Need to match pinion and ring gears?

[RobJ]

I agree with Whitetiger that theymust be replaced in sets. A very slight mismatch results in enormous forces being carried by a very small amount of tooth contact area. You cannot determine this visually. I believe usually the two parts are "blued" and run together as a set to see contact area. Whining is the least of the problem.

Andy

Have you guys actually set up a gear set? I have, many, it's not rocket science. You need a dial indicator for end play, and some marking compound, most people use grease. I don't know if Kubota uses a crush sleeve or not, that's used to set the pinion bearing preload. Then shims behind the pinion are used to set the gear mesh. The contact area is supposed to be in the middle of gear, It's checked with the human eye, there is not full surface contact like straight gears. With CNC machining these days and computer checking the machining, I bet they just come off the machine and straight into a box.

Now with that said, if I had to buy a complete set I would look hard at what is needed to install the complete set, but would not feel bad about just replacing one. But this is on my personal tractor, if helping a friend I would replace both. OK so do as I say...not as I do. sometimes.

But remember this is a 10mph tractor not a race car. And the ring and pinion are probably the strongest points in the 4wd system. We can see that because the shaft twisted off.

Good Luck,
Rob

 

[RobJ]

Too many unknown variables to analyze precisely, but don't forget that wear and failure in a set of meshed gears is more a function of the pressure developed at the mating surface of the teeth than it is of raw speed.

I don't know what power is being transmitted through the ring and pinion in either of the two cases mentioned, but remember that for the same HP, higher speed means lower torque and tooth surface pressure. In other words, if 50 HP is being transmitted to the wheels in both cases, the 80 MPH gears are only seeing 1/8 the load the 10 MPH gears are seeing. Assuming, of course, the same sized gears in both cases.

Tom, since I don;t know I have to ask...what's your avatar a picture of? It looks important but i haven't got a clue.

I did look up your occupation, like that, my son is heading to Texas A&M next year for that.

 

[dbdartman]

Rob, that's the Navy insignia. Coast Guard insignia is similar, but the CG eagle looks less like a crow & more like an eagle (just a light-hearted little "jab in the ribs" thing that happens between squids & shallow water sailors).

Back on-topic: I'd go through the trouble of changing the set rather than HOPING the new pinion will not adversly effect the old ring gear. In other words, I'd rather do it right the first time than do it over again!

 

[scott_vt]

Just to add a bit more to this gear thread, years ago I worked for an outfit that built gear cases amongst other heavy machinery. On the top of the line helical and herringbone gear cases we would actually run the mating gears together in a lapping pit with copious amounts of lapping compound. This all happened years ago before the real precise machining capabilities of today. By going through this process, we were able to reduce the running noise level, and insure lifetime wear on the gears !

On to the question of this thread. I believe I would be inclined to get a matched set unless it was cost prohibitive, and if the cost was a major factor then I would look at the amount of time on the tractor. Which I believe someone stated was minimal. In that case I would try to replace just the broken gear !

Years ago after we had lapped the mating gears together, we would completely clean them and then use high spot blue and red lead to check the mating contact surface area before final assembly.

 

[Soundguy]

I agree with Whitetiger that theymust be replaced in sets. A very slight mismatch results in enormous forces being carried by a very small amount of tooth contact area. You cannot determine this visually. I believe usually the two parts are "blued" and run together as a set to see contact area. Whining is the least of the problem.

Andy

Hey.. now.. that's an idea.. he can get some bluing, and paint the teeth, and then just spray / squirt some grease or gaer lube in there and spin them over in the sump a few times and look at the wear patterns. The blue scrapes off rear easille with wear. It should be real obvious, real fast where the high and low spots are.

All that said... I know of lots of old fords that were not run with matched gears that are still running today... However.. it's doubtfull thet they will get the amount of work out of those gears as if they were matched.

