smithyrc30 wrote:
A common misconception about bushes is that they will support greater loads than needle rollers. This is incorrect. A bronze (leaded tin which is the strongest composition avaliable) bush has a maximum load bearing capability of 100 N/mm2. A typical needle roller will support around 4000 N/mm2, over an order of magnitude higher.
Smithy, considering the Needle Roller on it's own, yes.
However, when applied in this application and that (as you have also referred to) they only run on shafts of variable quality then as I've found, they are not up to the job, but not through a failing of the bearing, but the shaft. Also, Bearings really only support higher loads when there is some moderate speeds involved, not the extreme low speeds of the trailing arm arc movement.
They had similar issues on the Crawler that's used to move the Apollo Rockets, they initially fitted bearings to the crawler tracks and I think it only went a few hundred yards on it's first try out before the bearings spewed out over the gravel. I think it was Timken who were called in to sort it and they came back with bushes, which I understand are the same ones from back then that are still in there to this day.
This too is why Bushes are used on King Pins in Trucks - High Loads and Low Speeds. It's also in part why we have slipper bearings in our engines too, though the speeds are higher, but thet's dealt with by lubing with a continuous flow of oil.
Coming back to the job at hand, if you look at the 1100 and 1800 series, they used Tapered Rollers on the swing arms to basically get bigger balls in there, for the issues that I raised in my earlier posting regarding the huge spot loadings from needles. You can clearly see this when you remove the old shafts, the bearing end is always buggered and the bush end is OK - provided they were greased.
I'll add too that there does appear to be some concern here about getting grease in to the bush and bearings. I've always made sure that the grease tube between the bearing and bush (or other bearing) is pinched firm by the tube. I don't bother with the plastic ones, I always reuse the steel ones. This will reduce the grease that 'leaks' in to the arm, it won't eliminate it. I also jack the vehicle up and get the rear wheels airborne before greasing. This is to un-load the normally loaded parts of the bearing & bush to get the grease where it's needed. I can't say I've had a lube problem here.