Repairs The classic lost speed & power w/Tuff Torq K46BN tranny

HillsvilleScott

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  • / The classic lost speed & power w/Tuff Torq K46BN tranny
I have a 2007 Craftsman MTS 5500 (917.287420) lawn tractor. I regularly cut no more than 2 of the 8.2 acres I have here in SW Virginia, very hilly country. No such thing as "flat" around here. I bought the tractor new from a local Sears dealership and it has done very well until recently. The tractor has a 26hp V-twin B&S motor and a Tuff Torq K46BN transaxle. The tractor had developed what seems to be the classic Tuff Torq K46 lose of speed and torque for climbing hills. According to Sears, the tranny is "not serviceable" and their exploded parts diagram for the tranny consists of only outside of case parts. Nothing about the insides. I read several threads online pertaining to the K46 of which there are 58 different variations listed on TT's website, each with several different serial number ranges with possible part differences. (26 major transaxle designs available).

The first step toward solving the problem was change the drive belt. I had done that task once before. However, this time I didn't get the same positive results as last time. Getting more specific with the tranny, I read how the oil (recommended synthetic 5W50) is probably 10W30 and therefore probably not as protective. "Not serviceable" means, no drain plug or filler hole accessible while the transaxle is in the tractor. Out of the tractor there is a rubber cap that can serve both purposes. The apparent service frequency of oil change is preferably around 50 hours, once a season I guess in most cases.

I dropped the tranny, drained the oil and refilled with 2 qts of Castrol Edge (formerly 'Syntec') and re-installed the transaxle into the tractor. The same problem existed and was more like what I had read were the common complaints than I experienced to begin with, that being a lose of power after running for 15-20 minutes due to heat. The first time, I had been running for well over an hour before coming to a stand still. BTW, conventional oil thins with heat. Synthetic tends to thicken with heat. Hence the recommendation (and availability on Tuff Torq's site) of synthetic 5W50 oil as opposed to probably requested by the manufacturer, 10W30 conventional oil.

I decided after more reading to split the case and replace the three most common high mortality parts causing this power lose, the cylinder block motor, the cylinder block pump and the center case. After doing the change the 'smoke test' provided the pedals causing tractor motion in the reverse order, ie: forward pedal caused reverse and reverse pedal caused forward. The only explanation I could find was that I had in-stalled one shaft of parts containing a part referred to as the motor housing or 'ramp' upside down. Before starting this extensive surgery, I had found two different threads explaining the procedure. One was a YouTube video and the other was a now very lengthy thread originated by "LotsOfGreenGrass" (on another site) a text presentation with pictures. Adding to those the actual parts exploded diagram from Tuff Torq's site for the "K46BN" version of the tranny, I figured I had enough reference to help with parts orientation, even to the extent of special notations that it could go in upside down and to watch the orientation when re-installing.

I'll be honest, I did not take note or click a pic before I started but I left motor housing installed the same way that all three references (including TT's diagram for the K46BN) picture it as the correct position, the wide end of the block facing upward (and an opposite narrow end downward) creating the ramp or diagonal surface the five spring loaded pistons of the cylinder block motor come in contact with.

All that said, I have a call into the guru whose name was all over the several year old threads, Derrick Dalton at Tuff Torq questioning any other reason for the direction being reversed. I am not interested in just flipping over the housing, closing the case for the third time, hang it back up in the tractor's rear end for the fourth time while knowing no good reason why I should make it look different than three independent pictorials show. Wondering if Craftsman had any say in special design. Apparently that is not an unheard of practice thus the 58 suffixes of the basic K46 tranny, one of 26 different major transaxles they have available.

Anyone who has ventured into this surgery for the K46BN in a Craftsman with success, please post. Thanks in advance.
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Later the same day... I have just compared the exploded parts diagrams for my K46BN and the diagram for the K46AC, the John Deere models repaired and documented in the two online presentations. While the orientation of the motor housing for mine is displayed wide end up, which is the way I installed in my transaxle, the same part in the K46AC diagram displays it narrow side up. Conclusion: either TT has to edit at least one diagram on its website or the two tractors in the online presentations did not go in the right directions as they both have the housing upside down according to their TT parts diagram. Neither presentation mentioned any problems...after the first try.
 
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irishnotoffended

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  • / The classic lost speed & power w/Tuff Torq K46BN tranny
The K46BN diagram shows the motor housing wide side up. This will be with the narrow side facing you when you are working on it as you will be working from the bottom cover side. You are correct that the K46AC is shown the opposite way with the narrow side facing up. The orientation of the motor housing is model specific. Some have wide side up and some have it the opposite. Replace yours per the diagram of the model that you have and it should turn the correct direction.
 
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