How do I fix a stripped thread in the transmission tail where the trans mount goes? This is one of two holes on the tail of the aluminum part of the trans where the trans mount bolts up. I stripped it when I was installing the trans mount bolt! :mad I was very careful and did not over torque it but I think what happened is a piece of aluminum thread broke off when I removed it and was stuck in the bolt threads when I went to install it. This tore up the threads on the way in. :eek:

What size is the bolt? I think it is 3/8 " but I'm not sure. I went to Autozone and checked out their thread repair kits. I found a 3/8" one but when I tried to put the bolt in the heli coil it did not fit. Also, the tap threads don't match the threads on the bolt.

I'm so confused :confused: and bummed :( right now. This was supposed to be a simple trans mount swap that has turned into a real PITA! :cuss

Please let me know the exact parts and tools used to fix this. Thanks!

 

Sounds like it may be a metric fastener. Check the head stamp; metric fasteners have unique headstamps. Where unified national (standard) fasteners have an alphabetic headstamp identifying the manufacturer, metric fasteners will have numbers like "9.9" or something.

For a good reliable repair, I think you are looking at a helicoil here.


[Modified by Chuck Sangerhausen, 9:53 AM 8/30/2001]

 

You need to know the thread pitch ie tpi. It could be 24 (UNF) or 16 (UNC). I don't know my Vette well enough to tell you what threads are used, but UNC/UNF would seem to be a good starting point (as a lot of British vehicles were converted to Unified for the US market). Use a pitch gauge on the bolt to work out the tpi (or just count the turns per inch) & buy a Helicoil kit for that size. Once you've repaired the stripped thread it may be worth converting the other to Helicoil if the thread looks dodgy (Helicoils are stronger than original threads in ally - just don't ever strip a Helicoil!). ReCoil kits (made in Oz) are also good kits.
Good luck
Paul

 

Common problem and easy fix. Just Helicoil it. You can buy a Helicoil thread repair kit at your local NAPA store - most NAPA's stock the kits for course thread sizes up through 5/8". The trans mount bolt holes in the tranny are either 3/8" or 7/16" course thread - I can't remember off hand...

The kit comes complete with the inserts, tap, and installation tool. You then need to stop by the hardware store and buy a drill of the recommended size (drill size is shown on the Helicoil package). Drill out your stripped thread, tap it with the tap provided (you have to use your own tap handle), install the Helicoil, and you're all set. It'll take you about 5 minutes.

 

I hope it's not a metric bolt as that means I'm gonna be buying metric Helicoil kits when I've got a full set of UNC/UNF already :eek:
You'll need a metric pitch gauge if it turns out to be metric. If it's slightly over 3/8" then it's probably an M10 with a likely pitch of 1.5 (course) or 0.75 (fine) but could also be 1.0 (spark plug thread) or 1.25 (something else!) - this is why I much prefer UNC/UNF
A possibly easier way is to take your bolt to a bolt supplier and match it up to a known bolt. Once you know the size you can buy the Helicoil set. The set should come with a drill bit to drill out the old thread (drill it true), a tap to cut the thread for the helicoil (again, do it true), coils & a tool to wind the coil in. Once you start to wind it in DO NOT try to back it out as the driving tang will probably break off or, even worse, the coil may distort. Turn the coil in until the end of it is just below the top of the hole & then break off the tang. There should be comprehensive instructions with the kit. The crucial things are to drill and tap the hole true & then meticulously clean it before inserting the coil (this is starting to sound a bit medical ). It's a good idea to practise on a bit of gash metal before you start on the important stuff (your Vette). Once you've done it once, it's an easy job & I quite enjoy doing Helicoils - maybe I'm just warped :D
Good luck

 

Vettesite,
It is probably metric as stated above, If it was me and it sort of just was as my new race trans had a later tail on it (metric) we went with a 7/16 thread. Try to run a 7/16 tap in it before you heli-coil. ..redvetracr

 

Thanks for the responses!

I did some research and found it is a 7/16" coarse (14 UNC) thread bolt.

I will try to run a 7/16" coarse tap and see if that works. If that doesn't work, I might try drilling and taping the hole to fit a 1/2" coarse bolt if it will fit the trans mount hole. The $3 1/2" bolt will be a lot cheaper than the $30-$40 Helicoil kit and $10 special size drill bit. It's kinda a bubba fix :smash: but it might be worth it in this case.

 

How much? :eek: If you need to do any thread repairs see if you can find somewhere that sells ReCoil kits (made in Oz). My 3/8 UNF kit cost about £25-00 (around $30-00) & they include the drill bit required.

 

It's fixed! :yesnod: Here is how an why.

I drilled out the hole 27/64 and tapped it for a 1/2" bolt. This was a lot cheaper than the heli coil kit. It cost about $1 for the 1/2" bolt and lock washer vs. the $20-30 heli coil kit. I also went this route because the drill size for a 1/2" bolt (27/64) is less than the heli coil (29/64). I figured I'm taking away about the same material and the 1/2" bolt fit in the trans mount with no mods.

Thanks for all the suggestions.