John Deere 855 flow divider noise

[Nick S]

Hi,
I have a John Deere 855 compact tractor with a front end loader and backhoe.
The front end loader works off the tractor hydraulics and has started to make a screeching sound when in operation. The sound seems to be coming from the flow divider and only occurs at high revs when the front end loader is stationary. The noise disappears when the loader is lowered or raised. I suspect that it is the pressure relief valve. I have stripped it down and cleaned it but the noise is still there. Is this the likely cause and will a new poppet and valve seat cure the problem or is it likely to be something else. Any help appreciated. Thank Nick

 

[J_J]

You should be able to put a gage in the system and determine if it is relieving.

Hydraulics:
Type: open center
Capacity: 4.5 gal [17.0 L]
Pressure: 2050 psi [141.3 bar]
Valves: 0 to 2
Total flow: 5.6 gpm [21.2 lpm]

Your system is open center, so the return hoses should have a clear path to the tank.

Lowering the loader does not generate much pressure, and raising the loader with out a load does not generate much pressure.

The relief should only go off when you are lifting max load, or you are in full extend or retract.

The other part of the flow divider is probably going to the steering. Maybe something in the steering circuit is binding.

Does the divider valve have a relief valve or is it on the loader or both?

 

[Nick S]

Hi J_J,
Thanks for the swift and informative reply.
When the flow divider lever is in the neutral (centre position) everything is fine. (I assume the hydraulics are recirculating back to the tank on open circuit)
When I move the flow divider lever to engage the front end loader hydraulics the engine comes under load and the noise starts if the engine revs are raised.
When I activate the front end loader lever to raise or lower the bucket the noise stops.
There is a pressure relief valve in the flow divider and its as if it is imposing too much load on the system and chattering when hydraulics are fed to the loader (but there in no oil flow to the loader to reduce the flow through the pressure relief valve) and all the recirculating oil has to go through the relief valve.
When the loader lever is activated and the bucket raised or lowered there is flow to the loader and the pressure relief valve can then cope with the reduced oil flow.
The schematic is attached.
Thanks for your help.
Nick

 

[J_J]

Your schematic does not show.

Your flow divider may be different than the ones I am familiar with as the flow is set for two output all the time.

A divider valve is just a routing device, and when all levers are in neutral, there should be free flow through the divider to tank.

The flow is either split equally, or a set ratio like 70/30.

The only time the fluid should go over the relief valve is when there is max resistance like a fully extended cyl or a motor under max load, or a blockage of any kind, like an unplugged QD.

So check those QD and reconnect them.

The relief valve is usually on the priority circuit or controlled flow.

The attachments hyd circuit, including the 3pt is probably fed by the excess flow.

Do you know which circuit is the priority circuit.

I would think the steering circuit, but not sure.

Try re-posting the schematic.

http://www.surpluscenter.com/_MoreSpecs/i9-4158-xx.pdf

 

[Nick S]

Hi J.J.
Sorry for the delay in replying but I have been trying out some of your suggestions.
I attach a copy of the hydraulics schematic and hope that you receive it this time



The status so far is as follows:
The front end loader (FEL) is fed (pressure and carry over) from the flow diverter and the priority is to the steering as you say.
Because of this I have to hold the flow diverter lever down whilst operating the FEL.
The tank return runs to the back of the tractor in a flexible hose (connection 24 on the attached schematic). I have disconnected the far end of this hose and there is oil flow whilst the flow diverter lever is depressed and the FEL spool valve is in the open 'centre' position. It flows but does not 'gush' out and I do not have the experience of hydraulics to know whether it is partially blocked.
I cannot understand why the FEL control spool valve is supplied via the flow diverter and would have expected it to be on an independent circuit to the flow diverter.
I was told that the JD855 had separate connections in accordance with the schematic attached. When I accessed the top of the hydraulics unit I discovered that mine is an earlier version and does not have the connections (18 and 19) shown on the schematic. I do not know if my unit has suitable connections in a different location.
This still leaves the problem that I cannot understand why the engine comes under load when the flow diverter is engaged and squeals when the revs are raised (as if a pressure relief valve is overloading.
Any help would be very much appreciated. Thanks Nick

 

[BigEddy]

Sounds like the fluid return path to sump is blocked forcing the relief to open when the loader scv is not being operated. If you have any disconnects in the system, disconnect and reconnect the hoses. Could be that the last time you disconnected the hoe the hose connections did not get properly mated.

Yours must be plumbed differently than mine. I have no diverted valve that needs to be operated.

 

[Nick S]

Thanks BigEddy,
I will try you suggestions.
Do you know how and where yours is connected to the hydraulics?
Thanks Nick

 

[Farmerford]

Nick:

Try cleaning the screens at number 27; there appear to be plugs that give access to the screens. The diagram is hard to read when enlarged, but the flow from the pump through both the float valve and the regenerative valve appear to pass through these screens before passing through the TPH valve to the tank.

Then check adjustment of the TPH control linkage; if it is not adjusted properly, when you move the TPH in the far "up" position the valve may remain open, continuing to direct the fluid to the TPH ram which is stalled, causing pressure to build up and open a relief valve somewhere.

Let us know what happens.