I'm in the process of installing a 1" BD to my 1997 4Runner SR5. I was wondering is there any risk in damaging the A/C & Heater Core lines that are routed thru the firewall. I check all the lines and it seems that there not a lot of play or clearance. I read contless threads regarding BD, but none of them mentions anything about these. Can someone please help!

 

You probably haven't heard anything about it cause its not an issue.

Though I haven't actually done a BL on my 4runner yet. I have done them on many other vehicles and the heater core lines usually don't have to be extended unless you go over 2". The 1" you're looking to go with is very small and won't require a lot of play.

The only reason I can think you would have a problem is if the hoses are already dry rotting, in which case you should replace them anyway.