The original Simplex rear derailleur on this mid-1970s Raleigh was later upgraded to a better-shifting Suntour derailleur of about the same vintage. The changeover was simplified by Raleigh's penny-pinching--but ultimately helpful--decision to outfit the frame with a mounting claw instead of a brazed-on hanger.
Integral Mounts vs. Mounting Claws
The good news is that if you’re working on a relatively recent bike and components—anything after the late 1980s, say—you can bolt pretty much any derailleur onto any frame, because the interface between them has been almost entirely standard since then.
But of course, most readers of this blog will be retro-grouch types who are likely to be dealing with older equipment. In the 1960s, 70s, and on into the early 80s, the standardization we see today hadn’t yet taken hold, and there were at least three competing systems for mounting rear derailleurs. Each was promoted by a component manufacturer who hoped to lock in future derailleur sales by selling frame makers and the bicycle-buying public on the virtues, if any, of its own proprietary approach.
All three mounting systems were available in two variants: In an integral mount—sometimes called a braze-on mount—the tab that supports the derailleur is a permanent part of the bike’s frame. In bikes that use a mounting claw, the derailleur itself is bolted to one end of a shaped metal plate—the mounting claw—that is itself bolted to the frame at the other end.
Below, the previously pictured Raleigh with the derailleur removed to better show the claw. The bolt to the left of the axle slot is threaded into a specially shaped nut that engages the rear half of the slot.
But despite their undeservedly lowbrow image, claw mounts have some real advantages. Since they’re not part of the frame itself, a claw that gets twisted out of shape when the derailleur gets tangled up in the spokes can easily be replaced at low cost (don’t ask me how I know this). The same sort of mishap on a bike with an integral hanger would require having a frame builder cut off the damaged piece, braze on a new one, and repaint or rechrome the affected area.
As an added plus, the hardware that fastens the mounting claw to the to the dropout is generic, so a claw made for one company’s derailleur can typically be exchanged for a mount of another style without a lot of head-scratching.
Developed by Campagnolo for its own product line, this type of mount is easily recognized by its 10 mm threaded center hole and a characteristic notch at the seven-o’clock position, which engages the derailleur’s B-limit screw for fine-tuning of its rotational position. Integral Campagnolo hangers were used on a great many Italian bikes, as well as those high-end French ones—like the Gitane Super Corsa—that were originally equipped with Campagnolo derailleurs.
This system has since become the de facto world standard. If your old ride is set up this way, it will (with a few exceptions) accept any non-French derailleur manufactured from 1960 or so to the present. Everyone should be so lucky.
Campagnolo’s chief competitor was Simplex, a French company that went its own way with product design. Simplex mounts are recognized by their more rounded shape and the absence of threading in the mounting hole, since their mounting bolts—unlike Campagnolo’s, which screwed directly into the claw or hanger—passed all the way through the mount and were secured on the inside with a nut. (Some Simplex derailleurs were fastened with a shoulder bolt that was inserted from the back of the dropout and threaded into the derailleur).
There are a couple of other oddities to the Simplex mounting system. Although a Campagnolo-type derailleur can't be mounted directly on an unmodified Simplex mount (more about this in a moment), a non-claw-type Simplex derailleur can be bolted directly onto a Campagnolo mount. This can seem slightly strange, since it involves passing a 9-mm bolt through a 10-mm threaded hole. In practice it works okay, although few people seem interested in this particular component combination these days.
The second oddity is that although Simplex mounting claws are bolted to the dropout with the same generic hardware used for Campagnolo claws, the claws themselves are somewhat model-specific. In other words, there's no universal Simplex claw that will accept any Simplex derailleur. You need to have the correct claw (and the correct derailleur-to-claw mounting bolt) for the particular derailleur you plan to use.
To make matters worse, there seems to be no product marking or numbering system that makes it possible to tell which hanger goes with which derailleur. And some people claim that French bikes are difficult to work on!
In any event, new derailleurs designed for the Simplex mount haven’t been made for decades. Used examples are fairly easy to come by, but pose problems of their own: Simplex derailleurs were typically made almost entirely from Delrin plastic, which was reasonably tough when new, but now, forty years later, tends to break with discouraging ease.
Worse yet--at least from the standpoint of the recreational cyclist, Simplex catered mostly to racers or would-be racers, so most of the derailleurs it did make were short-cage models. In the late 70s and into the 80s—near the end of its corporate life—the company did make a few long-cage models. These turn up on ebay from time to time, but they’re scarce and tend to command high prices.
