Is it possible that too much grease is in the boot, and at high speeds centrifical force is expanding the boot out to the point it tears? If you're adding grease every time you reboot, you could concievably have gotten enough in there to do some weird stuff. /ubbthreads/images/graemlins/dunno.gif
I've had this problem before with older, more weathered boots. Once they get some little cracks in them, that's where they will flex, further cracking them, until they tear. They were coming apart pretty consistently at 100+... /ubbthreads/images/graemlins/banghead.gif
A while back, I started putting o-rings around the accordian section of the boots, and found that it stabilises the boots considerably. This cuts way down on the ballooning/stretching at ummmm... commuting speed. /ubbthreads/images/graemlins/devil.gif
When I re-boot the outers, (if they're not dirty/contaminated) I wipe out as much grease as I can with a clean rag. Then, I use a plastic hyperdermic needle filled with the grease pack from the boot kit, and force the grease down the ball tracks past the balls, and try to fill the outer shell. The shape of the housing will retain a lot of grease down where you want it. That little envelope holds more than enough grease, especially if you don't wash the joint out with solvent, so I wouldn't recomend adding any more.
The boys at raxles sell the Empi brand boots. They might also be available at a local chain store in the beck arnley brand as a re-box. They work fairly well, and I get ~ 2 years/60k from them before they require attention.
Has anybody ever bought the $40 boot kit from the dealer? I've always wanted to try them. They seem to last 10 years as originally installed. My problem is I never plan ahead, and I'm usually doing this job in a parking lot somewhere out of state. /ubbthreads/images/graemlins/tongue.gif In fact, I've done it twice in Delta, Utah. (Love that highway 50... /ubbthreads/images/graemlins/devil.gif /ubbthreads/images/graemlins/devil.gif /ubbthreads/images/graemlins/devil.gif )