I have a 1981 W123.130 617.912 300D. My power steering pump is leaking like a fast dripping tap. It's a Zf 76 series, and have replaced the front seal successfully, however the rear is the major problem. I have got the seal kit to do the job (2 O'rings and a washer), but some advice or instructions on how to replace the seals would be very welcome. I've not been able to source any schematics or instructions, and Mercedes just don't supply that information unless you spend $265 on a CD manual. (I won't do that!!, and Haynes Manuals are useless!) Any tips would be greatly appreciated.

Try here: http://mb.braingears.com/

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Thanks anyway, but that was of no help

Get the pump out and on the bench.

The rear of the pump pushes in, there is a spring behind it.
A couple screwdrivers hold in a tension ring around the circumference.
Remove that ring (you may not need to push the back in to do that).

The back pops out.

The two large orings are replaced right there.
You probably will not have to remove the guts of the pump at all.
But if you do - absolutely do not let the vanes get out of order or
get put in backwards. Plenty has been written on this site about
losing pressure after reinstalling the vanes backwards.

I have one disassembled on the bench right now and have not gotten around
to putting it back together. Maybe some pictures would be in order.
You are right, have not seen a write up on this yet.

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250

Cheers mate, much appreciated.

Mission successful. "G" clamps are of great assistance when removing and installing backing plate.

Good show.....

Guess I'm thinking of something else, what be a "G" clamp and how does it help remove the back plate. I remember have a bugger of a time getting that plate off

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Yeah... clamps. I had not thought of that.
I'll use them during reassembly.

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250

Furthermore, once the backing plate is removed, there is another Black plate which requires the removal with a couple of screwdrivers (gently prising only), and there you will find the second seal (O'ring). It's probably a good idea to note how it comes out, in order to place it back in the same fashion, on the same lugs. One of the lugs is for locating purposes.
G Clamps will help to avoid bending the spring when removing and installing the backing plate.