Running a diff "in reverse"

I need a right angled gearbox, with about a 3:1 ratio (faster out than in). With the prices of these things for Ag use (20HP or so) I was wondering if I could use a diff, blank off one end, lock its end of the axle and drive the axle to get power out of the tail shaft.
I will use two if it does work. One will be running a large saw, the other a tractor-driven compactor. The second one will probably se several hours of use from time to time. The saw will only run briefly.
Will this work OK? I realise it will work. But are there any gotchas or long term problems in arse-face-backward driving a diff?
Any help appreciated. ***************************************************** Have you noticed that people always run from what they _need_ toward what they want?????

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It will work fine-just tack the spider gears to the side gears...
http://home.tir.com/~artemus/Roy%20Doty/Scan10051.JPG

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Ever notice that if you were stuck in the mud, and one wheel stays still (usually the one out of the mud) and one spins like crazy? I think you get the picture. Just keep one of the two axels from turning any way you can. Welded or otherwise. If you weld the spider gears together, they will BOTH spin. If thats what you want it to do (spin both I mean) then do that, ohterwise only weld one axle fast. As far as long term gotcha? Nah.. rj

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    Note that there *is* a difference in the results. If you lock one shaft and feed power in the other, the crown gear will turn at half of the speed of the input shaft, while if you tack weld the actual differential gears in the middle, both shafts and the crown gear will turn at the same speed, so you will get twice the speed out of the driveshaft port. You may want to take into account the actual reduction ratio needed and the reduction ratio of the differential to crown in what you have to see which comes closer to your needs.
    *If* the locked (tack welded) gears in the center give you the speed you want, you can pull one half-axle out cut the tube, and weld a cap on it to make the overall package somewhat smaller and neater -- and to reduce the oil running down the tube to the locked shaft.
    Also -- check which of the two axles you want to drive before cutting things off, because one will get you CW and one CCW at the driveshaft port. That can save you an extra set of gears to reverse direction.
    Good Luck,         DoN.
    

On 11 Oct 2004 23:18:28 -0400, snipped-for-privacy@d-and-d.com (DoN. Nichols) vaguely proposed a theory ......and in reply I say!:
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Ahah! Yes.
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***************************************************** Have you noticed that people always run from what they _need_ toward what they want?????

Is there an issue with the way that diff. gears are hardened? Maybe only if direction of rotation is opposite normal?? Also, pinion housings are designed to absorb non-axial torques, etc. They aren't a big hunk of cast iron just 'cause they look good, right? So a bit of care might be necessary in the design of input to drive the more flexible driveshaft with it's lack (relatively speaking) of rigidity. This might actually be an advantage for your application.
Old Nick wrote:
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Old Nick wrote:
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Of course it will work, the same as it dows when you take your foot off the gas and the momentum of the car you're driving pushes the engine forward.
But, be aware that if you do as you suggested and just freeze up one axle shaft, the speedup will only be half the rear end's "stated" final drive ratio, or closer to 1:1.5 than to 1:3.
Follow the prtevious poster's suggestion and tack weld the differential gears so they won't turn. HTH,
Jeff

"Jeff Wisnia" wrote: (clip) But, be aware that if you do as you suggested and just freeze up one axle shaft, the speedup will only be half the rear end's "stated" final drive ratio(clip) tack weld the differential gears so they won't turn. ^^^^^^^^^^^^^ If you freeze up one of the axle shafts, it is correct that the drive ratio changes by a factor of two. If you tack weld the planet gears, the ratio stays the same, BUT BOTH HALF-SHAFTS MUST ROTATE. You cannot do both, or the thing will just be locked up. If you freeze one of the axles, the differential planet gears will be forced to rotate continuously, so will waste power, and may wear out, since they were not designed to turn to turn continuously. I was once told that having tires of unequal size on the drive axle of a car causes the differential to precess, and shortens the life of the differential. Seems like this could be true to some degree.

Leo Lichtman wrote: I was once told that having tires of unequal size on the
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Oh yeah. Brings back a memory from my youth. I was working swing shift at my uncle's Texaco station. A logger came in breathing fire. The guy on the day shift had mounted a small tire on one side of his tractor and he said he could "fry an egg" on the diff, and he had just rebuilt it the week before. He had already fired the driver that bought the tire and now he was looking to kick some "stupid kid" ass....