The correct advice is of course to repalce as a set. If this were a beater 'seldom used' tractor.. etc.. I may not. If it was newish or in med-heavy duty and up.. i think I'd bite the bullet and do both.

Lastly.. with only 350 hours on the old ring gear.. i really wonder how much wear it has accrued.. considering that running gear may well go for 4000-10000 hours and still be good...

Soundguy

 

[RobJ]

Lastly.. with only 350 hours on the old ring gear.. i really wonder how much wear it has accrued.. considering that running gear may well go for 4000-10000 hours and still be good...

Soundguy

Good one, how many cars and light trucks (or 18-wheelers) have 200-300k++ on the odometer and are still running and don't even leak!!

Look at it this way, 350 hours, If you got on your tractor and drove it none stop you'd reach 350 hours in 14.58 days. And you should have changed the oil 4 times!! (50,100,200,300 hours). I'm sure some of the large combines and pickers run 24/7 certain times of the year.

 

[hayden]

Thanks for all the input.

Several people wondered how this broke. I believe it's entirely the result of a shoddy previous repair, not defective materials or abuse. The front axle was previously removed/replaced to replace the drive shaft cover. It appears that during replacement the mechanic cross threaded one of the 4 main mounting bolts that hold the axle to the frame, and decided that 3 bolts was good enough. I've concluded this because I found one bolt missing, and I found mangled threads in the receiving nut which is welded to the frame. The result of all this is that the axle had worked lose and was rotating around the mounting point. There is no U-joint at the input shaft, so the poor input shaft was getting both lateral bending and torque forces at the same time. I'm not surprised it broke. I only wish I had noticed the movement in the axle mount before it broke.

The ring and pinion gears are only available as a set, so I have to buy them both. It's really an issue of how much more the axle has to be torn down to replace both gears.

After all this input, here's what I'm leaning towards. When the gears come in I'll look them over to see if there are any matching numbers or marks to suggest that they are gears made for each other. If they appear to be, then I'll probably replace both. Otherwise I'll likely conclude that selling them together is more about matched wear than about two gears that are made for each other (does that make sense?). I think with precision machining, it's much more about matched wear, not about gears that are made for each other. Since I only have 350 hrs, which is nothing, I'm not worried too much about wear.

 

[Tom_Veatch]

Navy? NAVY???? Oh, we're in trouble now!!!!!

Hhhmp..squid, indeed. I might buy "Leatherneck", "Gyrene", or even "Jarhead" (if said with a smile), but "SQUID". Them's fightin' words.

Actually, it's the Eagle, Globe, and Anchor of the USMC. The particular style in the avatar (silver and gold) is representative of the emblem used on the dress uniforms. The style used on the khaki, tropical, and green uniforms is a dark bronze color.

I served with the 1st and 3rd Marine Divisions from 1960 through 64.

(Oh, OK. If backed into a corner, I'll admit that the USMC is part of the Navy, but please don't quote me on that.)

 

[AndyMA]

$1600 is what it cost me on a 2120 when a dealer did not shim a set of front differential gears correctly and they had to be replaced twice. The shim error was very small but changed the contact area radically. I really don't think that the fact we are talking low speed allows us to be sloppy. I still vote for changing them out as a set.

Andy

 

[hayden]

I did a little more work on it tonight, mostly focused on re-tapping the crossed threads for the mounting nut so the axle can be remounted correctly.

I tried tried removing the pinion shaft, and it turns out you can't get a drift against it without removing the drive shafts, which means I really need to tear it all down anyway. Given this, I'll probably end up replacing both gears.

All the adjustment is via shims that set the depth of the pinion shaft. The workshop manual only calls for adjusting the backlash by swapping shims. There is no other adjustment. The probability is high that the shims I have will be wrong and I'll have to order new shims, which will mean another week or more waiting for parts. I could have ordered (maybe should have) one of each available size, but with 8 different sizes, I decided not to. Maybe I'll get lucky with what I have.