GMC Western States
Tech Center Number 14 - March 1996
RENEWING THE POWER STEERING HYDRAULIC SYSTEM
by Egon Elssner
ANYONE WHO HAS NOT HAD HANDS-ON EXPERIENCE WITH THE GMC POWER STEERING SYSTEM IS ADVISED TO READ SECTION 9 OF THE X7525 GMC MOTORHOME MAINTENANCE MANUAL. THE MATERIAL CONTAINED HEREIN IS ONLY OFFERED AS A SUPPLEMENT TO THIS MANUAL.
Three groups of parts make up the hydraulic system: steering gear box [called Gear Assy. Steering], power steering pump [called Power Steering Hydraulic Pump] and connecting hoses. Only the pump and connecting hoses will be considered here.
Power steering pump [PS pump]. A pump that leaks, makes unusual noises or fails to deliver adequate pressure is a candidate for rebuilding or replacement. Although these pumps can function for well over 100K miles, sometimes it's a good idea to renew them before they fail. One indication of pump deterioration is when you can feel surges [kickback in the steering wheel] while you turn the steering wheel, an indication of internal pump wear.
Hoses. Because hydraulic pressures of up to 1400 psi are common when power assist is called for [while, for instance, parking on dry pavement] these high pressure hoses can split or leak causing a potential fire hazard. If the steel lines in the pressure side of the pump are in good condition [no corrosion] there are local shops that can replace the flex hose part of these lines [and metal too] at very reasonable cost. The hose from the steering gear box to windshield wiper motor is a metal reinforced hose [similar to the Aeroquip hose used on the original engine oil cooler lines] with reusable end fittings. It too, can be renewed very inexpensively.
Preliminary: Remove the left [drivers side] front wheel fender. Raise the front of the coach and block up the main frame so that you can safely work under the coach. Raise the coach high enough so that the front wheels can be turned from limit to limit without dragging. Remove engine hatch cover.
Loosen Alternator and PS pump securing bolts, slip off the fan belts and remove them or drape them over the water pump/fan pulley to avoid getting oil on them. For more visibility or if replacing the Alternator at the same time, remove it.
Cut/remove the PS pump low pressure return line hose [the line with hose clamps that goes from the pump inlet to a steel tube running up the side of the radiator housing] and drain the oil into a suitable container [this is a sloppy process]. To remove some of the old oil from the steering box, turn the wheels from lock to lock, being careful to catch the old oil. Spinning the pump pulley clockwise, by hand, [viewed from the front of the engine] may also help drain the pump. Remove the upper low pressure return hose [from the outlet of the windshield wiper motor going over the top of the radiator housing to the steel tube mentioned earlier]. Loosen the PS pump high pressure line from the rear of the pump, again, catching the oil.
Remove the two large sheet metal screws that fasten the clamps holding the high pressure line. These are found on the inside of the curved front frame section. Loosen and disconnect the two lines from the steering gear box using tight fitting wrenches or flare nut wrenches to minimize distortion of the fittings. Remove the high pressure line [with attached short hose]. Loosen and remove the steering gear box to windshield wiper high pressure hose after removing the hose clamp bolt on the radiator housing.
Remove the Filter Assembly [looks like a short brass nipple] from the windshield wiper motor, using a small pipe wrench to unscrew the nipple [be careful not to drop this Filter Assembly because one end is a machined cone for a flare fitting]. Using "brake cleaner" from an aerosol can, flush out this fine mesh filter from both ends, and keep in a safe, clean place. It is reusable.
Take the two high pressure hose assemblies to your local hydraulic hose shop and have new hoses fitted to them or made-up. The working pressure of the high pressure hose [PS pump to steering gear box] is approximately 1400 psi. A hose rated at 2500 psi should be a good choice. A good shop will know what is suitable.
To remove the PS pump it is necessary to remove what is called "the adjusting link" or pump mounting plate with the pump still connected to it, and a bracket [the rear pump pivot] as an assembly [See the X7525 GMC Maintenance Manual, Fig. 7 on page 9-15 for pictures of the pump and mount]. This is necessary because the pump cannot be removed from the adjusting link as is.
