Any body here ever rebuilt a hydrostatic tractor transmission?
 

My little trim tractor ( 18 hp 42"craftsman) finally let the smoke out of it's hydrostat trans.
It's top speed has gradually declined over the last season, and the trans has the sound of a bad auto transmission pump.
I priced it new, and it is nearly$ 700.00, but the guy at sears was unable to locate one, however, they do stock most of the internal parts for it . I have two of these little pos tractors, and I think this is a common problem with them, the spare I have has also been slowing down over this season, and the trans is getting noisy. There is really no maintenance on these, there is no drain, hole, and no fill hole, neither one of them ever leaked out a drop.
I figure it should be somewhat simple. Anybody?

There is maintenance on hydros...fluid changes based on hours and time. I change the fluid on my tractors hydros every year just because it is easy, no flush involved.

I have 800 hours on both of them, really stupid, hard hours.

You probably have the skill to rebuild, I don't.

Throwing good money after bad. Maybe you would be ahead just going for a new/newer/different one and seeing if you can recoup some of the cost by trying to part them out on Ebay.

Any chance it's a Sundstrand unit?
Jim

fastfredracing,
Mine too is the 'maintenance-free' type... which troubles me because changing the hydrostatic fluid is a wise thing to do. Although you did not specify whether your mower is a conventional rider or a zero-turn, the biggest difference is one hydrostatic unit versus two. The link below covers my 'maintenance-free' unit and instructions are provided on how to change the fluid and purge the unit (granted, draining requires completely removing the unit and flipping it upside down). Check again to see if yours has a fill hole and/or vent because there had to be a means to get the original fluid inside the unit.


http://www.outdoordistributors.com/pdf/HYDRO-GEAR/ZC-ZD_service_manual.pdf

I'd find a used one here:

Tractor Forum : MyTractorForum.Com Tractor Forums

and swap it out........

If it's made by Tuff Torq, which many craftsman small tractors used, you can contact their parts department and get the parts you need along with good advice and instructions. When you rebuild it, drill and tap a drain plug for future fluid changes. They will also suggest using synthetic oil for better longevity.

Here's a link that might get you there.

https://www.tufftorqservices.com/EnvEElogin/html/login.html

Some info - I have overhauled a few automatics....Mostly they are hydraulic actuated clutch packs..and or a band the stops a sun gear drum from spinning.

If you can get a "oil route schematic" have it on the bench with valve body off, you can apply air pressure to the given ports.(40 lbs?) This stops all the guess work as to blown "O" rings or worn clutches. If you have no air leaks then you have worn band and or clutch pack problems...No expert here....some or most this should apply I would think.
All the "car" autos were pretty simple...I would guess a little lawn mower might be too?