I'm new to the macrumors forum, and wanted to share my story about my lawn tractor transmission too... I just did the K46 (actually a T40J) to K57R upgrade on my JD D110. Thank you velocityg4 for the inspiration! I picked up the K57R from Surplus Center at ~$270 + ~$50 shipping, shipped next day and got here fast and safe. The housings are identical. I opted to crack open the new unit, flip the wedge and replace the axles with my old axles - absolutely no problems there - axle mounts are identical. I also ordered some new axle seals - I highly recommend this since the teeth on the end of the axle mess with the seal/spring when you pull the axle out through them. I took apart more than I probably needed to as I was looking to replace the input drive shaft to avoid belt alignment, but found that I did not need to, since the k57R "stack" includes toothed two bolts as spacers that I can simply slip them on to reorder to match my T40J belt alignment exactly (see pic). These bolts are also great for driving the shaft with a socket on your drill to bleed the air out of the unit when refilling with oil. I tapped the mounting hole as velocityg4 did, and replaced the drive pulley with my original pulley. I also opted to replace the exterior forward/reverse and brake levers with my originals to avoid any pedal issues. I used Permatex UltraBlack for the new gasket and replaced the oil with Mobil1 5w-50. Note the k57R takes a bit less oil than the T40J - probably due to the extra pump hardware in the unit. The hardest/most time consuming parts of the task were scraping all the old gasket off of the housing and getting the roll pins out of the exterior forward/reverse and brake levers.
View attachment 1674167
I put the mod k57R back in and mowed my lawn. Everything works fine, and it does seem a bit faster (see below) especially in reverse. Most importantly, it has no problem going still going as slow as I want it to. (Well, most most importantly the transmission still works after I opened it up and messed around with it
).
According to TuffTorq, my old T40J delivers 176.4nm torque with a max input shaft speed of 3,000rpm and a 28.04:1 reduction ratio. The k57R "hopper" I picked up delivers 231nm of torque with a max input shaft speed of 3,600rpm and a 23.02:1 reduction ratio. I'm assuming this is about a 30% increase in torque and a 20% increase in output speed. Since I am using my existing old pulley, there would be an additional 20% increase in output speed based on the difference in pulley sizes. The slower drive rpm would erase 20% of the speed increase, yielding a net 20% speed increase. I'm not sure how the slower drive rpm might affect the torque output vs. greater pull on the engine, etc. I assume the extra hardware in the k57R provides some incremental output, since everything else is the same (they have the same pump and motor rebuild kits) with perhaps the exception of some of the gearing which would yield the difference in reduction ratios (I didn't count the teeth when I had both the units open).
My requirement, and reason I'm replacing my T40J and opting for a (arguably) beefier transmission is *not* mowing my 1.5 acre flat lawn in the suburbs, not even that it is less $ than a k46 rebuild kit, but what I do with it in the winter. I haul it out to my cabin in the mountains and use it to clear snow off my steep, long driveway with the John Deere 42" snowblower attachment (which I love, is built like a tank, and is a different story). I snowblow it instead of having it plowed because we use it is as a sledding run, so I need to control the snow I leave on the driveway and leave clean "walls" of snow on each side to keep sledders in bounds. I have chains for the tractor, the OEM weights, and then another ~200lbs of sandbags I lash to it to maintain traction. Add another 190lbs for me and the fact that my garage is downhill from the road (requiring me to clear the initial path through the snow on an uphill run through typically 6-12+" of snow at a time), it creates a use case way beyond the design spec of a k46 (much less a T40J). While it is typically below freezing out, heat is still the enemy - I can through clumps of snow on it and it not only steams, the snow sizzles and dances. I typically change my transmission oil every year, and have seen water in my oil (from water getting in through the breather cap?) in the past so I don't do this anymore...
This brings me to my next mod, which some (including me) may find disturbing (reader discretion advised
). I bought a 30 pack of 20x20x10mm heat sinks on Amazon for $9, got some JB weld, and got busy. My placement of the heat sinks was driven by flat spots on the housing, clearance for moving levers/arms and access to housing bolts, proximity to the internal pump, motor and oil sump, and avoiding gravity based pile up of clippings and debris around heat sinks/housing fins, and no up-facing heatsinks that debris will settle into. My first thought was this mod was that even with mounting side and down facing, the heat sinks will be a magnet for grass clippings and debris which could actually insulate instead of dissipate heat. But remember my use case, I'm not going to run into heat issues mowing my flat lawn, it is when I'm working in snow. A long highway speed trailer haul out to the cabin and an once over with some compressed air once a year should get the fins cleaned up for the hard work in the snow. It looks funny, but the math is compelling, ~128 square inches of additional heat dissipating surface area. Still, probably not a mod for everyone.
View attachment 1674168
All in all, I would absolutely do the k57R replacement and mods again. It is less $ than the rebuild kit, and you have to crack open the transmission anyway to do a rebuild. I looked into the Husq 348XD over the summer - it has the k66 with locking differential and a twin cylinder engine which all would be wonderful, however their snowblower attachment appears to have significant issues and I don't know what it would take in terms of mods to get my JD attachment to work with it. I've got about 160 hrs on my JD D110, so I'm going to run with that as long as I can. Wish me luck!
