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Discussion Starter #1 (Edited)
I started this thread with Al's advice as a place to bring a lot of the info about the Gravely 800-series limited slip differential or LSD.

You cannot tell what axle your tractor has by spinning one tire, this LSD does not work with clutches/springs and such that everyone is accustom to in a automotive style LSD. You can tell by looking at it or using it or if its 72 or older its very likely to have one.

Since the last S/N to have a LSD is 18930.
The S/N range for 1971 is 7523 to 10877 every 1971 will have a LSD from factory.
The S/N range for 1972 is 10878 to 15044 every 1972 will have a LSD from factory.
There was 5435 total built in 1973, S/N range from 15045 to 20480 so that makes 1550 with LSD and 3885 without or about 28% of 1973 have LSD.


Standard differential and side by side comparison.

LSD on the left shows how the diff side housings are machined smooth flat plates. The standard diff on the right shows the diff side housing is tapered and cast with open areas allowing you to see inside.



Standard diff. Easily showing the cast diff side covers.



LSD diff. Showing the smooth machined flat diff side covers.



It should be very easy to spot this difference when looking into the back of the trans with the engine removed.

Standard diff. Disassembled showing the cast diff side covers and the bevel cut differential side gears or sometimes refered to as axle shaft gears.



Standard diff. Showing the inside of the ring gear with the spider gears and cross shaft.



LSD differential

This shows the LSD in the case that is painted inside.



LSD diff. Showing the smooth machined flat diff side cover and the axle shaft gear. The four bolts holding everything together are much larger and pass thru four of the spur gears.





LSD diff. Showing the ring gear and the 8 spur gears inside.






This style only works when it's full of oil and spun fast, the oil inside the LSD is what provides the resistance. When each of the teeth on the 8 spur gear is full of oil everything turns together, when one wheel tries to spin the oil has to get out of the way of the corresponding/meshing gear (another spur gear or the axle gear). The only place the oil has to go is to be push inbetween the small gaps at the sides of the gears. The smaller the gear clearance and/or the thicker the oil the slower the oil can be squeezed out of the way. So jacking up the tractor and spinning one tire by hand to see if the other one turns the same direction will never happen with this style LSD (maybe if the gears was pack full of grease) and will not show you if it has a LSD. Spinning it by hand gives the oil enough time to move out of the way. Spinning a dry LSD will spin in opposite directions and very free just like a standard diff, you might by able to hear the more gears spinning in a side by side comparision. I'm not saying or recommending using a thicker oil to improve the LSD and the packed full of grease comment was just a example.

I'll add more info as it becomes available and thanks to everyone that provided pics. Jason
 

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Discussion Starter #2
Posted by Ron.

LSD diff




Regular diff

 

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Now I really get it. Good layout Jason.
 

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Posted by Ron.

LSD diff




Regular diff

So while we are inside some transaxles, and all these great pictures are side by side. . . .

Transmissions painted inside? are always/usually? What?

Only on LSD?

Also, it might be a good time to lay out the differences between these red and blue PTO clutch springs?

The blue are old style?

The red newer and heavier?

More desirable?
 

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Needs to be a sticky. Great thread Jason.
 

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So while we are inside some transaxles, and all these great pictures are side by side. . . .

Transmissions painted inside? are always/usually? What?

Only on LSD?

Also, it might be a good time to lay out the differences between these red and blue PTO clutch springs?

The blue are old style?

The red newer and heavier?

More desirable?
There is a name for the red paint but I don't recall it at the moment. It's actually a sealer to seal the pores in the cast iron casting. I've seen it used past 1973.

The blue is the older spring, rated at 750 pounds, the red is 1000 pounds. I'm not sure when the change over occurred but my guess would be about the time the 60" decks came out. Just a guess.

It's and easy upgrade if you are changing out your PTO.
 

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Discussion Starter #8
The paint inside the case is Glyptal. It's use to seal the casting and to improve oil drain back. It's sometimes used in performance automotive engines and sometimes used in some electric motors armatures.

Gravely might have used the painted cases up to around 1974 well past the last LSD. As Ron said the blue PTO spring is 750lbs the red PTO spring is 1000lbs and appeared around the time if the long frame tractors possibly to accommodate the 60" deck
 

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Great thread Jason, and nice "through the hole" pics Ron. Thanks.
Agreed, this will make a great reference thread. Good job Jason!

Don E took the LSD pic. The standard pic is my parts 16G.

