Operation in 4 Wheel Drive?

Harrygoodwrench · Dec 27, 2004

Bored??????????who me?????????no way. I just think this subject went off on a tangent with "open" differentials, "Limited" slip diffs, "Locking" diffs. All this did was confuse those that were already confused. Soooooooooo lets try to un-confuse this. Forget limited slip, locking, open closed or whoever just came out of the closet.
We are dealing with real old technology. Way back to Henry Ford days. The rear differential on your/my tractor regardless of brand is just like a old car has.
If you happen to have one wheel on ice it sits there and spins,
Why? because its designed by its gearing to send the power to the axle/wheel with the "least" resistance to turning.
Why send power to wheel with least resistance? it necessary so you can go around turns thats why.
If perhaps your placed rocks, sand under that wheel and the other wheel had less resistance to turning it would then turn/spin(hopefully the car would be out of the spot you were stuck in).
Now we are going to make this vehicle a 4WD vehicle.We add a front differential to the front which also allows the wheels to turn with steering wheel. We add a device called a transfer case that takes all the power and transfers it 50/50 to both the front and rear differentials.
Everybody happy so far? we can go anywhere BUT we have a problem. The ratio's of turning the wheels will never be the same. This is due to several reasons but mainly due to steering the vehicle. If we are on soft (snow, mud, grass, sand, anything that provides slip) no problem but on HARD surfaces we place very hard forces unto the driveline,gears etc to make the ratio's the same. End result is a possible broken component in the drivetrain.
Thats why the statement..........DO NOT OPERATE IN 4WD ON HARD SURFACES.

Now getting back to the rear diff. It does have a diff lock. Remember the diff is designed to allow different ratio's of the wheels while driving the vehicle. Well, we can mechanically LOCK them together and make them turn as one. End result Excellent traction equal 50/50 each wheel regardless of surface. Trouble is,,,,,,,,you may break something making a turn especially on a hard surface.

End of lecture, I'm tired, somebody had to work today and pay the taxes.. If you understand any of this than we can move to limited slip and lockers, etc. That is if you want.

Thanks for the thoughts JohnK about Bobby. He called Christmas day. Said his Humvee got blew up by IED while on patrol. No one hurt as the insurgents buried it too deep. He said they had to burn their underwear.

johnk · Dec 27, 2004

With all due respect Greg,
If you lived close by I would want YOU to work on my tractor because of your knowledge of these contraptions. Tractor GURU was a compliment because you do add great information to the tractor boards and thanks for your inputs...

BTW, Back in 1973 I had a Jeep Wagoneer with a Quadratrac drive that actually did have a clutch in the transfer case that would slip between front and rear wheels. Had a lockout in the glove compartment to lock the front and rear drivelines together back to the basics of our tractors.

John

greg_g · Dec 27, 2004

I'm completely on board with the "open" concept for the rear end, I've got no problem with care and feeding of the diff rear diff lock. And I acknowldege the transfer case gear assembly as the weak link, when front wheel drive is engaged.

The question that remains unaddressed, is why my front wheels rotate with seemingly equal traction - or lack of. Neither of the Jinmas nor this KAMA front drive exhibit behaviour identical to the rear drive. I can make them lose traction, but not individually. When I get into a low traction situation up front - they BOTH spin. And there is no front diff lock control. This is far more apparent on the KAMA than was on either Jinma, but then again the KM454 is almost double the horsepower.

I was boxblading snow with the KAMA this morning, on several occasions both fronts and one rear started spinning. Grabbed the diff lock lever, and had all FOUR spinning. I used snow as an example this time, as it was the most readily available "source" of low traction. But I've also observed this behaviour in gravel/dirt/mud on other occasions, hence my earlier questions.

It's clear how the rear diff lock essentially shifted the rear (open type) differential from 1 wheel drive to 2. But how is my front wheel drive performance (or lack of) consistent with the "open" differential concept, when compared to that exhibited by the rears?

//greg//

Egon · Dec 28, 2004

Greg:

Lift up the front of the tractor and disengage the four wheel drive. Rotate one of the front tires and the other should turn in the opposite direction. Indicates all is well.

Egon /forums/images/graemlins/grin.gif

greg_g · Dec 28, 2004

( Lift up the front of the tractor and disengage the four wheel drive. Rotate one of the front tires and the other should turn in the opposite direction)

Thanks Egon, what little I know on this subject does include a rudimentary understanding of planetary gears. But my questions so far have been about Jinma/KAMA operation. Are you assuming my front diff is designed the same as that on your Kubota HST?

