TN75da brake issue

   / TN75da brake issue #1  

elkhurst1

Bronze Member
Joined
Dec 19, 2010
Messages
56
Location
Clay, WV
Tractor
NH tn75da & tn55
Hello all, been a while since I've posted and have questionable brake issues. I definitely need some expert advise!
A little long winded, so bare with me....
Back about 6 weeks ago, I had to roll my TN75da out of my heated shop to remove a tree from the main road at the foot of my driveway. I hadn't used the machine since late fall of last year. Traveling down my driveway I needed to downshift, so I hit the clutch and brake and both brake peddles (pinned together) went nearly to the floor! It did stop so I continued on to finish what needed done trying not to use the brakes. I got the tractor back to the shop and the next day, my helper and I added brake fluid and tried bleeding both sides. The left was no problem, 2 or 3 times and what little air it had was gone. The right doesn't seem to want to bleed out after several try's.
While bleeding the right side, (like an idiot), I wasn't catching the fluid and started running short, so I had to stop while it still had some air and ordered more from my dealer. At that point, (for some reason), I decided to measure the amount of oil in the reservoir with a set of calipers and by the time I got new brake fluid, (7-10 day's later), the oil level had dropped about .050", so we bled both sides again. The left side had no air, the right still had air, (and seemed like more). After bleeding the right several times, the air never did go completely away. At that point I tried pumping each individual brake as if you were running the machine to see if the oil level dropped in the reservoir wondering if I might have a brake pack bypassing under pressure. After about 75 pumps each, no oil level drop. I wound up getting busy on other things and came back to it about 10 day's later and it had lost another .050" of oil from the reservoir in which the tractor hadn't been started or moved out of the shop. We bled both sides again and the left still had no air and the right had air. We did the complete routine again Friday after the reservoir dropping another .040" in 7 days, and again, we still weren't able to get all the air out of the right side.
There are no apparent oil leaks in the complete brake circuit, and both pumps were replaced appx. 5-6 years ago with no leakage on either of those.
The tractor has just over 3000 hrs. on it.

The oil is going somewhere and creating air, is the right brake pack leaking internally under (no) pressure?

Gary
 
   / TN75da brake issue #2  
Most likely the brake piston in the rear end is leaking into the axle as you have stated there are no external leaks. You could measure the oil on the dipstick for the rear end/hydraulics, but you have pretty much ruled out anything else.
 
   / TN75da brake issue #3  
I didn't look up the parts breakdown on your tractor, but if it's similar to many NH's it has a balance line between the two master cylinders. When I got my 8160 I knew that the wrong fluid had been used in the brakes do i flushed it quite well and still ended up replacing both master cylinders. I could not get that system well bled. It was kind of a nightmare I even reverse bled the system going through 3 quarts of that expensive mineral oil. If you pushed both pedals at the same time you would think that you were doing great, you could bleed each side separate and one side would feel good and the other would be spongy. If you double pumped the brakes she'd skid either tire. When you would push both pedals half way down then press harder on either one you could pump them like bicycle pedals, one down the other up and you could do that for as long as you wanted.
Until I removed and plugged the crossover line I could not get good brakes on her. Removed the balance line and plugged the ports and both brakes are working great.
Which is a good thing as replacing the seals on those brakes is an involved job.
 
 
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