Check your rear subframe for cracks

From Tony Fox's article "Stag rear suspension" in Stag News issue 117 (Autumn 2022), the magazine of the Triumph Stag Club USA. Summarised here; the full article is in the club's magazine.

Tony's Stag lost the support for a rear trailing arm at about 30 mph. The subframe that carries the trailing arm (it runs from the pinion nose out to the outer rubber body mount) had cracked right through at its outer end, at the joint where the body mount support is welded to the box section.

When it lets go, the outer end of the trailing arm is free to move rearwards, which pulls the handbrake cable tight. At speed it could be dramatic.

How common is it?

UK Stag specialists Tony asked had never heard of it, so he first put his own failure down to a bad weld from the factory. Since then there have been at least three more: Dave Bergquist's car in California, one in Australia, and a German owner who posted about it on the Stag Owners Club forum. It looks like a fatigue crack that grows slowly over the years before the final break.

How to check

1. Get the car up safely and clean all the grease off the outer end of each rear subframe, around the body mount.
2. With a good inspection lamp, look for a hairline crack at the joint between the body mount support and the box section.
3. You can see three sides well enough. The top is hard to get at, but if the other three are clean Tony reckons it's fine.

If you find one

Tony had his MIG welded as a temporary fix until a replacement subframe arrived. At the time of writing, new right-hand subframes were still available (part number 215160) and left-hand ones only secondhand (215159).

For more on the Stag's suspension, see Suspension and steering at The Stag Archive in the UK.

Found a crack on your car? Tell us in Tech Q&A so we can keep count.