The right side of the rear pump pivot bracket is fastened to the engine by a single large bolt. Remove it. The adjusting link is fastened to the engine with 3 bolts. Two are on the left side near the engine crank pulley and one is on the fight side. The right side one [a small one] fastens the adjusting link to a small brace which is, in turn, is bolted to the cylinder head. After this brace is removed, loosen and remove the lower left nut holding the adjusting link to the front of the engine with a socket wrench fitted with a short extension. This nut is accessible if the PS pump is tilted clockwise as far as it will go. From the inside of the coach, find the top nut holding the upper left part of the adjusting link. Loosen this nut while holding the pump, adjusting link and rear pump pivot bracket assembly. Make sure the whole assembly is now loose and can slide easily [forward] on these two studs. If it looks like it will stay put [or have someone watch it from on top], go under the coach and remove this assembly by pulling forward and carefully lowering it to the floor [turning the wheels one way or the other may buy you more clearance between radiator, frame and steering drag link/relay lever]. Separate the rear pump pivot bracket from the adjusting link by removing one bolt and, of course, the rear pump nut.
If you have bought a replacement pump you will most likely need to remove and reinstall the pump pulley with an appropriate pulley puller. Beware of bending the pulley, they bend rather easily.
If you have a pump rebuilder handy, they will take the pump with pulley and adjusting link and return it to you as a unit. This is the easy way to go.
Installation: Bolt the rear pivot bracket to the adjusting link, [loosely] and add the rear pivot nut [loosely]. Lift the pump and assembly into place and hold temporarily with the upper nut [loosely]. Reinstall the lower nut [loosely]. Replace the large bolt fastening the pivot bracket to the engine[loosely]. Install the brace on the right side of the adjusting link to cylinder head [loosely]. Starting with the two left nuts on the adjusting bracket, tighten but do not torque. Temporarily tighten the pump front pivot bolt and rear pivot nut. Tighten the rear pivot to the engine bolt followed by the pivot to adjusting link bolt. Finally tighten the bolt/nut and bolt on the brace. Torque all fasteners, but loosen pump pivot bolt and nut so that it can be turned easily for belt installation.
Reinstall the hoses, starting with the high pressure line/hose. With the line loose, start the fitting going to the inlet side of the steering gear box [the left side, slightly lower than the fight side]. See the Maintenance Manual if in doubt. This fitting may be hard to get started. It must start by finger tightening only. If you use force there is great danger of cross-threading and destruction of the threads in the steering gear box. While the line is still loose, tighten but do not torque this fitting. Clamp the line to the frame with the two large sheet metal screws. Connect the hose to the pump outlet fitting, again using care not to cross-thread. At this time torque the steering gear box end only. The PS pump end will be torqued after the belts are installed.
Reinstall the Filter Assembly [brass nipple] to the windshield wiper motor using a small amount of Teflon tape on the threads on the upper end [taking care not to get any tape residue into wiper motor after assembly]. Attach the other hose assembly to it and tighten. Run the hose through the hose clamp [bolted to the radiator housing], and attach the free end to the outlet of the steering gear box using care not to cross thread. Torque both ends and tighten clamp bolt.
Install new hose for the two low pressure return lines and install clamps. Using new high quality clamps that do not "pinch" the hoses is a good idea.
Adding a Delco PF 883 power steering fluid filter at this time is
Cut the lower low pressure return line [between the PS pump inlet and
tube running up the radiator shroud] and install the filter with
Pay attention to the direction of oil flow marked on the filter. Pump
PS pump and Gear toward the steering gear box.
Add new oil to the PS pump reservoir. Spin the pump, by hand, counter-clockwise [opposite normal rotation] to oil the pump vane cavities. Reinstall alternator, if removed, and all fan belts. Tension Power Steering Belt with a tightening tool that looks like an oversize screwdriver between a tab bent out of the Adjusting Link and a boss on the power steering pump hub. Do not put force on the pump reservoir, you will damage or destroy the pump reservoir housing. Tension remaining fan belts. Torque the high pressure hose fitting on the PS pump, pointing the direction of the hose end in a way that will minimize mechanical hose stress after the fitting is torqued.
Filling and bleeding: You have drained out roughly a quart of old oil. The reservoir does not hold that much oil so it is important to use the follow procedure to prevent a great deal of aeration of the oil [foaming] while adding oil. Add oil to the reservoir [OK to fill moderately full when starting out]. It is OK to leave the cap off the reservoir to watch the oil. Start the engine and run for a couple of seconds only, shut off As all the oil is pumped from the reservoir you will hear cavitation [air going into the system], something you don't want too much of, but there will be some foaming at this time anyway. Add more oil. Restart and repeat. Listen for cavitation, the pump will make gurgling sounds telling you that the system still needs more oil. When the system is full, the foam will disappear and it will be possible to see the oil in the reservoir. Turn the steering wheel from complete fight to complete left [avoiding hard lock to lock] to ensure a complete fill. Top or siphon off as needed.
Check for leaks, replace the wheel housing and lower the vehicle.
drive and recheck the oil level. For the first few hundred miles watch
for leaks and keep an eye on the oil level. Investigate any unusual
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