On Mon, 11 Oct 2004 11:29:52 -0400, Jeff Wisnia
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I've never broke one when stomping on it in reverse at 35 mph in the forward direction. :o)
It would be newer in reverse.
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Yes. You can't run a diff continuously. However you aren't trying to do that, what you're using is just the crown wheel and pinion.
You can do this, and it should work pretty well, so long as you weld the bevel gears (the real "differential") up solid first. You should be able to do this by taking the oil pan off the diff and working through the hole with a stick welder. Earth to the rotating cage or a halfshaft, not the axle casing, or else you may damage the bearing races. Those bevels are _really_ badly made and they're just not designed for much use.
The crown wheel and pinion will be running in reverse. This isn't ideal and they're likely to be a bit noisy, but they should survive pretty well in "20hp" use.
I suggest you find a "fully floating" axle to use. These have a substantial wheel bearing at the outboard end that's capable of working without the diff or halfshaft in place. The lighter axles used on cars are usually semi-floating. Provided you keep the alignment right, a fully-floating axle isn't too hard to butcher or shorten - a semi-floating axle can be difficult, because of the inter-relation between the two ends of the halfshaft.
Another convenience is to find an diff (like a Land Rover) that is demountable by unbolting. Some axles (mainly Fords, IMHE) need a "spreader" clamp to dismantle them, which is a nuisance you don't need.

"Andy Dingley" (clip) You can't run a diff continuously. However you aren't trying to do that, what you're using is just the crown wheel and pinion. ^^^^^^^^^^^^ That's true if you follow the procedure you outlined (welding the pinion gears). But, I believe the OP was contemplating locking one of the half-shafts, and letting the diff rotate. This would be equivalent to turning in place, like a Bobcat, and them li'l ole gears would really spin.

You've got the correct answer in a couple of responses. Weld the spiders and you get the actual ratio of the ring and pinion. Lock the non-powered axle and you 1/2 the ratio of the ring and pinion. You can't do both! Note that if you lock the axle and require the spider gears to revolve in constant motion against the carrier and pins they will fail in a short time. The spider gears are only designed to allow the inner and outer tire to revolve at a slightly different rate when going around corners. Going straight down the road with tires of equal rolling radius there is no relative motion in the spider gears. They have no real bearings in them to allow constant motion. lg no neat sig line
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vaguely proposed a theory ......and in reply I say!:
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One reply. If I tried to answer all the help I'd never get away! <G>
Well....rcm does it again! <G>
Thanks a heap, guys.
I had forgotten about the ratio halving, had not even realised that the idler gears were so "delicate". That's just the sort of gotcha I was looking for and thanks a lot.
Fully floating and semi-floating. hmmmm need to look into that.
and http://home.tir.com/~artemus/Roy%20Doty/Scan10051.JPG
What the....? I see the diff buried there in the middle, but what the...? <G>
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***************************************************** Have you noticed that people always run from what they _need_ toward what they want?????

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That was a test rig to run a transaxle. Those were Westinghouse dynamometers, a 400 HP input and two 200 HP outputs (if I remember correctly).
If I get a chance I'll upload another pic of a rig used to run carrier fatigue and differential cycling durability on rear axles. It used a 125 HP induction motor, a magnetic coupling, and a Falk marine gearbox to drive the pinion of the test axle. The outputs shafts were coupled to a tractor axle (driven reverse, by the way) via sprokets and chains The tractor axle pinion was connected to a 200 HP inductor dynamometer. A microphone was taped to one of the axle tubes and the gear noise was monitored until a "pop" was heard. That meant a pinion or ring gear tooth had cracked. If you didn't shut it down you had a real mess in a few more minutes...

proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email
OK. Thanks. It sort of looked as if it would disappear up its own fundamental, with the same whwtvers on every shaft! <G>
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***************************************************** Have you noticed that people always run from what they _need_ toward what they want?????

Old Nick wrote:
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I'm coming in to this one late, but here goes anyway.
Do a search for the term "junkyard hammer" or "junk yard power hammer". There are a lot of blacksmiths out there that have built their own power hammers, using a rear axle/diff as the basis of the power transmission.
IIRC the basics involved the power input though the driveshaft, output to the hammer off of one wheel, and the control of the drive via the brake mechanism off the opposite end.
You should get an idea of what can be done, perhaps.
Cheers Trevor Jones

On Sat, 23 Oct 2004 10:00:36 -0600, Trevor Jones
......and in reply I say!:
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hmmm...now you've done it! I see the possibility of application to yet another crazy scheme! D'Oh! <G>
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***************************************************** Have you noticed that people always run from what they _need_ toward what they want?????