Slipping forward excellent reverse

[Alvisr]

've got a tao tao 125 with a drive, neutral and reverse. Last week after it was rode for about 2 hours it wouldn't go forward reverse still worked. Put it up for about 2 days changed the oil then started working again. after about the second day my daughter was riding a few hours on and off it stopped again.If you lift up back tires they spin and if you hit the gas they'll spin faster. but if it's on the ground on pulls half speed in reverse and not at all forward. I would appreciate any help anyone could give.

[Fang502002]

I had a similar issue with a 180cc Aeon quad bike. It would drive fine in reverse and Drive would just grind.....after taking the gearbox apart , I found that the bearings on the main sprocket shaft was shot. This mean that if in reverse the shaft was pushed up against the cover , but when in drive it was pushed down away from the gears. After changing all the bearings, quad is driving fine again.