Air being drawn into power steering system '92 Beretta

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  #1  
Old 11-19-17, 05:46 PM
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Air being drawn into power steering system '92 Beretta

The car is my son's '92 Chevy Beretta 3.1L V6.

The pump was leaking fluid from the rear cover o-ring and he had been dumping in a p.s. fluid/ leak sealer combo in order to continue driving the car. Other than the leak, the system was performing normally.

We removed the pump and replaced that o-ring as well as the shaft seal, reinstalled it including new fluid and attempted to bleed the air from it by cycling the rack lock to lock, with wheels raised and engine off, 40-plus times per the service manual.

The fluid leak no longer exists, however, it now suffers from substantial air ingress. This air entry is somehow caused by the turning of the wheel; we could cycle the rack (again, engine off) all day long and not see any improvement; air bubbles continue to be observed in the reservoir.

He has driven the car daily for some time now with no improvement noted; he says the pump is very noisy when cold, improving only somewhat as things warm up. Another observation that he mentioned is that when cold and particularly noisy, it seems to put a load on the engine, pulling the idle speed down.
We double checked fittings and they are secure.

In a nutshell, we know what the problem is; we just don't know where it is and we don't want to throw parts at it hoping one will stick.

What do you think?
 
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  #2  
Old 11-20-17, 05:52 PM
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Vacuum

Not uncommon to have air in a pump system after a repair, and can be difficult to remove solely with the procedure you have done. You can get a vacuum adapter for where the fluid cap is, and pull a 25 inch vacuum. You can use eg. a Mighty Vac hand unit, or an ac vacuum pump. You pull the vacuum, turn the engine on and turn the steering wheel lock to lock a dozen times. Turn engine off, release vacuum, check fluid level, and then repeat. That should get the air out of the system, this is what a dealer would do.

At the beginning of this procedure, if you leave the vacuum on for say 15 minutes, if it holds you do not have any leaks where air could get into the system.

It sounds like you may have a bearing failing in the unit, perhaps distorting a seal and sucking some air in, but more likely you would see a fluid leak as well. If the system is dry, I doubt there is air being sucked in somehow, more likely you never got all the air out in the first instance.

Of course, make sure you are measuring the fluid level correctly, you need the proper level and high pressure on the rack for the system to function well. Sometimes the solution is in the obvious, so make sure you are measuring the level as per the manual.
 

Last edited by flatcrank; 11-20-17 at 06:13 PM.
  #3  
Old 11-21-17, 12:13 PM
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Hi flatcrank, thanks for your thoughts.

I'll have a go at applying a vacuum and see of that helps.

I wonder though, if new air is not entering the system, would the fluid level not be dropping as all this air is rising to the surface in the reservoir and venting to atmosphere? He has driven the car for weeks and the fluid level is correct and stable.

What about all that stop leak he fed it before the repair; is it possible that the seals in the rack and pinion unit became unnaturally puffed up from the stop leak solvents, then receded when no longer exposed to that?
 
  #4  
Old 11-21-17, 03:14 PM
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Air

Air can stay in the system if not vacuum bled, otherwise there would be no need to vacuum bleed in the first instance. Same can happen when bleeding ABS brakes, somehow the pump design creates an air pocket trap and the air and can't get out without pressure assistance.

That said, the only way to get air into a pressurized system is through a seal or fitting, and there would be fluid leak as well. If the system has no signs of weeping or fluid loss (ie. when you measure after the weeks of driving is the level the same?), there will not be air getting in there (others can weigh in if this is incorrect, eg. I have heard a very worn rack can sometimes let air in, or the suction line is cracked or has a leak at the fitting but no fluid leaks out?).

It is possible you have a vane on the pump impeller damaged, and the pump is cavitating the fluid giving the appearance of air being in the system. Or an internal seal in the internal pressure regulator might be failing, or the internals of a fluid line perishing, and blocking the fluid flow, creating a starved condition similar to having low fluid, which will give rise to cavitation. Some cars have a filter built into the reservoir and if that gets clogged can create cavitation. Cavitation will make the system look like it has air in there.

The pump being noisy when cold tells me it may be worn, once the fluid warms it flows easier and puts less load on the pump. It is possible the pump was damaged by the original leak and fluid level was too low for a while before he caught the problem and topped up prior to repair.

Do double check the belt is tensioned and not slipping, belt slip can also mimic a worn pump, if fluid got on the belt it may have degraded.

If vacuum bleeding, fitting tightening and inspection for leaks, and a new belt/inspection does not solve, then you would appear to have a failing pump with noise and cavitation being the expected symptoms.

Not sure how one could diagnose a clogged reservoir or internally failing hose, without just replacing these parts preventatively. With the age of the car, this would not be a bad idea, eg. a 25 year rubber hose in engine bay heat is pretty good service life. Once a car gets this old, you are in the zone where you are restoring the car, if you do your own labour and the car is in good overall condition, the economics of keeping a car going can work out ok.
 
  #5  
Old 11-22-17, 06:32 PM
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Thanks flatcrank; I'll have another look at it. Hey, if nothing else, it can be good father/son bonding time!
 
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