[kyle_blake]

Hi guys,

My 1 caliper bolt on front disc is stripped. I have a tap and die set and started investigating what I need to heli-coil it.

I found the "kit's" for $80 bucks. You can see the 7/16-20UNF labelled clear as day and the 29/64 drill bit

Well I already have a $100 tap and die set plus full drill set. Why would I re-buy.

So I figure why bother buying the kit if I have the tap and can either make or buy the rest that I need.

So the drill bit 29/64 didn't even cut any material, next size up didn't even cut any material. So I moved on not doing anything.

Pulled the tap from my kit.

It created some new thread but the heli-coil would not go in. Didn't even look like it made the new threads wide enough.

So correct me if I'm wrong, does the kit contain an "OVERSIZED" 7/16-20UNF TAP that does not come in the typical tap and die set?

This makes me believe the tap and die set is for CHASING threads.

PS, after using the tap I tried the caliper bolt and to my surprise it actually grabbed much better. go figure.

Thoughts?

[kyle_blake]

My friend confirmed the tap in the "kit" is oversized and designed differently than a tap in a typical set.

[25stevem]

Roger that!

[dataway]

Yep the kits use a special tap that is usually labeled with the thread size of the heli-coil that will be installed, not the thread that the tap is cutting.

[dmorg1]

Yes,


The STI tap is required for helical inserts.

"Screw Thread Insert" tap.

McMaster https://www.mcmaster.com/91709A155

or https://www.mcmaster.com/91709A458

Dave

[Half-Inch Stud]

For those reason, i keep the Heli-Coil taps with the Coil inserts, to be on the ready and remove all doubt.

[Shiny]

I still like eBay for stuff like this. Many options when you search 7/16"-20 STI tap. Some as low as US $10:

https://www.ebay.com/sch/i.html?_fro...I+Tap&_sacat=0

[kyle_blake]

Ah hah, awesome. Thanks everyone.

Any know know the torque spec for the caliper bolt? I'll see if my re-thread with non STI tap holds it .

Guessing 40 ft.lbs.

[kyle_blake]

Well, not sure why I would of thought that taping it with non over size would miraculously fix the hole when the drill bit to use a helicoil didn't even need be done. Of course tightening the caliper bolt spun in the new threads.

Sometimes gotta learn by doing.

Off to buy a STI tap.

[Half-Inch Stud]

Originally Posted by kyle_blake

Ah.....Any know know the torque spec for the caliper bolt? I'll see if my re-thread with non STI tap holds it. Guessing 40 ft.lbs.

Tighten till it gives way, then back off a 1/4 turn. Maybe 23 ft-lbs is safer than 40. Best ro look it up.

[HoovDaddy]

Originally Posted by kyle_blake

Guessing 40 ft.lbs.

Service manual says 35 ft. lbs.

[kyle_blake]

My question is why wouldn't mechanics have a full kit of "STI taps" that are for all sizes?

You see tap and die kits for standard sizes all the time FOR CHEAP , what would it really take for them to make the taps a bit bigger and sell a kit for $100 for all of them like they do for normal sizes. Guess we tap threads more than we HELI COIL threads in the answer.

[Schurkey]

Originally Posted by kyle_blake

I found the "kit's" for $80 bucks. You can see the 7/16-20UNF labelled clear as day and the 29/64 drill bit...

...So the drill bit 29/64 didn't even cut any material, next size up didn't even cut any material.

Are your caliper bolts actually 7/16-20? The correct tap drill for a Heli-Coil 7/16-20 insert is 29/64. (The regular tap drill would be 23/64) So if your 29/64 drill bit didn't cut any metal...maybe you already have oversized caliper pin(s).

IF (big IF) you have oversized pin(s) already, when you Heli-Coil back to standard size, you'll need new standard-size pin(s), too. Hopefully, there's enough iron left to make decent threads for the insert to grab. If not, this is sounding like time for a different steering knuckle. God Bless the Treasure Yard. Or, a different-style of thread repair kit--Timesert or something similar, perhaps.

Originally Posted by kyle_blake

Off to buy a STI tap.

Do you already have the proper Heli-Coil insert and installation tool?

If not, you might as well buy the entire kit.

Originally Posted by kyle_blake

My question is why wouldn't mechanics have a full kit of "STI taps" that are for all sizes?

You will, when you buy enough sizes of Heli-Coil thread repair kits.

