I have in in my head that most of the “in the truck” main seal replacements I’ve read about here…have involved the rope seal.
Can the neoprene seal be installed “in the truck” as well?
Yes it can. To remove one, disassemble a windshield wiper blade and remove the thin polished stainless steel piece that acts as a stiffener. Bevel one end and remember to insert this so the bevel faces the old neoprene seal and not the bottom of the slot. Lower the crank (2~2.5mm)...remove transmission, harmonic balancer (once it is removed you can lower the crank a bit without damaging that seal), oil pan and loosen all main bearing bolts to let the crank drop a bit...some will also remove connecting rod nuts and push the pistons up and out of the way. Once you push or lightly tap this piece through, the old seal will come loose...if it doesn't, grab the exiting end with needle nosed pliers and tug it toward you. To install one, Skooter is on the right track. First draw a piece of t-shirt wet with naphtha or mineral spirits through to clean the groove as much as possible. Then apply non-hardening gasket sealer to the new seal (just a thin layer), guide it over the crank and lift the crank by tightening the bolts (except for the rear main cap, that is) a bit as you guide it in.
However...important note: if your crankshaft sealing area is pitted and damaged from an old rope seal the neoprene seal won't work well nor very long. In that case you'll need to remove the crank and install a Speedi-Sleeve over the sealing area just like you need to do for the harmonic balancer shaft.
Another comment: If you have a rope rear main seal which is leaking, I've seen people use the windshield wiper stiffening piece as a fix. Trim for length using the lower main bearing cap. Lower the crank a bit and drive this piece through the channel on the back side of the rope piece (leaving the rope seal in place), which forces it outward by the thickness of that stainless steel piece (usually these are something like .015" thick or so). Then replace the rope seal on the lower bearing half and tighten all up again.
