Power Steering Blowback

[ChrisInNashville]

Greetings Group!

This relates to my power steering.

I have a new symptom that I don't see addressed specifically in the archives or in Haynes.   My mechanic is puzzled and that leaves me a bit unsure of where to start.  

Haynes describes the symptom well:   "Steering wheel hard to move when moving slowly during parking"...I'll add, it's also noisy when under stress.   But this weekend, I noticed one additional symptom that I'm hoping can narrow down the problem:   When the steering is under stress, a fluid blowback occurs from within the fluid reservoir (through the lid)sending a spray into the engine compartment.

Without addressing the blowback specifically, Haynes suggests one of four reasons:
 - Loose pump drive belt
 - Low fluid level (not the case)
 - Fault in hydraulic pump
 - Internal fault in steering gear

There is 'foam' in the reservoir after this occurs indicating a leak in the system, but I'm wondering if this is a different problem.

Any ideas as to where I should start my repair?   This group has been a godsend to me on other problems...

[Ricardo]

Hi
Don't know if this is relevent or mentioned in the Haynes manual, but I had similar symptoms when I bought my car which had a recently replaced used P/S pump. I read either in the BBB or Haynes about the proper method for bleeding the system, which involves jacking the front end up and turning the steering wheel slowly from lock to lock with the engine running. I did this and have had no problems or noises since (4years)
Ricardo

[mdsalemi]

Hello Christietz,

If you have checked the obvious and inexpensive (fluid levels and belt-tightness)it's probably time to move on to the pump.  As the pump is what draws on the fluid reservoir, and you are getting some "feedback" from this (and making a mess of your engine compartment to boot), that would my first choice.  Suggest fitting a rebuilt pump unless you have the wherewithall, parts and time to rebuild the pump yourself.

If you are using a mechanic--as I often do--sometimes diagnosing the problem on older cars by addressing the symptoms (in your case, changing the fluid, changing the belts and adjusting, bleeding the system, etc.) one by one can be a time consuming and expensive proposition with shop labor being what it is.  Sometimes the cure can be (not always, mind you...)less expensive.  What I've done repeatedly on my car is to change the suspect parts; if the old part was not the problem, onto eBay it goes.

Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored

[A Dalton]

Change the Filter..
 Some don't even know there is a filter , as it is below a drain plate in the bottom of the res.....

[Douglas]

Good call, Arthur. Most people never change the filter at all. It's a screen at the base of the reservoir.

Douglas Kim
New York, NY
280 SL #016220

[Vince Canepa]

This sounds like a system full of air.  The return from the steering box enters the reservoir at the side, outside the filter.  The pump suction is at the bottom, inside the filter.  It sounds to me like the system is blowing oil with entrained air back into the reservoir.  Leaks on the suction side of the pump might draw in air (but I would think they would be visible with the engine off).  This may sound silly, but is the oil level in the reservoir correct?

Vince Canepa
1967 250SL
113.043-10-001543
568H Signal Red
116 Caviar MB-Tex

[n/a]

I had the same problem ... air in the P/S system.

First you need to bleed the system. I can't remember the process, but I think it's on this site somewhere. Involves running a hose from a bleed fitting back into the resevoir and letting the fluid circulate until the air is out. I also cleaned the resevoir and filter of lots of crud.

I've heard a common cause is a leaky seal on the pump that draws air into the system.

Shawn Rock
Philly, PA USA
1968 280 SL 4 speed

[A Dalton]

Originally posted by srock

I had the same problem ... air in the P/S system.

First you need to bleed the system. I can't remember the process, but I think it's on this site somewhere. Involves running a hose from a bleed fitting back into the resevoir and letting the fluid circulate until the air is out. I also cleaned the resevoir and filter of lots of crud.

I've heard a common cause is a leaky seal on the pump that draws air into the system.>>>>

 The reason we check the filter first is b/c with a blocked filter , the suction side of the pump will pull into a vac and any weak points in the suction side of the system will pull in air....be it at the seal, a line , a clamp, etc..
 

[erickmarciano]

anyone have the part # for the filter?

1971 280sl
1962 VW
1954 Allstate vespa
1958 gs150 vespa
1962 gs160 vespa

[A Dalton]

quote:Originally posted by erickmarciano

anyone have the part # for the filter?

