John Deere 7800 Low transmission oil pressure warning light

[yamahahonda]

Hello. My friend's JD 7800 started to show "Transmission oil pressure

 

[Phil P]

Hello. My friend's JD 7800 started to show "Transmission oil pressure

Powerquad I presume?
Is it on all the time or just when hot or certain gears?

If it’s on all the time will probably just be the sensor however it’s worth a pressure test to be sure.

 

[yamahahonda]

Powerquad I presume?
Is it on all the time or just when hot or certain gears?

If it’s on all the time will probably just be the sensor however it’s worth a pressure test to be sure.

Hello, sorry, I'm gonna add more information to the main post. I'm new to the forum and accidently posted this too soon.

 

[yamahahonda]

INITIAL POST

Last September, my friend bought a JD 7800 Powrquad for his 60 hectare farm. The tractor is mainly used for ploughing and cultivating. Last autumn and this spring it had no problems towing a 5 furrow reversible plough and cultivating with a 6 meter cultivator. However, a couple of days ago, the alarm beep started to sound and the instrument panel started to show "Transmission Oil Pressure" and "Stop Engine" lights when ploughing.

The warning light is not on all the time, it only starts to flash after ploughing for around an hour. Sometimes sooner, sometimes later. Also, it is only blinking when the plough is raised up and the engine is running at idle. If you rev it up, the warning light disappears for as long as you hold the revs higher. My friend can actually plough as long as he holds the revs high enough. When it's time to raise the plow, and the RPMS drop to the idle, the alarm and warning light comes back.

Other than that, the tractor seems to be working as normal. All the ranges, gears seem to work as intended, there is no loss on power, 3 point hitch raises/lowers the implements just fine.

When my friend bought this tractor, there was some oil leakage through Auxiliary Steering Pump seals, but there were no warning lights flashing whatsoever. We have replaced those seals last week, and it seems that there still is some minor oil leakage, but nothing excessive – something like an oil sweat after a whole day of working in the fields. The leakage was definitely bigger when the tractor was bought.

We have already change transmission and hydraulic oil filters, we have also cleaned the suction screen in the differential housing. The hydraulic oil has been changed last year, if I recall correctly.

The local John Deere dealer checked the transmission pressure and he said that is is close to ideal.

So, is the sensor the next step we should look at?

 

[Phil P]

Did the dealer test the pressure with the oil hot?
By all means you could try a sensor but I’ll put money on the transmission pump been worn and down on flow at low revs.
I’ll guess it’s got around 8000h?

 

[yamahahonda]

Forgot to add: when we put back the hydraulic oil after changing the filters and cleaning the suction screen, we have filled it to the upper mark with a 3 point hitch in the lowest position, just as the manual says. Few days ago somehow the oil level was a bit higher than the upper mark. Could we have somehow put too much oil?

Diagnostic mode shows only one code: CCU 026.
I've also checked the hydraulic oil temperature via CCU when the tractor was hot, and the hydraulics temperature was 77-78.

 

[yamahahonda]

Did the dealer test the pressure with the oil hot?
By all means you could try a sensor but I’ll put money on the transmission pump been worn and down on flow at low revs.
I’ll guess it’s got around 8000h?

I would need to ask my friend about it, but if I remember correctly, the oil wasn't hot when the pressure was checked. The dash shows a bit more than 10,000 hours.

 

[Phil P]

I would need to ask my friend about it, but if I remember correctly, the oil wasn't hot when the pressure was checked. The dash shows a bit more than 10,000 hours.

Needs testing with oil up to temp (above 55 deg’c) or the gauge won’t show any faults, but at 10000h I’m more than confident that it will need a pump which means pulling the powerquad.

 

[yamahahonda]

Is there a lot of work pulling the transmission out and getting access to the pump? If I understand correctly, it is located in the front of the Powerquad? Also, how much could it approximately cost if we try to repair it ourselves? Will we need to change the whole pump or only the worn out parts?

 

[Northeastfarmer]

I know a completely different machine but my jcb loadall did exactly the same...I changed the transmission pressure sensor and washer and it cured it

 

[yamahahonda]

I know a completely different machine but my jcb loadall did exactly the same...I changed the transmission pressure sensor and washer and it cured it

I'll tell my friend to try changing it, and pray it fixes the problem. We live in Easter Europe and any engine or transmission repairs on these western tractors are extremely costly here, compared to the earnings you get from farming.

 

[Hesston4860s]

I'll tell my friend to try changing it, and pray it fixes the problem. We live in Easter Europe and any engine or transmission repairs on these western tractors are extremely costly here, compared to the earnings you get from farming.

Welcome to our world !.

 

[Phil P]

Is there a lot of work pulling the transmission out and getting access to the pump? If I understand correctly, it is located in the front of the Powerquad? Also, how much could it approximately cost if we try to repair it ourselves? Will we need to change the whole pump or only the worn out parts?

I’d get it tested properly before pulling it to bits, but if it does come to it it’s not as straight forward as a 6000 series as you need to pull the back end of the tractor out of the chassis. Ideally you’d need a splitting kit, looking around 1-2k depending on the condition of the pump/housing. It’s worth going through the whole quad though and checking the clutches while it’s out though.
Until it’s been tested properly don’t rule the sensor out.

 

[yamahahonda]

I’d get it tested properly before pulling it to bits, but if it does come to it it’s not as straight forward as a 6000 series as you need to pull the back end of the tractor out of the chassis. Ideally you’d need a splitting kit, looking around 1-2k depending on the condition of the pump/housing. It’s worth going through the whole quad though and checking the clutches while it’s out though.
Until it’s been tested properly don’t rule the sensor out.

All right, thank you for your help, I really appreciate it. So, in the end, it mainly comes down to either the sensor or pump, right? Is there anything else we could check, besides the pressure tests?

 

[Phil P]

All right, thank you for your help, I really appreciate it. So, in the end, it mainly comes down to either the sensor or pump, right? Is there anything else we could check, besides the pressure tests?

If oil and filters are good then not much else other than pressure test. Make sure they test all the quad gears, f/r and the mfwd for leeks as they can all affect the system pressure.

 

[yamahahonda]

If oil and filters are good then not much else other than pressure test. Make sure they test all the quad gears, f/r and the mfwd for leeks as they can all affect the system pressure.

Understood. I'll make sure my friend gets all this information and we'll see how it goes.