Originally Posted by kyle_blake

You see tap and die kits for standard sizes all the time FOR CHEAP , what would it really take for them to make the taps a bit bigger and sell a kit for $100 for all of them like they do for normal sizes.

Enough demand to make it worth while.

For most of us, the taps are useless unless you've also got the inserts. You get the tap and the installation tool with a starter-package of inserts. So where's the demand for a kit of taps without the inserts or the installation tool?

Now, let's say you're running a machine shop doing production-line work that involves thread inserts. You're buying inserts by the hundreds--or thousands. The installation tools are fairly durable, but you'll count the number of holes you tap, and just before the tap wears-out, you'll fling it in the scrap metal bin. So sure, McMaster sells taps to commercial users, or one-at-a-time to individuals who've lost or broken theirs--but still have inserts left.

Originally Posted by kyle_blake

Guess we tap threads more than we HELI COIL threads in the answer.

For most of us...yes.

I clean, restore, or tap virgin threads a hundred times more than I put in thread-repair inserts.

The last time I repaired a steering knuckle for a caliper pin, I had to clip the top couple of coils off the insert--the insert was longer than the hole in the casting was deep. By the time the top of the insert was below flush, the bottom of the insert was coming out the back side of the hole. I had to screw it all the way through, then shorten the insert before re-installing.

[Schurkey]

Ooops. The "regular" tap drill for a normal 7/16-20 thread would be 25/64, not 23/64. Too late to correct my post above.

[kyle_blake]

Hey shurley,

Thanks for detailed answers!

Well I never thought of that.

Like a caliper bolt being larger for one bolt but not the other on knuckle? I mean could be possible?

I see the only kit that contain one of those is this:

https://www.carid.com/1969-pontiac-g...638224895.html

I mean crap, there is probably no way i have the old bolts hanging around. I sure will go look but what would they even be???

I'm 99.99% positive it's 7/16 - 20 UNF. Measured the caliper bolt a couple times. Used thread pitch gauge for 20. Used bolt identifier gauge below:

https://www.ebay.com/itm/16405529305...Bk9SR-LT_IuIYQ

Yah I was in shock the drill bit 29/64 didn't even touch the edges.

I have heli coil inserts ready.

I made a custom tool to drive the inserts in.

THANKS FOR TIP ON COIL BEING TO LONG.

I found the kit local for $50 bucks, a week out.

All the STI tap's are in USA with $20 shipping on and 2 weeks out .

It does sound like a RISK buying the kit as the hole may already be so compromised, could be a waste of money.

Don't even want to think where to get a knuckle from.

I see why they don't make sti kits, not enough demand

[Schurkey]

Originally Posted by kyle_blake

Hey shurley,

Don't call me Shirley.
https://www.youtube.com/watch?v=KM2K...hannel=pmw8000

Originally Posted by kyle_blake

Like a caliper bolt being larger for one bolt but not the other on knuckle? I mean could be possible?

I see the only kit that contain one of those is this:

https://www.carid.com/1969-pontiac-g...638224895.html

I'm 99.99% positive it's 7/16 - 20 UNF. Measured the caliper bolt a couple times. Used thread pitch gauge for 20.

IF this is an oversize bolt, it'll have the thread-cutting section on it just like the photo in your link shows.

It'll still be 20 pitch, but 7/16 + a few thousandths.

[dataway]

Just an opinion ... but I have never regretted buying a Heli-coil kit, I bet I still have every one I bought in the last 40 years ... and man do they come in handy sometimes.

[dmorg1]

Just putting this out there.



If your hole is already to large for the helical insert, there are other insert options to save the part.


Key-Locking/Keenserts are available in Thin and Thick Wall as are the various types of Thread Locking inserts

[kyle_blake]

Sorry I meant - > Schurkey ... I liked the video, that cracked me up.

No, I don't think any caliper pin I've seen over the last 10 years on this car has had thread cutting ability. However I did not even know about these so I wasn't looking. With new calipers I always got new pins, so of course I used them.

Lastly the hole right now as it sits is to big for the drill bit but the heli coil will not go in.

Sooo the "kit" should tap it larger and I should be good, hopefully? Lets hope the spring doesn't need to be cut shorter as someone suggested it may.

Thank you everyone

[kyle_blake]

Guys, correct me if I'm wrong but here is a picture of the hole. Decided to look further - It almost looks like an insert was already installed??? The material looks different than the knuckle?

thoughts? This might be another insert/heli coil?!!?

Gosh it almost does?!?!?