Originally Posted By: 1 FMF
the hydrostatic drive from a honda hrx lawn mower, hrx217hxa to be exact.
here it is with the fill cap off and completely full of atf, before i had not filled it completely like this which was my whole problem. If you have any problems with a hydrostatic drive, it's most likely low on fluid and pumping air.
once out of the mower, take the lower block off first. you need to take this off first before you can split the case in half.
with the lower pump body off, you're now looking at the pump block. this is on the small vertical axle shaft which is connected to the pulley on top of the drive, the belt connects this pulley to the pulley on the engine just above the cutting blades. whenever the engine spins, this spins and is pumping but not driving the wheels unless the drive lever is pulled on the side of the unit. notice the little pin on the lower left of the pump block, just inside and to the right of the bottom left hole where the green gasket is. This is the lever that when you activate the drive, which rotates the swash plate, this lever comes up into the pump body which opens a valve and lets oil pump down through the lower pump body then into the motor block to drive the main axle shaft.
with lower pump body off, you can split the drive case apart. you will need to wire brush and polish the axle so the large side of the case on the left can slide all the way off.
as you split the case, the swash plate comes out. the pump block which was shown above rides against this swash plate. and below you can also see the motor block which is the same as the pump block just larger
here's all the parts to the pump block and pump shaft, and on the far left bottom is that pin that rides on the swash plate
here's another shot of the same along with the swash plate, couple thrust washers and bearing set
the motor block
installed back in the mower, what was said to be not serviceable has been serviced.
tools needed:
3/8" socket 14mm
1/4" socket 8, 10, 12mm; might want 12mm in 3/8
good pair of snap ring pliers- the axle shaft is secured via snap rings so you got to remove all these before sliding the axle out. A very small flat blade is helpful in getting under and removing the snaprings.
hard part will be getting the plastic bag/mulch shroud out and finding the 2 bolts that hold that in, one is on either the left or right side of the frame just in front of the rear wheel, the other is up in the bagging area of the frame and will probably be covered and hidden by solidified grass. After that, you need a strong hand to pull on the hydrostatic drive pulley to rotate the whole unit forward so the drive belt will go slack and you can undo the belt from the hydrostatic drive pulley. and to get the drive out it helps to remove the far side wheel/height adjuster bushing from the frame, it's secured via large snap ring on the inside/underside of the frame.
getting the drive on a bench is the hardest part. once there, it's pretty simple. You could probably use any oil. I used redline d4 atf figuring the 30-40 cSt viscosity at 40C would be ideal seeing how optimum viscosity for hydraulics is 20-35 cSt... higher viscosity than that and you lose efficiency due to pumping loss. I looked up some tuff torq fluid recommendations for their hydrostatic drives and they've superseded nearly everything with 5w-50 motor oil. And I had called tuff torq and they didn't admit to making this drive, there's no serial or casting number on it so I honestly don't know who makes it but it does somewhat resemble their k61 which you can download a pdf of and see very similar internal parts.
mobil 5w-50 has kinematic viscosity around 100 at 40C (a 5w-30 oil is ~60 cSt at 40C) which i think is too high but what do i know. I suppose if you never touch the unit, and with the oil contaminated with dirt and dust which I saw mine was when i drained the original oil, you'll end up getting wear which I suppose the higher viscosity could make up for. i also chose atf figuring it would be a better hydraulic fluid than motor oil and not be as likely to aerate, after all it gets pumped under significant pressure in an automatic trans and the same thing is happening in the torque converter. I still have a bit of amsoil 5w-30 tractor hydraulic/transmission fluid and i might give that another shot when i feel like pulling the drive again. but for now the atf seems to work great, and just to be clear i didn't use redline d4 atf because it's a synthetic, i chose it because i wanted to get rid of it and figured it had the most optimal (more near 25 cSt) viscosity at 40C of all the oils i had on my shelf. The amsoil 5w-30 i have is rated 50 cSt at 40C, so that's just slightly higher in viscosity. But so far with the atf i put some load on the drive for a few minutes and it was still cold, and it went pretty frickin fast; will find out in the next few weeks cutting the grass.
Why is it that these (the most important pics) are X on my screen yet I can see the other posters pics?