In replacing the hoses in my 1984 300D, I started with this thread:
Repairing hydraulic hose for SLS hydropneumatic suspension on TD
The Self-Leveling-Suspension and power steering hoses are similar. The factory used what Gates terms "Field Attachable Couplings" on the high-pressure (HP) hose, which means they can be re-used and just the hose replaced. Most other cars use permanent "crimp fittings". You can buy a complete HP hose assembly ($50, crimp fittings). I decided to take the challenge of re-using the factory fittings, as SLS guys have done. My hose had 2 pinhole leaks in the body, that occasionally sprayed up on the hood liner (messy, my son had the car then). You can see the slight bulges in the photo. I summarize what I found to make the task easier for others. Please add your experience, unless advice "just buy the correct M-B part" (always useless, snide comments).

Getting suitable hose proved challenging. Others said they just went to NAPA, O'Reillys, or a hose supplier and walked out with either hose material or a full assembly. My local NAPA was less helpful. If I went to their warehouse store far away and some back & forth I might have eventually scored. There is a Pirtek hose shop and a Parker store here, but both have M-F hours and looked like high prices. I decided to order hose off ebay, though I spent hours researching what might work. I share my research with you, so relax and file this away. The HP hose is 21" long.

If I did it again, I think the best hoses would be:

High-pressure hose:
SAE 100R3-6: 2 fiber braids, 3/8"ID, 0.75"OD, 1125 psi working, ex. Gates 6G3HXCTN

Low-pressure hose:
100R6-8: 1 fiber braid, 1/2" ID, 400 psi working, ex. Gates 8GTHXCTN

My HP hose (factory?) had no markings. It appears to be 3/8" ID (cut in middle, measured w/ vernier), w/ 1 fiber wrap, no steel, and a smooth rubber surface. Gates PS-188 is 3/8" ID "for automotive p.s. hose", but couldn't find where to buy it. One of my old Mopar cars has "SAE J188 Type I" HP hose (Gates Safety Stripe 3/8"), but couldn't find that either. BTW, J189 is return hose and you can buy that on e-bay.

Most SLS hose fixers used SAE 100R2-6, which is 2-wire 3/8" ID, 4000 psi. It is over-kill, but is readily available at truck parts and tractor supplies. Before dis-assembly, I measured the tube fitting at my Vickers pump as 0.4" OD, so figured the hose ID would match. I bought 10' of SAE 100R5-8, 13/32" ID, 0.77" OD, 1 wire braid, 2000 psi (Parker 206-8, $3/ft ebay). I know many are thinking #8 hose is 1/2" ID, but not true for the 100R5 above (Gates C5) or AC hose (see table).

Those who used 100R2 3/8" hose found it was very hard to get started and they couldn't screw the mandrell in all the way. With my 13/32" hose, it started fairly easy and I was able to bottom out the mandrell, but it took enough force that I resorted to a crow's-foot to not risk rounding off the nut, so I would be surprised if the hose could ever pull out of the fitting. With the more rubbery 100R3 hose (like factory's), 3/8" shouldn't be too hard to install. With wire braid hose, it seems my 13/32" is a better fit. The mandrell measures 0.405"D at the threads. Be sure to read the above link about screwing the hose CCW to go into the outer metal shell (left-hand thread). Not sure why Gates instructions below say CW (their coupling differs?).

I think better to avoid steel wire hose (hard to cut, inflexible). I also don't like the braided polyester shell on my hose since I expect it will get grubby. While 100R3 hose is rated for hydraulic fluid and power steering ("heavy equipment only"), it is more commonly used for air brakes (label on mine). I spent a lot of time searching details on Gates' C5 couplings to compare to the M-B fittings, but found no dimensions. Not sure what M-B used, but the fitting at the steering gear end appears unique. It has a round end, similar to the fittings on the injectors and oil cooler, and isn't in the Gates catalog.

