Topic: Changing the oil in struts (79-04 Mustang)
Today I decided to try changing the oil inside of the front struts for something else and added a shrader valve so that the oil can be changing fairly easily to something else if we want to experiment with different viscosities. These struts were bought at Autozone in 2007 and there are about ten races on them. I decided I would drill/tap the bottom of the strut since there is room down there when they are mounted on the car and the metal is thick enough to tap/thread.
I used a pair of shrader valves from Napa. They are 1/8 NPT made of brass and cost about $2.50 each.
Drilling the first one made me a little nervous because these are gas charged and I had no idea how much pressure there would be inside. I drilled a pretty small hole first and it wasn't that bad. I then went up to the right size drill bit for the 1/8 NPT tap while using a shop vacuum to catch the shavings. Tapping the hole was mostly straight forward except that you need to use a bottom or finishing tap because you can only go down about a half an inch into the hole. I ended up cutting the tip of my tapered tap off to get the job done.
I packed the tap with grease to catch as much of the metal shavings as possible.
And now drilled, tapped, and ready to drain. I waited to drain them at this point to flush out as much crap from the drilling/tapping.
Next I turn them over and start cycling the strut while catching the oil in a container. It is a pretty vile looking fluid, but it must work alright if they lasted as long as they did. It seems about as thick as cooking oil.
I measured how much fluid came out and tried to put back in the same amount. I used some 15 motorcycle fork oil. You have to put it in pretty slowly, but eventually it will all fit.
Finally I used thread sealant on the shrader valve threads and tightened it down. I charged the strut with about 40psi, but I do not know for sure how much pressure should be inside of there.
Now I have no idea if this will actually be an improvement over the way the struts were. I figure we can play with different oils and see if it actually makes a difference. Just judging by hand in the garage the struts actually feel softer? That doesn't seem possibly because the new oil was definitely thicker that what came out, but I'm pretty sure they are softer now. Everything I have read about this subject suggested that you should start out with the lower number oils first so you don't damage the seals. And now you know....
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