Ok, so I stopped at the car on the way to the salvage yard and sure enough, the pump would turn but it would apparently start binding after a few rotations. At the time though I just assumed that the problem was in the pump and not elsewhere.

I fetched the new PS pump at the salvage yard and before I removed it I checked to see whether it would spin without binding and it did. I was therefore confident that it would suffice.

Once installed however, the new pump took on the characteristics of the old pump (D'oh!) and binds after a few rotations, which tells me that the problem is likely upstream from the pump, on the pressure side, since the reservoir isn't being drained I find it hard to believe that there's a restriction in the return flow that would cause this.

Any insight now would be great, the only thing I can think of would be if there's a check valve at the gearbox itself that's a problem or perhaps the gearbox just crapped out.

MB says the steering box on the 95 S320 (closest parts donor to me) is not the same although I've checked 15 different part numbers on my 300SD gearbox and they are the same as the 95 S320 so who knows. There is a VIN cutoff for this part that I haven't been able to rationalize yet...who knows.

lets here some suggestions...

Thanks
Steve A

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Steve A
92 W140 OM603
97 VW Jetta TDI
90 Passat variant TDI 6 speed MT
94 Chevy K1500 6.5TD
05 E320 CDI
+ others