I spent all of Sunday removing my speedo cable and installing a new one. Major PITA, but I didn't wanna pay $$$ to my local mechanic for this, so I gave it a go. I pulled out my old speedo cable (with casing) to the grommet on the firewall, but it got stuck there, so I had to cut the grommet a little to pull it through, and push the new one in.

But the grommet has pulled itself off the firewall and I can't snap it back in. I try pushing it and hammering it back into the hole, to no avail. Any ideas?

 

If you have enough room, use a hairdryer to heat it too hot to touch. Then use gloves to squeeze it back in place.
(you did say any ideas)

 

That might just work. I'll give it a shot, thanks.