# MTD YardMachine Hydrostatic Transmission Problems



## MowerGuy

A little while ago I purchased an MTD Yardmachine 18hp 42" Lawn Tractor used, I'd say its from the late 90's. The mower was great, the engine is really strong and we like everything about it. However a couple of weeks ago I was mowing the lawn when it just really slowed down, eventually coming to a complete stop.

My Tranaxle is a Hydrogear 718-0255a.

So I changed the oil in the tranaxle by pumping it out and it was blacker than black and there really wasn't the specified 2.5 quarts, maybe more like a quart. It seemed to be leaking oil out of one of the sides. We put new oil in and it ran, but slow, it never slowed down and stopped though. I also noticed that the mower would move even with the neutral lever not engaged. We changed it again and it was still black but this time we noticed a lot of metal in the oil which had me concerned, it looked like one of the gears was sheared. Put new oil back in...no change still slow. So I completely remove the tranaxle and open it up...everything looks perfect, gears are in excellent shape with no wear that was visible, from the splined shaft to the whole differential it looked perfect. We did not completely disasseble the transmission because we didn't want to destroy it. I think it has something to do with the neutral actuator or maybe when I purged the tractor I didn't get all the air out. I'm not sure, any ideas or experience with such things?


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## dangeroustoys56

Air and heat are the big issues in hydro transmissions - id try to put the recommended amount of proper oil into the trans.

Its probably black from the old oil still trying to be purged out of the pump .

Ive herd the way to bleed them is to shift from forward to reverse multiple times - sorta like power steering in a car, cycle the steering wheel back and forth.

Make sure the cooling fan is intact as well.

Id also check the brakes while youre at it- make sure those arent seized on ( its a common issue).


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## MowerGuy

Yea the 3rd time I pulled the oil out of the trans to completely remove it, it was fairly clear. Every time I changed the oil I always ran it for a little while (both foward and back and on different surfaces)

Cooling fan is fine.

I'll have to check the brakes but I doubt that is the problem.


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## jhngardner367

Hydro gear recommends 20w50 oil in their units,and that's the same trans as my buggy has.The creeping is caused by the selector being out of adjustment.With the engine OFF,look under the tractor,at the left side of the trans.Have some one move the pedal from forward,to revese,& you'll see the bolt moving,up,& down.Loosen the bolt,and slide it,in the slot,to adjust to a neutral setting.It has a neutral setting when,with the engine running,and the rear wheels off the ground,they don't move.Hope this helps!


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## MowerGuy

Brakes checked out ok, linkages are not the problem, we looked at those first to see if they were moving all the way and they were.

I think I'm gonna attempt purging it right on the benchtop and getting all of the air out instead of trying to do it in the tractor.


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## MowerGuy

Decided I would take it apart so I did, as I started to take it apart I found the problem. One of the springs inside the pumps had broken and was just grinding up against the block sending metal shavings everywhere ruining that block and the pump. Once I get new parts I'll just have to reassemble and hopefully it works.


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