Air in power steering pump

[w113abudhabi]

Hello, I hope someone can offer some support.
My mechanic has installed a replacement power steering pump seal kit on my 1970 280sl. The kit is genuine mercedes purchased from the classic center. Prior to removing the pump the only issue was a fluid leak. The steering functioned well.

Now there appears to be a lot of air trapped in the pump resulting in no power steering at low revs. They have tried bleeding the air out of the pump following the mercedes manuals but still air remains.

Any suggestions please?

[Cees Klumper]

All I know to bleed air from power steering systems is to turn the wheels lock to lock with the engine running, until the air is purged. Not sure whether this is supposed to also work 100% on our W113's.

[MikeSimon]

Any P/S system will purge itself after a while, using the procedure Cees described. Some have a bleed screw to ease the process. The Pagoda steering gear has that. It sits on top towards the steering shaft input. Connect a hose to the nipple and stick the other end into the open reservoir on the pump. Open the nipple two full turns and let the air come out.
When done, close everything up, let the engine idle and turn the steering wheel several times end to end. repeat the bleeding to ensure all air is out.

[w113abudhabi]

This is exactly the process that has been followed repeatedly yet still air continues to be present and prevent any power assistance at low revs.

[MikeSimon]

Air in the p/s system will show itself by noise and/or a foaming fluid in the pump reservoir. If you do not have that, your power steering pump may be faulty, especially as you refer to "no support at low revs".
Air can be trapped at a high point in the circuit. Make sure hoses are properly routed and there is no high loop where air could sit. Other than that, it is, maybe, a matter of being persistent and keep bleeding.

[w113abudhabi]

Yep plenty of foam

[Benz Dr.]

That's because someone didn't read carefully back when I posted about this procedure. ( others may have as well )

 Do this with your engine OFF. A running engine will only churn all of that air into foam. Remove the cover on your canister and add ATF as required because it will lower as the air gets purged out. You really don't need to go full lock and side to side will work well enough until you can't see any more air coming out and then go full lock a couple of times. This may cause the tank to overflow so leave it a bit low until finished and then top up at the end.

Do this on well rested ATF without any hint of trapped air in it.

 

[MikeSimon]

Dan: How do you get the air out of the system without the pump running and pumping?

[Benz Dr.]

Dan: How do you get the air out of the system without the pump running and pumping?

When you turn the steering wheel it moves the steering box internals and forces any air out with the ATF. The trick is to lift the front of your car so the tires are not touching the ground so the wheel turns more easily. Trust me, it works like 10 men.

[MikeSimon]

I figured that this was the idea behind it. But this way, you only move the piston in the steering gear. Any air way down in the system and the hoses will not come out. If the bleed nipple is on the highest point in the system, you may have success.

[MikeSimon]

If continuing efforts to purge the air will fail, you may still have an issue with the pump.
While I worked for Vickers, all our power steering pumps, by design, had a bore that connected the space immediately behind the front shaft seal to the inlet.
This was done to "suck" the fluid that would accumulate behind the seal back to the inlet and avoid building up pressure in the area, which would cause leaks.
I don't know if the VT27 had that feature already, but I assume so.
The shaft seal is a double-lip seal, which seals towards the inside and the outside. If this seal does not sit right or the lips do not make proper contact with the shaft, the pump will "suck" air through the seal and you will continue to have air in the system.

[Benz Dr.]

I figured that this was the idea behind it. But this way, you only move the piston in the steering gear. Any air way down in the system and the hoses will not come out. If the bleed nipple is on the highest point in the system, you may have success.

It actually sucks fluid out of the canister as you move the steering wheel then it pushes it back into the canister when you turn the wheel in the opposite direction. During this process any trapped air will simply escape. I can only tell you that it works.

I've used the bleed nipple on the steering box with engine running and usually ended up with a mess.   

[MikeSimon]

Mmmmh….That will not make sense to me. If the engine does not run, the flow control valve inside the pump is in the "closed" position, which will effectively cut off the connection between the pump and the steering gear. I cannot see, how moving the piston in the gear will "suck" fluid out of the reservoir.
But if that method works for you, Dan, more power to you.
Sometimes "engineering science" does not have an explanation for everything.

[Benz Dr.]

Mmmmh….That will not make sense to me. If the engine does not run, the flow control valve inside the pump is in the "closed" position, which will effectively cut off the connection between the pump and the steering gear. I cannot see, how moving the piston in the gear will "suck" fluid out of the reservoir.
But if that method works for you, Dan, more power to you.
Sometimes "engineering science" does not have an explanation for everything.

