Main transmission shaft backlash

Anonymous-0 · Sep 22, 2009

As a new member to this forum, I have a question I hope someone can answer. I was plowing snow last winter and my transmission started knocking. I split my tractor in two and found what the problem was. The bearing between the main transmission shaft and the transmission drive shaft was bad and the nose of the main shaft was damaged. I purchased a used main shaft today and and a drive shaft. The main shaft is mounted at the rear of the transmission with a triangular plate. there are several shims under this plate which set the gear backlash. Since I am replacing the main shaft with a different one from a different tractor. I need to set the backlash by adding or subtracting shims. I don,t know what the backlash specs are. If anyone knows this, please let me know. Thanks, Gordon Mercer, Spearfish, SD

CenTex Farmall · Sep 22, 2009

How bad exactly is the damage to the old input shaft? Sometimes the bearing race inside the input shaft will take all the beating and is good to go with a new race.

The reason I ask is that after 50+ years the gears will have developed a wear pattern unique to themselves and you can expect there to be some whine once you get going again. It won't hurt anything, but just be aware that you will likely get some noise.

As for the ring and pinion, if it was my tractor I would try my best to match up the existing patterns on the gear rather than set the specified backlash. Some of the tractors I've seen had obvious wear on this gear set and some are hardly noticeable.

Look very closely at the pinion and look for a slightly depressed area that is more or less centered on the teeth where the ring gear teeth contact vs. the extreme ends of the gear teeth where there will be no wear.

What is likely is that in order to get the backlash "in spec" (without touching the carrier shims) you will have to shim the pinion so far to the rear that the actual contact points on the gear teeth will be on a high spot and the load will be highly concentrated and be more likely to result in tooth failure. In order to try to hit the specs properly you will also have to shim the carrier left and right.

Certainly it is better to have the backlash within spec than not, but if I had to choose, due to combined wear between the ring and the pinion, I would go for a best match of the pattern.

Having more backlash than what the book says is not nearly as bad as it sounds. Since the tractor is under a steady load for the overwhelming majority of the time, the gear teeth are not ratcheting back and forth.

Before I forget, to answer your original question the backlash is .008 to .012

Gmercer · Sep 23, 2009

(quoted from post at 19:45:06 09/22/09) How bad exactly is the damage to the old input shaft? Sometimes the bearing race inside the input shaft will take all the beating and is good to go with a new race.

The reason I ask is that after 50+ years the gears will have developed a wear pattern unique to themselves and you can expect there to be some whine once you get going again. It won't hurt anything, but just be aware that you will likely get some noise.

As for the ring and pinion, if it was my tractor I would try my best to match up the existing patterns on the gear rather than set the specified backlash. Some of the tractors I've seen had obvious wear on this gear set and some are hardly noticeable.

Look very closely at the pinion and look for a slightly depressed area that is more or less centered on the teeth where the ring gear teeth contact vs. the extreme ends of the gear teeth where there will be no wear.

What is likely is that in order to get the backlash "in spec" (without touching the carrier shims) you will have to shim the pinion so far to the rear that the actual contact points on the gear teeth will be on a high spot and the load will be highly concentrated and be more likely to result in tooth failure. In order to try to hit the specs properly you will also have to shim the carrier left and right.

Certainly it is better to have the backlash within spec than not, but if I had to choose, due to combined wear between the ring and the pinion, I would go for a best match of the pattern.

Having more backlash than what the book says is not nearly as bad as it sounds. Since the tractor is under a steady load for the overwhelming majority of the time, the gear teeth are not ratcheting back and forth.

Before I forget, to answer your original question the backlash is .008 to .012

The half inch bolt that holds the roller cage bearing on the front of the main shaft was off but still inside the back of the gear on the drive shaft since it is a blind hole. When this happened, the cage bearing moved half way off the shaft but continued to turn. the front half of the nose is roughed up and the diameter is smaller than the back half. I was uncomfortable using the old shaft and putting a new $103.00 bearing on it since only half the surface of the nose would be in contact with the inner race. So, I went shopping for a shaft. I found one still in the tractor. I bought the main shaft and the drive shaft which still had the bearing and race. They looked in good shape. I understand what your saying about the wear on the gears. I hadn't thought about that but will look closely at each gear today for any wear spots. On that .008 to .012. Is that the clearance between two teeth between the ring and pinion. Thanks, Gmercer

Janicholson · Sep 23, 2009

No that is measured with a dial indicator on the perimeter of the ring gear tangent to the gear diameter. with the pinion (shaft) held still. Any tooth on the ring gear will do for the measurement, as long as the dial probe is tangent to the gear. See some diferential setup procedure in a auto or tractor manual.
I definatly agree that the pattern is far more important than the backlash. Prussian blue marking paste (in a tube) is great for reading patterns. JimN

CenTex Farmall · Sep 23, 2009

The .008 to .012 is between the gear teeth and as Jim is saying it is measured by using a dial indicator with a magnetic base set up to read off of a gear tooth.
You want the dial indicator set up to be perpendicular to the gear teeth and the ring gear is the most practical to use.

CenTex Farmall · Sep 23, 2009

For sure your original mainshaft is now junk. You're doing the right thing to replace it. I am just wondering if you can use your original input shaft (if you can extract the race out of it).

Gmercer · Sep 23, 2009

Thanks, I Googled "measuring backlash" under images and saw several examples of the procedure using a magnetic base dial indicator. I have one so I will check the backlash with it. I havenn't checked the teeth yet but will probably set it according to the wear pattern. I think I'll have to jack the back of the tractor half up in order to turn the ring gear. Not sure if I need both wheels off the ground or just one. I'll try to locate some blue paste. Gmercer

Gmercer · Sep 23, 2009

I haven't tried removing the race from the rear of the input shaft. It's the only thing left in there. Since the input shaft with a good race was with the main shaft at the salvage yard, I bought both pieces which match up and are in good shape. I'm not going to buy a new bearing. I probably could have saved money by buying just the main shaft and a new bearing. About $35. But I decided to buy both pieces and eliminate the trouble of removing the old race and pressing the new one in. Thanks for all the help. I'll post updates. I'm ordering oil seals and gaskets today to get ready for the reassembly. It's been an interesting project so far. If I'm succesfull, I'll be buying a new manifold and battery box next. Gmercer

Owen Aaland · Sep 23, 2009

To remove the outer race inside the input gear, remove the front bearings from the gear. There are two holes in the gear so that you can use a punch to drive the race out of the gear.

CenTex Farmall · Sep 23, 2009

I see no problem with using the bearing you got with the set as long as it checks out. Good luck and have fun!

Main transmission shaft backlash

Anonymous-0

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CenTex Farmall

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Gmercer

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Janicholson

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CenTex Farmall

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CenTex Farmall

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Gmercer

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Gmercer

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Owen Aaland

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CenTex Farmall

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