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Tim, you have described the pump non return ball. If the ball is not centered it will wander off and can cause low pressure. If it is wandering, the plate it rides in is installed upside down or flattened. Be default, the ball seeks the center of the dished plate and covers the hole the fluid gets pumped through. A spring helps keep it there as the car leans in corners and up and down hills.
The relief valve can best be described as a disc with a small rod stuck up from the center of one surface. The disk rides on top of a couple of springs and the rod sticks though a sleeve which has a hole in the side. When pressure on top of the rod pushes down on the springs, pressure is relieved as the hole in the side is exposed. Since the springs are contained in a closed end cylinder, a dashpot, when a small amount of pressure is applied below the dashpot, it is amplified in relationship to the small surface area of the top of the rod. This causes a pressure build up below the dashpot and above the relief valve which eventually engages the OD. At some point the pressure below the dashpot is proportionaly the same as that above the relief valve and any excess proportional pressure is then relieved through the side port of the sleeve.
The relief valve in the OD has one O-ring around the disk to act as a positive seal. There is negligible pressure on this O-ring and once the OD has been engaed by the factory or anybody else it is not usually subject to wear or deterioration. The total movement of the valve is less than 1/4 inch under normal operating parameters with a max of about 5/16 inch before the dashpot bottoms out on the plug that seals its opening. Once in it does not like to come out as the combination of disc and O-ring is greater than the diameter of the hole it is installed in. It takes quite a bit of effort to remove it even with a special tool. It is possible for the valve to get stuck with those symptoms being either no engagement if stuck down or self engagement if stuck up. If somewhere in between, slippage would most likely occur in starting in second and continuing through four with no OD engagement possible since the valve cannot move to block the relief port sufficeintly to cause full lock of the sliding member.
Duane
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