C-120 transmission troubles

[WheelHorseEnjoyer 25]

I don't know if anyone has this trouble or knows how to fix it. But everytime I go down a hill with my C-120 automatic it starts to coast down the hill kind of. And once I reach the bottom of the hill it takes some time for the transmission to work again once it's on flat ground. Sometimes like today I had some problem trying to get it to go again. I had the engine running while engaging and disengaging the transmission for about a minute until it started to mover again. I was scared when this happened because I was about 2 miles into the woods clearing paths and I really didn't want to walk back. On the dip stick for the transmission it says the fluid is halfway up the stick. If anyone has somthing to say about the matter I am all ears. Thank you.

[WHX?? 48,828]

When was the last time you changed fluids/filter on it or checked the drive belt and idlers. Perhaps a slipping drive line?

[kpinnc 12,082]

Check the tow valve to make sure it's closed. Change the oil and filter. The filter could be long overdue a change. If it's the correct filter, it has no bypass. That means if it's full of garbage you could be starving the pump for fluid.

 

If all that fails- and others may have better advice: I've only ever opened one Sundstrand, and it was more for exploration than anything. It might be getting time to rebuild or replace it. Just my opinion.

 

Good luck!

[daveoman1966 3,752]

I have rebuilt a few dozen Sundstrand power units.  Yours would be model 90-1136 which is nearly identical to the 3 or 4 Sundstrand '90-xxxx' series. Internal components are virtually identical.  DIAGNOSES; (1) change oil and filter.  Take EXTREME care to wipe off ALL surfaces in doing the oil change & filter.  The slightest particle of debris can tear up the brass internals of the Hyd pump and Hyd Motor.  (2) There are 2 accelleration valves on the Hyd Motor section.  Before refilling oil, remove both of these valves... (front and rear of the Hyd Motor).  Inspect for faulty O-rings or stuck passages.  (3) With any luck, you'll be able to open the Tow Valve.  If so, work it back & forth to (maybe) reseat the valve tip. (4) The motion control linkage MAY be worn to the point of retirment... OR... there is a broken weld on the TAB of the motion control shaft (left side of Hoodstand). VERY COMMON, but removing / repairing / refab can be daunting.     

 

[953 nut 55,290]

8 hours ago, WheelHorseEnjoyer said:

everytime I go down a hill with my C-120 automatic it starts to coast down the hill kind of.

 

As others have said a little TLC, oil change and filter, is a good idea. If the fluid in your transmission is amber use  10 W 30, if it is pink use ATF. The filter needs to be a Hydraulic filter, not an auto oil filter. Go with a Wix 51410 or NAPA 1410.

       Are you letting the tractor freewheel down hill or are you reducing it's speed by pulling back on the motion controller?   If it is freewheeling the overspeed may be frothing the oil and introducing air bubbles into the fluid. Air is compressible and the charging pump can't produce any pressure with air in the fluid system. Try going down a hill (closer than 2 miles away) while holding back on the motion control and see if that helps.