Buick Grand National Steering Box Build - Straight Arrow

Volume Check

The power-steering pump is a less complicated animal but still deserves the same level of blueprinting. Tom Lee explained that the factory Chevelle pump is a sound piece that delivers adequate pressure (about 1,250 psi at peak) for low-speed or no-speed turns. Volume, not pressure, is the important factor in matching an older pump with a newer, faster-ratio steering gear. Charlie Hutchinson led us through the teardown and reassembly. The Chevelle uses a vane-style pump that's pretty simple in operation, so it's straightforward to rebuild. After Hutchinson pulled it apart, the shaft was bead-blasted and polished. A new seal was installed in the housing for good measure. Hutchinson checked for excessive clearance between the rotor and the liner and found tolerances to be within spec, so they were lightly sanded and the pump was reassembled with new O-rings and seals.

The size of the flow control valve (FCV) orifice dictates how much fluid volume is pumped through the steering gear. Additionally, the FCV contains a spring and a check-ball to cut off the maximum pressure the pump will generate, for example, when the driver spikes the pressure at full lock during a parking maneuver. Aiming for a 2.75 gpm flow rate, Hutchinson drilled out the orifice in the FCV to 0.148 inch (#25 drill) on a lathe. The 1,250-psi cutoff pressure was verified on an in-house test machine, and while it can be changed with shims or springs, we left it alone. Pumps are bench-tested on Lee's own test rig, and ours flowed exactly 2.75 gpm as expected.