Looking on tire-rack, they have HR springs for gas model W-126 and it specifies not for diesel models and there is none available for diesels.

So anyone know what the difference is?

Really wanting to lower my 300SD about 2"

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81 300SD daily driver/project
86 420SEL (sold)
85 380SE(in the graveyard)

Maybe try going to the gas motor front springs and using a shorter rear block,,,PROBABLY give you somewhere between an inch and two inches lower, make sure you have it realigned.