Air in PS fluid

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TacticalTruck

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I've got an M916 that has a power steering problem. I first noticed it when I found the fluid low and added some. The fluid over flows after the truck is shut down. If the cap is on it come out like a geyser. I've tried turning it from lock to lock a hundred times and tried bleeding the lines to the cylinder on the passenger side. I even threw another pump on it. There are no leaks. Any ideas where the air is coming from. The TM says turn lock to lock and you're done.
 

simp5782

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Are the flares on the fittings on the steering gear box cracked or broken? What condition are the hoses in.?
 

NDT

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Exact same problem with mine. Totally confused about how air gets in the lines as they are all under pressure. Except for maybe the cooler lines?
 

TacticalTruck

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If NDT doesn't know that's trouble. Lines and fittings all appear good. You'd think they'd leak when under pressure if there was a hole.
While bleeding the cylinder, I seemed to get a lot of air on the left turn side. I keep going back to something internal on the steering box. I've got another one but it's not the kind of job I want to do on a guess.
 

someoldmoose

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Suggestion, but you won't like it. Make a plate and gasket to sit on the reservoir fill opening and pump a vacuum on it. Have someone turn the steering wheel lock to lock with the engine OFF. Much easier with the front wheels off the ground, obviously. Had to do this to many rack n pinion cars. Those lil bubbles hide in strange places and get compressed when the system is under pressure then expand with the same force that was applied to them when pressure drops. No promises, but not a complete mystery problem.

If air is still getting in somehow the seal where the pump attaches to the reservoir body can leak air in when the pump draws fluid from the reservoir. That's the only place in the system that is under "vacuum" at any point.
 

someoldmoose

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Not as long the fluid isn't all the way to the top of the fill opening, which it shouldn't be anyway. You're just making a negative pressure above the fluid for the air to find it's way into.
 

NDT

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I noticed on mine, after it puked fluid several times, looking in the PS pump reservoir, the fluid pouring back into the pump is severely aerated. Leading me to believe this is happening somewhere other than the pump.
 

someoldmoose

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NDT, is your reservoir can dented anywhere ? I am making the assumption that you have the cast metal pump that sticks out of a "tin can" reservoir. ( Sorry not somewhere that I can throw in a sample pic ) It only takes a tiny amount of air to turn the fluid to foam when the pump runs. My tip works best after the foam has settled down but will work, just takes longer. I sometimes had to do it a few times to get it all.
 
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TacticalTruck

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I'm using a high dollar hydraulic fluid I had left over from a defense job and it's brown but it also gets so aerated that is gets a chocolate milk look to it. Yes, oldmoose, that's what these look like. I threw a pump at it originally because I thought the only place it could be sucking air was between the casting and the tin reservoir.
 

someoldmoose

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Unfortunately the tin can often gets pushed on when adjusting belts. Total NO NO. If the seal is disrupted "just enough" air can be drawn in but it will still hold the "head" pressure of the liquid in the reservoir ( no wet spot on outside ). Fords were notorious when they switched to plastic. Engine heat warped the reservoir, the seal let air in, power assist was lost, owner stopped, reservoir cooled, power assist came back. They switched to a remote reservoir and the problem disappeared.

The fluid you are using should not make a difference as long as it has the same characteristics as ATF ( low viscosity, high anti-foam index) although I always recommend using the approved fluid whenever possible.
 
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someoldmoose

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Ah, right procedure, wrong pump. The vacuum trick will still work for getting all the air out that is already in. Finding where "new" air is getting in can be the main pain.
 

Postman515

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I have my cooler disconnected and works a lot better now. I've noticed if you idle these trucks a few seconds before shutting off and not turning wheel it won't gyser the fluid. if you turn and then shut off right away for whatever reason it blows out of overflow
 

TacticalTruck

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Ok, thanks for responding. It's not exactly the answer I was looking for but it might keep me from hanging a replacement steering box.
I've just got to be able to explain it to my customer buying the truck. I just disconnected the cooler and the right ram and it made no difference.
Still foaming bad.
 

Wildchild467

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I am not sure if they are a similar, but here was my finding with an M818 that had a problem like that:

Make sure your steering linkages are all tight. I mean the slave cylinder on the right side and the steering box on the drivers side. If the ball and socket is loose, it can cause it to shutter back and forth trying to find the happy medium but it wont let it. I saw this once on an 818 I worked on. If they are loose at all, tighten them up according to the TM.
 

Jbulach

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I would flush that "high dollar fluid" and put the correct stuff in before throwing anymore parts at it...
 
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