Need advice on hydrostatic transmission

[Platoxia]

I have an old Scotts 1642H riding mower with a Tuff Torq K51A hydrostatic transmission. This past weekend we put a cinder block under the transmission and took off both rear wheels. After putting them back on and removing the cinder block, the transmission has no power. The mower will not move in forward or reverse but it is obvious that it is trying. Only one of the wheels has a wheel key (my helper says it was already like that) but even with the wheels off and the mower jacked up (properly this time) the axle has no power at all. It spins when you put it in gear but even the slightest touch stops it from spinning. None of this was an issue prior to putting the cinder block under the transmission and removing the wheels.

After reading up on the transmission on the internet and watching some videos I was convinced the issue was in the transmission. The oil level was fine and there was only a very small amount of metal particles found in the oil (for some reason there were no magnets at all in the transmission). I spent the last couple of days tearing it apart and cleaned and inspected everything inside but cannot find any problems. All of the gears look good and show no unusual wear, all of the splines (both inner and outer) look good on all parts (no damage or uneven wear). All bearings and surfaces that they contact look great and work perfectly. None of the parts with splines are loose and seem to be within tolerances, including the pump bearing assembly that attaches to the fan/drive-belt that so many people have problems with (splines getting worn out - mine are fine).

The Center Case, Pump Cylinder Block, and Motor Cylinder Block all seem to be fine despite one (or all) of these being the suspected point of failure (as per Tuff Torq). The pistons are all tight yet slide fine, the springs all seem to be fine, there are no blockages, and both swash plates look pristine. These are the parts that make up the repair kit sold by Tuff Torq (including a seal kit) but, frankly, it is just to expensive for me to buy without any evidence that there is something wrong with any of those parts (other than the fact that SOMETHING is causing this). I'm at my wits end and am about to put it all back together and see what happens. This may be a case of having put the cart before the horse and missing some obvious linkage problem before starting in on the transmission. I just want to be thorough and inspect everything inside the transmission while I already have it apart. Any advice on what else I should check inside the transmission would be greatly appreciated. Also, I have everything cleaned and organized on the garage floor at the moment so I can provide pictures of any of the parts in question.

Thanks in advance for any and all advice.

 

[bertsmobile1]

You need better help.
There is a key in both sides or the axel can not transmit power to the wheels because there is a diff in between them.
Sometimes they stick on the axel then drop off.
However they never seem to hit the floor but get zapped into that parallel universe along with all your left socks and spare car keys.

You are not going to do any damage by jacking the mower up by the tranny.

OTOH you now know how hydros work, pretty natty arn't they. All that high precission engineering, mechanical porn for sure.
While it is apart, change the internal filter if it has one then reassemble.
As you have seen, clean is the magic word so reassemble on a clean bench, I cover mine with clean white paper ( short ends from a local printer )
Wear freshly washed clean overalls and gloves when assembling hydros. If I have to leave the job it gets covered , if I have to leave it for a long while then it gets wrapped in pallet wrapping ( glad wrap on steroids )
I find it seems to work better and purge easier if I add as much oil as will fit in before I seal the units.
Hydros are really sensative about the grade and in some case the actual brand of oil used

 

[Platoxia]

Thanks for the advice, it makes sense that I need two wheel keys. The main reason I thought the problem was in the transmission was that when I jacked it up and took the wheels off again then put it in drive I could stop the axle from spinning just by grabbing it. Is this normal or does that indicate power loss in the transmission? Then again, I suppose it could have something to do with the lack of keys and wheels that enables me to stop the axle from spinning?

Edit: Yup, forget that last question...I just looked up a bunch of images of differentials. Makes a lot more sense now. Also, I'm obviously no mechanic but I did enjoy the experience of going through the hydrostatic transmission. As you say, it is definitely a work of engineering art.

 

[Mike_Goad]

i am not familiar with tuff torq but i do not think they are much different than hydro-gears. inspect the axle and differential carefully. i have heard of people pulling the axle out so that it is no longer in the spur gear. this normally takes a lot of force when removing the tire/wheel assembly.
the only other reason for loss of power is that the bypass valve was engaged. there needs to be a lever that you push/pull so that you can push the mower if needed. if that was engaged, there would be no power at the axles.