I have a Super LJ front derailleur with a Delrin insert. I don't believe the Delrin is structural- more like a decorative insert. (Unfortunately I'm having issues adding and posting from Flickr from my phone).

The plastic part has "dried out" and has turned grey- I don't think it's under any stress, so it shouldn't matter if it cracks- but I was wondering if anyone had a good tip how to keep the Delrin looking nice and black.

Would ArmorAll or WD-40 or something bring that back?

I use Triflow.

I was thinking Sharpie...

Vegetable oil..... Like Canola oil....
An old car enthusiast trick to rejuvenate unpainted, black plastic bumpers that had greyed out from age and exposure. Just put a little bit on a rag and rub it in.
Actually last a much longer time than other treatments like silicone based products and supposedly not harmful to platics. Now whether it reverses in any way any degradation of the plastic, I don't know.
Recently tried it out on a Delrin cupped Stronglight B10 headset that had greyed out and it worked great!

The Golden Boy-

If you prefer not to use vegetable oil because it attracts dust, use Armour All. I use it on Simple Prestige, Criterium and LJ 1000 Delrin and they come back to deep black with a slight gloss to the surface finish.Allow it to soak in for a while and then buff with a paper towel or micro fiber cloth. You may need a couple of applications to get to the deep black original colour and then simply re-coat as necessary.

Everything solution I've tried on Delrin eventually turned back to grey, except cleaning it well then wiping on a thin coat of SuperGlue. Shines brightly and makes it permanently black.

I was worried about that when I first tried it but found out thst it does not attract dust more than than most things else you might treat the plastic with. It penetrates the the surface of the plastic and the surface does not feel oily at all after you wipe off any excess with a microfiber rag or paper towel. Try it, it works really good.

Pretty much this one:

Back to Black comes to mind. Automotive use. Ever seen Jeep fender trim that turned grey? Use a hair dryer to turn it back to back.

That's the SLJ front derailleur from the 80's. I have a few of those in my stash and on my bikes. The black Delrin part with the Simplex logo is just a garnish cap over the gap between the parallelogram arms of the FD mechanism. No structural loads on it at all, so these pieces never really fail, just sometimes get lost when not snapped back in correctly.
Actually, what fails on those FDs are the aluminum clamp and body assembly that cracks at the hinge and at a slot molded into the aluminum, to house one of the pivot arms, where there are corners that are stress risers.

It took almost twenty years, but Simplex eventually figured out that Delrin is ideal for non-structural applications.

Like mentioned above, heat will re-blacken the plastic but you have to be quick. I've seen guys use automotive headlight repair kits to fix plastic as well but most are just thin clear coat. A quick wipe with lacquer thinner may work too but don't let it soak in, just a damp rag and a quick wipe. The dealer I bought a car from back in the late 80's was doing that to rejuvinate faced black and gray trim pieces made of plastic.

How about linseed oil? Anyone try that? Since Delrin was born in the 1960s, (or 1950s?) I wouldn't be surprised if that was the main ingredient.

Finally, able to upload mine...

SimplexSuperLJ by Dave The Golden Boy, on Flickr

So you have used Armor All?

I know people used to use it on the 70s ragtop hardtop cars- I never used it on my convertible top just because I didn't care for *that* look, but I'm really kind of looking for that 'new plastic' look here...

I know a lot of "car people" do not care for Armor-All, saying (w/out data to back it up) that it's bad for the plastic it's supposed to protect. Many, including myself, use 303 Protectant instead.

That said, we've all then the TV ads for plastic-care products "that make plastic trim look like new!"... never tired it. Another possibility is plastic polish like Novus. Mostly, I suspect, you just need to get the oxidation off the plastic.

I think the failure of Simplex FD had more to do with engineering and design. I never had a problem with the delrin rear derailleurs.

So I'll be the polemic and say that Delrin is awesome. Great mechanical properties for a thermoplastic polymer. Ideal for belt and strap buckles...

Actually, I think there is someone working on carbon reinforced acetal resin (delrin). It may be the material of bike frames in the future. Unlike epoxy and other thermosetting resins, it is at least potentially recyclable.

AmorAll works fine and will not harm the Delrin (or convertible tops). Do not use WD40 as it has very strong solvents and can harm some materials. I have kept the original top on my 1980 TR7 pliable and in good condition since 1993 with no ill effects. Back in the day car guys were afraid of things like silicone making it difficult to repaint. I'm following this thread as I have a much older Simplex to restore. Sliding rod type.

That's interesting to read from someone of your experience level. With as many photos of broken Delrin derailleurs I've seen on the internets- I'd avoid any components that had structural use of Delrin or plastic where other materials and alloys have proven themselves superior.

I had intended to sell this unit- aside from the weathered plastic- it's in really nice shape. I've been in the very slow process of putting together a 1978 Trek TX700. My initial thoughts are to use first generation Cyclone derailleurs as they're pretty age appropriate and are some of the finest units evAr- But since I'm using a Stronglight 99 BIS crankset, and I've got this nice top of the line Simplex just sitting around I've been playing around with the idea of mixing and matching. When I had the Simplex on my Trek 720- it was reliable and completely unremarkable- I never had to think about it- it just did what it was supposed to do- which, I guess is one of the best compliments you can give to a component.

Yeah, strange but true. The fronts would break, the rears, no. Of course when I was working on these all the time they were like 5-20 years old, not 40 years old like they are now. I'm sure age and accumulated UV are detrimental, and I'd be more suspicious of any plastic Simplex derailleurs that are still around.

The Simplex FD were in a way a clever design. The acetal/delrin is self lubing kind of like teflon, so it worked really well as a bearing for the pushrod mechanism, and it was easily mold-able to the correct shape. Killed two birds with one stone. But the tension on it from the clamp killed it. In theory it's about 1/4 as strong in tension as say 6061, but they made it pretty much the same dimensions as if it had been aluminum. It was bound to fail. Still I rode one on my commuter for like 10 years and it never failed. That was a while ago though. I gave that bike to a friend of mine a long time ago, and she broke it about a year later...

I wonder if 40 years from now when everyone's epoxy/carbon frames are failing, if people will say, "what were they thinking using plastic for that?"

I recently rescued my childhood fishing rod from my folks' house, and promptly broke it. Decades had made old composite brittle as a dry twig. Makes me cynical about composites.

I use a product called "Back to Black" on plastic parts that have faded or been waxed.
https://www.amazon.com/Mothers-06112.../dp/B00GZLMEN4

Wasn't the Ofmega Mistral derailleurs made out of Delrin too.
Ofmega pretty much made the RD almost totally out of the stuff except for the pivot bushings and the cage assembly but I haven't really heard of those failing, as much as Simplex stuff did......

Oil. Any oil. Delrin was designed for engine mountings. It thrives on OIL. Just wipe down with some oil, polish off the excess and it's instantly black and shiny. And the oil actually nourishes it, too. Armour All is useless on delrin.

This Simplex FD was done with Mothers Back to Black last fall and has been sitting on a shelf in the garage. Its still grayish but not bad. I hope to use it on my '58 Sun someday when I find a double CR.

The Golden Boy-

I do use Armour All on Delrin. I just restored a Peugeot PB 12 with a Simplex 1000 rear derailleur. It was dull and slightly grey and the attached photo shows "after Armour All".