Cannondale Moto FR suspension forks. Why did Cannondale saw off disc brake mount?

[marka-ee]

I recently purchased some used Cannondale Moto FR suspension forks. These are the ones which use needle bearings in both sides thereby highly reducing any static friction, which is sometimes called stiction. One peculiar thing about these, and I've seen other examples with the same situation, is that apparently Cannondale has surgically sawed off the disc brake mount for some reason, which is unknown to me. Does anybody know if there was some kind of strange recall or some other reason that they had possibly done this surgery? What I'm wondering also is if I could TIG weld on a replacement disc brake mount to exactly where the decapitated one used to be. There's a nice rectangular block where you can see, obviously, where the disc brake mount was situated. I'm not sure what the alloy is exactly. It appears to be aluminum.

 

[amberwolf]

A quick google doesn't find a specific recall for this fork, but this post
https://www.mtbr.com/threads/hey-cannondale-bring-back-the-boot.1015566/post-12697234
references "the Moto debacle", which I can't find details for either in a quick poke around.

Speculation is that either the mount was manufactured or designed incorrectly, so it didn't line up the caliper with the rotor correctly, or caused some sort of problem (braking force snapping forks at lowers, or crown, etc) and was recalled, but since the fork was otherwise usable they then removed the source of the issue by removing the ability to use disc brakes with them.

The images found in a search all show rim brake boss mounts, so they're still usable since they have those (you just need the thread-in posts), so they may have found a secondary market that way, rather than being destroyed.


Without knowing *why* the mounts were removed, then even if you can re-heat-treat the lowers to bring them back to the original strength after welding so they're not weakened right at the mount, they may still have a hidden weakness that could cause them to fail from disc brake usage at any moment of braking.

They must be a weldable alloy, as there are clear welding beads on it

 

[lnanek]

Maybe it's just some models had disc brakes and some didn't? This ad on Pink bike shows both:

Cannondale Moto FR Headshok Missy Giove? For Sale

Cannondale Moto FR Headshok Missy Giove? For sale on Pinkbike buysell

m.pinkbike.com

No reason to weld the disc brake mount on the tube if the fork was sold with that lower right model that used rim brakes?

They must be a weldable alloy, as there are clear welding beads on it

Yeah, but they may have welded it, then heat treated it. Most enthusiasts who can TIG weld don't also have the ability to heat treat something (disassemble/strip to bare metal only parts, then put it in a big oven, then reassemble, basically). It's not common to weld aluminum after manufacture due to the need to heat treat after, not because it can't be welded. So weld beads don't mean it can be economically welded later on, unfortunately.

 

[marka-ee]

I'll try to take a picture of the area tomorrow, but in the meantime they were definitely amputated because the area of the mount definitely protrudes several millimeters and there was an intention to put something there, but then surgically removed. If I can't weld something to the protruding boss, then maybe I can somehow design some other type of a coupling to go around it, possibly even threading into it, to be able to mount a disc brake caliper. Or I guess I could just go with some old Magura rim brakes that I have lying around that work perfectly fine as well.

 

[Stealth_Chopper]

That late '90s was early during disk brake standardization and the one offered on the next model 'MOTO' was I believe unique and perhaps a SACHS brake that must/should be collected along with the vintage disk fork and, I think a unique downhill axle.

 

[amberwolf]

I'll try to take a picture of the area tomorrow, but in the meantime they were definitely amputated because the area of the mount definitely protrudes several millimeters and there was an intention to put something there, but then surgically removed.

Do they have threaded holes in the back side of the mounts? If so, those are probably just post-mount types.

If I can't weld something to the protruding boss, then maybe I can somehow design some other type of a coupling to go around it, possibly even threading into it, to be able to mount a disc brake caliper.

Well, as I said before--they probably removed them for a reason, to keep them from being used that way. If you use them that way anyway, then depending on why they removed them, you could be risking a fork failure during braking while riding, and that kind of failure will probably throw you hard off the bike into whatever you were pointing at, as the front end of the bike collapses under you and digs into the surface.

Or I guess I could just go with some old Magura rim brakes that I have lying around that work perfectly fine as well.

You'd almost certainly be safer just using the rim brake boss mounts (just get the threaded posts you need for that).