I got a wild hair to check out why my "new to me" John Deere 430 will change speeds at will while driving, usually only downhill. It would be going along fine, then suddenly slow, then speed up again. So I took off the rear fender pan & fuel tank, along with removing the mowing deck. It didn't take long to see exactly why it is doing it. Where the axle tubes bolt to the frame, the frame is broken & all is loose. Also, the cross member at the front of the hydro is loose at the frame, and very loose where the single bolt goes into the front of the differential housing. It flexes all over the place, so when hitting uneven spots in the ground, the speed changes are even worse. But even on smooth ground it does it also, due to all the slop. Here are some pics, and I'll add video later of how loose it is.