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

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

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=43481
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Topic: Differences in Rear Axle Ratios WD/WD-45/D17

Posted By: Brian G. NY
Subject: Differences in Rear Axle Ratios WD/WD-45/D17
Date Posted: 09 Jan 2012 at 1:40pm

Going a little farther with the prior discussion of the differences in rear end ratios I calculate that, based on Dr. Allis' tooth counts these are the resultant ratios.

WD: 12T Pinion 43T Ring 3.58:1 Ratio

WD-45: 13T Pinion 43T Ring 3.31:1 Ratio

WD-45D & D-17: 9T Pinion 35T Ring 3.89:1 Ratio

Last year I went thru the parts books and determined that a D-17 Tranny output shaft/pinion gear is (as Dr. Allis states) the same as the WD-45D and that the D-17 ring gear will bolt right in to the WD-45 (gas) rear end.

Of course I didn't know the actual tooth count at the time!

Based on this info, a friend of mine bought a used set of D-17 gears and made the change to his WD-45. Everything bolted up nicely.

He wanted to slow it down as he used it for spraying his orchard.

I asked him if he noticed a difference and he only says" well, it's hard to tell!"

You know how non-committal some guys can be. LOL

The difference has got to be significant!

Compare it to changing your "Hot Rod" car rear end from 3.31 gears to 3.89 gears.

So, slowing down the WD-45 Gasser can be done but I'm not sure what can be done with the WD.

Replies:

Posted By: Gerald J.
Date Posted: 09 Jan 2012 at 2:36pm

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.

Posted By: CTuckerNWIL
Date Posted: 09 Jan 2012 at 4:21pm

Swapping gears out in a differential might be a possibility but knowing how to line them up is a little tricky. I use to work the gear factory at CAT in Peoria and spent some time on ring and pinion final inspection. We rolled the gears on a special fixture, with a yellow paste and shimmed both gears to match them up with a good wear pattern. The sets were engraved with the shim used so assembly people got it right the first time. If the pattern isn't right, the teeth won't take the load.

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http://www.ae-ta.com" rel="nofollow - http://www.ae-ta.com
Lena 1935 WC12xxx, Willie 1951 CA6xx Dad bought new, 1954WD45 PS, 1960 D17 NF

Posted By: Gerald J.
Date Posted: 09 Jan 2012 at 4:34pm

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.

Posted By: Don(MO)
Date Posted: 09 Jan 2012 at 5:09pm

Like Charlie said the gear set are stamped from the factory with a number on the pinion shaft like .003+ the plus stamped you will add .003 if it's stamped .003- then you will remove .003 from the shims on the pinion shaft. Now that's just a starting place you will need to blue the gear setup to get it just right.

The number of teeth on the pinion shaft or ring gear will not make a diff it is determined by the center line of the bearing on the pinion shaft to the center line of the ring gear carrier. I know that's clear as mud but after you have setup a rear end or two it will.

Don

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3 WD45's with power steering,G,D15 fork lift,D19, W-Speed Patrol, "A" Gleaner with a 330 corn head,"66" combine,roto-baler, and lots of Snap Coupler implements to make them work for their keep.

Posted By: DrAllis
Date Posted: 09 Jan 2012 at 5:18pm

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.

Posted By: Chris/CT
Date Posted: 09 Jan 2012 at 6:28pm

I have 2 of those WD45D pinion/ring w/ carrier set-up's ready to ship for anyone needing that ratio in there tractor.

Posted By: Brian G. NY
Date Posted: 09 Jan 2012 at 6:29pm

Good point Doc,

And I'm trying to figure if there is a direct corellation between the % increase in "differential" ratio and "axle" speed.

After all, if a WD has 3.58:1 ratio and the WD-45 has a 3.31:1 ratio, an effective 8% increase in speed, how could (according to the Manual) this account for a 19% increase in road speed at the same RPM; 9 vs 10.75 MPH?

It's obvious I'm no mathemetician so I guess I shouldn't try to understand? LOL

Posted By: DrAllis
Date Posted: 09 Jan 2012 at 7:00pm

On the speed charts, the WD had 12.4 x 28 tires and WD45 had 13.6 x 28's, or maybe 13.6 x 28 and 14.9 x 28's......I come up with 16% not 19%......9.0 x 100% divded by 10.75 is 83.7% or almost 16%. Sure, there's a direct connection to ring&pinion ratio and axle speed.

Posted By: Brian G. NY
Date Posted: 09 Jan 2012 at 8:58pm

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.

Like I say, I'm no mathemetician and at 70 I do realize that I'm not as smart as I once thought I was. LOL

However, 19% of 9 = 1.71 and 1.71 + 9 = 10.71; almost 10.75.

I do agree, however, that 9 is about 84% of 10.75.

On the other hand, 10.75 is about 119% of 9.

The WD-45 manual says the 45's 4th gear was 11.25 MPH with 12X28 tires. I calculate that to be about 25% faster than the original WD.

Understand now, I'm only going by what is printed in the original A-C manuals.

I guess there is a "direct connection" between ring and pinion ratio and axle speed (poor choice of words, maybe) but I think the "final drive" (bull gear) ratio has to come into play somehow? Maybe not?

I think this discussion is interesting but many probably think it's boring?!

Posted By: SteveM C/IL
Date Posted: 09 Jan 2012 at 10:38pm

I have complete trans/rear assm from 45D. I put it in my gasser for a while and I really missed the ground speed in 3rd for bush-hoggin open ground and cultivating.Changed it back after a while. It WAS noticable. On the plus side,I could pull my 4-16 SC plow in 3rd!

Posted By: Gerald J.
Date Posted: 10 Jan 2012 at 12:53am

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.

Posted By: MACK
Date Posted: 10 Jan 2012 at 7:55am

Final drive Ro. is the same on WD-D17. MACK