Krov9

I am building up a 70's French bike with period correct components. I have a Simplex push-rod type fd with a nice original chainguard that I would like to use, if it weren't for the bad rep of those old pieces of plastic.

I wonder if there's any sort of chemical that could, perhaps to a degree, reverse the damage done by UV exposure and restore some elasticity/shear strength to these parts?

I've previously used automotive plastic trim conditioners to a good effect on some stuck and dried-out handlebar grips, which are, of course, made of a more rubbery material. Anyhow, that made me wonder if there's something that could be done to those fragile old bits of DuPont Delrin...


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3alarmer 

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...the Car Guys make and sell this plastic/rubber/vinyl restoration stuff, that works pretty well on brake hoods, but I've never tried it on Simplex Delrin. It might have trouble sinking in deeply enough on something well aged. I'm not especially sentimental about the Simplex plastic stuff, even though I'm old enough to have used a lot of it over the years. I think of it as a bold experiment that ended in failure. If the front derailleur looks iffy, I replace it with Suntour. If the rear looks iffy, I usually replace with whatever all metal rear derailleur fits the dropout easily. Often that is something from early Shimano (e.g. Crane).

Kontact 

Frequent ladling of warm butter will...


I'm sorry, that's my Chateau Briand recipe. Nevermind.

dsbrantjr

One reason hat plastic items tend to get brittle with age is called "plasticiser migration. Plastic items contain plasticisers to help keep them from becoming brittle and when they are lost from within the plastic brittleness starts to set in. I know of no way to replace them into the structure of the item. UV exposure also changes the plastic's structure with similar effects. Eventually they are going to fail.
What I would suggest is to make some detailed measurements of the items and see if you can perhaps replicate them by machining or 3D printing.

KerryIrons

Delrin is similar to nylon, and is subject to oxidation over time just like any plastic. There really is no way to reverse this as it is a chemical reaction. You might find something that improves the surface but nothing can be done to change the physical properties.

Andrew R Stewart 

Back in the early 1980s I read that Russian yak butter was the best Simplex plastic preservative. That's what the winning Russian Olympic team lubed their chains with in 1980. Andy......(and can I sell you some?)

Kontact 

In all seriousness, there is no chemical that you can put on the surface of a solid plastic that is going to effect anything but the surface.

canalligators

I think the most important advice is the same as it was in 1973: Do Not Ever Adjust Spring Tensions in a Simplex Rear Derailleur. It was not unusual for a customer to think the chain tension was too low, and tried to tweak the spring tension. Often in the attempt, they’d strip out the hole in the delrin which the spring fits into.

rickpaulos

Even more common was breaking the springs. The LBS I worked at had a box of springs that we went to often. Kinda bizarre that the derided plastic was sometimes tougher than the steel bits.

Krov9

Thanks for the input guys!

I've been thinking of 3D printing a replacement, but the shape is pretty complex... trying to figure out how they were put together back in the day.

Also, this is likely not going to be a long term solution, since the printer at my disposal uses PLA filament which is supposed to be biodegradable 😅

I'm pretty much stuck with Simplex gears due to the proprietary RD hanger (other compatible RD's such as Shimano Crane and Campagnolo Rally are pretty expensive/difficult to find these days).

I have a Simplex RD (not sure about the exact model) with aluminum knuckles etc. Guess I'll have to look out for a non-Delrin FD too.

3alarmer 

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...the Shimano Crane short cage rear derailleurs can still be found on ebay in the slightly overpriced but not absolutely outrageous category.

Vintage Shimano / Dura-Ace Crane Short Cage Aluminum Rear Bike Derailleur

Shimano also made and sold an identically designed derailleur, called the Titlist. There are currently a number of them offered on ebay in the $30 range. Here is a quick search result. The Titlist is not all alloy, so a tiny bit heavier, and the finish is slightly less polished, but they work just as well as the Crane. They seem to get little respect, but I use one on one French bike with Simplex dropout, and it works well. The search list also has one or two more Crane short cage rears in the $40 range.


The short cage ones will handle a range of rear cogs similar to the original Simplex. For more gearing range than that, you need a long cage. Those are usually more expensive, as is the Rally. If you have an all alloy Simplex rear already, you should probably use it. Those are also increasingly expensive on ebay (which, apart from the bike co-op, is my main source for this stuff.)

WizardOfBoz

Andy, Given the Russian's exceptionally fluid regard for the ethics of chemical additives, one wonders what was in that yak butter....

But dsbrandtjr is correct. I used to work at the DuPont plant that made Delrin(R), and it's a terrific material. But if its degraded, it's hard to magically restore its properties.

If the part is simple enough one might find someone to CNC a part. 3D printing of Delrin is difficult (apparently due to poor bed adhesion) but can also be done. Or, just buy a metal FD.

I used to install the Simplex derailleurs in the 70's and never really liked them. But if you have your heart set on a period restoration, good luck!

Krov9

If anyone has a clue where to find better structural diagrams of such derailleur, that would be extremely helpful in 3D-modeling the part.

This is the only one I've been able to source so far:

Germany_chris

Are we stuck on Simplex or period correct 70’s French?

bikemig 

The delrin front derailleurs just don't last. I don't know if I've ever seen one that hasn't cracked. The rear derailleurs on the other hand tend to be OK and it was a pretty good design (other than the plastic) for its day in terms of shifting. They also can handle a surprisingly large freewheel which was unusual for vintage short cage derailleurs. The shimano crane/titlist is a good idea if you have forged simplex drop outs. If the RD is on a hanger, you will have more choices.

Krov9

Well, the frame's got a threadless, stopless Simplex RD hanger, and I quite like the look of this chainguard


that I found NOS for a dime. I suppose it could be attached to other FDs too, as long as they have the clamp bolt on the drive side
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Chuck M 

It seems the only way to make these last for decades is to never install them.

Krov9

The collector behind disraeligears.co.uk website commented on Simplex's "outstanding ability to grasp the wrong end of every available stick" or something to the effect.

That's very well visible in the example you posted - other side of the clamp is an overbuilt, hefty cast metal piece, while the one that matters, is made of fragile, UV-degrading plastic.

WizardOfBoz

The other thing is , in asking for dimensional drawings, that Simplex seemed to tweak designs every few months. So in asking for the drawing for a mid-60s FD made of HOM/Acetal, one would have to ask when? 1965 you say? Early or late. The number of revised designs from Simplex is breathtaking.

roadcrankr

Take off the Simplex units, place in a box in a dark closet, and you will never worry about this matter again.
I 2nd the notion of replacing with Shimano or Suntour. You might try Huret stuff, if you wish to keep the French theme.

rickpaulos

here here! I had an Arctic bike (Arctic Cat snowmachines) last summer with a broken jockey wheel on the Simplex derailleur. The Simplex jockey wheel id, bearing and bolts are different sizes from the Japanese brands. I did find a low end Huret Challenger that works fine on the bike. It's French, nearly no plastic and country correct.

WizardOfBoz

Couldn't see the pic, but one other thing: Injection molded parts are generally going to be stronger than 3D printed parts.

maddog34

Will this fit? And as the others all point out, "renewing" those Simplexes is a lost cause.
I tear down over a hundred bikes a year.. i rarely find ANY usable simplex pieces. I searched: NOS simplex... you should too.;-) https://www.ebay.com/itm/35457756390...Bk9SR9Lw1prJYQ