Help needed with aratio on a diff??

Hi guys, bit of a stranger these days but just hoping for some help. My mate has just bought a 1994 RR classic TDI, we went to Tong the other Sunday and on his return we found he had a strange banging noise from the rear axle, anyway when we took the wheel off we found that the rear bolts on the hub have been sheard, so after repacing the hub we found that the Diff had chewed some teeth, so we found a front hub off a disco 24 spline which his is a 24 spline and raplaced it today, BUT it was pulling against itself on the front near side and rear off side so we lifted it up on to some axle stands and low and behold the back wheels are going faster than the front so this would indicate that the ratio is siffrent so has anybody got ant idea's.
Thanks Colin.