It sounds like a couple of problems happened.


First was the threading of the "new" cable into the old shifter went bad. Sometimes it's a blind effort. using a flashlight shinning in from the adjuster can help give one a spot to aim the inner cable end at. Sometimes it's just a mater of hit or miss over and over. I find a slight bend at the last half inch of inner and rotating the cable to move this dog legged last bit about helps to match all up.


Second it seems that the shifter pod's ratchet pawls were gumming up. A classic Shimano shifter pod issue. If happening when guiding the cable through it's likely the shifter spool wasn't fully released to low gear position and the cable didn't have a straight path to feed it through to. Simple WD40 is a meek attempt to fix the old lube's dried out condition. I have seem more then a few shift pods that were "fixed" with simple thin lube spray ins that later gummed up again. The thin stuff usually dries out soon. So at work if we charge we remove the pods/cables and soak/blow out/thin lube/blow in/thick lube blow in/cover with a grease slime before reassembling with new cables. FAR better a long term fix. In the LBS view a far better service for the customer by making the return not likely to happen.


But simply replacing the shift pod is also good. Andy.