Repairing Stripped Threads Using Inserts 

Many of us have found stripped holes on our TRs-- or stripped them ourselves by over torquing bolts or nuts.  I've had the most trouble with the cast aluminum trailing arms and gearbox cases.  (This past weekend my friends and I have found three stripped trailing arm holes and two stripped gearbox holes.)  The studs that secure the wheel hub and brake backing plate are the problem on the trailing arm.  These studs are 5/16-24 (fine thread) and the fine threads don't have much of a bite and tear out of the aluminum rather easily.  All the holes I've had trouble with on the gearbox are 5/16-18, course thread.   I think the problem with the gearbox is partly due to wear.  The gearboxes are getting old enough that the bolts have been removed so many times that the aluminum threads just wear away.    

One way to repair the threads is to use Heli-Coils.  The Heli-Coil requires a minimum enlargement of the hole.  However, special taps and tools are required which makes it pretty expensive for the home mechanic, especially if one wants to do several size holes.  A search of the Internet will bring a wealth of information about Heli-Coils.

I've repaired stripped threads in the past by drilling out the holes, tapping the hole to an oversize thread and then screwing in a thread insert.   The inserts I've used in the past for 5/16 inch holes either required 1/2 inch holes or 7/16 holes with fine thread.  I preferred to use the smallest hole possible and course threads to get the best bite in the aluminum castings.  I've recently discovered thin wall 5/16 - 18 and 5/16 - 24  E-Z LOK inserts  that have an outside thread of 7/16-14.   No special tools are required to install the inserts. They cost about a dollar each and are available from McMaster-Carr  and probably your local fastener store.  

I plan to keep a few spares of both the course and fine thread 5/16" inserts in the future.   Some of my stock of 5/16-24 inserts is shown on the right.

The following is scanned from the instructions in a box of 10 E-Z LOK inserts that show the sizes available the how to install the inserts.