And since the front drive activity I describe occurs with four wheel drive engaged, please explain point of this exercise on a KM454.

By the way, can anybody explain the function of a HARF gear?

//greg//

ToolManRick · Dec 28, 2004

HARF? Maybe I know it by a different name. What's HARF stand for?

greg_g · Dec 28, 2004

( HARF? Maybe I know it by a different name. What's HARF stand for? )
I wish I could provide more info Rick, Google is stumped too. There's always a chance it could be a glitch in the Chinese>English translation, but I'm at a loss to figure out any alternative interpretations.

Look at the front diff diagram (attachment), upper left corner. #34, #36,#37 comprises the planetary gear set. Standard stuff. But then look closer to the center; #25, #27, #28 are identified as components of a "harf" gearset.

If you want, I can upload a diagram of the rear diff as well. But if you take my word for it, there's no mention of "harf" - or anything even resembling "harf" - in the REAR diff parts diagram or parts list. Just the standard planetary gearset, and that's it.

In my KAMA at least, I'm wondering if this additional gearset has something to do with my front end not working like what others are calling an "open" differential.

..greg..

bluechip · Dec 28, 2004

Greg, they call that a "Half Gear" in the TS book. So I think HARF is a typo. These are the gears driven by the planetary gears, which are driven by the differntial housing driven by the knee bone connected to the shin bone...

I thin you will find that if you raise one rear wheel and one front wheel your KAMA will not move in 4wd.

I think the reason you see both fronts pulling is because the back is pushing and so the traction of the fronts stays pretty equal. If you jack up one rear wheel and chain the tractor to a big tree with the front wheel in soft dirt, I think one wheel will end up turning more than the other. Not sure this is a good idea to actually try this, might pull the tree down!

If you want to check the differential you should raise both wheels of the ground and with 4wd engaged, turn one wheel and the other will turn in the opposite direction. If you do not engage 4wd you might end up turning the driveshaft instead of the opposite wheel.

JerryG · Dec 28, 2004

Both 28s are just the gears that spline onto the axle shafts.

greg_g · Dec 28, 2004

( Greg, they call that a "Half Gear" in the TS book. So I think HARF is a typo. These are the gears driven by the planetary gears... )

I thought of that Chip, but the fact remains that there are no harf OR half gears listed as components of the KM454 rear differential. Did you look at both KAMA exploded diagrams to which I referred? I also examined diagrams of the transmission assembly, the Shaft 1 (driveshaft) assembly, the Shaft 2 (brake) assembly, and the PTO shaft assembly, and the final drive assembly - looking for a rear equivalent. No mention anywhere - of harf/half gears - except in the front diff.

Attached by the way, is the front diff exploded diagram for Mike1's JM304. Interestingly enough, that particular Jinma model doesn't seem to have that extra gearset (by any name).

The "boxblade in snow" example I described earlier is little different than your tree experiment. The tractor was completely motionless, held back by the grounded boxblade. All four wheels were spinning simultaneously. I throttled down, lifted the hydraulics to clear the boxblade, let the clutch back out, and the tractor drove right out of an otherwise immobile full traction situation.

//greg//

Harrygoodwrench · Dec 28, 2004

It is not a "planetary" gear set at all. that is a whole different set-up with a Sun gear, ring gear, and planetary(planet) gear set. Different animal all together.
These are a conventional differential gear set, there are two 'side' gears, two "Diff pinion" gears. These are housed in the diff housing which is your ring and then pinion. Guarantee,,,,,if you place in 4WD and have one front wheel on ice and one rear on ice the tractor will spin those two wheels. Now if you engage your rear diff lock now the other rear wheel will have traction. I helped a guy rebuild one of these Jinma diffs by internet and have many pics of the parts and assembly and know whats in there.
There is NO limited slip diffs in these Jinma's. Maybe, It is just a coincidence that Greg had equal traction on both front wheels and they both spun, this I don't know for sure. Unless they(Kama) do have a different system that uses a locker type for the front. This would place tremendous stress on the front shafts as they have to transfer torque thru the shafts on angles. Makes it even more critical operating on hard surfaces in 4WD if this is the case.
Attached is apic of a Jinma diff with parts labeled.

Egon · Dec 28, 2004

Greg:

If the front wheels turnin different directions when off the ground you have an open differential. If they both turn in the same direction you have locking differential or positract.

Egon

greg_g · Dec 28, 2004

( It is not a "planetary" gear set at all. that is a whole different set-up with a Sun gear, ring gear, and planetary(planet) gear set. Different animal all together.)
Wrong choice of descriptives on my part Harry, I won't let it happen again. Maybe you could let Jinma and KAMA know too, as all their parts manuals identify bits and pieces of "planet stuff" in their differentials.

