Question about gear repair

[56FordGuy]

A friend of mine is restoring a John Deere model 60 tractor. He's found the differential ring gear is damaged, the original was missing about 30% of one tooth. Bought a replacement, only to find one tooth of the replacement gear is also cracked.

The gear teeth seem to be hardened. We've done a bit of reading on potential repairs, but it sounds like building up with a weld or braze would damage the heat treating of the gear. I'm a green hobbyist, so this type of repair feels very out of my league. I've included photos of the damage on both gears. Would these be considered repairable? They take a pretty good load when the tractor is moving, and the tractor has to be split in half to access them. If one was repaired, and the repair failed it's a pretty big job to get back in there.

Any advice would be appreciated!

 

[Kennyd]

Subscribed!

Hey 56FG, didn't know you where a member here as well!

 

[56FordGuy]

Hey 56FG, didn't know you where a member here as well!

After your recommendation, I am. Do more reading than posting, working on the lathe is a different ballgame from working on the anvil.

As for the gears, we've found that they're two piece gears similar to the flywheel and ring gear of an engine. The inner web is cast, the outer ring is press fit and appears to be pinned as well. Not sure if that would make a difference on repair options or not.

 

[4GSR]

You might try nickel-silver braze build up and set up on a mill and grind a flycutter to match the tooth profile. Then make an attempt to re-cut the gear tooth profile. But looking at the heavy wear from use, I doubt any repair without re-hardening the gear tooth is going to last for any period of time. Best bet is searching for a good replacement. Someone out there is bound to have one. It might be pricy though!
Don't get me wrong here. A new gear can be made, but again, the gear teeth need to be surfaced hardened for it to do any good. Suggest good allow steel like 4140-4145 that can be flame or induction harden on the teeth or 8620 that can be carburized. Ken

 

[Terrywerm]

The first thing you should ask yourself is what is this tractor going to be used for?? You indicated that he is restoring the tractor. If it is being restored for just riding around at tractor /threshing shows, IE: never putting a real load on it, I would put the original gear back in. The load on it just driving the tractor around is miniscule. The replacement gear with it's crack and damage directly in the tooth contact area should definitely NOT be put in.

Now, if he's planning to plow with it, or do some heavy pulling, such as antique tractor pulls, or maybe use some other ground engaging equipment, the gear should be replaced with a good one. You cannot properly repair either gear by brazing or welding. Heat treatment issues would definitely be a problem, and even if you were to send it out to have it heat treated again, what specs would you use??

Here is why you can probably use the original gear if the tractor will not be heavily used: The missing piece of the gear still leaves most of the normal tooth contact area intact. If this is just going to be a "Sunday tractor" that broken gear would run for decades and chances are no one would ever know that there was a problem with it. The only thing to make sure of is that the edges of the damaged area are not overly sharp or rough. Does the mating (drive) gear show any odd wear on the side that runs on the damaged side of the ring gear?? If not, you've most likely got nothing to worry about. Any idea how long it has been this way?? Probably for quite a few years!! I would be willing to bet that the damage to the broken tooth was caused by a piece of foreign material of some sort getting caught in the gears. It's broken in the wrong place for it to be from shock loading or overloading. The replacement gear on the other hand, was damaged by a shock load of some sort, no ifs ands, or buts, and it is useless.

Thanks for the good photos, though!! They made this one easy.

 

[Davet]

Just a thought - if the gear consists of a ring and a centre hub, could you not cut the rings in half and screw/bolt the two good halves onto the hub?

 

[56FordGuy]

A replacement gear would be ideal, however finding one in good shape has been difficult. Few sellers really clean them up and inspect them, they pull them out of the tractor and put them up for sale. Buying online complicates it further, because you're completely at the mercy of the seller's inspection. The hunt is still on for a good replacement though.

The tractor originally suffered a transmission problem, ended up jammed into two gears at once with a bent countershaft and a few other gears damaged as well. It then sat outside for several years before he got it and began working on it. Good used replacements for the other gears have been found, it's just this one that's been a bit more difficult. I believe the tractor will mostly be a show/ parade tractor when it's finished, but he's talked about doing some tractor pulls with it as well. I think this gear will wind up being replaced, just so it's 100% the first time.

Thanks for all the input!

 

[Terrywerm]

FordGuy, more information was good, as now we know how the gear was most likely damaged, though it doesn't really matter at this point. JD 60's were pretty common, so finding a good replacement gear might take a little time, but be patient, it will come. If you like, I can check around with a few of the guys that I know, and maybe you'll get lucky.

I often used to get laid off during the winter months and spent many winters doing heavy repairs on farm tractors for some of the farmers in the area. I rebuilt quite a few powershift transmissions, and worked on a few manuals and rear ends too. PTO gears seemed to be a popular item too, but you still had to split the tractor most of the time. When I was younger the mere thought of splitting a tractor was quite daunting, especially with the larger, modern tractors. After doing a few of them the job gets a whole bunch easier, but it really helps to have the right kind of splitting stands. I no longer have mine, but the second set I had were what were referred to as the 'track type'. You would jack the entire tractor off the ground using the stands, then split it, rolling the front half away from the rear half on inverted angle iron tracks. Getting the two halves back together was a breeze that way, as everything lined right up. My original set of splitting stands had plain old swivel casters and would allow you to misalign the two halves, and it took three men and a small boy to get one half mated back up to the other again, and even then only with quite a bit of cussing. The track type set was worth every penny it cost me to build them!

ON EDIT: Where did you get the replacement gear?? My son restores tractors as a part time sideline - and he knows quite a few people in the business. Some of the suppliers that he knows part tractors out all the time. If you happened to get the replacement from one of the guys that he knows, they all have replacement guarantees if a part is bad when you receive it.

 

[NoShopSkills]

I might be late to the dance with this post, but since my main purpose for joining had to do with several damaged/destroyed gear repair projects, I thought I'd share how I "fixed" one of the bevel pinions that tightens my 3-jaw lathe chuck. Long before me it looks like someone either started with the key in (ouch), or banged on the key with a hammer and sheared off one of the teeth that drives the spiral plate. It still worked, but it would bind and jump as you opened and closed the chuck. Didn't like that and knew that at some point I'd be wanting more torque at that same spot where the gear tooth was sheared off and that it would eventually cause trouble.


Armed with a file for testing hardness and a magnet to determine composition, I guessed it would be O.K. to tig on a little stainless filler rod.



Next, I got out the smaller files I own and started profiling the part. Had to reassemble and disassemble & file some more several times but it's almost as good as new now. I've been able to use the chuck almost continuously with none of the jump and bind that was going on before the repair.

 

[Terrywerm]

Nice work, NoShop! I think you chose your screen name incorrectly, as your work shows both patience and skill. The type of repair that you performed may work well for a spider gear in a lathe chuck, but would probably not work too well on a gear like FordGuy is looking to repair. Too much risk of damaging the heat treatment in the neighboring gear teeth, possibly resulting in a larger failure. It would work for a while, for certain, but I have my doubts about it holding up for a long time under heavy stress such as from tractor pulls. If it were a cast iron gear, other options would be available, but heat treated steel changes everything.

Don't be afraid to post other things you have done, as it appears that you have better skills than you give yourself credit for!