2/1/2002
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Repairing John Deere Drive Axles
By Paul Savadin
Four years ago, a customer asked me if I would be interested in repairing some John Deere tractor axles. My first concern was if they would hold up. I consider myself a pretty good welder and have often repaired some race car and passenger vehicle axles with great success. A tractor, like a John Deere 4850, is a monster of a tractor, and I could only imagine the load on the front wheel drive axles. My first instinct was to pass on this project. Although all the axles needed was about a .030˝ overlay of weld, I was not sure that the heat wouldn’t cause the axles to fail. I told the customer that I would have to think about it for a few days, but I finally decided to give it a try.
On a John Deere 4850 tractor with MFWD (mechanical front wheel drive) each front wheel is driven by two axles, a short and a long one. The long axle goes to the front wheel drive unit, and the short axle goes to the front wheel. There are two axles per wheel for a total of four axles for the front wheel drive. These axles run in a sleeve in oil, and when they wear, they will leak oil. Frankie Kauffmann from Hondo Ag Supply in Hondo, TX, told me that when the axle seals begin to leak, the seals need to be replaced. However, when the new seals still leak, then the axles themselves must be replaced or reconditioned.
Kauffmann said that most axles on which the seal goes bad have been in use for 10 to 15 years. The axles that we have repaired have been in use now for about four years with no failures.
Initially, my biggest concern with the project was that the axle would warp or bend from the welding. The area to be welded is a 1.5733˝ OD with a length of about 3.500˝. To minimize the amount of bend from the welding heat, I decided to divide the 1.5735˝ OD into three sections of the weld. In other words, I welded an area 3.500˝ long and a little more than 5/8˝ wide. From there, I would move to the opposite side and weld an area, then rotate the axle again and weld a third area. This practice allows for the weld not to pull the axle in one direction, but when it bends in one direction from the weld, welding on the opposite side pulls it back to where it is straight again. I used stainless 308 1/16˝ diameter welding rod and a Miller Tig welding machine. I use stainless for most of the welding I do, and I have had excellent success using this rod.
After the axle had cooled and it was checked for bend, it was determined that the axle was off by .010˝. This is a very small amount of bend, and since we put on about .040˝ or more of weld, the surface will clean up to standard size without straightening. The majority of the time, the axle will not bend more than .015˝, which will grind out with no problem. I prefer doing this rather than beating or pressing the axle to get it straight. After the axle has cooled, it is ready to grind.
The correct sequence of applying the weld is as follows:
Weld the first pass of Tig using 308 stainless 1/16˝ rod on the yoke end of the axle. Weld all the way around up to the radius by the yoke.
Weld a second pass around the first weld you laid down near the radius to widen the first pass.
Move to the left of the yoke at the end of the surface to be repaired and lay down a pass of weld around that end.
Lay a second pass around that end to widen it.
Now, fill half the distance from the weld you placed by the yoke to the left of the yoke. Make this weld by going from right-to-left, side-to-side, for about half the width of the surface to be welded. Weld an area about 5/8˝ and then flip the axle and weld on the other side. Do this in about three places to minimize the bend from the welding heat.
After you weld the area closest to the yoke, then weld the last half using the same procedure. Let the axle cool and check it for bend, and you are then ready to grind.
Set the axle up in the grinder by placing the splined end of the axle in the head stock. Place a dead center in the tail stock chuck. Be sure to dial indicate the center in the tail stock to where it runs true. Place the center in the tail stock in the center in the yoke end of the axle. Then indicate the axle on the head stock side. You are now ready to grind.
Grind the area closest to the yoke, on the right, first. Grind to .010˝ above standard size, which will be 1.5835˝. I do this using a 1˝ wheel. It may be necessary for you to sweep sideways. I prefer plunging straight in as the stainless material will wear the side or radius of your wheel.
Once you get the right side to within .010˝ of standard, then grind the rest of the weld on the left to .010˝ also. You will now need to redress your wheel to do the final grind to size. Again, start at the right and go to 1.5735˝ which is the finished size. Then move to the left and go to finished size. I prefer to plunge grind as I can hold the size better. Sweeping I sometimes lose a little size so the plunge works best for me.
Check the axle for size. You can now give it a light polish and you are done. To weld one axle takes me about 15 minutes. To set it up in the grinder and grind it to size takes me about 20 minutes. I have been charging $50 per axle. I have no idea what a new axle costs but knowing John Deere, they are not cheap. I would say that you can probably get from $75 to $100 for one axle. At the rate I do them, I make about $85 per hour, and that keeps me happy.
One nice touch is to shot peen the axle after it has been welded. This removes the blue from the weld and just gives you a nicer looking product. There are thousands of these 4850 John Deere MFWD tractors all around the country that will need axle repairs. That means some good profit for any shop willing to use their grinder to tackle this niche market opportunity.
Paul Savadin
Contributing Editor
psavadin@engine-builder.com