Originally Posted by
fishboat
The WD in WD 40 is for "water displacement". I'd guess, in addition to mineral oil that is left behind, the solvent/carrier portion of WD40 is water-miscible components(small alcohols?) mixed with some higher carbon, volatile solvents. As such, it will degrease/dissolve greases..which is sort of the point as the lube that Shimano uses in their shifters has a history of hardening up over time. This causes shifters to get sticky or sluggish. Do a youtube search on cleaning/restoring sti shifters..you'll get plenty of hits. The mineral oil in the formula is left behind after the lighter components evaporate..displacing any water and offering some lubrication.
The nice thing about WD40 is that it works, is mostly benign chemically(from a safety standpoint and it won't harm painted finishes or plastics/rubber), and most of it evaporates. I suppose you could use mineral spirits and then follow with a light machine oil(spray).
No, WD-40 doesn’t contain alcohols. It is mineral oil and mineral spirits and is completely water insoluble. The oil that is left behind forms a film over the metal which keeps water from sticking all that well. But if the part is wet, it’s unlikely the WD40 will “displace” it. Other solvent sprays like brake cleaner, carburetor cleaner, or bicycle specific sprays like Finish Line Speed Degreaser are just mineral spirits and will only strip out the old oil and grease without replacing it.
Originally Posted by
dmeans2anend
Hi Cyccommute:
Isn't WD-40 a degreaser? I was told that it's not a good idea to use it on bikes.
It’s both a degreaser and a regreaser. There’s lot of mythology about WD-40 and bicycles out there and most of it is wrong. No, WD-40 spray is not a good choice as a chain lubricant but that is mostly due to overspray. The oil in WD-40 isn’t that much different from the oil you find in most oil based lubricants. It’s not going to harm anything but it’s going to be messy…just like
all oil based lubricants.
Is the intent with the shifter to simply get moving parts going again so it's not an actual 'lube' requirement where a degreaser would interfere with it?
I haven’t taken a Shimano shifter apart (most people haven’t) but I have restored many shifters to working condition with WD-40. As noted above, something changes inside…probably due to the grease…which causes the shifter to not work. Simply spraying in a degreaser removes the grease but doesn’t leave anything to help lubricate the internals. Many people will try to drip oil in to the shifter hoping that it will get to where it is needed. WD-40 just skips that second step. It won’t harm anything.