Power steering increases rpms

[waqas]

Searched through the archives and came up empty. Recently, I've noticed a very peculiar symptom:

- When the steering is near the lock position (left or right extreme), the idle increases by 500-600 rpms.
- I've observed this with and without pressing the brakes.
- While at one of the extreme positions, I switched on the A/C and there was no change to the high idle (remained at 1400 rpms or so).
- It takes less than half a turn of the steering wheel from lock to drop the idle back to normal (usually 850 rpms).
- I looked at the reservoir, and it was full, and free of any 'froth' (presumably meaning there are no air bubbles in the system)
- The pump belt seemed a bit looser than when I last checked (a few months ago), but was clearly not loose enough to slip. (besides, there is no belt whine).
- There is no discernible sound emanating as I turn the wheel from lock to lock (except the rpm variation)

Any ideas why this might be happening?

This weekend, I plan to tighten the belts, replace the fluid and filter in the reservoir, and bleed the system as per standard procedure. I'd love to hear about anything in particular to look for while going through this.

Thanks for any guidance.
Best regards,

Waqas ('Wa-kaas') in Austin, Texas

[al_lieffring]

There were some models that had a hydraulic idle lift for when the steering was at the full lock position, This was on the 250sl models, not sure if it was also put on late 230s or early 280s.

another possibility could be a loose P/S belt.

Al Lieffring
66 230Sl
Jones'n for a new gas tank

[Benz Dr.]

I would agree with Al. This could only be a hydrolic lifting device causing the RPM's to increase at full lock.
It's actually a pretty nice feature but yours is out of adjustment. There is a place to adjust it back so that you only get 200 RPM increase or enough to make it work smoothly. My 250SE coupe had this option which worked nicely.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[France]

Hi Guys,

In the locked position, the hydrolic pump creates increased drag, and as the pump already uses several horsepower, this increased drag may result (e.g., when the engine is cold) in a stalled engine.  Soooo...in the 60s, the factory thought raising the RPMs in this condition was a positive feature.  (Same as raising RPMs to compensate for A/C on startup.)

To avoid wearing out your steering pump, best to never put your steering onto full lock--you are only wearing out componants, even if you adjust to only a 200 RPM increase.  Does the Benz Dr. agree?

Trice
1968 280SL US, signal red/bl leather, auto, kinder seat
Sarasota FL; Alsace France; Switzerland
Think of your Pagoda as a woman with a past...

[Benz Dr.]

I think when you go to full lock it opens a by pass valve in the pump. Best not to force things although it's designed to work this way.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[hands_aus]

http://index.php?topic=6113,steering,speed,increase

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[waqas]

Bob, thanks for the link!  I always wondered what that device was (mine has a manual transmission, so no constant speed solenoid).

Any ideas on how to adjust it?  I couldn't find any information in the BBB or the Haynes manual. How much higher is the idle supposed to go when the steering reaches either lock position?

Waqas ('Wa-kaas') in Austin, Texas

[hands_aus]

quote:Originally posted by waqas

Any ideas on how to adjust it?  I couldn't find any information in the BBB or the Haynes manual. How much higher is the idle supposed to go when the steering reaches either lock position?

Waqas ('Wa-kaas') in Austin, Texas

Earlier in this post Dr Dan said about 200 rpm increase.

Adjusting? If it pushes on the linkages like the constant speed solenoid does, then there must be some kind of adjustable nut/bracket/lever/bolt? on it.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto