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  #1  
Old 01-19-2021, 12:01 PM
cornemuse's Avatar
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Changing Power Steering Fluid

How does one go about completely changing power steering fluid on my 300CD turbo car?
I added ATF (my merz owners book says it takes ATF), but Merz dealership says use power steering fluid. It did not look like either in the resevoir.
I figure it best to completely change fluid.

-c-

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  #2  
Old 01-19-2021, 02:11 PM
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Check out Kent Bergsma's online store. I buy often from Pelican Parts and feel uncomfortable mentioning their competitor here. Kent's prices are higher and his inventory is not as deep. Where he excels, though, is in the DIY help. His videos, manuals, and kits are great. Many of the posters here are experienced, skilled mechanics. Some of us are still on that long learning curve. I replaced the power steering fluid and filters in both my W123's with his instructions.
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  #3  
Old 01-19-2021, 02:29 PM
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The last time I did it I just sucked out the power steering fluid with a turkey baster and replaced the filter. 1981 300SD.

Does it need to be more complicated than that?
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  #4  
Old 01-19-2021, 02:45 PM
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There’s a plug on the bottom of the steering box. If you really want it all out, that’s the way to go. Quite a few tutorials in the archives on what comes next.
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  #5  
Old 01-19-2021, 02:47 PM
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I just sucked it out into a vaccum brake-bleeder bottle when changing the filter. That doesn't get everything in the gearbox, but since the fluid was clean, it is likely good-enough. I don't recall a drain plug on the gearbox. I filled with ATF+4 which Chrysler uses and a TSB recommended when servicing all older power steering, presumably back to the 1960's which had a similar Pitman-arm gearbox. They amusingly sell the same fluid in a "power steeing" jug at dealers at much higher price than Autozone. Many power steering systems spec Dexron III ATF fluid (GM). ATF+4 is fully-synthetic and pricier, so might be better, plus I keep jugs for my Mopar vehicles. You could also go to a M-B dealer and pay whatever for fluid. With ATF, you will have to live with red dye, though might help in finding leaks.
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  #6  
Old 01-19-2021, 04:03 PM
A guy who likes to Benz
 
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Quote:
Originally Posted by cornemuse View Post
How does one go about completely changing power steering fluid on my 300CD turbo car?
I added ATF (my merz owners book says it takes ATF), but Merz dealership says use power steering fluid. It did not look like either in the resevoir.
I figure it best to completely change fluid.

-c-
At the time your car was sold Power Steering Fluid wasn't really a thing. It is now. So you can use either.

I recondition these boxes and I use Castrol Dextron-III/Mercon ATF F-30341 as specified. That can be found at pretty much any part store, just get Dex 3/4. I have used Power Steering fluid in certain cases when the customer wants the fluid to be clear (ATF being red and most P/S fluids being clear/yellow). I've also been told about a few customers that they used hydraulic fluid (like that which is used in the SLS pump). That's a bit overkill, but it can work.


To change the fluid, start with the wheels turned to one side or another slightly (reason will be clear in a moment). As has been said above, take a turkey baster or fluid removal pump and suck the reservoir dry (removing the filter will let you get most of it).

Then go to the steering box underneath the car and remove the 12mm nut on the bottom of the box to drain the fluid in the box. If you didn't turn the wheels to one side or another the fluid won't drain as there is no path to drain in the center position.

Put the plug back in the box and fill the reservoir will fluid up to the line. You'll want to be really quick about this or have a second person available. As soon as you start the engine fluid will start to circulate in the system and will run the pump dry, start filling as soon as the level drop. With the engine running, turn the wheel from lock to lock slowly, adding fluid to the reservoir as needed. This will work all the air out of the system.

Done!
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I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


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  #7  
Old 01-19-2021, 08:07 PM
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I've just done this procedure on both my W115 and W123 diesels. Note that the fluid flushes through the system very rapidly when turning the steering wheel.

Also, I recommend use a modern non synthetic power steering fluid instead of ATF. Febi Bilstein yellow is what I used in my cars with great results.
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  #8  
Old 01-19-2021, 11:10 PM
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Although I don't know for sure if it'll work on your car, you might want to scroll down a bit in this thread

Michael
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  #9  
Old 01-20-2021, 02:23 AM
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Mobil 1 synthetic ATF meets all the requirements and will last for years without breaking down and turning black like power steering fluid does.
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  #10  
Old 01-20-2021, 02:50 AM
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Who needs a drain plug?

