Recently, the smog pump on my 1986 420SEL died. The local dealer wanted to charge me $1200 for the new part alone. I managed to find one at an auto recycler for $350. It looks very simple to replace. There are only two bolts that hold it in place. One on the top and the one on the bottom that slides to provide belt tension. After that the two hoses slip on on and you plug it in.
My problem is getting the old one off. The bolt on the top of the unit looks more like a screw. I tried fitting various types of screw diver and hex keys into what looks like a wide slot with a hole in the middle. Nothing I have comes close to fitting in it. Is there a special tool, or tric to getting this off, or is it just a pin and when I undo the bolt on the bottom will it just slide off (unlikely)?
Thanks for any help.