Throttle cable failure analysis

Last time out I had a throttle cable failure. Had been sticky over several weekends and finally locked up hard. It was a Control Cables push-pull model that had been on the car for about 13 years, replacing an identical model.


There were several theories about the failure - water intrusion, perhaps heat - the green outer jacket was melted in several places). I decided to cut it open and do a failure analysis.


It’s a pretty robust assembly - there’s the plastic outer jacket, the sheath is a teflon liner surrounded by a twist of several stranded stainless cables wrapped by a piece of flat stainless strip.


The “cable” appears to be a very flexible solid wire (or else there are a LOT of fine strands) wrapped in a spiral of teflon tape.


And that’s where the failure was - no rust or other metallic damage. The teflon tape had broken, shredded, and clogged the works.


So, I decided to cut open the original that I’d kept as a spare. It still worked a bit, but wasn’t nearly as smooth as a new unit.


Nothing obvious there - except the teflon wrap had developed “bumps” here and there. I assume the tape had scooted and rolled to produce the bumps, or else it was dirt that had migrated under the tape. No broken tape, I assume the bumps were the cause of the additional friction.


So I have these suggestions for long cable life - first, use no lube. Anything that messes with the integrity of the teflon wrap will shorten the cable’s life. Second - ensure all the seals are in place to prevent dirt from getting inside. Third - pay attention to the bend radius, and try to shield it from heat.