Bicycle Mechanics - interface problem: mounting indexed DT shift lever on Cannondale 3.0?

I'm overhauling and putting lots of new parts on a buddy's Cannondale 3.0 that he was given by his brother. I replaced the dead STI shifters (I didn't have the patience to try and resurrect them) with indexed down-tube shifters, but am not sure how to mount the shift levers on the bike.
The frame does have down-tube lever bosses but they're different than what I've seen on steel frames in that they have a flat mounting base built in.

The problem here is that the shifter bosses have a plastic base that's built into their attachment to the frame. These do not allow the mounting of standard down-tube shifter base-pieces; standard ones are designed to match the curvature of the frame's down-tube, and in this case the already-installed (and permanently-installed) mounting base is flat.
However, the mounting base on the frame doesn't include the interface for the shift levers so that they can index.

Are there metal base-pieces with the correct flat backside to fit over the plastic base on the Cannondale? Alternately I could put the curved base-pieces on a grinder and flatten the back so they fit over the flat based on the Cannondale's shifter bosses. 'Cept that I don't have a grinder.
Here's some pictures to illustrate what's going on - I don't think I've described it all that well. I just want to get these shifters on the frame.

http://www.unc.edu/~cupery/pics/bike_parts/IMG_6038--cannondale_dt_lever_boss.jpg
http://www.unc.edu/~cupery/pics/bike_parts/IMG_6035-36--dt_shift_lever_mount.jpg
http://www.unc.edu/~cupery/pics/bike_parts/IMG_6040--dt_shift_lever_interface.jpg

Weird... is this one of the CAAD 3.0 criterium frames with the funny dropouts that extend beyond the seat stays? I had one of the frames but sold it, it was a 1991 model I believe. It had Suntour Edge Accushift downtube shifters which appeared to be totally normal, but sat a couple mm from the frame rather than lying flat against it. That's pretty much all I can remember about it, sorry :(

Yup, it's the Criterium frame with the funny dropouts. Nice frame, very light and stiff (to the point of being uncomfortable, so it's weird that my friend's going to use it for pleasure-riding and with his kids).
There's another current thread asking about getting down-tube shifters on a Cannondale, although I'm not sure the frame has the same setup as the one I'm working on... the OP in this thread does refer to "black plastic spacer"
http://www.bikeforums.net/showthread.php?t=231962

Yeah, they are nice lightweight and cool-looking frames. I built mine up briefly before deciding to sell it, and the combination of extremely short chainstays and aluminum fork combined to make a very stiff and jarring ride.

Have you tried just putting the shifter straight onto the mounting thingy built into the frame? I have a vague recollection that it was done like that on mine. I'm trying to think of why that would prevent it from indexing...

Have you tried just putting the shifter straight onto the mounting thingy built into the frame? I have a vague recollection that it was done like that on mine. I'm trying to think of why that would prevent it from indexing...
I can put the shifter straight on, but it doesn't index that way. In the pictures of the shift lever and the metal mounting base/spacer, you can see the teeth that interface. That's what's necessary for indexing.

Just file down the curved portions of the shift levers until they are flat. I did this on two Cannondales from the mid-90s, with two different brands of levers (Shimano and Sun Tour) and they have been working perfectly for years.

Just file down the curved portions of the shift levers until they are flat. I did this on two Cannondales from the mid-90s, with two different brands of levers (Shimano and Sun Tour) and they have been working perfectly for years.
Okay, great. Thanks. This will be more work with a file than with a grinder, but not too bad since the curved metal spacers are aluminum.

I have the flat pieces that you need.

I just upgraded the DT shift levers on my bike and the new levers came with a complete set of mounts.

The curved piece would fit over the boss and then the flat piece would slide on top of that.

My 1994 Cannondale R400 has the curved pieces already mounted on the frame so all i needed to mount was the flat part and then the lever on that.

Actually-- go visit your local bike shop(s). You can probably pick up what you need for free/super cheap.

If that soesn't work out, drop me a line at:

brian(dot)p(dot)johnson(at)gmail.com

Here's a picture of what's going on in this system. the flat spacer (alternate #6 - for light alloy frames) replaces the curved spacer (regular #6) for use on a fat-tubed or other frame that already has a flat base on the dt shifter bosses.
http://www.unc.edu/~cupery/pics/bike_parts/Shimano_dt-shifter_boss-covers.jpg

I had the same problem mounting 105 7-speed downtube shifters on Kelly Take-Offs. The Take-Offs have a flat mounting surface and the shifters' base plates were dished like the ones you are using.

Solution: grind/file/Dremel the base plate flat and they work perfectly. Before he went out of business, Chris Kelly sold base plates so modified as accesories for his Take-Off kits.

I'm assuming you've solved your problem with the flat boss covers from the RX100. I have the same frame with RX100 downtube shifters, and indeed the spacer or boss cover is flat on both sides.

Tim,

I think your setup is exactly like mine however your images don't show the shifter apart. Mine is currently apart because I'm missing some pieces. So anyone who wants to sell a RX100 shifter for a Cannondale large tube see my other post. Here are some images I took tonight. Your first image shows the metal nut, black spacer and curved spacer as one unit. That nut goes from the outside of the curved spacer, through the black plastic flat spacer and extends to engage the shifter lever. The diagram you furnished earlier is for a Dura-ace shifter which is slightly different.

(I got this frame with the shifter loose and obviously missing some parts). I've got the proper metric threaded rod though!

Eric