Differences in Rear Axle Ratios WD/WD-45/D17

What would really be effective would be the 9 tooth pinion on the 43 tooth ring. If the gear teeth are the same size and spiral angle, there would be a need for a serious spacer on the ring gear to mesh with the 9 tooth pinion, but the pitch of the teeth is probably different enough they wouldn't mesh at all and these tend to be made in sets from being ground in together so that one can't swap just one gear and get a good fit. To bad its not a Ford 8.8 or 9" housing because there may be dozen ratios available for each of those. And I'd have expected AC engineers to have shopped for stock truck gears to cut the cost so maybe that's not as wild an idea as it looks like.

Gerald J.

I've replaced bearings in a car rear end once, and then set up the mesh by bearing adjustments before the day of shims. I wanted to change gears in my '98 F150 so it would pull and I studied the procedure with the shims. I paid a hot rod axle shop to supply and fit the gears. They've run 100,000 miles without a problem so far. I know those desired wear patterns but I'm not patient enough to work them out with shims and then add .040 more shims to preload the bearings.

Changing to gears not made for the tractor might be a major task and then some. It might be easier to build a tractor from scratch or as easy.. That's why the Sherman drive in the bell housing sold well.

One other way of slowing the tractor is to go to smaller diameter rear tires at the cost of ground clearance. I considered that for my truck but I needed some ground clearance for rutted gravel roads and hiring the gears changed was cheaper than four custom rims and very low profile tires.

Then there's the final drive reductions on most vintage AC tractors. One could conceivably change those gear ratios but there is a limited selection without changing the gear centers too.

Gerald J.

Remember, the 3.89 to 1 only had to have the engine RPM's increased from 1400 to 1625 or 1650 to get the same ground speeds. ...15% of 12 MPH doesn't feel the same as 15% of 60 MPH.

Good point Doc,

I wasn't comparing the WD to the WD-45, I was comparing the early WD to the late WD. And... the manual doesn't list but one tire size for the WD; 11X28.

So far all the discussion have presumed the final drive ratio has been unchanged. It was easier for the factory to change that than the ring and pinion gears because the gears were less difficult to make.

Gerald J.