Thanks for everybodys' attempts, but I guess I've just got to 'suss this one out on my own. All I can say is that there is a definite, consistent, and observable difference between the way my KAMA front drive wheels and and its rear drive wheels perform in low traction conditions. Some day I might even figger out why.

//greg//

TruChaos · Dec 28, 2004

Greg,

You're right. Today, I was pushing a pile of unsplit firewood (up to 24" dia.) with the FEL and I noticed that both front wheels were spinning but only one rear wheel. Trust me, they were under load and on semi-hard ground. I was using 4WD because I kept getting the front wheels caught in ruts and the rear wheels would spin and I would have to shift from 2WD to 4WD. By the way, engaging the axle lock in this situation only caused both rear wheels to spin.

While I don't know for sure, it appears the front axle may have some sort of "posi-traction" limited slip setup.

SPIKER · Dec 28, 2004

not sure of the KAMA but the jinmas (olderones anyhow) are of the open diff design in the front drive axel: though if you want to weld up one of the planetary gearsets then you will have posi traction permatly! /forums/images/graemlins/wink.gif this is what is done to demo derby cars when people say they welded the rear gear set. it doesn't have to be pretty either as just a gob of weld will make a big difference. this may also be why some people SEE that BOTH wheels spin under load in front as there may be a broken , bent or damaged planetary gear set. (I think that is right, the little gears shown as #36 or the gears shown as 28 in this pic posted above. the RING gear is the one shown as #38 and the pinion gear is the one on the end of the shaft # 15
http://www.tractorbynet.com/forumfiles/554609-454%20frontend.jpg

anyhow it has been many many years since I tore into any of these but I do still have a few ford 9'' rear pumpkins/3rd members setting down stairs! /forums/images/graemlins/wink.gif one is a HD with 32k miles on it the other is out of a truck which had 70 somethink K on it... seems I kept them around because I thought they may one day break in somethign I owned... (was used to owning chevies back when and the fords just plane don't break!)

MarkM /forums/images/graemlins/laugh.gif

bluechip · Dec 29, 2004

Greg,
The rear diff also has Harf gears (Half) page 79 item 17 and 18. I think the reason you saw all 4 pulling with you blox blade buried could be because traction was so similar on all 4 corners. In effect the resistance of one wheel turning is applied to the other wheel, if that makes sense. if you had 0 resistance (off the ground or on shear ice) you would get 0 drive to the other wheel, but there is always some resistance, and so that transfers through the "planetary" or spider gears to the other side. If your frond diff was locked, you could not turn without one wheel really doing a lot of digging, and I think something would bind pretty bad.

Harrygoodwrench · Dec 29, 2004

I've had my Jinma spin both fornt wheels many times pushing snowetc and it has an "open" differential. I think you guys are just making the wrong assumption that the Kama front diff is limited slip. I'd wager on it. Too many stresses on front wheels/shafts to make that way.

bluechip · Dec 29, 2004

NO! the front diff is not limited slip or posi traction or self locking on either KAMA or JINMA. The diffentials operate the same front and rear. except the rear has the locking feature.

greg_g · Dec 29, 2004

( Greg,
The rear diff also has Harf gears (Half) page 79 item 17 and 18. )

Naw, my book calls them cone gears. I do however, recall occasionally hearing one axle (of a pair) referred to as a half shaft. So adding that to an earlier JerryG statement, perhaps a more appropriate wording for the mysterious "harf" gear would be half shaft cone gear

I only used snow as the example that most can relate to this time of year. The same simultaneous 4 wheel tractive force has been observed many times since you delivered the tractor last spring. I'm not complaining mind you. I'd much rather see purchase, than spin. I was only trying to understand why the fronts seem to display more consistent parallel traction that do the rear.

I'm now ruminating that this may be related to ratio that KAMA selected for the transfer case gearset. Perhaps just the right amount of horsepower is delivered forward to make the observable difference. It would be interesting to see statistics on how different transfer case gear ratios affect the front/rear horsepower split.

//greg//

ToolManRick · Dec 29, 2004

Greg, I agree with you about the equal traction. On my Jinma with regular spider gear differentials front and rear, referred to in this thread as open diff's, I spin all four in stone or moist clay when pulling the box or pushing the bucket. If I'm on uneven ground, creating a twist down the length of the tractor I can get one side or the other to break loose, but on grades without a twist it pretty much delivers equal traction to all the wheels. I'll just pretend it has, limited slip, power-lock, a Detroit locker or one of the many others.