D4 7U Serial # 1894 steering issues

Hi Angelo, breaking down what you wrote:
- pulling uphill drifts to left >> indicates left steering clutch is slipping (assuming things like different length track chains are not a factor)
- unable to steer right >> requires the left steering clutch to be driving while the right is disengaged >> left steering clutch slipping
- requires hard left braking to turn left >> requires left steering clutch to be disengaged >> left disengagement action not fully disengaging

I suspect that a) the left clutch is out of adjustment, and b) the lever assembly / rods etc. have lost motion (worn/collapsed bearings, broken pins, etc.) You can remove the steering clutch cover and review the linkage from the hand lever all the way back to the disengagement yoke and the throwout bearing. My guess is you'll need to do this before you can make any meaningful clutch adjustment.

Hopefully someone else will chime in with more suggestions / refute mine : )

I suppose he can start it up, engage in gear, and pull back on both levers simultaneously or individually to isolate the problematic side. Yes, adjustment either out, or worse, his release bearings collapsed and he would get the honor of splitting the cross shaft and steering packs. Fun job for any novice...Same deal, the proper tools make the job go easily.
***When he was on the phone with me, he mentioned lack of free play as well*** JM

Thanks to both of you Neil and JM. When things dry out, I will get up there and try to make the adjustment. 

I had something similar happen to a D6 9u. I had several 100 hours overs 2 or 3 years everything was good. Did a 7 acre field with a disc. Moved to another that laid so it was fastest to go up and down. Pulled one lever as I was headed up hill and it stopped moving. I managed to do the 2 acres and get it driven to the yard. Pulled steering clutches and nothing out of the ordinary until I started testing the springs. I don't remember the reading but way less than speck from Cat. I want to say about 1/3 of the pressure the manual say they need to be.

Just a big surprise it had been good as long as it had and just stopped after several hours of use one day. One of those too cheap to pass up as the tracks where near new and would of cost more than I paid for the whole tractor. But from other equipment in the yard it came from, you could tell maintenance had been very lacking for some time.