Refreshing Armstrong Shocks

I have been waiting months to restore these Armstrong shocks, mostly because I was unsure which oil to buy. I did not know how much oil I would need to flush and fill them, and I know the recommended oils are quite expensive. I finally made a decision and got started by draining the oil from the rear shocks as shown.

Moss does not show a replacement gasket for the rear shock top cover, so I need to clean these up very thoroughly so that a liquid gasket would work. I sanded down both surfaces with 600 grit.

I went through several steps of flushing, covered in more detail below, then refilled with fresh ISO 68 hydraulic oil.

Then both surfaces got a thin coat of 3M black super weatherstrip and gasket adhesive.

I mounted the shock on the side of my work bench to keep it level while the adhesive cured and then check it the next day for leakage, all good. Then I was able to move on to the bleeding any remaining air from the shock. This is essentially the same process as show below with the front shocks.

Moving on to the front shocks, I drained the old oil, then mounted the shock to the workbench so I could actuate the lever to help rinse out the old oil. This was done with the valve removed and the valve plug reinstalled so that the oil would circulate easily. I cycled the arm 100 times and then drained and refilled. The front shocks were apparently serviced more recently so I only had to do one flush and fill. The rear shocks were much dirtier in comparison and required three flushes and a final fill.

Holding the shock level for final fill with new oil.

The front shock gaskets were in good shape and were reused.

This is an example of the flush phase, you can see the oil has, what looks like, a lot of aluminum in it from years of use, this is the first flush, not the original oil.

Here we have the valve, all good, just replaced the large O ring, shown at left.

After filling and reinstalling the top cap, the shock is bled by topping off the valve area, and then cycling the arm a couple of times, repeat until no more bubbles come out and the level stays pretty constant through the cycle, as shown above. Then you put the valve back in, and make a big mess.

I used a cup under the valve to catch most of the oil that overflowed when the valve went in.

I started with a gallon, four quarts of oil. After flushing the rears three times each and filling and one flush for the fronts then fill; this consumed only 1.5 quarts as you can see in the picture.

Sorry the picture is not better. I used Mag 1 Hydraulic Oil, AW ISO 68 rated. I got a gallon of it on Amazon.com for $23.64. So, not cheap, but still less than motorcycle fork oil. I will have to wait for a test drive to see how it performs, but ISO 68 is the right stuff, so fingers crossed.

Finally, some paint, silver for the rears, black for the front, just because.