"Sundstrand Drift??"

[paxz71usa 173]

Saw this in a thread a week or two ago and at the time I didn't pay much attention, but then I got to wondering if this is what's going on with my "73" 12 Automatic. I was thinking that perhaps I had a valve hanging up in the drive system or belt slip. My tractor seems to pull up hill fine, hold down hill fairly well, but when it transitions from down hill to flat ground it seems to free wheel (for lack of a better explanation) for a second or two then every thing seems to engage again and all is fine. Hubs are tight and the drive belt is new. The belt tension pulley seems fine. Wondering now if I have an issue or is it "Sunstrand Drift?" Can anyone explain this condition to me?

Thanks,

Gary       

Edited May 13, 2018 by paxz71usa

[Ed Kennell 38,687]

I can't explain why,  but the downhill drift exists in most of my hydros...  Sundstrands and Eatons.

[Sarge 3,463]

Any wear on the pistons or the plates can cause fluid to bypass, which allows for a certain amount of "slop". It can also contribute to a lot of heat buildup (at least in the Sundstrand units). The used pump I put in my D was horrible about it at first, but during the process of chasing leaks I went ahead and did the surfacing work on both the pistons and plates, made a world of difference. Also replaced the swash plate bearings/seals, that really tightened things up. I'd bet most times it's a matter of light wear in different places adding up to create a problem, it is - after all, hydraulics. I have yet to go through the main motor section on the rear Unidrive but would like to address that since the pump has already had so much work - should finish making it run/drive like new again. If you have one that is really bad about creating heat/slop you might have to replace the valves/springs for the acceleration control circuits as well as the piston block/pistons itself, which could get really expensive in a hurry. 

 

Sarge