Need to match pinion and ring gears?

   / Need to match pinion and ring gears? #1  

hayden

Veteran Member
Joined
Sep 23, 2000
Messages
2,281
Location
VT
Tractor
Kubota L5740 cab + FEL, KX121, KX080
In another thread on the Kubota topic I've described how the input drive shaft to my B2910 front axle has sheared off. The input shaft is integral to the pinion drive gear, and it can only be purchased together with the ring gear that it drives. I've ordered the set, but am trying to understand how critical it is to replace both gears as a matched set.

What do all of you think? The workshop manual is silent on the topic. It looks like replacing the drive pinon can be done without further dissassembly of the front axle, where replacing both requires tearing down the whole front axle.

The tractor only has about 350 hrs on it, so I'm not worried about uneven wear between the new and old gears. If I had a lot more hours on the tractor, I'd definitely replace both, but in this case I wonder how important it can be.

Thoughts?
 
   / Need to match pinion and ring gears? #2  
hayden said:
...
The input shaft is integral to the pinion drive gear, and it can only be purchased together with the ring gear that it drives. I've ordered the set, but am trying to understand how critical it is to replace both gears as a matched set.
...

How critical is it? It really depends on why they are available only as a matched set and the manufacturer is the only one who can authoritatively answer that.

If it is a marketing ploy, that's one thing. But if the mating parts are matched at the factory for fit, function, dimensional tolerances, clearances, etc. that's a whole 'nother thing and should be respected.
 
   / Need to match pinion and ring gears? #3  
I would think it would be a whole lot more critical in an automobile running down the hi-way at 80mph than on a tractor that runs 10mph. Just go back with the same shims in the same place. A little wear is a good thing because you will have a little slack. I know in automobile differentials if shims aren't put back right thats where a lot of whining will come from.
 
   / Need to match pinion and ring gears? #4  
Welllll,

To do it "right" you need to replace both. Tolerances are now in tenths of a mil on down for R&P. Didn't used to be that way, but computer controlled machining and laser cut tools and spindle tolerances that are tight as a ...a...a well real tight!


However, as you only have 350 hours, you probably can skate by and only put in the broken part. BUT, you should make sure that there wasn't a binding up in the axle that caused the break in the first place. It may brake somewhere else next time.

after you do the repair, you will be back to a 50 hour maintenance schedule on the front axle. Should be no issue as that would put you at 400 hours and as I recall the front juice is changed then anyway!

jb
 
   / Need to match pinion and ring gears? #5  
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.
 
Last edited:
   / Need to match pinion and ring gears? #6  
Tom, good point. But I would like more info on how the break happened in the first place, wouldn't you? I would bet it happened trying to pull something in reverse, because the gears are weakest in that direction. Also, it may have been factory defect if going in forward direction. I used to work on heavy equipment (American cranes, truck cranes, etc.) and on the truck cranes which were on Crane Carrier truck units, they purposely put in a drive shaft that was about 18" long as the weak link to keep from tearing out transmissions and diff. which cost thousands of dollars compared to a couple hundred for new drive shaft. You would think the tractor manufacturers would do the same to keep repair costs down.
 
   / Need to match pinion and ring gears? #7  
BTDT said:
...
But I would like more info on how the break happened in the first place, wouldn't you?
...

Have to know more to do anything other than WAG it.

BTDT said:
...
they purposely put in a drive shaft that was about 18" long as the weak link to keep from tearing out transmissions and diff. which cost thousands of dollars compared to a couple hundred for new drive shaft. You would think the tractor manufacturers would do the same to keep repair costs down.

Sometimes known generically as a "fusible link". The only place I know tractor/implement manufacturers do that is the shear pins in PTO attachments. Ain't saying they don't, just that that's the only ones I know about. And yes, it would be nice if that were done where it could be done.
 
   / Need to match pinion and ring gears? #8  
If the input shaft sheared off it is not a gear problem. If it was me, and I have many years experience as an auto tech, I would visually compare the new pinion gear to the old gear. First, I would count the number of teeth and see that they are are the same. Then, as long as both parts look identical, I would do a pattern check to see how the gears mesh together and adjust with shims if possible to get the pattern correct. Once the gear pattern is correct I would install the new pinion and leave the ring gear alone. Mismatched ring and pinion gears can cause the differential to whine at certain speeds. I doubt if that would be a problem in a tractor. I wouldn't go to all the extra work of changing the ring gear unless it is absolutely necessary. Good luck.
 
   / Need to match pinion and ring gears? #9  
They MUST be replaced in sets. At the manufacturer a pinion and ring gear are set up in a fixture to run together, submurged in an oil vat and ran under load far a length of time. They are then removed, inspected and either packaged or tossed. The manufacture can not look at a pinion and tell if it will run with a certain ring gear and neither can any one else. If you replace one and not the other there is very little chance of it living for any length of time. Then you get to buy another set and do it right. If they do not run together perfectly, one or the other will start to flake of small peices and they will in turn flack off larger peices. The flakes then get into the differential and flake your spider gears, bearings and maybe wear your differential carrier. If you tractor has a limited slip differential the flakes will also get into the pack and destroy it also.
 
   / Need to match pinion and ring gears? #10  
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
 

Tractor & Equipment Auctions

2018 John Deere S780 Combine (A50657)
2018 John Deere...
2022 RAM 2500 (A50854)
2022 RAM 2500 (A50854)
2020 CATERPILLAR 289D3 SKID STEER (A51242)
2020 CATERPILLAR...
197390 (A50459)
197390 (A50459)
1999 24DTA pintle hitch trailer (A51039)
1999 24DTA pintle...
71069 (A49346)
71069 (A49346)
 
Top