Dia Compe 610 DC (Dia Compe) va GC (Gran Compe) Physical Comparison Results
Well I forgot I had a single rear GC brake on the way that arrived in todays mail. I have several old DC versions lying around so I was able to sit them down for a side-by-side comparison. Here are some of my observations:
1) The GC are indeed a much better finish, i.e. so much smoother. As T-Mar indicated the GC is a very nice clear anodized finish.
2) Even with several differences to report here they weighted exactly the same. I removed all the mounting washers, spacers and nuts and
both came in at 130.5 grams. BTW, the through frame bolt lengths are the same. Strange that T-Mar found a slight catalog spec'd difference. The weight was also a surprise considering they are constructed a bit different.
3) The Mounting Bolts are different. The DC model has only a wedge fit head that keeps the mounting bolt from turning when attaching the mounting nut. Holding the brake assembly while tightening the nut is what keeps it in place. On the GC version their is an added extension to the bolt head. It has the wedge head as before with additional flats on the extension for a open-end 10mm wrench. So it offers the user a secondary means of holding the brake assembly in place while tightening the nut. See the side-by-side picture below (note the DC versions bolt is pushed back a little from it's normal secured position):
4) The anchor holes for the transverse (straddle) cable ends are slightly larger on the GC version. GC measured 7.6mm while the DC version was 7.4mm. Your can see the slight bit of play around the ends in the comparison picture below. Of note on the DC version my ends were frozen in place and I will need to use a bit of penetrating oil to free them.
The structural dimensions of both the DC and GC Arms are the same, except for these forged Anchor Holes! The DC version is noticeably bulkier.
5) There is a rotational forged Pin and Slot mechanism that assists the Outer Arm and Inner Arm rotation when opening and closing.
The interesting situation here is this Pin-Slot system is used on the cheaper DC version and is absent on the GC. The following two pictures illustrate the difference. Note that the Pin is on the back of the outer arm and the slot, which can't be seen in the pictures, is on the front side of the inner arm.
So, in conclusion and as others have expected, the Gran Compe version is by far a better finished specimen. However, from an operational standpoint you probably won't see much difference. If you want to spend the extra money to snazzy up your vintage Dia-Compe center-pull braked bike, and yet stay in the correct time period, the GC upgrade might make your day. This is especially true if you also go with the higher end levers that probably came with the GC brakes.
It's always fun to investigate these things. For me it keeps the technical side of this hobby/sport interesting. Any additions would be appreciated.
Great day to all - Don