Delrin and Polyurethane are plastics, no doubt. I've been running Polyurethane bushings since they came out. I will never run Polyurethane on the lower control arm pins or strut rods. That is race car stuff in my mind, whether you run them on the street or just at the track. For me it has more to do with shock and vibration, all slamming into your K Frame constantly. I also do not like the lower control arm sliding forward when I back up. My strut rods are tight, the strut rod does not have enough leverage to keep it in position at the angle it is mounted. I have had all kinds of Mopar's all my life and have never seen a completely failed LCA bushing. I also don't use cheap or soft stock bushings. Typically, heavy duty MOOG stuff.
I put "plastic" in quotes for this exact reason. Yes, Delrin is a
type of plastic. Polyurethane is a
type of plastic. Just like steel is a type of metal. But just like you don't use "metal" interchangeably when you mean steel, it's not right to just call polyurethane "plastic" - it's not the same stuff as your shopping bag or kids action figures. Do you refer to connecting rods as metal? How about cylinder heads? "Give me a set of those metal cylinder heads" No. You specify the type of metal, because there's more than one. Same idea. They're not just plastic, they're a specific kind with specific properties.
If there's any space for the LCA to move forward on the pin with poly bushings, they've been installed incorrectly. The bushing should be against the shoulder of the LCA pin, with nowhere to go. That's how they're supposed to be installed. I feel like we've had this conversation before.
See the space between the bushing and the shoulder of the pin? No? It's because there's no space there. This is how it should look. Agree to disagree or whatever, but if this isn't how the poly LCA bushing looks when it's installed it's incorrect. The LCA can't move forward unless it compresses the bushing. This is a poly bushing, so, it might compress slightly, but it won't move even as much as a stock LCA will when it compresses the rubber bushings in the LCA and strut rod. The strut rod, if it's the right length, will keep it from sliding back on the pin. That's why I use adjustable strut rods with poly bushings, because the stock length strut rods aren't good enough for that. This is where I feel the poly bushings get a bad rap, improper installation. They have to fit tight to the outer shell. Same on the inner shell, there should be no play and the bushings should not slide easily into or out of the original outer shell. It doesn't take a press, but it should take a lot of grease and you should have to lean on them a bit to install the bushings into the outer shells once you've added the pins. Also why I use greaseable LCA pins that don't have an inner shell, they're sized better for the poly bushings and you can add grease later as needed, so no poly squeak. But since the factory tolerances on the shells wasn't great, the poly bushings don't always fit the old shells properly. If they don't, you will have issues, and its not because of the bushing. It's the install not being correct from the beginning.
As far as the failed LCA bushings, I don't know how you haven't seen one. I've seen several just on my own cars. As I said earlier, the LCA bushings on my EL5 GT were so bad the inner shell on the pin was wearing against the outer shell in the LCA. The LCA literally
fell off when I pulled the torsion bar on the passenger side of that car. My Duster wasn't any better, one LCA just fell off the pin, on the other the pin came with the LCA but I just pulled the pin out of the bushing by hand. Both were wearing into the shells. Those were ~80k and ~90k original mile cars. The original bushings on my Challenger weren't that bad, but they were toast. Same for the one's on my '71 Satellite. Yes, they're there, but they'll get replaced before I drive the car further than around the block. So I dunno how half of the stock LCA bushings I've encountered have been failed, while none of the ones you've seen have. Good luck I guess.
Moog isn't any better than the stock stuff either. Nowadays it's mostly Chinese made stuff anyway. One of the Moog bushings that came in my CAP tubular lower control arms failed in under 50k miles. Of course, so did one of the LCA's, but that was crappy CAP welding. And it was the other side from the one that broke.
Here you go, failed stock LCA bushings.
From my Duster. Yeah, these are bad. No, I didn't press the pins out. Arrows show where the pins were riding on the shells. My Dart had one like this too, but it was fixed and reinstalled. I swapped these for a set with sway bar tabs, so no work was done on them.
This is an early style arm I bought (early sway bar tab). Hard to tell, but the pin is totally crooked. Not entirely fair, I don't know the history on this arm. But that bushing has failed.
And here's the tubular LCA I ran on my Challenger for ~50k miles. Purchased brand new, new MOOG bushing at time of install. Tightened with weight on the suspension, etc. The other side was ok. This one, not so much. Both on the same car, both installed and treated the same way. So much for Moog quality.
