for listening. Peter
They will leak because the packing (1/2" think ribbed washer)that is retained in the zinc body has become hard, or has gotten contaminated with grit salt, or whatever from the road. Oil or tar can attract the grit and also grind away at the shaft allowing a faster leak. If things get too dry, the shaft may start to wallow out the shaft bore in the zinc body, as there is no bearing. If it gets really dry and empty, catastrophic things happen, like splines on the rocker stripping, or pistons blowing their poppet valves. That's when you suddenly get no damping.
Something that I preach in my tech seminars is that there is a downside in overfilling the shocks; namely that eliminating the necessary air space will cause the shock to leak as the oil needs to expand when hot.(in use) In the early small shock (TR3, 4) the filler plug is on the side of the body. Oil should be below that, and above the level of the shaft. On the later big shocks (TR4A, 250, 6)the filler plug is on top of the lid, but has a boss to prevent overfilling. But, some people work real hard at getting the shock full, and that's where the problem lies. Essentially, if the shock is not leaking, then it doesn't need to be "topped up", as there is no oil being used.
Briefly, what we do (aside from cleaning, etc) is pull the arm with shaft from the shock, pry out the packing and retainer. We bore the body and install Delrin/nylon bushings (bearings) and bore for and install a radial lip sprung oil seal. To restore the shaft, we install our custom made stainless steel sleeve. Of course everything, pistons, valves etc. are all inspected, and repaired or replaced. There is some labor in each shock. There are other details that I can supply if you want. Thanks for listening. Peter
