How do know it's the clutches? My bet is it the cross shaft worn in the case. That's why it changes backing up, everything is loaded the opposite direction. How did you check the pattern? It can't be dead on if it howls. I say pull it, disassemble and inspect.
Doug
It can howl if the carrier bearing is worn.
Howl is usually the pattern, incorrect pinion depth/backlash. Bad bearings will growl. A loose set-up, (no preload) can cause howl due to the pinion or carrier moving. I can see the clutches possibly snapping but on a non worn correctly set-up sure grip this is seldom a problem. I agree clutches don't know forward from backward unless something is worn out. The two prime candidates are the cross shaft hole worn in the case. If it is a cone type the cones are worn causing contact at the outer edge of the cone.
Doug