OK, maybe I can't explain how it works, yet I know for a fact that it does. Why don't you try it and see for yourself? 

 I'm not talking about the  pump; I'm talking about the steering box, which when moved through the steering wheel WILL in fact push all of the air out. If your canister gets too low during this process you will indeed hear a suction sound so fluid is moving in that direction. 




 

[Aaron h]

Mmmmh….That will not make sense to me. If the engine does not run, the flow control valve inside the pump is in the "closed" position, which will effectively cut off the connection between the pump and the steering gear. I cannot see, how moving the piston in the gear will "suck" fluid out of the reservoir.
But if that method works for you, Dan, more power to you.
Sometimes "engineering science" does not have an explanation for everything.

Mike, the valve you make mention of is an over pressure valve, and will remain closed until hydraulic pressure from the locking of the steering wheel (full left lock or full right lock) opens it.  It's in place to prevent excessive pressure build up when in full left/right mode.  Otherwise oil would spew out of every O-ring and radial seal on the high pressure side of the pump and gear box.  What you call a "flow control valve" is actually a "pressure" valve, and is located inside of the steering gear box itself.  It is actuated by movement of the steering wheel.  It essentially directs oil under pressure to the front or rear side of the power piston inside of the steering gear box. 

Benz Dr.'s method of bleeding the system is, in fact, a very easy and fool proof way to bleed the system of air.  By moving the wheels left to right WITHOUT the engine running causes the power piston to literally suck oil into the system, and when moved in the opposite direction the displaced air escapes through the reservoir.  You must remember that the procedures listed in the BBB aren't always the best, correct, or easiest methods. The BBB isn't the law.....it's only a suggestion.

You mentioned that you don't understand how moving the piston in the gear will "suck" fluid out of the reservoir.  It's simple......imagine a syringe sucking a liquid up into it.  The only difference is in a syringe there is no air to displace, and if there is you simply turn it needle side up and depress the plunger until the air bubble has escaped through the needle.  An even better example is one of those under water water pumps you use in something like a koi pond.  When the system is new or has been serviced the water lines are full of air.  As soon as the pump starts moving water the water displaces the air in the lines until the lines are full of nothing but water.   Likewise, the more times the power piston in the steering gear box moves from top to bottom, and them from bottom to top, more and more air will be displaced.  Though, during the process keep the bleeder screw open and plug it off with your finger when the power piston is on the down stroke.  Otherwise it'll constantly suck air in.  On the upstroke of the power piston release your finger off of the bleeder screw.  When oil starts to emerge from the bleeder screw all/most air has been displaced.  Any residual will be displaced by running/driving the car.  Even if you didn't bleed the system at all the system would eventually displace all of the air on its own.  It would just take several miles, initially no power assist, and putting up with some groaning from the system until all of the air was displaced. 

There is ALWAYS a hydraulic connection between the pump and the steering gear box.  There is no valve that prevents this (except when in full lock left/right).  There are several ways to achieve bleeding the power steering system.  The methods listed in the BBB and by Benz Dr. are the easiest, cleanest, and less time consuming methods.  All methods lead to the same end result.  How you get there is your choice.  Just keep an open mind about how to approach things like this.  Never take the BBB seriously, and never overthink the process or try to improve upon it.

[Pawel66]

I am sorry to interfere here, again, ahead of the front line of my knowledge...

But I was working on the steering box of my W463 recently. I think the control valve is open, in essence, and it is closed in "far" positions by piston or something moved by piston to cut the flow in the "far" or lock position, to cut fluid/cut power to stop turning the wheel.

Am I correct or it is too late here already?

[Aaron h]

Well, there are actual mechanical stops to stop the wheels from turning on the spindles.

The control valve you make mention of......are you referring to the over pressure valve in the pump itself, or the actual pressure valve in the steering gear box? I have to assume from your commentary that you're referring to the over pressure valve.  If so, then I have to assume that it's always closed since it's under spring pressure upon installation, and opens upon over pressure, which allows fluid under pressure to bypass the steering gear box and return to the reservoir.  Then again I could be very wrong......I often am! 

[Benz Dr.]

Mike, the valve you make mention of is an over pressure valve, and will remain closed until hydraulic pressure from the locking of the steering wheel (full left lock or full right lock) opens it.  It's in place to prevent excessive pressure build up when in full left/right mode.  Otherwise oil would spew out of every O-ring and radial seal on the high pressure side of the pump and gear box.  What you call a "flow control valve" is actually a "pressure" valve, and is located inside of the steering gear box itself.  It is actuated by movement of the steering wheel.  It essentially directs oil under pressure to the front or rear side of the power piston inside of the steering gear box. 

