Power Steering Saga

[cofred]

OK gents....this has been going on a long time and would appreciate your input. I have a '85 M635 which has been undergoing a partial restoration. I've had the engine out replacing all of the cam gear/chain/tensioner/oil pump--essentially all of the wear parts without rebuilding the head or bottom end and a complete respray. After I put the engine back in, I had power steering noise/groan. I switched out the pump which didn't fix it, but it was time to go to the body shop, so off it went.

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

TIA!!!

[sansouci]

Have you put a stethoscope or long screwdriver on the pressure regulator to confirm that is the source of the noise? Although I have a stock 633csi, I get a whine from what I believe is a pressure relief valve. And no, I'm not going to futz with the pump at this stage.

[rhanley 635csi89]

What a pain, you've done a lot of work on the PS system.
A little more history may aid in the solution.
Which fluid are you currently using in the PS system?
Have you flushed the system several times?
I've read that fluids should not be mixed.
Place a magnetic in the PS filter reservoir to check for metal wear.
A decent quality DexIII ATF should be used.
Good Luck,
Roger

[Brucey]

if you have a source of air bubbles (NB most commonly these appear when you have a leak on the feed hose to the pump) then you will get all kinds of weird noises.

If you have had air bubbles in the system, don't expect them to go away immediately. Bubbles hang around in ATF for ages, especially when it is cold. Once it is hot, existing air bubbles will come out of ATF a lot quicker.

BTW you say the pressure rating of the pump is too high, but IIRC the M635 used a higher pressure rating to the pump than other E24 models.

Also some noise from steering boxes when they are under load isn't that unusual. So if you put any torque into the steering wheel and the steering box isn't moving (eg when the car is stationary, or when you are on full lock) some noise (rather than none) is quite usual.

cheers

[slofut]

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.

TIA!!!

My car (88 635) just recently started moaning more than usual (when it's low on fluid) and I found that the same hose you're talking about has ruptured inside. I've been watching it closely anyway as all the hoses are leaky but one. So that hose is definitely causing a problem, it's not leaking outside but the outer layer has now bubbled out under pressure so I know that it's compromised inside. Could be blocking flow as well which would cause the pump to groan more. Got the hose for around $80, but only after some due diligence. And mine's not an M. I would advise to replace your hose...
Bill

[cofred]

What a pain, you've done a lot of work on the PS system.
A little more history may aid in the solution.
Which fluid are you currently using in the PS system?
Have you flushed the system several times?
I've read that fluids should not be mixed.
Place a magnetic in the PS filter reservoir to check for metal wear.
A decent quality DexIII ATF should be used.
Good Luck,
Roger

Thanks Roger....I've flushed it twice. I'm using Castrol Transmax Dex/Merc which is rated for DexIII. I have not placed a magnet in the reservoir--good idea!

[cofred]

if you have a source of air bubbles (NB most commonly these appear when you have a leak on the feed hose to the pump) then you will get all kinds of weird noises.

If you have had air bubbles in the system, don't expect them to go away immediately. Bubbles hang around in ATF for ages, especially when it is cold. Once it is hot, existing air bubbles will come out of ATF a lot quicker.

BTW you say the pressure rating of the pump is too high, but IIRC the M635 used a higher pressure rating to the pump than other E24 models.

Also some noise from steering boxes when they are under load isn't that unusual. So if you put any torque into the steering wheel and the steering box isn't moving (eg when the car is stationary, or when you are on full lock) some noise (rather than none) is quite usual.

cheers

Yes, Brucey, you are right, I misspoke...the other pumps were too low pressure, not the other way 'round. I haven't road tested it so perhaps getting the fluid up to temp may help as well. Thanks!