There is also a member of this forum who bought a similar spring compressor and is willing to rent it - similar terms as Performance Products $85-$90 rental, plus S&H both ways, plus $500 refundable deposit. Do a search for this member if you want to rent this tool because the PP tool (they rent 2 or 3) may not be available.
I used the PP tool and it worked fine for the front and back springs. I also had to level my back end a well as replace the collapsing rear springs (did a complete rebuild on the front end and springs were OK). The PP tool was a bit hard to make work on the rear springs for removal only because they were the "comfort" ride springs that have some of the coils less wide making it hard to get the plates far enough apart so the spring could be compressed enough to remove. The new springs that had evenly spaced coils went in and out much easier (I had to R&R the springs a couple of times as I tried different spacers to level the rear end).
You'll need to cancel your alignment appointment because you're not going to get a spring compressor in time - and no other tool will work other than the ones made specially for compressing M-B springs. In fact, trying to use a spring compressor tool not made for M-B springs is dangerous and serious injury could result.
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1977 300D: 300,000+ miles
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