Benz Dr.'s method of bleeding the system is, in fact, a very easy and fool proof way to bleed the system of air.  By moving the wheels left to right WITHOUT the engine running causes the power piston to literally suck oil into the system, and when moved in the opposite direction the displaced air escapes through the reservoir.  You must remember that the procedures listed in the BBB aren't always the best, correct, or easiest methods. The BBB isn't the law.....it's only a suggestion.

You mentioned that you don't understand how moving the piston in the gear will "suck" fluid out of the reservoir.  It's simple......imagine a syringe sucking a liquid up into it.  The only difference is in a syringe there is no air to displace, and if there is you simply turn it needle side up and depress the plunger until the air bubble has escaped through the needle.  An even better example is one of those under water water pumps you use in something like a koi pond.  When the system is new or has been serviced the water lines are full of air.  As soon as the pump starts moving water the water displaces the air in the lines until the lines are full of nothing but water.   Likewise, the more times the power piston in the steering gear box moves from top to bottom, and them from bottom to top, more and more air will be displaced.  Though, during the process keep the bleeder screw open and plug it off with your finger when the power piston is on the down stroke.  Otherwise it'll constantly suck air in.  On the upstroke of the power piston release your finger off of the bleeder screw.  When oil starts to emerge from the bleeder screw all/most air has been displaced.  Any residual will be displaced by running/driving the car.  Even if you didn't bleed the system at all the system would eventually displace all of the air on its own.  It would just take several miles, initially no power assist, and putting up with some groaning from the system until all of the air was displaced. 

There is ALWAYS a hydraulic connection between the pump and the steering gear box.  There is no valve that prevents this (except when in full lock left/right).  There are several ways to achieve bleeding the power steering system.  The methods listed in the BBB and by Benz Dr. are the easiest, cleanest, and less time consuming methods.  All methods lead to the same end result.  How you get there is your choice.  Just keep an open mind about how to approach things like this.  Never take the BBB seriously, and never overthink the process or try to improve upon it.

I keep the bleeder screw closed - cuts down on the mess. BTW, you're hired!

[Pawel66]

Well, there are actual mechanical stops to stop the wheels from turning on the spindles.

The control valve you make mention of......are you referring to the over pressure valve in the pump itself, or the actual pressure valve in the steering gear box? I have to assume from your commentary that you're referring to the over pressure valve.  If so, then I have to assume that it's always closed since it's under spring pressure upon installation, and opens upon over pressure, which allows fluid under pressure to bypass the steering gear box and return to the reservoir.  Then again I could be very wrong......I often am! 

I thought I talked overflow valve in the steering box. Then I go t it wrong. Thank you and sorry for messing around.

[MikeSimon]

Sorry, guys. I worked for the manufacturer of the W113 power steering pump - Vickers in Bad Homburg, Germany
I appreciate all the opinions of what the p/s system does and how it works, but I was actually paid for knowing that.
The pump has a valve, which is a combined flow control/pressure relief valve.
The flow output of the pump is direct proportional to the pump speed, i.e. rpm of the engine.
The pump would put out an excessive amount of fluid at high rpm and /or cavitate. That is why it has a "flow control valve"
This is a spool, which sits inside a bore. It moves horizontally and allows  flow to the pump discharge port until its horizontal movement opens an orifice inside and thus limits the flow at that point.
The spool also has a check valve inside which works against a calibrated spring and opens at a certain back pressure. When a maximum pressure is reached the check valve opens and bypasses output flow thus limiting the pressure in the system preventing seals and hoses from blowing up.
There is only one other valve in the system, and this is the steering valve actuated by the steering wheel/column. This is a rotating sleeve valve which directs flow to either the right or left side of the piston in the steering gear creating support.
Hydraulics 101: No pump creates pressure. A pump creates only flow which in turn, depending on the resistance and diameters of the output creates a pressure. If you disconnect the "pressure hose" from the pump to the steering gear and rev the engine up, you would just see fluid splashing out. The pressure relief valve in the pump would not cut in, no matter how high the engine revs or how far you turn the wheel. If you connect everything, you will hear the pressure relief valve "hissing" when you turn the steering wheel to a stop, thus preventing the piston in the gear from moving further and the pump "working against a wall". A safety feature.
All bypasses are happening in the pump.
There are steering systems that have an additional relief valve in the steering gear/box, but the Mercedes gear is not one of them. This is done when engineers try to prevent the pump from overheating by recirculating flow at pressure relief internally. You should never hold the steering wheel at wheel lock (end of turn) for longer than 30 seconds. You will "fry" the pump.

