loubikes

Hi all, I was hoping to upgrade a 1970's Motobecane Mixte for my wife to use but I've been told by a forum member that 1970's Motobecanes (or more generally, mixte's) have "butter soft" forks. His friend went to the ER because one of these bikes' fork 'snapped' and says that "they are likely rusting out from the inside."

I'd like to know if other's think the fork is a legitimate safety issue or if the bike/fork would be safe to use regularly.

Thanks!

*note: I'd like answers to focus on the safety of the bike vs views on aesthetic-degradation or cost-effectiveness of upgrades if possible.

https://www.bikeforums.net/bicycle-m...ane-mixte.html

repechage

Any time a fork is chromed there can be problems. The main issue here is a fork that was not completely internally rinsed between tanks in the plating process.

to eliminate that concern - buy a fork that has never been chrome plated.

I recall the very basic Moto' (Nomad?)
was sans chrome.

better yet - have Belinkey make a Mixtie frame for you- he did a terrific one for Brett Horton. Of the Horton collection. Surely she is worth it.

BFisher

There is no inherent design flaw in 1970s Motobecane Mixte forks.

Any 40-50 year-old steel object can rust out.

Nobody can inspect your fork over the internet.

If concerned, have it inspected by a good mechanic.

Happy riding.

Kuromori

One has to wonder if one can simply replace the fork with one from a diamond frame, or if the act of mounting them on a mixte somehow softens them.

desconhecido 

Just have to say, that's a pretty bike and probably makes somebody happy. And, that's all good.

As for the rusting of the forks, there was a discussion here not so long ago (past year or two) about the chromed stays on a somewhat expensive bike rotting from the inside. First sign, apparently, was evidence of rust bubbling through the chrome and noise of something rattling inside when the frame was turned upside down -- rust debris inside the frame. If it were mine, I'd look it over for any signs of rust on the fork and I'd probe any that I found to see if they were from the outside or inside. Also, check for the sound of any loose rust debris. Otherwise, if the fork is in good shape, I wouldn't worry. There are about 10 kajillion bikes from the 70's with chromed, or half chromed, forks still live and kicking -- including cheap forks by Raleigh, Peugeot, Moto, et al. Surely, if these forks were "soft", someone else would have noticed.

3speedslow

+1

ollo_ollo

Have someone look at it, but I have seen Zero evidence of any rust on my small sample of a Grand Jubile Mixte, a Mens Grand Jubile, and a Mens Grand Record and their forks are no "softer" than any of my other French rides... Don

Kabuki12

My daughter bought a 1978 Motobecane Gran Jubile’ Mixtec a few years back and right after we purchased it I had a bike mechanic with alignment tools check the bike out and he said the forks are the most common problem on most bikes as far as alignment goes . Hers was out a bit and I helped him do the fork. I could not believe what it took to move the fork to bring it back to alignment , that fork was solid! I have never really worried about forks on my vintage bikes . I have some that have chrome , even my ItalVega , that was so rusty on the outside that most would have let die, I don’t really worry about. It is a high stress area of concern , maybe I am naive? I dunno I always inspect a new acquisition for cracks or bends that would indicate a crash , but I really don’t worry beyond that.

big chainring 

I was selling a Bottecchia mixte a couple years ago. Really cool bike in orange with upright bars, cool Itaian saddle, and of course outfitted with Simplex Delrin derailleurs. So a guy comes to look at it with his girlfriend. He proceeds to tell me about all the things wrong with it, and of course the self destructing Simplex derailleurs will have to go. And really its a common practice with bike junkies. Because they have rebuilt a bike or two, they know everything about bikes. And because one person they know had a fork fail on them, every mixte must have soft forks...a term I have never heard. Cyclists are a peculiar lot.
Anyway, I told my prospective buyer that yes you could totally rebuild and update the bike, but you could also enjoy it the way it was. Old and funky with tons of character. He bought the bike. But I am sure the VO parts were ordered. Some generic wheels replaced the ultra cool Gnutti hubbed wheels. And God knows whatever crap was put on the bike, the original 50 yr old parts hitting the trash barrel with a hard thunk.

CliffordK

If one bought an English/ISO fork, then one would have to change the headset & handlebar stem, but it should work.

That fork above has quite a bit of rake, but there are some who rerake the forks.

verktyg 

BULL PUCKY !!!

In almost 50 years experience with French bikes, I've never seen a fork failure in a Motobecane. The first French bike I rode was a GF's early 70's Motobecane mixte.

For starters. the tubing wall thickness of the carbon steel fork blades used on entry level Bike Boom French bikes was 1.2mm to 1.5mm thick. You would start to see signs of exterior rust pitting and especially rust seeping through the seams where the dropouts were brazed in.

I have seen quite a few old frames that suffered from internal corrosion caused by improperly neutralized chrome plating. The forks and stays on those frames had much thinner wall thicknesses - 0.6mm to 1.0mm. None of them were entry level models.

Here's an example of a severely rust out chrome plated fork. Seat and chain stays are where you most frequently find this kind of corrosion because they are made of thinner tubing.



One area that I've seen fork failure is in the steerer - fork crown braze. Never in a Moto but ran across a few cheap Gitanes with the problem BITD. It wasn't limited to cheap bikes either. Here's an old Cinelli fork also 1969 Raleigh Pro fork.





The problem was the result of careless or lazy workmanship. The parts were never properly degreased or had the rust and corrosion removed. The fantasy was that the brazing flux would do the job!

This rarely resulted in a catastrophic failure. The first symptom was the headset kept coming loose as the limited brazing failed. The brake bolt would be the only thing holding the fork together.

The other comment about "Butter Soft" ?

Most of the tubes on carbon steel gas pipe bikes were dead soft. I know this from experience. During the Bike Boom many bikes needed to have the forks or rear triangle realigned out of the box in order for the wheels to fit properly! They were very easy to bend on the first attempt to align them. As the bending was repeated, they work hardened and became much tougher to adjust.

When you deform steel to the point where it takes a permanent "set" that is it doesn't return to the original shape it work hardens and becomes harder and stronger up to the point when it becomes brittle and breaks. Think of bending a coat hanger until it breaks.

I'm temporarily north of 220 lbs but I'd have no reservations about riding your wife's Moto mixte. One comment about mixte frames is a tendency for the front end to flex back and forth when pedaled hard. They are more flexible than a diamond frame in that regard.

Have her ride and enjoy her nice Moto mixte.

verktyg

Reynolds 531 

Motobecane are even clear painted over the chrome, which reduces the chance of rust compared to more "expensive" bikes.

loubikes

I was really hoping to get a response like this, thanks for taking the time to write it. I can move forward with confidence.

Chicago Al 

Loubikes, you've got good information here, from people with a lot more experience than me. But that won't stop me from chiming in!

In ten years (late bloomer!) of obsessive vintage bike enthusiasm and work, I've never seen or even heard of this supposed fork failure phenomenon. We have a nice 70s Motobecane Mirage mixte in our garage, converted to SS for city riding by me, for my wife's grocery-getter use. It would never occur to me to worry about the fork failing.

Further, the guy on that other forum who described the 'problem' also said that at his co-op they routinely straighten bent forks. WTF? Re-aligning a fork that isn't symmetrical is routine, but as anyone on this forum can tell you, an actual *bent* fork means the bike has been crashed and that fork needs replacement.

But if that beetle-green Motobecane in the photo is your bike, the rakish fork shows no sign of bending whatsoever. If that's just an example of what you want to end up with, then go for it. It's beautiful!