1971 280sl
1962 VW
1954 Allstate vespa
1958 gs150 vespa
1962 gs160 vespa

 000-236-00-55 is the original.

[Vince Canepa]

Make sure you have the right filter set up.  There should be a brown fiber filter element about 25mm tall and 50-60mm in diameter.  On top of the filter is a round plate with holes.  I've seen several of these cars with bogus filters, presumably from other models, and they end up with no filter action because nothing fits right.

Vince Canepa
1967 250SL
113.043-10-001543
568H Signal Red
116 Caviar MB-Tex

[ChrisInNashville]

Keep the good advice coming...I may not be able to address until the weekend, but I'll keep you posted on the results.

Thanks,
Chris

[ted280sl]

Chris,
  If oil is blowing out of your resevoir I would also suspect that the seal on the top of the resevoir is missing or should be replaced. My power steering fluid is leaking from the steering box. If you have fluid in that region it might be worth looking into.
Regards,
Ted 1969 280SL - waiting for the snow to melt!

[ChrisInNashville]

OK, I'm going to work on this tomorrow.  Before I start, I have a really stupid question.   Where is the full point in the reservoir?   Is it the 2 inch tick mark about 3/4 inch below the top?   SHould I be pickey about the type of fluid I use?   Any suggestions?

[Vince Canepa]

There should be a line stamped inside the reservoir on the inboard side, about 25mm long, about 17mm from the top.  The original spec was for ATF.  Any Dexron III ATF should be fine.  M-B makes a special P/S fluid now and I would probably use it if I was changing out all the fluid, but it really isn't required.

Vince Canepa
1967 250SL
113.043-10-001543
568H Signal Red
116 Caviar MB-Tex

[WillS]

Something about the PS reservoir filter I don't understand:  why does the large washer that pushes down directly on the filter (the 250-280 Owner's Manual calls it a 'thrust washer') have three good sized holes in it (see picture)?  Doesn't this put the PS filter into permanent by-pass, no filtration being done?  

Also, A Dalton said "The reason we check the filter first is b/c with a blocked filter , the suction side of the pump will pull into a vac.....".  Is there a filter thrust washer that doesn't have the permanent by-pass holes in it?  That would be the only way I can see that the pump would pull into a vacuum, and also properly filter the PS fluid.  Do I have the wrong PS filter 'thrust washer'?  Thanks.

Download Attachment: PSCannisterThrustWasher.JPG
49.81 KB

[bpossel]

Hi Chris,

I recently replaced my ps pump and also some of the gaskets on the steering gear box (top and bottom).

I had a lot of foam (air) in my system when I started the engine back up after all of the work.  Here's what I found to work best to get the air out.  Obviously, if this doesn’t work, then you might need to replace your pump.

Raise front of car and put both sides on stands.  You need to get the front wheels off of the ground.  Connect a hose (I just purchased some clear hose ~2-3 ft from Lowes) on the bleed nipple of the steering gear box.  Run the other end into the fluid reservoir.  I ran this end through the ring of the oil dip stick to help keep this end in the reservoir to prevent the hose from kicking back and spraying fluid.  With the engine running turn wheels to their full lock position (left and right).  Turn wheels back to front, straight position.  Open bleed nipple and you should see a lot of air bubbles going through the hose.  I then also left the bleed screw open and slowly turned the wheels fully left and then right several times.  Do this until all air bubbles are gone.  Again, if this doesn’t work, you may have a bad pump (bad seals in the pump).

Good luck!
Bob


bpossel
Memphis, TN.
1971 280SL
1997 E320

[ted280sl]

Chris,
  It definitely sounds like air. I had  similar problem and it was caused by a pinched hose. The hose that runs from the resevoir to the pump makes a sharp 90 degree turn. If you have an older hose or a non-mercedes hose it is prone to folding and blocking the flow of fluid. If you have not replaced the hose do it. It is cheap. If you have replaced it, make sure that it is not pinched or folded.
Ted 1969 280SL - Just went out for a ride. How many weeks until Spring?

[J. Huber]

Guys. For what its worth, I notice you are answering Chris -- but that his post is year old. Now Will's is current.

James
63 230SL

[Naj ✝︎]

WillS,
I just had a look at the pas filter (looks like a collar/bangle) - and I confused  :oops:

If the 3 holes at the bottom of the resevoir are for bypass, how does the fluid get to the steering box?

naj

65 230SL
68 280SL