NH TN75 Hydraulic Problem

[mustangmarty1967]

The Loader and 3-point hitch do nothing, but the steering and transmission both work fine. Does a New Holland TN75 have just one hydraulic pump that runs everything? Or is there a second hydraulic pump that runs the loader and 3-point separately from the steering and tranny?

 

[TractorTech]

It uses a steering pump, rear pump on LH side of engine and main hydraulic pump on the front side. May be an air leak on the suction side or broken drive or shaft

 

[mustangmarty1967]

So, three hydraulic pumps then? Since the steering and tranny work, which pump should I focus on first? The rear pump on the LH side of the engine or the main pump on the front of the engine?

 

[Harry in Ky]

I think you're both confused. The TN series has two pumps, both on the RIGHT side of the motor. The one on the front of the timing cover is hydraulics, the one one the rear (under the injection pump) is steering/transmission circuits. They share a common suction and filter, and each drive off opposite ends of a timing gear Fiat refers to as a PTO gear.

 

[TractorTech]

So, three hydraulic pumps then? Since the steering and tranny work, which pump should I focus on first? The rear pump on the LH side of the engine or the main pump on the front of the engine?

Oops, right, left sorry. It is the right front. Two pumps mounted on engine cover

 

[mustangmarty1967]

Okay, I finally got around to pulling the front hydraulic pump on the right side of the engine. It had no hydraulic fluid in it whatsoever. However, it did have a very small amount of what looks like engine oil. Both the drive gear in the timing case and the drive gear in the pump, as well as the ring they lock into together all look good. I can see the innards of the pump turning smoothly when I turn the pump gear by hand. It seems like it’s just not getting hydraulic fluid to it for some reason. I’m assuming the larger hose on the bottom is the feed line and the smaller line in top is the pressure line? Both lines run into the front side of the block that the hydraulic filter screws into the bottom of. I’ve read about bleeding air out of the system by running the loader and the 3 point hitch several times once the fluid it warmed up. But without any fluid to that pump, is there another way to bleed it?

 

[Harry in Ky]

Here are the basics. Both pumps (steering and hydraulic) share a common suction and filter. If one pump works it's safe to assume the suction (supply) and filter are not the problem. If the drive portion, coupling, ETC are intact and functioning then chances are the pump is just too tired to function. You can tear the pump down for inspection and probably find the body and wear plate seals are hard, brittle, and possibly shattered to pieces. The pumps are not really worth repairing. Replacements can be had for a couple hundred dollars from numerous sources. Just order a pump and be done with it. Anyone who works on these tractors has probably replaced dozens of them. I know I have.

New Holland TN75 hydraulic pump - Yahoo Search Results

search.yahoo.com

 

[mustangmarty1967]

That may be what I’ll end up doing. But I would still like to find a way to get the air out of the system first to be sure that the pump is the problem and not just air in the system? Also, is there a screen anywhere else in them system before that front pump that could be blocking the flow of hydraulic fluid?

 

[Harry in Ky]

Your problem isn't air in the system. If it were the other pump wouldn't work either. You need a new pump.

 

[mustangmarty1967]

Before buying a replacement pump, I decided to try the air in the system route first.

I pulled the suction tube and elbow from the filter block to the bottom of the front hydraulic pump and cleaned them up a bit. Put new seals on both ends of the tube and one in the flange of the elbow. Turns out, the seal in the elbow flange was the wrong seal. I think it was too small and not making a good seal to the bottom of the hydraulic pump.

Anyway, slapped it back together and the 3-point hitch and loader are both working now. Instead of sucking hydraulic fluid, I guess that front pump was just sucking air through bad O-rings.

Thank y’all so much for helping me figure this out. Good to know there are such knowledgeable folks around always willing to help out.

 

[RiversideFarm]

I’m having the same issue with my TN65. I hope yous is fixed but I just replaced the o-ring with a plastic spacer on mine and it took it about a week for the issue to happen again. Actually, I just made a post about mine and then found this one! Guess I should have looked harder before posting.

 

[mustangmarty1967]

Just putting in new o-ring in the elbow that feeds hydraulic fluid to the front hydraulic pump fixed it. However, I wasn’t too sure how long a round cross-section o-ring would last in a groove made for a square cross-section o/ring. So, I bought a few of these off eBay, and it seems to be working fine. Pulls hydraulic fluid like it should and holds prime fine as well.