Who needs a drain plug when you can suck fluids out with a Topsider or MityVac extractor??? Just plunge the plastic straw of the MityVac into the reservoir and suck it out. I used Prestone Stop Leak stuff over 10 years ago when I first bought this car used because the steering fluid was leaking and I've never had a leak since.
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  #11  
Old 01-20-2021, 09:29 AM
A guy who likes to Benz
 
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Quote:
Originally Posted by jbach36 View Post
Who needs a drain plug when you can suck fluids out with a Topsider or MityVac extractor??? Just plunge the plastic straw of the MityVac into the reservoir and suck it out. I used Prestone Stop Leak stuff over 10 years ago when I first bought this car used because the steering fluid was leaking and I've never had a leak since.
About half of the fluid in the system remains in the two hydraulic lines and the box.

That would be why.

And from someone who rebuilds these boxes on the regular, don't use stop leak. It causes certain seals to soften but its a bandaid. Every seal in your system is now compromised and you're going to have an issue sooner or later.
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Huius auctoritatis est, quod latine dolor facit me respice.

I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


1984 300D "Elsa" odo reset 6/2011 111k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]
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  #12  
Old 01-20-2021, 01:07 PM
μολὼν λαβέ
 
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Quote:
Originally Posted by tyl604 View Post
The last time I did it I just sucked out the power steering fluid with a turkey baster and replaced the filter. 1981 300SD.

Does it need to be more complicated than that?
You only changed about 1/3 of the fluid. No different from changing the coolant or the brake fluid - only a small amount exists in the reservoir, most of the fluid is in the other parts of the system.

The majority of the fluid is out of reach, down inside the pump, steering box, and hoses. To do a full power steering fluid exchange, you disconnect the return line from the fluid reservoir. Aim the return line into a catch can, and plug the return line flange in the reservoir. Put the front wheels on jack stands. Have a helper turn the steering wheel from lock to lock a couple times (with engine OFF), while you keep the reservoir topped up. Once the fluid flowing into the catch can starts looking clean, you're done, the system is fully flushed with new fluid.
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  #13  
Old 01-20-2021, 04:22 PM
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Thanks martureo & shern, this is what I wanted to know. Thanx to the rest of ya's too, , , , ,
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  #14  
Old 01-20-2021, 06:31 PM
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Post Routine P.S. Fluid Change

It's important to remove the filter and use lint free towels (think blue windshield towels) to wipe up the black sludgy crud in the bottom of the reservoir .

The best way is as mentioned, to remove the drain plug in the steering box but the average DIY'er can simply use a Dollar Store turkey baster to suck it all out then clean the crud , re assemble and re fill, then repeat every routine 3,000 mile oil change until the fluid remains red and smells sweet .

This works fine and is the lazy way to go, many DIY'ers don't like to jack up the car and so on so the important job never gets done .

Whilst you're doing this, check the back of the drive pulley, is it's wet the input seal needs replacing, another simple job that requires no special tools, just time, some effort and clean LINT FREE rags / towels .
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  #15  
Old 01-21-2021, 03:18 PM
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I went through my power steering fluid change a few months ago. I agree with the people that say turning the steering wheel from lock to lock pumps/flushes out most of the old fluid. Post:

1995 E300D comments on my power steering fluid change

I disagree about not using a good additive like Trans-X for reconditioning seals. I've used it several times in different vehicles and have been able to make problems go away and never appear again during my ownership. I put on over 350,000 miles on a Range Rover, over 200,000 on a Chevy suburban, a 1 ton ford box van, multiple olds auroras with close to 200,000 miles, farm tractors. I typically used a bottle in transmissions and sometimes full strength in power steering pumps. It eliminated shifting problems and eliminated noise and heavy leaks in steering pumps. Basically i believe that if my only other choice is to remove and rebuild/replace the transmission or power steering pump I might as well try the additive. It has worked every single time and believe it is a good proven product.

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