Starter Problems ::help::!!

I have a 1970 Chevelle 350 and i have had the worst luck with starters. I've had the car for about 14 months and i have gone through like 5 starters. I origanlly thought it was the starters were bad, that turned out not to be true... at leat i think. Then we thought since its not the original engine it could be the wrong starter. Nope I was getting the rite starter for my 168 tooth ring gear. Then after it made its horrible grinding jack hammer like noise and diddnt start.. i brought it to my father in laws garage (lucky he has one) and we loosened up the bolts and put it back up and it started fine. Perfect that whole day.. IT always is at first. So we concluded that we needed a repro starter brace for it.. Maybe the torque of starting the car would make it move enough to screw it up... Well sure enough we installed that and yet again its doing the same thing. I cant just jumping under my car wiggling the starter every time it does this WHAT DO I DO!?!?!?!?!??!?!??!?!?!?!?!?!

Did you check the flexplate/flywheel and see if the teeth are ground down as well? If you have an automatic, check if the flexplate is warped (remove the flywheel/flexplate cover and crank it over). If it's standard, do the same and check if "starter tooth ring" is out of alignment. Stater tooth ringscan be replaced, so it's possible that either the ring moved, or wasn't installed correctly if it was replaced previously. Or maybe, just maybe, you should add shims between the starter and engine block..unless you already have shims, and could try removing them. Good Luck :)

the ring gear is spot welded to the flex plate, check to make sure spot welds are not broken