Farmall 450 priority valve

[TXZane]

So its time to repair the power steering on my 450. Really hard to steer unless I move a hydro lever so it sounds like its my priority valve. Where can I find information regarding rebuilding the priority valve or where can I get a rebuilt unit.

 

[used red MN]

Probably in the IH S-400 book; a little spendy., see link. I You will have to scroll to the 450 manuals. I am not sure how well the IT book covers that part of the hydraulics.
YT manuals

 

[Janicholson]

This parts diagram shows the pilot valve and others. Parts 7-8-9-10 are responsible for pressurizing the system There is likely a screen in the stack that can be plugged up as well as issues with the orifice. The orifice may be hammered part way shut, (the ball is often the problem and IIRC can be left out, as it hammers the orifice closed. The orifice can be enlarged to as much as .040 inch (max i think) Jim
Untitled URL Link

 

[Stuart]

We have many 400 and 450 tractors on the farm. What we ended up doing was installing a power steering pump from a mid 70s ford car/truck. We drove it off the front pulleys of the engine. Steers with one finger now. The priority valve setup wasnt a great design from the start

 

[cornerpost]

In the early 1970s dads 400started having hard or non-existent power steering. Good parts man said dead head remote and see if better. Dad just put on new flow control valve if memory serves. My
Dad and brother did the repair while I was on National Guard duty. They succeeded as it worked after that.

 

[D Slater]

Most common problem that fits your description is a worn bore and piston that handles priority to the steering. Piston that sits horizonal in the control block. place called steel wheel ranch used to sell rebuilt blocks exchange. Business was for sale so don't know. Machine shop was used to fix bore and piston clearance.

 

[Dick S]

I agree mostly with Jim that parts 7 through 10 in the diagram control the hydraulic pressure going to the steering -- but only in a properly working priority valve (or if one of the hydra-touch valves is in operation). From what TXZane is describing, the major problem is almost certainly wear in the piston, part 22 in the diagram. A good replacement for this part is unlikely to be available as well as detailed instructions for working on the priority valve in general.

It's been years since I worked on the one on my 450, but as I recall the solution was restricting the flow through the slots in the flange on the right side of part 22 (see diagram) using some JBWeld. This was a multi-step process -- added a little bit and things got better but not good enough. So take it apart again, add some more, and retry until satisfactory. Have to use care not to over-restrict flow through the slots as that will over-pressure the valve. Another approach might be using a heavier spring for part 21. I seem to recall that it isn't necessary to remove the priority valve from the tractor to access part 22, but that port is spring-loaded and pieces are liable to fly if care isn't exercised.

For anyone interested in a long-winded explanation of what's happening... The hydra-touch system without a priority valve circulates low-pressure hydraulic fluid until a control valve is actuated -- which pressures up the system rather than dumping the fluid back into the reservoir. Adding the priority valve before the hydra-touch system puts a high flow of potentially high-pressure fluid directly into the priority valve. The piston (part 22) works to divert a fraction of the total flow at a high-enough pressure for the power steering when needed with the rest going to the hydra-touch system at low pressure (until a control valve is actuated). The goal is to do this at a relatively low pressure to avoid loading the hydraulic pump.

In operation, the flow going to the power steering goes through the hole in the middle of the right end of part 22 with the balance going down the sides (mostly through the little slots in the right-end flange) to a port going to the hydra-touch system. The amount going to the hydra-touch system is controlled by the position of the piston - more flows when the piston is pushed further to the left in the drawing. After decades of wear, too much clearance exists in the slots (and probably the flange as well) on the right side of part 22 and not enough pressure builds up in the flow going to the power steering to operate it properly.