I have a Case 580 Super M that I use on my farm. I was using it last night a mile from home last night and when I was driving home on the road I noticed it was pulling hard in 4th gear. Found that the brake pedals were not all the way up - lifted up on the pedals with my toes and that solved the problem. Had a good look at it this morning - unlocked the two pedals and when I push on the right pedal it fully releases as normal. When I push the left pedal down it is a little stiffer to push and when I release it the pedal does not return to home position unless I lift it up with my hand or foot. When the pedal is all the way up I can move it easily on the shaft to take up the free play in the linkage to the master cylinder clevis and rod. To me that indicates the pedal is moving freely on the pivot shaft in the cab and the problem has to be the master cylinder or brake mechanism in the rear end. I lubricated the pedal pivot anyways to be sure. If the brake mechanism in the rear end was binding somehow would that stop the pedal from returning ? I wasn't sure but seemed to me with hydraulic brakes if the brake mechanism was binding in the rear end and the master cylinder piston was free to move it would still return to home and just draw more fluid from the reservoir - does that make sense ? My best guess is the master cylinder piston is sticking in the bore but before I start replacing the master cylinder I would appreciate any comments on what the problem might be.
Check the springs on the pedals.
Have you had to add any fluid to the master cylinders, A common mistake is to add brake fluid instead of Hy Tran. This can cause the rubber parts to swell and could cause the cylinder to tighten up.
My thought as well, melben.
The master cylinders are self filled from hyd. system. The master cylinder is more than likely bad and will need to be rebuilt.