Power Steering Question, late 1958 JD 620

I don't have my I&T handy for the later (-20 series black dash upgraded) worm area, and my SM2050 is an "original" which shows only the helix screw type used on the original design on the numbered series, so I can't refer you to the exact page until I get those out. Most of the numbered tractors by now have been upgraded to the adjustable through-the-front-of-the-worm tension adjustment that came out on the -20's, but yours might not. See if you can determine from the parts book which style that you have. In your parts catalog PC-528, Page 50-7, Item 18 and 19, the adjustment bushing and the thru-socket set screw are present in the upgraded style. It's important that we know. That is the check that you need to set using a dial indicator if you really want it to be right.

With the actuator/cam assembly in your hand, it should index (that is up the hill of the cam and down the hill of the cam) to the left and to the right with equal ease. Also, make sure that your steering wheel shaft forward is free enough in the bushing to slide forward and aft a small amount easily as this movement is required so that the cam can deflect and push the lever arm forward or back when attached to the valve poppet, and make the valve slide smoothly.

I don't think that you have a pump issue or you would not be getting that pressure, and I don't think that you have a vane seal issue because you have a fairly low leakage rate.

You can increase the flow up to the point of flutter and see if that makes any difference, and put it back if it does not, but I still think that you are not getting proper fore and aft movement of the valve body, which means that you get no fluid flowing into the cylinder to aid in turning. What you describe sounds just like the valve is stuck, or maybe the lever is loose, or some other wear point has caused more play than the cam face can equal in deflection distance.

Frank

As a point of background, when you exert more torque on the steering wheel than the spring-loaded cam can withstand, the wheel begins to turn, and the pins slide up the angled cam face. This moves the toggle for or aft, which pushes or pulls on the valve body. This movement translates into exposure of the fluid posts which route pressure to one or the other side of the hydraulic cylinder, aiding to move the wheels. If the pins don't slide on the cam face, or the valve body is sticking, the valve will not displace and the wheels will get no assist. One other problem comes from a steering wheel shaft that is binding in the bushing up at the instrument panel as the shaft has to be able to move in and out ever so slightly so that the cams can displace for and aft, and hence move the valve body. Start at the wheel end, make sure it is free and correct, then check the worm end play inner spring setting. This is the slight play (like .0015") that is set between the cams/pins/actuator cam using the internal spring. Look that over to make sure things are set correctly, not too tight, or the bingding might keep the cams, etc. from sliding and working to deflect the actuator valve. Unless you have a huge divot in the cam faces to the point where the pins hang up when attempting to slide, I am betting that you have a valve hanging up. OR, before you try all of this, you could try increasing the fluid flow rate, but since you have enough pressure and volume to generate a measurable leak down past the seals, I still think you have a valve body sticking issue.