Below: A Simplex hanger--originally similar to the one above--that's been "butchered" to accept a Campagnolo derailleur. The mounting hole has been threaded and a notch has been cut with a file to act as a derailleur stop. (The chainring bolt in the dropout slot has no bearing on the derailleur mount--it's there to serve as a stop for positioning the rear wheel.) Photo courtesy of H. Vanneck.
The Brutalist Approach: Cut off the Simplex hanger with a hacksaw, then use a file to clean up the cut area, shaping it to match the non-drive side of the rear dropout. Paint or grease the cut and filed surface to prevent rust, bolt on a Campagnolo mounting claw and the long-cage derailleur of your choice, and you’re in business. If done carefully, the result can be hard to tell from a dropout that was manufactured without an integral hanger to begin with. Done crudely, it looks like hell.
Pros: Cheap and effective.
Cons: Widely regarded as a crime against humanity. It may also reduce the bike’s resale value, if that matters to you.
The Modified Brutalist Approach: Bring bike to a good frame shop and have the Simplex hanger cut off and a standard hanger brazed on in its place.
Pros: Difficult to tell from original if done by a skilled professional.
Cons: Costly, since the frame will have to be at least partially re-chromed or repainted where finish is damaged by brazing heat.
The Hybrid Approach: An integral Simplex hanger can be modified to accept Campagnolo-style derailleurs by running a 10 mm tap through the unthreaded bolt hole and filing (or grinding, but be careful) a stop in the body of the hanger, using an existing Campagnolo hanger as a pattern. Again, paint or grease disturbed original paint or chrome to prevent rust.
Pros: Invisible when derailleur is installed. Modified hanger will accept Simplex as well as Campagnolo-type derailleurs.
Cons: May reduce frame’s collector value. Scorned by Francophiles.
The Purist Approach: Track down a functioning long-cage Simplex derailleur (be aware that this may cost beaucoup d'argent), and install it on the unmodified hanger. (Several vintage non-Simplex derailleurs are also said to be compatible with Simplex hangers that have had a 10-mm tap run through their original 9 mm bolt holes. This will at least spare you the stigma of grinding a stop into the hanger as well. Among these are the Shimano Crane, the Schwinn Le Tour—which was also manufactured by Shimano—and the first-generation Campagnolo Rally. There may be others as well. I have no first-hand experience with any of these, so don’t ask me.)
Pros: No criticism of the purist approach is possible.
Cons: Expensive; limited derailleur options.
The Hermaphrodite Approach: Leave the integral Simplex mount alone, and mount a standard derailleur claw on the dropout in the usual manner/
This sometimes takes a little fiddling. Some claws have a sort of S-shape when viewed edge-on, allowing the derailleur to sit a little closer to the freewheel than it otherwise would. But this can cause interference between the claw and the integral hanger. A flat mounting claw will usually avoid this problem, but if the derailleur mounting bolt is long enough to protrude through the back of the claw, it may bear against the integral mount beneath and make it impossible to tighten the bolt all the way. This can be addressed by switching to a derailleur with a shorter bolt, or grinding or filing the end of the bolt enough to eliminate any interference. Adding a washer between derailleur and claw may also work, although this will sometimes move the derailleur far enough outward that it will lack enough travel to shift onto the largest freewheel cogs.
Pros: Cheap and fast; leaves integral hanger intact for the benefit of generations as yet unborn.
Cons: Presence of both integral hanger and claw is not noticeable unless you look closely, but the knowledge that both are there may lead to persistent low-grade angst on the part of some riders.
Huret, another bygone French component manufacturer, also had its own proprietary derailleur mount. As you can see in the photos above, it's superficially closer in appearance to the Campagnolo hanger than the Simplex version. The threaded mounting hole accepts a standard 10 mm bolt, but the notch that serves as a stop is located at about four o’clock, rather than seven o'clock.
A Campagnolo-type derailleur will thread right on to a Huret mount, but will likely sit at a crazy angle relative to the chainstay. The derailleur may even function in this position, more or less, but shifting performance is likely to be lousy.
A Huret hanger can’t be modified to accept standard derailleur by filing or grinding it, as a Simplex hanger can. That leaves you with the choice of cutting it off and using a claw (the Brutalist option), having a frame builder braze on a new one (the Modified Brutalist option), or using the Hermaphrodite approach of keeping the original brazed-on mount while adding a mounting claw.
The Purist approach—finding a Huret-compatible derailleur—can also work, but be aware that just because a derailleur was manufactured by Huret doesn’t necessarily mean that it was designed for the Huret mounting system. The company also made derailleurs for the Campagnolo-style mount. Some models were convertible from one to the other by using special tabbed washers, which came in two different versions. Good luck.