Noticed this evening that the 1984 300DT has a slow power steering fluid leak. I refilled with power steering fluid to full. I now need to find the leaks. I'm thinking I'll spray everything with degreaser then power wash everything down to help find any leaks. I'm also thinking of changing both low and high pressure hoses just for grins because they are most likely original.

Question: If I drain the power steering gear box and remove all fluid from the pump using a turkey baster, can I refill by replacing the filter then filling the power steering pump? Or, is there a refill bolt/cap on the power steering gear box that can be used to refill the gear box?

Thank you for any help, it is appreciated!

What’s the benefit of draining the steering box?

Why not just find the leak, fix it, then flush the system? As in... put the return line in a waste canister, cap the nipple on the pump, add new oil as you L/R the steering wheel

The service article on this website recommends against performing that type of flush.


https://www.pelicanparts.com/techarticles/Mercedes-W123/23-SUSPEN-Power_Steering_Filter_and_Flush/23-SUSPEN-Power_Steering_Filter_and_Flush.htm

Why not do the typical procedure?
IE, drain the pump reservoir with a baster, fill it with new fluid, start engine, turn wheel lock to lock a few times, repeat as necessary.

I did that with my 300D and it was very easy. In my case, the new fluid was a different color than the old so I knew when all the old stuff was out.

Here is a photo of the top of the steering gear box; there appears to be a fill hole/nut you can see in the photo. If I drain the fluid from the steering gear box, it appears I could remove this fill cap and refill the steering box with power steering fluid. I have the genuine MB power steering fluid, BTW.

Attached Thumbnails

   

Yes, you are on the right track.

Suck all the fluid you can from the filter housing/reservoir. Then turn the steering slightly to the right or left and remove the drain plug from the box. (if you try to drain it with the steering centered you'll get nothing out)

Doing it this way gets not only the fluid in the reservoir but also the fluid remaining in the lines and the box. Its the best way to get as much as you can out of the system before refilling it.

When adding fluid back to the system have a second person around or be really Johnny on the spot about filling the reservoir. Add your fluid directly to the filter housing/reservoir with the filter installed. Fill almost to the top of the reservoir about an inch or two lower (don't go to the top as when you start the engine some will be sloshed over the side).

Start the engine and continue to fill the reservoir as the system is filled by the pump. You'll see lots of air bubbles. Make sure the pump doesn't run dry.

Then have someone steer from lock to lock somewhat slowly. Add fluid as needed.

__________________
Onus probandi incumbit ei qui dicit, non ei qui negat

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


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

DO NOT for any reason touch that nut.

It's not a fill hole. That's an adjustment screw and jam nut to adjust the lash of the pitman shaft to the working piston.

Don't mess with it.

__________________
Onus probandi incumbit ei qui dicit, non ei qui negat

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


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

Martureo, my car and myself thank you for the words of wisdom. I will follow your advice to the "T".

Should I drain the steering gear box as well as use a turkey baster to drain the power steering pump?

A legitimate authority speaking concisely and authoritatively. How refreshing.

Mercedes dealers just remove filter,suck the fluid out refill,turn the steering lock to lock
several times,suck out,refill repeat in till clear,install new filter.
Do any way you wish,pulling the alignment centering plug could introduce air that could
be a problem to bleed out. This is a high pressure high flow system,when turning just
how much cleaner will it be by draining?

Sounds right, it is certainly easier than trying to wrestle the steering gear box.

I got under the car yesterday to check the steering gear box for leaks, it is dry as a bone. Seems the leak is the low pressure line although the fluid had dropped about an inch so it must have leaked over time.

Alignment centering plug?

You're confused. The drain plug can be removed and used as a.... drain plug. It's nothing more than a M8 x 1mm x 10mm bolt.

If the drain plug is removed one can insert a locking tool to help lock the box in the center position. Just because they use the same threads doesn't mean they are they same thing.

The benefit to using the drain plug is that it allows the user to drain the fluid from the line and the box. At least a cup of fluid can be drained by this method. And there is no issue with bleeding out the air, at least no more issue than there is bleeding the system after sucking fluid from the reservoir alone.

Mercedes dealers and other mechanics often do what you've said and dilute the fluid in the system. However there's no reason (beyond lack of access to the box) that draining the system wouldn't be a better practice.

__________________
Onus probandi incumbit ei qui dicit, non ei qui negat

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


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

Just in case there's any room for doubt.

This picture below shows both a homemade locking tool and the drain plug.

(The drain plug on the bottom and the locking tool on top)

__________________
Onus probandi incumbit ei qui dicit, non ei qui negat

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


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

Martureo,
What fluid do you recommend for the W123 power steering?
ATF, power steering fluid, any particular brands? I changed to Febi PS fluid and now have a small leak.
Thanks!