IMO, there is no difference in "internal castings" between the various units (unless someone can prove otherwise by taking open the boot on a new unit and take pictures). Sankei 555 is the manufacturer and various companies distribute this brand, such as Raybestos, TRW, Moog, Napa Premium etc etc. I have examined the lower ball joints sold under the TRW and Raybestos brand and I will attest to the fact that they are Sankei 555. However, even if these are made in Japan, they suck. I have also examined a set of OEM Toyota ball joints so I can comment on why the Sankei 555 ones are terrible. I made a post about it here:
http://www.toyota-4runner.org/3rd-g...tos-poor-quality-design-flaw-my-findings.html
In summary:
1. Metal on metal, unpolished ball stud. As mentioned previously by rickashay, the Sankei 555 feels like they bind when they move. The unpolished stud, I believe, is to allow for grease to better adhere to the surface. However, if you look at the pictures I posted in the above link, the ball surface scratches EASILY just by moving the ball by hand. This can't be good. If I am creating these scratches by human strength, imagine what is happening to the ball as your 2 ton vehicle is hitting bumps. The OEM joints do not have this problem. In comparison, the stud on the OEM joint moves smoothly as it had a low friction polished stud. Just by moving the stud on the Sankei 555, you will feel that it is an unnatural feeling and I would not be confident at all with installing such joints on my truck.
2. Crappy rubber boot. In comparison, the OEM joints have a noticeably thicker and stronger NOK Japanese branded boot.
3. No rust protection finish. Not really a big deal, but the OEM joints have a coat of black paint to protect from rust. The Sankei 555 does not have this and will rust quickly.
I wish there was a way to make the OEM sealed joints grease able, as lubrication is always the key to longevity. The OEM joint, as well as aftermarket joints, have the dust boot clamped only on the bottom. The top is free-hanging, and there is a possibility of moisture/dirt to get in. The ability to periodically grease the joint would be beneficial in being able to flush out old grease and increase longevity. However, even if the OEM joints are sealed and non-greasable, they are still a much better choice than any aftermarket unit because of the internal quality.
