Any of you techs happen to know what the pressure specs are for the mid 70's Ford steering pumps.

I have a steering assist system on a 73 F250. No leaks, but I am not getting much "assist". It doesn't seem to matter what the engine RPM is either. I would like to trouble shoot, but I don't know what the pressure specs are.

 

At least 620 PSI @ 165 degrees for a Ford Thompson Pump. Most I have tested were in the 700 range, the lowest one I ever tested was an AutoZone reman unit I found in the junkyard. It only mustered 400 PSI.

Josh

 

Are you sure the pump is the problem and not the control valve itself?

 

I think they typically make more than that. Mine runs my live hydraulics for my winch and snowplow and it deadheads at about 1200. I think the max. spec is 1250.

 

Running pressure is not the same as deadhead or the technical term "over relief".

The specs for the Thompson pump is a go or no go @ 620 PSI.

Josh

 

So when you say 620 PSI operating pressure, is that the pressure I should have in the system at idle, with no actuation of the steering system, or is that at idle with the steering turned to the lock.

Does the Thompson pump have an internal relief valve? I am wondering if the pump is possibly bypassing. I have never been around a Ford pump during this era that would not squeal when turned to the stop. (Or maybe the steering assist system won't allow the pump to squeal.) I just rebuilt the control valve, so I don't believe there is a bypass occuring in the valve.

 

To test the pump you bypass all the truck mounted hoses and install a new set of hoses with a gauge inline with a shut-off valve after the gauge.

You start the engine and let it idle until the P/S fluid reaches at least 135 degrees.

620 is the operating pressure with no load. For the life of me I cannot find the specs for the relief valve, but it's probably around 1200 PSI.

There is a pressure relief spring in the pump.

Josh

 

So if I understand you, after the operating temp is reached, then I close the valve that is in the line after the guage, and the pressure should raise to 620? Wouldn't that cause the relief to open?

 

No 620 PSI is running pressure with nothing closed.

Close the valve (my manual states DO NOT CLOSE THE VALVE MORE THAN 5 SECONDS) and you'll reach the relief pressure. However, the manual does not state what the relief pressure is interestingly.

The relief valve is just a spring and a spool. Nothing complicated.

My manual is the actual service technician's manual a dealer would use. You can download it on another Ford Truck website that I cannot mention on here.

What I have done is to just take a pressure hose from the output with a gauge inline and then run it back to the inlet on the pump. Start the engine and check the pressure.

If your gearbox is really stiff it's possibly from an overtightened pre-load and not the power steering.

Also if the p/s system was recently replaced or all the fluid was drained it can take a moment to work all the air out. Usually this involves topping off the pump and turning the wheels lock-to-lock several times.

And it's pretty normal for the pump to make some noise when you have the wheels full lock with pressure on the steering wheel. That would be the relief or "swash" going into effect.

If it is making that noise with no movement on the steering input then there are problems.

Josh

 

With wide open hoses as you have described and no restriction, your pressure is going to be pretty much zero.

The Ford test fixture has a calibrated restriction in it to allow comparitive measurements at a particular fluid temperature. If you don't have the Ford test fixture you're shooting in the dark at any meaningful results except a deadhead test. That won't tell you how much flow the pump will make or if the internal screen is plugged, but it will give you a good idea of the clearances in the pump and how worn it is, and if the relief valve works. There IS a deadhead pressure quoted in my service manual and it is 1200 lbs. for the Ford pump and 1350 for the Saginaw 'ham-can' pump.

The reason I quoted deadhead pressure is because probably 95% of the people on here do NOT have the Ford test fixture to test it per the book.

 

There is no test fixture. The Tech manual even shows pictures of the hoses and gauges installed in a vehicle.

A pump pumps fluid. Therefore there is pressure. If there is no pressure I dare you to undo the high pressure hose on your pump and start your engine.

As I stated the actual "REAL" tech manual is available on another Ford Truck website. Do a google search for 67-72 bumpsides and you'll find it.

Josh

 

You're confusing flow with pressure.

On my truck, I have the power steering pump outlet plumbed to an open-center solenoid valve that supplies power to my winch. From the feed-through on that valve, it continues on to another solenoid valve that supplies my snowplow lift. From the feedthrough on that valve it goes on to the power steering control valve, and then back to the pump from the output of the power steering control valve. There is a 0-1500 PSI gauge plumbed into the output of the pump before it hits the first valve so I can tell how hard the system is working.
With the engine running, both valves deenergized and the steering wheel centered, there is less than 50 lbs pressure showing on the gauge, as there are no significant restrictions in the system. If I turn the steering wheel, the gauge goes up to as much as 500 lbs, depending on how far and fast I turn the wheel. Once the wheel comes back to center, the gauge again falls to zero. When I run my winch unloaded, there is enough restriction to run the gauge up to about 200. When I'm dragging something out with the winch, the pressure goes up to 1000 lbs or more as the hydraulic motor in the winch creates backpressure. When I raise my snowplow, the gauge shows very little pressure until the cylinder is all the way up and hits the stop, and deadheads the pump, and then it goes up to 1200. Let off the up button and the pressure again falls to zero.
I am looking at the Ford truck shop manual right now (I've been trying to copy the page to post it here but it won't let me.) The Ford test fixture (Ford Tool T56L-33601-D) has a valve in series with a "calibrated flow determining orifice", and another valve teed in before that with a bypass around the flow determining orifice. The test procedure is to hook this up to the pump under test with the bypass valve open and start the engine. With the engine at idle, you close the bypass around the orifice, thus creating a restriction, and read the gauge. That's where you get your 620 lb. spec. With the bypass open, there is NO appreciable pressure.
Part 2 of the test is then to close BOTH valves and deadend the pump, and again check the pressure, which should be 1200 lbs. with the Ford pump, or 1350 with the Saginaw pump as supplied on the vans.
Ford Truck Shop Manual, pages 13-01-6 and 13-01-7. Steering -- General. Look it up .

 

Ok guys, I actually believe both of you, which doesn't do much for me, because I don't have power steering pressure kit, nor do I have the Ford Test fixture tool. I do have a hydraulic pressure guage which will give me the dead headed pressure, or I can tee it into the system on one of the lines going to my assist ram and see what operating pressures I get while steering the truck. Unfortunately that will not tell me if I am getting adequate flow.

Bullit390, I found the site you were refering to. Was there ever a tech manual that was specifically for the Garrison Steering Assist that was used on the 73-74 trucks? I would ultimately like to find some specs on the pressure design through the control valve.

 

Are the pressure specs any different for the Garrison c/v than they are for the Bendix c/v?

 

Don't really know, I have never seen any tech material for the Bendix system either. I believe the control valve drag link can be interchanged because the length from the pitman arm to the steering knuckle is the same. But I did have somebody tell me that the Bendix cylinder ram and the Garrison cylinder ram will not interchange due to differend lengths.

But who knows. It is amazing how little information there is for these steering systems. Even the Ford truck repair manuals refer to these systems very little, with basically no repair or service information. I'm sure there has to be some service manuals out there somewhere, but I can't seem to find them. I went to our ford dealer to see if they might have something in their archives, (which they didn't) and the mechanics really didn't even know what I was talking about.