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I have a John Deere LT155 that I am in the process of servicing. I know that the K51A transmission in the mower is not "serviceable" but I have seen many threads on the internet where owners have simply drained and replaced the fluid. I have done this same thing to the Hyrdo Gear 310-0510 in my Cub Cadet but I simply stuck with the recommended 20W50 conventional oil and did not see any significant changes in how the transmission felt or sounded. So here are a few questions that I have regarding the fluid change:

1) What is the best oil to put into the transmission? The manufacturer recommends and fills with 10W30 CD Class Oil.

2) Is there a way or is it even safe to try and spin the hydrostatic pump shaft while the transmission is mounted to the bench in order to purge the transmission and re-check the fluid level? I want to avoid having to put the hydrostatic back into the mower and taking it out again after it has been purged in order to top the oil off.

3) What is the best chemical to use to clean off the transmission to rid it of grease and belt debris without doing any harm to the seals or the aluminum casing?

I appreciate any help that you guys can give.

Mike

Tuff Torq recommends a 5w50 synthetic oil for the K46 boxes. Same basic unit (I think). There are a couple magnets inside the case on these and can have some serious build up on them. Best to remove, split the case and clean out the insides. Usual recommendation is to drain the oil, measure what came out, refill with like amount. I did this to my K46 and used regular 10w40 Havoline oil. Improved the operation quite a bit.

tom3 said:

Tuff Torq recommends a 5w50 synthetic oil for the K46 boxes. Same basic unit (I think). There are a couple magnets inside the case on these and can have some serious build up on them. Best to remove, split the case and clean out the insides. Usual recommendation is to drain the oil, measure what came out, refill with like amount. I did this to my K46 and used regular 10w40 Havoline oil. Improved the operation quite a bit.

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I am certainly not trying to get into the internals of the transmission, just replace the fluid. Currently, the trans seems to have good pedal feel and is responsive. The only reason why I am even venturing into this is that the transmission is 22 years old and never had the fluid changed. I figured at the very least I could empty the original 10w-30 and fill with the synthetic 5w-50 and see to it that I can get a couple more years out of it without any troubles. I understand that there are some magnets in there that hold fine metal shavings but assuming that I don't "disturb" them and in fact "clean" up the oil, then I should still be doing this transmissions service!

The oils that I am considering are:

1) Mobile 1 - Reportedly used by many others with great success.

2) AMSOIL Synthetic ATV/UTV Engine Oil

3) Driven Racing Oil High Zinc

tom3 said:

Tuff Torq recommends a 5w50 synthetic oil for the K46 boxes. Same basic unit (I think). There are a couple magnets inside the case on these and can have some serious build up on them. Best to remove, split the case and clean out the insides. Usual recommendation is to drain the oil, measure what came out, refill with like amount. I did this to my K46 and used regular 10w40 Havoline oil. Improved the operation quite a bit.

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Tom,

I reached out to Tuff Torq and they said that I could either use 10w-30, John Deere J20C or 5w-50 synthetic so I opted for the Mobil 1 which was on sale for $5.99 a quart. My plan was to buy some cheap 30w oil and use it to flush out the old stuff and then do a good drain before I fill up with the new synthetic oil but then I got to thinking of your post. How dirty should I expect the filter to be with 20 years of use but not currently exhibiting any leaks or operational problems?

I am hesitant to crack the case open with no need to replace any other parts in there just to get at the filter and magnets. I don't know how long I will have the machine so I figured an oil change alone would have to be better than doing nothing at all.

With the age of that hydro and the higher service rating it may have better internals than the disposable units produced today. An oil change might be all that's needed to insure it's around for a good long while.