Hydraulic problem on 4720

[rdp58]

Thanks guys for your input. I have the John Deere manual on cd. I have spent several hours looking at it regarding this problem.

In the hydraulic sections under trouble shooting PTO problems: PTO slips or loses power. Front gear pump faulty or PTO valve faulty.

As AKfish mentioned if I press the forward pedal down fast the hydro vibrates and the RPM does not go down. With this problem and the PTO I'm guessing it's the faulty gear pump. if the hydro worked fine I would lean toward the PTO valve.

I'm no master mechanic but I have worked on several tractosr in the last 20 years. I'm familiar with these compact tractors and have never heard of a pump failure. That's why I am second guessing the pump. I asked the question just thinking someone else might have had this problem. I think it says something for these tractors that nobody has. Also I thought I might be overlooking something simple before spending too much money.

 

[Jdman4x20]

Thanks guys for your input. I have the John Deere manual on cd. I have spent several hours looking at it regarding this problem.

In the hydraulic sections under trouble shooting PTO problems: PTO slips or loses power. Front gear pump faulty or PTO valve faulty.

As AKfish mentioned if I press the forward pedal down fast the hydro vibrates and the RPM does not go down. With this problem and the PTO I'm guessing it's the faulty gear pump. if the hydro worked fine I would lean toward the PTO valve.

I'm no master mechanic but I have worked on several tractosr in the last 20 years. I'm familiar with these compact tractors and have never heard of a pump failure. That's why I am second guessing the pump. I asked the question just thinking someone else might have had this problem. I think it says something for these tractors that nobody has. Also I thought I might be overlooking something simple before spending too much money.

The pump on this unit is made up of two sections, the steering and the implement sections. The steering portion supplies charge pressure to the pto and the hydro.



The steering portion needs to be flow tested to determine if it is bad. What you could do is hold the steering wheel in a full turn left or right keeping pressure on the wheel and drive the unit forward or reverse and see if it affects the drive. If the tractor will not move while the steering is in relief them I would suspect the engine mounted pump is bad. If you have a gauge then you could monitor charge pressure while holding the steering in relief.

The steering portion of the engine mounted pump will effect the pto, steering and the hydro drive. The implement side will effect the rockshaft and scv.

Hope this helps

 

[AKfish]

The pump on this unit is made up of two sections, the steering and the implement sections. The steering portion supplies charge pressure to the pto and the hydro.



The steering portion needs to be flow tested to determine if it is bad. What you could do is hold the steering wheel in a full turn left or right keeping pressure on the wheel and drive the unit forward or reverse and see if it affects the drive. If the tractor will not move while the steering is in relief them I would suspect the engine mounted pump is bad. If you have a gauge then you could monitor charge pressure while holding the steering in relief.

The steering portion of the engine mounted pump will effect the pto, steering and the hydro drive. The implement side will effect the rockshaft and scv.

Hope this helps

You've outlined a very clear diagnosis... with one minor exception. The steering pump only supplies the makeup hydraulic oil to the hydrostatic drive pump @ 200psi.

If the steering pump was functioning so poorly that it was failing to provide 200psi return flow to the charge filter... I'd have to believe that ANY steering function would be extremely poor!!

Like; noticably bad steering!

AKfish

 

[Jdman4x20]

You've outlined a very clear diagnosis... with one minor exception. The steering pump only supplies the makeup hydraulic oil to the hydrostatic drive pump @ 200psi.

If the steering pump was functioning so poorly that it was failing to provide 200psi return flow to the charge filter... I'd have to believe that ANY steering function would be extremely poor!!

Like; noticably bad steering!

AKfish

The steering will have priority over the pto and hydro, it will be the last to lose function. The hydro requires the charge pressure "200psi" to function. It is supplied from the steering pump. Like I said the pump needs flow tested to determine if it is worn, but without a flow meter the least I would do is to test the charge psi per the TM.

Hope this helps

 

[jkflatt]

Did you find a solution to your Pto power loss? I have the same issue. Everything else seems to work properly, but the Pto stalls out when mowing in thick grass but the engine does not.