NH 2120 HSS No Forward or Reverse, How do I check/adjust the pressure relief valve?

[grcutter]

Happy New Year to All (except for me since my tractor won't move).

I have a 2000 Ford/NH 2120 with HSS. It has 1200 hours on it.
The tractor randomly slips into Neutral and won't move.
Shortening the Clutch linkage rod appears to help get it going again but only for a short while. If I shorten the link too much then it won't go into neutral but stays stuck in gear.
The PTO works just fine. Isn't this the same clutch for PTO and Forward/Reverse? If the PTO works fine does this mean that my clutch is still in good shape.
Front loader works fine.
The hydraulic fluid and filter were changed ~100 hours ago and the fluid level is just slightly above the line on the dip stick. The fluid is crystal clear.

It seems that my issue may be with the HSS.
There is voltage to the correct solenoids when the switch is moved between Forward and Reverse. Both solenoids measure 9 Ohm and I can hear them buzz when they are actuated but I have not pulled them to view the actuation.
I think that the correct solenoid voltages means that I don't have the control box diode problem.

I have read the forums and have worked most of the way through the many suggestions.
There is a suggestion to check the pressure at the pressure relief value. How do I do this? Remove it and screw in a pressure gauge?

There is a suggestion to check the pressure relief valve itself. I am hesitant to do this since I can't find any instructions on how to make sure that it is properly put back and adjusted.
Does any one know how to do this?

There are suggestions regarding the oil pump. Is this another name for the HSS pump? How do I verify that this pump is working?

I know this is a lot of questions.
Thanks in advance!

 

[chander]

Your voltage and ohm readings look to be proper for your tractor. The HSS clutches control the forward and reverse movement of the tractor, the PTO is controlled by the main clutch.
I have attached a flow chart for the electronic hss system that gives the pressure for the relief valve. There is a supplement for the service manual on these tractors. I don't have this on PDF, but I could attach important pages as needed.

To check the pressure you have to disconnect the top hard line on the control valve and attach tee to get your gauge on there.

 

[chander]

Here is another test for the control valve.

 

[grcutter]

Hi Chander,
Thanks for the quick reply.

If I understand you correctly, then having a working PTO only means that the main clutch is still OK.
Is the main clutch the one that requires the tractor to be split open to replace?

Where are the HSS clutches and do these need the tractor to be split open to replace? Where are they located?

In the first image, which is the EHSS troubling shooting chart, how do I preform the first test which is the pressure of the relief valve?

Assuming then that I have a 'NO' and then another 'NO' which takes me to the Hydraulic System box, steps 4 and 5 appear to require a removal of the relief valve.
I think that removal is probably an easy step, but when I put it back, what is the procedure to adjust it properly?

The control valve test looks messy but doable. I will need to get some hoses and a fitting.

Thanks!

 

[chander]

Yes, this tractor uses a single clutch for the PTO and transmission. I would assume the main clutch is operational if it drives the PTO. Have you had and clutch slippage problems prior to this, slipping in high gear, under high loads?

The HSS clutches are in the main gear box behind the main clutch. The HSS clutches work similar to a auto transmission, with appling hydraulic pressure to apply forward or reverse operation.

I have attached a more detailed page on checking and adjusting the pressure relief valve. I would start with checking the pressure first.

I also have attached a page on how the forward HSS clutches are applied.

I have lost reverse movement only on mine, and that was tracked down to a bad electrical switch. You have the proper voltage and ohm readings at the coils, so that is not your case.

I question if you could have a problem with the control spool being stuck? The pressure and flow test would tell you that.

Best of luck and let me know what you find.

 

[grcutter]

Have you had and clutch slippage problems prior to this, slipping in high gear, under high loads?

This problem first showed up once or twice about 8 months ago. It did seem to be triggered by a high (or medium) load but not necessarily a high gear.
When it first showed up, I think that I either changed the gear or changed the gear range, got moving again and then switched back to the gear that it was in before and the problem went away.
I was advised to change the hydraulic fluid and filter but I can't really say that the situation got any better with new fluid and filter since it happened so infrequently to begin with.
In the last several days, it was triggered both times by a heavy load while in a medium gear.
The characteristic was different; I could not change gears or range and get the tractor moving again at all.

Thank you for posting the pressure test. I don't have the equipment to make this measurement. I think I will start with the control valve flow test.

The picture showing the control valve forward flows is quite helpful. I can see the role that each component in the path has. It would appear that the pressure relief valve would have to be stuck in the open position to shunt off fluid.
In this diagram, there is a 'screen' before the oil filter.
Do you know where that screen is located? This is something that I have not checked.
If the screen and/or filter were clogged wouldn't there be other problems such as the front loader not working correctly?

 

[chander]

The screen that you are referring to is located in the bottom of the gear box near where the filter is located. I believe you are correct that if that was clogged, it would effect other hydraulic functions.

 

[grcutter]

I performed the control valve flow test this morning.
Both the forward side and the reverse side produced a little more than 7L/min. This was with the rabbit/turtle switch set to turtle. I didn't try rabbit.
Initially, after start and warm up, there was no fluid from either hose in Neutral.
After testing first the forward, then the reverse and then back to neutral there was a bit of a drizzle coming out of the reverse side but not very much.

I removed the outer portion of the pressure relief value. It was quite clean and the spring was in good shape.

After putting everything back together, I played some more with the clutch linkage arm and adjusted it all the way back to the position that it was in a few days ago when the tractor wouldn't move.
To my surprise, it worked in that position. I drove around for a while and went up and down a short steep hill in a bunch of different gears and ranges without any issue.

So it seems that my neutral problem is intermittent.

I spoke with the service manager at a nearby tractor dealer (nearby would be 1 hour away). He thinks my issue could be an intermittent connection in the electronic control box and that there was a test for the control box in the service manual.
Would you happen to have this page?

If the clutch arm can be returned to its original position and the tractor drives just fine, does this rule out the clutch as the problem?
I didn't try driving today with a heavy load out of fear of getting stuck in an inconvenient location. I thought that driving up and down a short by very steep incline would stress the clutch. Would a heavy load make a better test?

 

[chander]

From what you explain, the main clutch seem to be ok. If this clutch was failing you would have signs of increasing rpm's without matching tractor movement, also possible smoke produced from bellhousing area and vibration.

I will get you the test procedure for the electric coils latter tonight. From what I remember, when you select forward or reverse, initially you will see 2 or 3 volts, then goes to 0, then slowly goes to 12 volts. The speed varies from 0 to 12 based on the turtle/rabbit switch.

You mentioned that you had 12 volts at the coils. Also you felt the coils vibrating. With the tractor operating normal, did you feel the coils? (Coils operating at lower voltage produce more vibration).Could you be getting a voltage drop through a bad/dirty connector? Could you apply 12 volts directly to the coils to eliminate wiring or control box issues?

 

[chander]

Here are some more pages.