After I got it back, I dug in once again. I realized that both the pump that was on it when I bought it and the one I replaced it with were the incorrect bar spec (both too high), so I sourced one that was correct, rebuilt it, and installed it. No joy. After bleeding, I had air bubbles particularly after discharging the brake bomb. I've since replaced:
- *the brake bomb
*high pressure line from the pressure regulator to the pump
*high pressure line from the brake booster the pressure regulator
*low pressure line from the fluid reservoir to the pump
*low pressure line from the pressure regulator to the fluid reservoir
*low pressure line from the steering box to the fluid reservoir
*reservoir filter
After all that, no more air bubbles, but the groan persists...but it's a bit different.
Now the groan only occurs when the steering wheel is turned and worse with increased RPM. No noise at all with just increased RPM (steering wheel completely still). I asked my wife to help me (she was soooo excited), and now it sounds like the noise is coming from the rear of the engine compartment AND if I put my hand on the pressure hose running from the pressure regulator to the steering box, it vibrates at the same frequency as the noise. Does this sound at all feasible to anyone? I would have never expected (and am still not 100% sure) that the hose would be the cause. Anyone experienced this?
Now....there are two reasons I didn't replace that hose when I was doing the others...the cheapest I can find it is $305 (apparently it is specific to M635/M6/M5) and visually it looks fine while the other two pressure lines had visible cracking. The only thing I haven't tried that I can find by reading previous posts is to try a Redline or Petosin synthetic.
In the end, do I
- a) buy the expensive pressure line and hope it fixes it
b) try changing to a synthetic fluid
c) try to live with it and see if it worsens (will I damage something else in the system?)
d) take it to a good independent shop and see what they think
e) open to suggestions