There a Couple of things to check
Have you added any Brake Fluid?
Or only the NH Brake Oil?
Either or both brake pedals go all the way to the floor (loss of brakes)
Internal brake master cylinder leakage.
Information Updated May 2007
To confirm whether the braking concern is related to the master cylinders or the brake components in the rear axle, disconnect the outlet (pressure) line to the axle brakes at the master cylinder corresponding with the brake pedal that goes to the floor and cap the master cylinder port.
Depress or pump the brake pedal steadily for one minute.
If the brake pedal goes to the floor, there is an internal leak within the brake master cylinder. Remove and repair as necessary.
If the brake pedal does not go to the floor, the leak is external or within the rear axle typically at the brake piston seals or it could be caused by a warped brake disc.
Confirm that no one has added DOT-3 or DOT-4 brake fluid. This system uses a mineral oil (LHM type) brake fluid. If they have been mixed, seals will deteriorate and the complete system will have to be cleaned, flushed and new seals installed.
Brake pedals and linkage incorrectly adjusted.
This series of tractors uses two brake master cylinders, linked by a balance tube, to maintain equal oil pressure between the two cylinders and to provide equal braking effort when both brake pedals are depressed.
When using one brake to assist in turning, the brake master cylinder being applied operates only the right hand or left hand brake in the rear axle. Pressure equalization to the inactive brake is blocked by seals, on the master cylinder, not being operated. However, if the inactive pedal is depressed slightly, as the result of mis-adjustment, binding, or riding with a foot resting on the brake, it will open the pressure equalization port in the inactive master cylinder to reservoir. In this situation, oil from the brake being applied will cross through the balance tube and inactive cylinder to the reservoir, and the activated pedal can be moved slowly to the floor, with no braking action.
Ensure that the brake pedal linkage is adjusted properly by:
a) removing the master cylinder to brake pedal pins and checking that the pedals pivot freely without binding.
b) adjusting both pedal stops so that the pedals are level in their home position.
c) adjusting the length of the master cylinder rods so that the rod pin can be inserted through the brake pedals, without any interference and with the brake pedals in their home position.
CAUTION: When properly adjusted it is still possible to slightly depress one brake pedal and move the other pedal to the floor by continuously pumping or tapping it. This is a common characteristic of some dual master cylinder designs on both construction and agricultural tractors. The recommendation for all CNH tractors, as noted in the operator's manuals, is that braking with one brake pedal only should be carried out at low speeds, in field or job site use, and that the brake pedals must be locked together for highway or road use.