1972 Power Steering
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Heel & Toe
Joined: Sep 2006
Posts: 19
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From: Pittsburgh PA
1972 Power Steering
I am finishing my resto on a 1972 small block and was wondering if there are any tips on ensuring there is no air trapped in my power steering system. I replaced all of the components and can't seem to find a bleeding procedure.
Le Mans Master
Joined: Dec 2006
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Le Mans Master
Joined: Jul 2000
Posts: 6,001
Likes: 112
From: Saginaw Michigan
POWER STEERING SYSTEM DEAIREATION - CORVETTE
Some people think that the power steering pump must be spinning (with the engine running) in order to circulate power steering fluid and drive the air out of a freshly repaired or assembled system. This is really not the case and actually can cause a real lengthening of the time required to “get the air out.”
When you start your engine and begin spinning the power steering pump any air that is trapped in the system begins circulating throughout the pump, gear, and hoses along with the power steering fluid. When large bubbles of air pass into the pumping area of the power steering pump the air and fluid get whipped to a froth as they engage the spinning rotor and vanes. The results will be a milky colored mixture of entrained air and oil that is now being pumped through the system. The mixture takes up more room (and expands far more as the fluid heats up) than pure fluid. So many times you will find that suddenly you reservoir is overflowing. You have also created a somewhat compressible fluid (because of the many, tiny, air bubbles.) This can now cause erratic power assist.
Once the fluid is filled with entrained air, it will now take quite a while for the very small air bubbles to come out of suspension from the fluid and make their way as larger air bubbles into the pump reservoir. You will note that the pump reservoir is typically the highest point in the hydraulic system. Left on its own, air will eventually rise into it and escape to atmosphere. However, this fluid action may actually take a several days.
First jack both front wheels off the ground. (Make sure that your jacks have clearance when the road wheels are turned to full lock.) With the engine off you can rotate the steering wheel back and forth (full lock to full lock) and the piston inside the assist cylinder will act as a pump. Rotating the steering wheel will gently move the fluid along with any large air bubbles through the circuit until the air can rise directly into the pump reservoir - and out. It is a good idea to hold the steering wheel at full lock for about 5 seconds each time before turning in the opposite direction. This allows the air to rise into the pump reservoir with each steering cycle.
Refill the pump reservoir to the COLD mark on the capstick and rotate the steering wheel lock to lock many times again. This should get MOST of the air out. Then drop the car back down and start the engine. Try a few more lock to locks but now be sure NOT to hold the steering at full lock for more than just a few seconds. Recheck the fluid level and fill if required. Go for a 10 mile drive.
One last tip, I recommend that you use genuine GM power steering fluid that is available from GM dealerships. I don't recommend using the stuff that is labeled, "Meets everyone’s specifications." The only fluid that has been tested in tens of thousands of Saginaw laboratory tests and millions of vehicle test miles is the GM fluid. Also the GM fluid is pretty good at dispersing the air out of fluid suspension.
Jim
Some people think that the power steering pump must be spinning (with the engine running) in order to circulate power steering fluid and drive the air out of a freshly repaired or assembled system. This is really not the case and actually can cause a real lengthening of the time required to “get the air out.”
When you start your engine and begin spinning the power steering pump any air that is trapped in the system begins circulating throughout the pump, gear, and hoses along with the power steering fluid. When large bubbles of air pass into the pumping area of the power steering pump the air and fluid get whipped to a froth as they engage the spinning rotor and vanes. The results will be a milky colored mixture of entrained air and oil that is now being pumped through the system. The mixture takes up more room (and expands far more as the fluid heats up) than pure fluid. So many times you will find that suddenly you reservoir is overflowing. You have also created a somewhat compressible fluid (because of the many, tiny, air bubbles.) This can now cause erratic power assist.
Once the fluid is filled with entrained air, it will now take quite a while for the very small air bubbles to come out of suspension from the fluid and make their way as larger air bubbles into the pump reservoir. You will note that the pump reservoir is typically the highest point in the hydraulic system. Left on its own, air will eventually rise into it and escape to atmosphere. However, this fluid action may actually take a several days.
First jack both front wheels off the ground. (Make sure that your jacks have clearance when the road wheels are turned to full lock.) With the engine off you can rotate the steering wheel back and forth (full lock to full lock) and the piston inside the assist cylinder will act as a pump. Rotating the steering wheel will gently move the fluid along with any large air bubbles through the circuit until the air can rise directly into the pump reservoir - and out. It is a good idea to hold the steering wheel at full lock for about 5 seconds each time before turning in the opposite direction. This allows the air to rise into the pump reservoir with each steering cycle.
Refill the pump reservoir to the COLD mark on the capstick and rotate the steering wheel lock to lock many times again. This should get MOST of the air out. Then drop the car back down and start the engine. Try a few more lock to locks but now be sure NOT to hold the steering at full lock for more than just a few seconds. Recheck the fluid level and fill if required. Go for a 10 mile drive.
One last tip, I recommend that you use genuine GM power steering fluid that is available from GM dealerships. I don't recommend using the stuff that is labeled, "Meets everyone’s specifications." The only fluid that has been tested in tens of thousands of Saginaw laboratory tests and millions of vehicle test miles is the GM fluid. Also the GM fluid is pretty good at dispersing the air out of fluid suspension.
Jim
