Some on the forum were born after the demise of the black simplex gears. Worth knowing the history. The Criterium model mentioned long ago also had a superior jockey wheel cage. It worked well, but the plastic body parts... The top of the line levers were not. As a mechanic way back I disliked the front changer most, the return spring was I felt marginal, the plastic body tender, often bikes would arrive for service with that portion fractured, they got Suntour replacements.

I agree that the UO8 was a decent riding frame, it suffered in the market as time went on due to the derailleurs and shifters, they did migrate to stem shifters but the Japanese units were superior, by the time they abandoned the coffered crank it was way too late. The steel chainrings were too easy to get knocked out of alignment, Raleigh suffered the same till 1979. The revamped Grand Prix sold really well during the second gasoline crisis.

My first "10-speed" was a gas pipe Chiorda (around 1970) that came with Simplex (I was upset it *wasn't* Valentino!), but the levers were the alloy Criterium levers with black plastic covers. The AO-8 that replaced the Chiorda was also simplex equipped and came with all alloy levers. The first time I rode a bike with the "normal" plastic simplex levers I wondered what was wrong with the shifting, they flexed so much!

There is a very good chance that you will see this, sooner or later, on a Dupont Plastic Simplex derailleur, the front one being the worst culprit...

http://www.mytenspeeds.com/My_TenSpe..._Cracked_1.jpg

Get ride of the Simplex and replace with Suntour! That will solve the transmission problem. However, there are other Problems Associated with French Bicycles. Good idea to understand those and keep them in mind before you make a decision.

Ooooooh,......sun dried crispy crunchy!.......

Yeaah Simplex never die!!

just what I did BITD, and yet I now find myself chasing down Simplex bits for a PX 10 project.

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"Long live plastic" sounds like a prayer
But these actually do have a fan club among vintage rando riders

Compared to what SunTour offered? That choice is a no-brainer...

There are probably Delrin parts in your car. I just had to replace all three hvac door actuators in my wife's Impala because of stripped Delrin gears.

...planned obsolescence has been around for a while. Actually, obsolescence is a misnomer in this context. Think "functional demise".
I once had to repair an under-dash HVAC bellcrank made of plastic that broke (this was the for the door that opens/closes the duct for outside air. Naturally, this happened on a road trip from California up to Canada in December... ironically, at the same time, the thermostat failed wide open, so there was very little cabin heating available whatsoever...brrrr!, but that was an easy enough repair to make en-route).
Most likely, the replacement bellcrank was unobtainium, other than getting the complete HVAC assembly, but being under the dash, would have been an 8 hour job to re- and re-, at any rate. Fortunately, there was just enough space to get at it through the glovebox, and I was able to mend it with epoxy and multiple windings of strong thread. The repair held for the remaining duration I owned the car, which was about 20 years. The original part had lasted only 6 years since the car was manufactured. :rolleyes:

Maybe that's proof it's a good choice for some applications, and maybe it's not. I think time has proven that it was a poor choice for derailleurs.

And for accelerator position sensor cases, just ask Toyota.

Had one do that just sitting hanging up mounted on a bike inside a room.
Age, plasticizer migration, oxidization. Nylon is self lubricating to a point, absorbs water interestingly enough, swells and shrinks as it dries out. And you thought plastic was relatively inert and stable...