Risks of using an impact wrench on drain plugs
I used my electric impact wrench to take off the fill and drain plugs on the rear differential of my 2004 Forester. I changed the GL-5 lubricant.
I used the impact wrench because the subject plugs didn't come loose with my use of a 1/2" manual ratchet socket driver. The car has about 55K miles, this is the first time these have plugs have been taken off.
The torque wrench "zipped" the plugs right out. I used the 1/2" manual ratchet drive to put the plugs back in, I didn't bother to use a torque wrench.
I have torque limited extensions for my 1/2" impact wrench, but I think they over tighten... another point. Yet another point/question, as the Forester is Japanese it must be metric, yet the 1/2" drive fit okay (could be a small bit under size) into the recesses on the subject plugs. If the plug recesses are 13 mm, a 1/2" should work, but isn't the best fit.
After posting my experience on the differential oil change on a Subaru Impreza forum I got one response telling me to never use a impact wrench on these (or similar?) plugs. Keep in mind, I used the impact only to remove, not reinstall.
Back to other experience, I do the same when dealing with wheel lug nuts. When I tried the 65 foot pounds torque limiting extension on the impact wrench the lugs are a bit overtightened, I believe. Proper use of a impact wrench to tighten may be an "art". I hope the tire shop's air impact (mine is a low end electric) wrenches are much better calibrated on tightening torque.
Back to reason for post: it there a high risk of damage when using an impact wrench to remove items such as differential drain/fill plugs?