So far, it looks like the "easiest" way to identify the LSD on a unknown tractor is to pull the engine and take a peek. Beats tearing into the trans, but still a pain.

There is got to be a better way!
 

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The big mystery with Limited Slip Differentials is just when did Gravely stop producing them.

I've always used the end point of Serial number 18930. This was based on a Gravely IPL for 810, 812, 814 tractors that is not dated on the cover, but on the last page is a parts list that shows the parts for a standard (open) differential and states that this is for tractors after 18930. The parts list is dated 10-15-73. Sn 18930 is a 1973 serial number.

Now, the Customer Service Update 88/89 states that the LSD ended in 1974, but this document has many errors so some people ignored that date because of the IPL with the 18930 end number.

http://www.gravelymanuals.com/pdf/810_812_814_IPL_19731015.pdf

Now there is another 810, 812, 814 IPL that is dated 7-72 that states it's for tractors prior to SN 23211. It shows ONLY the parts list for the LSD. The strange thing about this manual s that it's dated 7-72, but 23211 is a 1974 serial number! :00000060:

http://www.gravelymanuals.com/pdf/810_812_814_IPL_Before_23211_19720700.pdf

There have been tractors with serial numbers AFTER 18930 that have LSDs and seem to be original engine/tans-axle units.

These manuals are for all but the 816. As of this posting, nobody has an IPL that shows 816 tractors for 1973 and 1974.

If you have an 800 tractor with a LSD and a serial number after 18930, please post it.

If you have an IPL for an 816 from 1973 or 1974, please pos that too.
 

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Discussion Starter #12
I looked thru my IPLs and just have the same ones Ron posted. My 1974 816 is S/N 24176 with splined clutches and I believe it does not have the LSD. I have a spare trans that I bought from another 816, I don't have the S/N but it came with the liftable rear hitch and rear PTO axle block and keyed clutches and has the LSD, the casting date I think is 3-21-73



Its funny that IPL Ron posted is dated 10-15-73, that's my birthday!

Jason
 

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This is timely and useful information. I'm just getting restarted on my 800 trans rebuild, and I want to use an LSD in it.

The thing I don't get is why only four of the holes through the diff have bolts through them. I would have thought you'd want bolts through all of them, to give all eight of the internal spur gears something to ride on. Though granted, they're pretty well captured, so maybe that doesn't matter?

Is it just that only four are required to hold the two halves together, or is there something else going on?
 

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This is timely and useful information. I'm just getting restarted on my 800 trans rebuild, and I want to use an LSD in it.

The thing I don't get is why only four of the holes through the diff have bolts through them. I would have thought you'd want bolts through all of them, to give all eight of the internal spur gears something to ride on. Though granted, they're pretty well captured, so maybe that doesn't matter?

Is it just that only four are required to hold the two halves together, or is there something else going on?
The gears "float" in the carrier, swimming in the gear oil and that is actually part of how it works. Even the ones with the bolts are not really on the bolts as a "shaft". Think of it this way, the ring gear is driving two oil pumps that want to go the same speed, the more one slows down, the higher the oil pressure gets to keep them the same speed.

Sheldon
 

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Discussion Starter #16
I've only seen pics of one LSD that was broken. Looked like something got in the gears. I always wondered if adding the other four bolts would plug up the holes keeping the oil more contained and making the LSD stiffer. Anybody thinking about swaping a LSD into another tractor make sure you get the axle shafts with the LSD diff. The shafts are different than the other ones and you will also need the 800/8000 straight hubs. The tapered hubs from a G-series won't work. Jason

link to some LSD axle pics.

http://www.mytractorforum.com/showthread.php?t=410706&highlight=lsd+axle
 

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Hey
As my 816-14 is N° 15770, is there a LSD in it?
I write 816-14 as it's a 816 repowered with a 14hp Kohler, but originally was a 816
 

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The serial number says it's a '73 so maybe. I'm thinking it does but the available information says it could go either way. The best way to tell is to look at the differential. You need to pull the motor or try to get a bora scope inside.
 

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I was getting curious lately about the 810 I have sitting on blocks behind the shop. It's basically been a parts machine since I got it two years ago. After all this talk I went and looked at the serial, which is 14128-A. Looks like I may have an LSD diff. I also noticed that it looks to have been retrofitted at one point with a bolt on R/P conversion, need to pull that off. Nice discovery after 2 years of it sitting there ;)


Sent from the MTF Free App
 
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