What causes the worm gear in a Ross steering box to get chipped up?

[NascarFastcar]

Years ago I was putting a 982 together and discovered the worm drive in the steering box was all chipped up. The picture shows a John Deere shaft above it as the previous owner though it was going to work.
I ended up installing a new cam follower and sanding down the chips in the worm drive and it worked. But ultimately I found a steering column out of a 1912 that was like new and have been using it since.

My question is what causes those serve chips along the worm drive? As these 982 steering shafts are getting hard to find I want to prevent the new one from suffering the same fate. I don't know the history of the 982 I got it. But it seems to have lived a hard life as there were also cracks in the frame.

I only use the tractor to plow the driveway and I'm gentle as can be. I always try to turn while in motion and never force the steering. I often check to make sure the cam follower is tight and haven't moved. But what would cause the chipping along the top of the worm drive.

I have attached a file below showing the original worm drive and that John Deere shaft above. The one out of the 1912 looked as good as that Deere shaft when I installed.

[garydee]

Looking at all 3 pictures and comparing them shows that there is a visual difference in the groove around each of the worm gears. If the cam follower is set where the groove is wider, it would be set deeper into the worm gear. When the steering wheel is turned and the cam follower is in an area where the groove is slightly narrower, it will exert more pressure on the outer edge of the worm gear channel possibly causing it to fracture. Another possibility could be end play in the box...or not enough lubricant.

Excess play in the steering is not necessarily something you want to have, however a very slight amount might prevent the unit from fracturing.

I have rebuilt two units...neither had any damage fortunately. Both tractors had a bit more end play than I preferred, so when they were rebuilt and reinstalled in the Cubs, I raised the front axle and adjusted the steering cam follower so there were no points where it felt like there was even minute resistance when turning the wheels. The result was acceptable with only the slightest play in the steering.

The slight excess play is a small price to pay to make things last, especially since the Ross units are getting more expensive and harder to find.

[NascarFastcar]

Originally Posted by garydee

Looking at all 3 pictures and comparing them shows that there is a visual difference in the groove around each of the worm gears. If the cam follower is set where the groove is wider, it would be set deeper into the worm gear. When the steering wheel is turned and the cam follower is in an area where the groove is slightly narrower, it will exert more pressure on the outer edge of the worm gear channel possibly causing it to fracture. Another possibility could be end play in the box...or not enough lubricant.

Excess play in the steering is not necessarily something you want to have, however a very slight amount might prevent the unit from fracturing.

I have rebuilt two units...neither had any damage fortunately. Both tractors had a bit more end play than I preferred, so when they were rebuilt and reinstalled in the Cubs, I raised the front axle and adjusted the steering cam follower so there were no points where it felt like there was even minute resistance when turning the wheels. The result was acceptable with only the slightest play in the steering.

The slight excess play is a small price to pay to make things last, especially since the Ross units are getting more expensive and harder to find.

These pictures are from 5 years ago when I was putting the tractor together. It was completely disassembled. But it looks like it originally lived a hard life. There were cracks in the frame from the engine plate mount holes up along the sides. So I don't know exactly what it was being used for. I repaired all of that back then and like I said I was able to locate a like new steering gear from a 1912.
When before I put the new steering gear in I followed the instructions for a rebuild and did replace the ball bearings and added a new follower. Everything was bench adjusted to specs. Shaft tension and the pinion plate, came follower was bottomed out and backed out 1/8 turn etc. I have super smooth steering since and keep it lubed and try not to force the wheels or anything while not in motion.
But I do plow my small drive with a haban 54 blade and that's about it.
I just want to take precautions to prevent what happend to the original steering. I do disconnect the tie rods every now and then and make sure it still feels smooth and that the cam hasn't backed out.