Power Steering Pump

[Shaun McCarren]

2000 ML55 AMG, 165k miles, well loved truck

Last night I was coming home and felt a little hesitation as I turned from the steering wheel, and noticed a groaning noise as I slowed down and/or turned. I thought "oh great power steering pump" knowing that the dealer told me that they recommend last fall that I replace the pump. Not one to through money at parts when many times something simple is the problem I declined to replace it at the time.

I limped home with only 3 turns (straight drive until my neighborhood), when I got home I looked for any obvious leaks (i.e. hose recall, puddles, etc). Opened up the reservoir and of course had bubbles/foam. The fluid was a little low, so I topped it off (I had MB Steer Gear Fluid at home) and started the truck and turned the wheels lock to lock, noise gone.

I know this isn't a fix, just need to buy time to get parts/or go to the shop. This morning, same problem, I stopped before leaving my neighborhood and topped the fluid off and got almost to work (10 miles) before the noise reappeared.

The truck has had the recall done to the hose, the hose looks good. My buddy/MB mechanic (now gone) a couple years ago replaced the o-ring between the reservoir and the pump.

I've searched the forum and it seems like a lot of the time it may be something simple (i.e. hose, reservoir, o-ring) and was wondering how common is it for the pump to go bad? I'll get to spend more time looking at things tonight.

To recap noise is worse when slowing down (don't have to be turning) or when turning more than 30º (i.e. left or right turns at a stop).

Thanks,
Shaun