Any one ever tried to use a 7 speed indexed RD with 8 speed Ergos? Will it work?

I think it would. The shifters just move the derailleur ----- Lp

I think it depends on the derailleur. Old recor geometry not likely... no Victory, triomphe, C-record, super record etc... CHorus and Athena? Maybe, but they did change quite a bit when they went to 8. Try it and let us know. Assuming you already have the parts to try it.

Not necessarly true. As with how Campagnolo derailleurs will not just "drop in" in place of a Shimano derailleur, it has to do with the ratio of cable movement to derailleur movement. Shimano has always been good about keeping the same Ratio (except for early indexed Dura-Ace). Campagnolo, has not been so consistant. In fact, it seems with every new cog they add, there's a new ratio to go along with it.

So, the short answer is: maybe.

The long answer is: you may get lucky, or you may strike out completely getting the two to jive together. The likely outcome will be that you'll get some cogs to play nice on one end, while at the other end you'll experience a lot of chatter if not full out skipped shifts.

Well, we'll know at some point in time. After it gets here, I'll be down to just needing a headset and I think I have all I need for the build.

Edit: If this doesn't work I'm going to try 9 speed. This 8 sp stuff is too hard to find.

I don't think running a 7sp RD with 8sp Ergo shifters will work, but I do know that running 8sp Ergo shifters with 8sp RD & 7sp freewheel/cassette works just fine.

By the same token, the 8sp Ergo shifters should shift a 9sp RD over an 8sp cassette just fine.

Another option is to obtain the 9sp Ergo insert for your 8sp Ergo shifters, as well as the appropriate RD & cassette/freewheel. My brother switched all of his 8sp Ergo drivetrains to 9sp by switching the inserts & cassettes.