[Benz Dr.]

Sorry, guys. I worked for the manufacturer of the W113 power steering pump - Vickers in Bad Homburg, Germany
I appreciate all the opinions of what the p/s system does and how it works, but I was actually paid for knowing that.
The pump has a valve, which is a combined flow control/pressure relief valve.
The flow output of the pump is direct proportional to the pump speed, i.e. rpm of the engine.
The pump would put out an excessive amount of fluid at high rpm and /or cavitate. That is why it has a "flow control valve"
This is a spool, which sits inside a bore. It moves horizontally and allows  flow to the pump discharge port until its horizontal movement opens an orifice inside and thus limits the flow at that point.
The spool also has a check valve inside which works against a calibrated spring and opens at a certain back pressure. When a maximum pressure is reached the check valve opens and bypasses output flow thus limiting the pressure in the system preventing seals and hoses from blowing up.
There is only one other valve in the system, and this is the steering valve actuated by the steering wheel/column. This is a rotating sleeve valve which directs flow to either the right or left side of the piston in the steering gear creating support.
Hydraulics 101: No pump creates pressure. A pump creates only flow which in turn, depending on the resistance and diameters of the output creates a pressure. If you disconnect the "pressure hose" from the pump to the steering gear and rev the engine up, you would just see fluid splashing out. The pressure relief valve in the pump would not cut in, no matter how high the engine revs or how far you turn the wheel. If you connect everything, you will hear the pressure relief valve "hissing" when you turn the steering wheel to a stop, thus preventing the piston in the gear from moving further and the pump "working against a wall". A safety feature.
All bypasses are happening in the pump.
There are steering systems that have an additional relief valve in the steering gear/box, but the Mercedes gear is not one of them. This is done when engineers try to prevent the pump from overheating by recirculating flow at pressure relief internally. You should never hold the steering wheel at wheel lock (end of turn) for longer than 30 seconds. You will "fry" the pump.

So, what are we actually talking about? I thought it was simply bleeding air out of the system.

[450sl]

If you connect everything, you will hear the pressure relief valve "hissing" when you turn the steering wheel to a stop, thus preventing the piston in the gear from moving further and the pump "working against a wall". A safety feature.



Mike, i hear no hissing but a loud Screaming sound when turned to a stop ,  (did swapped the pump but to no avail =same noise).

Can you advise?

thanks
Mark

[Benz Dr.]

Is your PS belt tight?

[MikeSimon]

Mark: Noise in a power steering system is a very complex issue. The pressure relief valve just produces a "hiss" caused by pressurized fluid blowing by inside the pump. But that in turn can create a lot of other noises caused by vibration transferring through the hoses and tubing. Depending on what car you have, metal tubes in the system should be isolated from the body through rubber grommets. The steering gear itself can create noise when the piston vibrates. Of course, like Pawel mentioned, the belt can also be a source of noise, but I ruled that out as you said you changed the pump and I assume you checked belt tension. My guess would be you have airborne noise coming from a tube or hose.

[Aaron h]

Also Hydraulics 101:  If a pump creating fluid flow moves fluid that has nowhere to go then the resultant is fluid under pressure acting upon all surrounding surface areas within the system.  I never said or eluded to any suggestive commentary that would lead one to believe that a pump creates pressure, directly or indirectly. 

You stated earlier, "I cannot see, how moving the piston in the gear will "suck" fluid out of the reservoir".  If after explaining to you why moving the piston DOES take fluid out of the reservoir you still can't comprehend then I guess there isn't much we can do to convince you.  It may not take the fluid out of the reservoir on the high pressure side.....it likely takes it in on the return side with the down stroke of the piston.  The fact remains that no matter how the fluid is taken in it still displaces air and achieves the intended goal.  With your knowledge you should be able to make sense of this, especially after your having further elaborating on what I had already stated.  I feel that if you'll keep an open mind and just try one of the aforementioned methods you'll see that what was suggested does work....  So well, in fact, that if done properly you can literally start the car an go with 100% power assist right away.  Still don't believe it?  Well, again, try it!  I learned a long time ago that the physical properties learned in the mechanics of fluids classes is pretty black and white, but the manipulation of fluids is not.....and this is exactly why there is more than one way to bleed this particular hydraulic system, be they conventional or not. 

And yes, this post is about bleeding the power steering system.  The original poster is probably very lost right about now.  So I'd like to apologize to the original poster for having hijacked his thread.   Back you you, Abudhabi.