I'm about done tearing down a donor PX-10. I have the crank, bottom bracket, headset cups and rear derailleur remaining. Too early to make noise tapping out the headset cups, and I need to borrow some tools for the crank removal. That leaves the rear derailleur.

I've never worked on one of these Simplex beasties before, but I vaguely recall seeing admonitions about the process. Do you loosen the bolt from behind the dropout, or mess around in front? Does the upper pivot spring go "sproing" if you're not careful, or is it pretty well self-contained?

Thx...

There may be some Simplex variants that I don't know about--I'm sure there are, in fact--but in all the cases I know of you remove the derailleur by unthreading the shoulder bolt behind the dropout. The bolt in front, that would be the mounting bolt on a normal (that is, non-French) derailleur is for tensioning the body-positioning spring. You'll break the spring if you just start cranking on the bolt.

But again, my Simplex knowledge is limited. Someone better versed in this stuff will probably chime in before too long.

If it's a Criterium the mtg bolt is on the inside of the dropout. They put little red plugs in the holes on the outside of the RD to deter people from trying to remove it from the outside.
I've never had one sproing on me

Definitely from behind the dropout. The most fragile part of these derailers is in fact how the tabbed washer is attached to the end of the sprung pivot bolt. It's easily forced, making your derailer useless. To be on the safe side, use 2 allen keys, one to loosen (inside of the dropout) and one to keep the pivot bolt steady.

Bingo. Something I learned the hard way. However, a local welder made what appears to be a very credible repair to the part, and so far it's working just fine.

[edit] I mis-read your post. I gather you are saying the hole in the washer gets rounded out. In my case, the 90 degree tab snapped off. The hole that press-fits on the bolt was fine.

^^^^ I didn't explain it very well. You could probably work the washer a bit when the hole is rounded but when the pivot bolt gets deformed you're stuck. Happened to me.

I'm not sure all of those tabbed washers are the same...doubtful...but I have a couple of spares, Due Ruote. Bought a handful of them when I was doing my Simplex to Campy conversion. Of course, you may not want to try to remove the old one at this point but, if interested, I could take a pic for you.

Very kind of you. This one looks to me like it will hold OK; it's not under much stress after all. Until I pick up a wrench, that is. If it fails, I will let you know for sure. Thanks.

Bookmark; I've noted these discussions before.