W126 Power Steering - Odd Behavoir - PeachParts Mercedes-Benz Forum

bolomiester · #1 10-23-2010, 06:04 PM

89 300SE

I changed the power steering fluid and filter for the first time since I bought the car. Before the change the power steering was quiet, now it makes a slight groaning sound as if it is low on fluid.

I used a Mann filter and MB power steering oil. I filled to the bottom of the minimum/maximum marks then took a drive, which is when I heard the sound. I checked the level and it was too high, so I sucked the resevoir dry again and refilled to the bottom of the minimum/maximum marks. It still groans slightly.

Any ideas of why it should be making noise after a fluid and filter change?

bolomiester · #2 10-24-2010, 04:23 PM

I tried draining and refilling the resevoir twice more. Once when the car was warm, filling to the upper mark, and once more, this morning when the car was cold, filling to the lower mark. After both I turned the steering wheel lock to lock a number of times to allow the system to bleed itself.

No change. The pump would still whine whenever the steering wheel was turned.

Then I did what I should have done in the first place. I checked the CD and found a procedure for "filling and bleeding" the power sterring pump.

You can find the procedure under "Main Function Group 46, Steering" then "Sub-function Group 715, Filling and bleeding power steering pump."

Basically, before starting the engine, I needed to fill the resevoir to within 10mm of the top, then start the engine and turn the steering wheel from lock to lock a number of times to bleed the system. When I did this there was no whine from the pump!

I stopped the engine and checked the fluid level. There were a lot of bubbles in the fluid, though they went away pretty quickly. The fluid level had dropped way down, almost but not quite to the upper level. I removed a little more to make the level correct.

I put the cover back on, started the engine, turned the steering wheel from lock to lock and the pump is now quiet!