During a DIY transmission fluid service (not the actual discussion topic, please!) one of the ~20 pan bolts broke off while removing the pan, leaving a chunk in the bolt hole. Tried a left-hand drill bit and and Easy-out extractor, but to no avail, although there is now a path/hole through the hole, it just still has some of the old bolt still in the hole that won't dislodge for some reason.

I replaced pan and re-filled fluid and watched carefully over time/driving to see if any fluid was leaking...so far so good, but it's only been a day. I've no intention of leaving it this way, but would appreciate some advice or thoughts on best path forward.

My best efforts at investigation seem to point me toward Helicoil solution. Also, is this something a numb-nutted numb-nut such as myself should attempt, or best left to a mechanic?

Thoughts?

If it's not leaking leave it alone. Like you said 19 other bolts holding that pan on and it's not under any pressure.

I've run a machine shop for 20 years. I've seen customers do way more damage than good trying to get bolts out. You'd still have to get the bolt out to put a helicoil in. Chances are doing it by hand under the truck you'll end up drilling the hole off center and/or snapping off a drill or tap inside.

If it weeps you'd be better off pulling the pan again and using some RTV along with the gasket to get it to seal off rather than messing with the bolt.

I like what Metal Head said. You could easily do lots more damage. The other bolts should hold it sufficiently tight. Heli coils work great in many situations, but you must get them in properly in order for them to work properly.

I've done worse. I broke two bolts when I reinstalled the pan. Reinstalled everything with a new gasket minus those two bolts and its been 3 yrs and 30,000 miles later. Not a drop of fluid has escaped and this truck has been hammered on off road. You should be more than fine.

Even though its embarassing to leave our trucks in this state :P

I worked at a machine shop too and it is very difficult to do this by hand without getting off center. Listen to Metal Head.

Just echoing what's already been said. Heli Coils are GREAT, but I would not want your first attempt to be in your transmission housing. You're good!

Yep...agree. It's a little strange to me that I heard several times, from different avenues/sources/persons, "Helicoil, Helicoil, Helicoil!" I suspect not one of them had ever actually had to remove, re-tap, and insert a Helicoil, but probably just wanted project "knowledge"!

Happily, I found out I have in my network a former Army mechanic that worked on vehicles large and small, including Apaches and Black Hawks, as well as being a professional BMW/German car mechanic for years while living in Germany. He took care of the issue, without needing a Helicoil, in about 15 minutes such that a new transmission pan bolt I had just picked up from Toyota stealership went right in as usual/normal, so...hooray.

And he's the guy that also recommended (well...ordered, really) me to use Liqui-Moly products, which is pretty much all I use in my vehicle now when it comes to lubrication or additives.

Do you know how he was able to remove the broken bolt so quickly?

Not exactly...but it had already been reamed out pretty well by some other folks (one very experienced machinist and one very experienced all-around fabricator) when original issue occurred. But they were expecting the broken bolt to simply back out with a left-handed drill bit (it didn't, even when tried with increasing diameters) and with an easy-out extractor. They left enough of a hole through the bolt that I had was able to easily thread a zip tie through and tighten it down to make myself feel better while driving it. By the time the Army guy got to it, he just did a little more of that and then use a correct sized/pitched tap.

So inadvertently I made it seem like he worked some magic when, in effect, the other guys had spent 20 mins on it previous. In other words "they loosened it" for him. :--)