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 how to best troubleshoot power steering
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srfsteve
Gas-fueled God

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653 Posts

Posted - May 04 2015 :  17:37:03  Show Profile  Send srfsteve a Yahoo! Message  Reply with Quote
Hello all!

now that my 745 is running again, Im back after long absence, and need your help with a power steering problem. I have a good 735 parts car to piece meal swap parts out of sequentially or en mass, till it works, but this board likely knows of a more intelligent approach and has a better understanding of the PS system.

The car sat for about a year. When i finally started it up, the steering fluid was low and the pump whined. So with the car off I pumped the brakes and filled the fluid reservoir ; now the pump makes no noise, but I have no power steering. (I had power before the car sat). I do continue to have power assist for the brakes, however.

I believe the brake bomb is OK , behaves normally when pumping the pedal, then stiffens up after 10 pumps or so.

Am suspicious about the PS pressure sensor on the distribution box above the break bomb. Is the function of the sensor to open a valve to the PS box to give it pressurized fluid ?

Am also suspicious whether the filter in the bottom of the reservoir ( if their is one) is plugging the PS line. not sure of the best way to check that.

I tried bleeding the steering box, and turned the wheel many times all the way in both directions .. no joy,

What may be a separate problem: The steering wheel turns about 8" of circumferential play before it begins to turn the steering linkage. Also the steering wheel does not come back to center on its own in a turn. this was the case even when the PS was working. I have verified that the struts and linkage are not causing this.

I tried adjusting the steering box screw many times, but even tightened all the way down its not helping, so I am suspecting air in the steering box, or the steering box is bad.

What approach to sort this out would be best?




greg_mazur
Over 745 Posts!

Status: offline


1234 Posts

Posted - May 11 2015 :  04:04:42   View greg_mazur's Photo Gallery  Show Profile  Reply with Quote
Could be the vanes in your pump are worn and not giving enough pressure.
Get under neath and check steering box bolts that hold the unit to body.
Disconnect center link and check for freedom of movement of each wheel ,
Check large nut on bottom of steering box arm that connects to center link.
You find any of this stuff worn, do a complete replacement of the steering.
You either don't have enough fluid force or you got bind, I suspect worn steering
Causing bind.
I have yet to see a bottom canister filter.
After all this give me a private message and I will give you the official BMW
Repair procedure .
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srfsteve
Gas-fueled God

Status: offline


653 Posts

Posted - May 15 2015 :  16:51:59  Show Profile  Send srfsteve a Yahoo! Message  Reply with Quote
Greg,

Thanks for your thoughts.

I had disconnected both tie rods and verified that both struts rotate freely. So the steering stiffness is caused by something else.

Also the pitman arm at bottom of the steering box has no play in it.

We drained the steering reservoir and found that there is a filter or maybe a filter housing at the bottom. i assume its a housing with a a filter inside it. Havent figured out how to get it out. The center rod that holds the res. cap on goes thru a 3" long spring that presses on the top center of the filter housing and goes through it to screw into the bottom of the reservoir. Havent figured how the spring and rod comes out. maybe from Real OEM diagrams i can get an idea.

drained the steering box. The fluid looks fine.
I
am pretty sure the steering box is bad, and so Im just going to swap it with the 735i box unless there is some other check to do first.

I dont know about the pump though, may have to change that too. Does it make sense that the pump could be strong enough to give good power to the brakes but zero power assist to the steering ?

I suppose if the distribution box at the top of the brake bomb is plugged or closed to the steering line but not the brakes line that could explain it. dont know if that is possible. may need to change that too.

I'll send you an email.
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