Retrofit John Deere 318 Power Steering into a Case 646?

DanMc77 · Jan 9, 2020

I have a John Deere 318 garden tractor that's a parts machine. I'm wondering about the possibility of pulling the Power Steering components out and putting them into my little Case 646, which doesn't have PS, but already has a hydraulic system operating the front loader.

Can one of you hydraulic experts give me a broad description of how the power steering in a 318 works? Is it merely pressure coming into a rotary valve at the bottom of the steering column, and that then incrementally feeds metered fluid to the PS cylinder when it rotates? I'm just taking a swag at this.

If it's really that simple, then retrofitting the PS to another machine wouldn't be too difficult.

What are your thoughts?
Thanks!

MossRoad · Jan 9, 2020

If you do it, you want to make sure that steering has priority over the FEL functions. Because there's nothing worse than driving along turning towards something and moving the FEL controls and finding you can't steer.

oldnslo · Jan 9, 2020

Your description is basically how the steering works on the 318

A couple things to keep in mind especially the concern mentioned by moss road

Your system relief must be the first valve from the pump.

Do you know Where does your Case get it痴 hydraulic flow from? I.e. stand alone hydraulic system or from hydrostatic tranny charge pump like the 318?

Case flow and operating pressure vs 318. Not sure of the flow or pressure rating on the 318 but would want to make I am taking components rated for 3 GPM @ 1000 PSI and installing them in a 10 GPM @ 2500 PSI system

DanMc77 · Jan 9, 2020

Well lookie here what I found. The Case 646 came with a service manual and included some hydraulic schematics for some of its cousins that have power steering.

This machine is not hydrostatic, but it uses a hydraulic motor and a valve to control the rear wheels. There's a Fwd/Rev shuttle lever up on the operators console. Speed is operated by a foot pedal. Both of those controls must go to the travel control valve. Looks like the addition of power steering is very straightforward from a hydraulics perspective.

Maybe some of you can comment on the flow divider? Is that anything more than a T? Also, this 646 tractor has a front loader, so there's an additional spool valve not shown here.

oldnslo · Jan 10, 2020

Dan,
The flow divider is a valve that divides the flow at a fixed ratio from the pump to insure that both the steering and auxiliary circuits have flow any time the pump is turning. With out this the oil would take the path of least resistance which may disable the steering or the auxiliary functions.

MossRoad · Jan 10, 2020

On my little machine, I have one pump that controls the steering and FEL. It doesn't use a flow divider. The pump feeds the steering valve. The steering valve has a power beyond port that feeds the FEL valves. So steering has the priority that way. One side effect of this is that if you have the steering wheel cranked all the way to one side or the other, the FEL will occasionally not move until you release pressure off of the steering wheel.

A flow divider is more complicated, but you'd retain control over the FEL while in extreme steering situations, I'd think.