One approach is the buy a HP hose for a U.S. car and adapt it. I show one for my 65 Newport that screws into the HP port on the Vickers pump. That hose is too short (1/4" in-line reducer), though the same hose installed on my Newport runs all the way to the gear. You can find the 3/8" male inverted flare fitting on hoses for Mopar cars that used either the TRW (~1969-) or Saginaw (~70+ some) pump. You could cut the hose and use your M-B re-usable fitting at the gear end. Some GM cars w/ a "female port" pump used the same fitting, but verify because some had 7/16" flare (rock details most hoses). You also need to guess if the metal tubing bends will fit your car, or if you can adjust them. All HP hoses I saw are 3/8" ID. Borgeson uses 100R17 (steel wire), but I expect others are normal J188 type fiber braid. Could be an easy click & buy solution (~$12). Boats have long power steering hoses, perhaps one way to get a lot of hose, but usually not the correct fittings.

For the return hose I bought a 5'L hose assembly on ebay (long enough for 2 cars, $10 incl shipping) and will just toss the fittings. Hose is Parker 611HT-8, SAE 100R6, 1/2" ID, 400 psi. The old return hose is labelled 'Parker Push-Lok 831-8 WP 300 PSI 1/2" 03/01/11'. It wasn't leaking, but was shrunken under the hose clamps and getting loose on the tubes, so while the fluid is drained I'm swapping it. If above means the manufacture date, it must be a poor hose choice. I think I might have replaced it a few years ago. If so, I bought it as a M-B replacement part (probably not Peach Parts).

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more photos.
I'll post if my new HP hose blows out, but I won't be driving that car for a while (injectors out, ...).

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Spent several hours today driving around town looking for suitable PS 12mm return hose. No shops had it including NAPA. Didn't try the dealer because I already know what list price/meter is!

I did buy 2ft of 11.9mm PCV J30R7 hose. It has almost same overall dimensions as original, but has low working pressure rating (2.4bar; 35psig), burst 175psig. Don't know what pressure there is in return line. Probably not much, so perhaps it might work on temporary basis?

The SAE spec for power steering return lines is J189. This is what it says:
SAE 100R6 is probably overkill (400psi rating) but may be easier to find?

I guess I need to keep looking!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Should work. The return hose just empties into the reservoir (most cars, M-B Victor-Reinz pump too I recall), so the only pressure build-up is from drop across the fittings and the hose itself. For others, a common gomer mistake is to try heater hose. It softens quickly in oil. In general, AC "barrier hose" works fine for any hot oil, medium pressure applications (<500 psig), though isn't rated for power steering high-side (~1000 psig).

As mentioned, the SAE 100R6 hose I used for return was cheap on ebay. It had fittings, but I just cut those off and tossed in my "fittings bin".

My wife thinks my stashes are "junk", but gold to me when I need it. Similarly, most of the public would love to close junkyards, but they don't want to know how their sausage gets made or their vehicles repaired.

The "take-away" from this post is to not whine when you can't get parts from the dealer or retail auto stores (affordably, or at all). Many parts can be replaced from generic stock. Just download the appropriate catalogs and browse. This has worked for me for hoses and V-belts (Gates, etc), roller bearings (most are standard metric sizes), air filters (my 1985 CA frame-mount filter), and similar needs on all my vehicles. In some cases, you can improve on the factory design, such as I changed to silicone heater hoses on several vehicles.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Bought a length of 1/2" marine fuel hose. Parker Wavemaker 7165. It is good for working pressure of 100psig at 212F. SAE J1527 A1-15. Doesn't have fabric abrasion resistant outer cover, but otherwise seems good match. Paid C$7.00 for 2ft.

1/2" slips on kind of too easily for my likes. But even OE original looked like it had the heck clamped out of it. AA and others have a 12mm CRP-Conti hose that is for this application. About $17.50 for 1 meter.

But I couldn't wait for that. Car is now back on road!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Try Metric Hardware, Metric Fasteners, Metric Bolts, Metric Nuts & Time-Sert Thread Repair : https://www.belmetric.com/smooth-high-pressure-oem-c-14_139/rh12x18hp-smooth-high-pressure-12x18mm-p-961.html

They also carry the crimpable hose collars.

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Sam

84 300SD 350K+ miles ( Blue Belle )