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OrangeMetalGuy

Anyone contemplated this mod (diff lock)?

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OrangeMetalGuy
It sure would be nice to be able to lock (on demand) the differential on a large-frame. Probably no way to accomplish this, but interesting to ponder.

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HubbardRA
It is easy to lock it full-time. There is also a way to tighten up the limited slip in one of the RBTs. I don't really have a way to lock it on demand. It could probably be done, but would take some engineering and fabrication.

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MikeES
Lock the differential and these tractors are almost impossible to turn. You will need an acre and you will tear up the lawn...but if you are only going straight :)

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CarlH
Locking the differential is very simple. Just reverse the gear keyed to the axle inside the differential. Learned that from a tractor I with a bad case of Previous Owner Disease. 8C

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a-cman
You just need to get yourself a Sunstar or Ultima, then you'll have the differential lock and 2 speed rear, and also power steering. I went from a 900 sreies Allis to a Simplicity Sunstar about 5 years ago, and I'm still amazed at the power and stength built in to the machine.

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SmilinSam
To make a diff lock for a 700/900 series you would have to make a steel ring to attach to the diff itself using longer bolts, and then fabricate a spring loaded heavy locking pin to go from that ring into a matching hole , or holes in the cast axle hub. Probably would be best to have two pins, on opposite sides of the ring to reduce uneven stress on the ring and differential.

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MikeES
You can also disassemble the diff and put a washer under each of the springs (newer diffs) and this will make the differential more positive without making it a complete lock.

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OrangeMetalGuy
There's a tutorial here somewhere on this. Basically you add a washer under the springs which adds add'l tension, meaning they push more (hence tightening the differential).

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78kitty
Here's the tutorial or explanation of shimming the rear diff with washers... [url]http://www.simpletractors.com/club2/topic.asp?ARCHIVE=true&TOPIC_ID=106811[/url]

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HubbardRA
If you are using an RBT, the shimming of the springs is all you need. I did the first one over 20 years ago and it is still working great. I first tried the locked diff, but that was a pain to turn any sharp turns. I then came up with the idea of shimming of the springs and that worked out great. It pulls like it is locked in slick situations, but when you want to turn sharply, it will slip just enough to prevent one tire from tearing up the turf. I used this setup on a pulling tractor for over twenty years. The tractor no longer competes, but we still use it to do work when we need it. Have not had the slightest problem with the shimmed diff, since we did it.

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HubbardRA
Mike, Depending on the washers that you use, you may have to do some grinding on them to make them fit inside the curve of the housing. Other than that, it is an easy job.

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Burntime
Any idea what thickness so I do not get full lockup? Just looking for something that will pull a trailer up hill a little better and take the snowthrower thru a little better...

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rokon2813
I'm thinking you should start with a standard washer. I would think the tension in the springs would change slightly with age and use so it would be hard to get a measurement. Regardless, a standard washer would not completely compress the springs so it will still work to some extent. I would think to completely lock the diff you would have to fully compress the springs so there is no room for movement JMO

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HubbardRA
Mike, Full lock is easier to do than the shimming. All you have to do is reverse the gear on the axle and it will lock up the diff. I used just a handful of standard washers from the hardware store. I have noticed lately that there is some variation in the thickness of the washers at the hardware store. I would suggest that you pick out a set that looks like they are all about the same thickness. A little variation will not hurt anything. By the way, you will not be able to completely lock up the diff by adding washers unless you put so much thickness under the springs that the coils bind up and become a solid cylinder. Even then it may not completely lock the diff. The friction that causes the limited slip feature is between the spyder gears and the housing. You can only put a certain amount of pressure on these and still be able to get the two pieces of the housing to bolt completely together. I like to assemble the diff with the threaded portion of the large bolts toward the axle tube flange so that I can completely assemble the diff before putting it on the axle tube. That way you can just slide the threaded bolts through the flange and put the nuts on the back side of the flange. It is much easier to do the diff assembly on the bench than on the tractor.

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Burntime
I am only looking to make it a little more tight. Being that I cut the lawn I do not want full posi... I noticed the new rear end I put in actually does a better job then the last... My old was a one wheel wonder, the new does kinda lock up... Wonder if someone was in it already?

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jmhusby
Have D.L. on the Prestige and had it on the Landlord Deluxe and comes in very handy cutting grass on the hillside and getting out of tight spots blowing snow. Wish the Agco Allis 1920H had it but want to find a set of wheel weights to put on it or add fluid to the tires. Of course a 4 X 4 Prestige or Legacey would solve the problem.:D:D:D:D

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sammiefish
when I reassembled mine I went to a local fastener (screw/bolt) place. They had what was called machine bushing washers. they were a little thinner than the comparable standard ISO washers. They were smoother as well and appeared to be of a better quality steel and not zinc coated. I dont know for sure but I imagine that is what was OEM in that application. In mine I just matched the thickness that was in there originally which was 3 of these bushings... probably just a little thicker than a single ISO. At the time Rod reminded me that the only way to be sure the diff would work properly is to use only one washer so I tried to "match" the thickness of one ISO washer as well as predict and duplicate what was originally in there. If I were to modify to "lock" the diff I would support and suggest you take Rods suggestion of reversing the gear.... I dont think it would be a good idea to "over shim"

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HubbardRA
Chris, I think you have the washers on the axle shaft that position the gear mixed up with the washers that we are talking about putting under the springs in the diff to tighten up the limited slip. Your problem originally was a locked diff because the axle gear was pushed too far toward the right hub and it was engaging with both sets of differential spider gears. That is why I said to put only one shim washer behind the gear and have the rest outboard between the axle gear and the hub gear. We are talking about tightening the friction of the limited slip by putting a washer under each spider gear spring in the diff (there currently is none there)to produce more force when the spring is compressed. This produces more friction to resist the rotation of the spider gear. Thus the diff will be more resistant to only spinning only one wheel when a difference in traction between the two rear wheels occurs.

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