rjag

'74 Stingray,
If it's not one problem it's another. Just finished installing new calipers in the rear and wouldn't you know it, the bolt holes were "kinda stripped". I know I didn't do it, so as I was tightening them they just didn't seam to tighten well. I even bought new bolts. However, I noticed the bolts on the right rear (stripped now) were different than the left rear. They were both 7/16" bolt but the right rear were longer. They had washers on them. When I reinstalled the new bolts I bought, I had a washer and lock washer, but they wouldn't tighten even though they were long enough and enough thread was catching. I took the washer off and was able to get the bolt to tighten snuggly as the thread went right to the end and was able to catch more thread, but I am not sure how long it will last. Both bolts did the same thing.

A few questions: How would I go about fixing the stripped caliper bolt holes? Will something called Heli Coil work? I've heard of them being used on spark plug holes.
Should I tap a new hold one size bigger? (1/2") Will a 1/2" bolt fit through the caliper mounting holes? (can't check now that they are on)
Should I fill the hole with weld, redrill, and then retap?
Is there enough room to weld a nut on the mount and use a longer bolt? or will it rub agains the rotor? not to mention look like crap?
What is the correct size of the original bolt and did it have washers?
What will happen if the bolts come lose? Major damage or will I know before anything bad happens? (like the caliper flying off) Drove around today without any problems.
Any other suggestions would be appreciated?
RJ

jcswm

That's the #1 answer in my book..... but first...
I'd remove all washers from the bolt & find a thin flat washer to use, locktight the bolt & snug it up .... let the locktight cure (24 hrs) & hope for the best.... check it often!!!

67L36Driver

One side of mine (RR) both stripped years ago when removing caliper. I simply drilled and tapped the holes for a 1/2"-20 tpi socket head cap screw. You will also have to drill the caliper ears to clear the 1/2" bolt.

69autoXr

A helicoil has worked perfectly for me since I stripped my caliper bracket about 6 years ago.

redvetracr

My vote (for what thats worth!!) "Heli-coil" look on ebay for a deal on a "kit". ...redvetracr

BerniesVette

Either mod will work, resize the holes for larger bolts or the helicoil. But do not drive the car the way it is. I had the right rear, rear most bolt back out, when I touched the brake the roter pulled the caliper around into the wheel locking up the right rear tire. Luckily I was in traffic and going slow; if I had been on the open road it is hard to tell what might have happened. I pulled the right trailing arm and replaced the caliper bracket.. In, fact I just pulled the entire rear suspension and rebuilt everything since it needed doing anyway. Good luck with your repair. Be sure to use loctite on whichever mod you do.
Bernie

texaswilkins

Helicoil's are your friend. Easy to use and last forever if installed right. No other mods required. Have the beer afterwards and NOT DURING installation.

Bill

CA-Legal-Vette

I agree with Bill on everything but the "NOT DURING installation" part.

i think that one before and or during instalation puts you in a more tollerant mood and dulls the pain of the cut and bruised knuckles.

rjag

Just purchased some Helicoil thread inserts today for about a buck a piece. Have never done this before. "They" say that Helicoil makes it stronger than the original, so I'm going for it. The kit was about $50 Cdn, but for just two holes, it seams like a waste, especially since I have the tap and the drill bit.
A few more questions:
Do I need the special tool to install the Helicoil or can I just improvise with need nose pliers?
For a 7/16-20 Tap size they recommend a 29/64 drill size. My tap set says I should use a 25/64 for a 7/16-20. Is the larger size recommended to accomodate the helicoil? I guess it is easy to tap with such a large drill size and smaller tap?
I purchased some grade 8 bolts rather than the grade 5 I have been using. Did the original install of the caliper have a washer, a lock washer or no washer and how long was it and what grade should I use?
The helicoil looks longer than the width of the caliper mount on the frame. Do you cut off (with a dremel) the excess helicoil or do you just leave it sticking out the end? Do you use locktite when installing either the helicoil or the bolt?
Overall, is it an easy or hard job? and can I screw it up?
Oh, and I will have a beer for sure!
Rob

jester4

According to Helicoil, the tap that should be used is STI tap (Screw Thread Insert), with I believe is different than a standard thread cutting tap, this is why they probably recommend a different size than the tap set that you probably have. I haven't used helicoils, so I'm not sure about using a standard tap to accept the helicoil whether it will work, or even be strong enough.....just my input

Michel B

You'l never get a helicoit in with pliers, they are like a spring and slightly bigger in diameter so that it presses inside the hole. The installation tool makes the installation a peice of cake. The drill size they recommend should be used because the special taps they provide for the coil are not the same as regular taps. And just use regular wire cutters to cut the coil the write size, there is a proper way to determine how many coils needed for your hole, I'm sure the web site can help you, personnaly I eye ball it and have excellent results. If you screw up, they are quite easy to pull out, just pry up the end and use needle nose pliers to pull out. finaly, I don't recommend using loctite, I would beleive this to be looling for trouble when removing in the future.. Have fun

Chuck Gongloff

TWEET!!! Stop!! You have to use the helicoil tap. You cannot use a regular tap. You also need "the tool" to install it.

Why? Lets use an example. A 1/4 inch coarse bolt is 1/4 x 20. A 5/16 inch coarse bolt is 5/18 x 18.

Let say you want to repair the 1/4 x 20 hole, AND let's say for conversation's sake that you need to drill that hole to 5/16 size.

The helicoil would be 1/4 x 20 on the inside where you would thread the bolt, BUT it would need to be 5/16 x 20 on the outside too (not a standard 5/16x18) SO...., the helicoil won't fit.

This is a simplification, and I don't have any of my helicoil kits in front of me as I write this, but I hope I've made my point.

You MUST use the helicoil tap, NOT a standard tap. Chuck

rjag

Thanks a million. I just don't know how people fixed cars before this Internet thing came along. The forum has been an amazing tool for getting things fixed. My mechanic buddy guys hate computers and the Internet, but when I tell them how much I learn on the forum, it really is an invaluable tool. Keep the info coming. I just can't stop learning. It's all good!
RJ

69autoXr

Just get the helicoil kit, it has everything you need (drill, tap, tool, coils)!

rjag

Going to purchase the helicoil kit today. A few questions for those of you who have done this before, especially on caliper mount holes.

1. When I tap the caliper mounting holes do I have to tap them the same way the bolt will be going into the hole (inside-out), or can I tap it from the outside-in? (reason being it is difficult to tap from the inside-out;not much room for the tap and then turning it)

2. Do I have to insert the helicoil the same way as I tap? I think this will be easier to do than tapping, but it will still be easier to insert the helicoil from the outside-in and then simply snip any excess.

3. Is the helicoil the same as any other tapped thread when it comes to removing and reinserting the bolt?

Thanks in Advance, RJ

Michel B

Yep! you can tap eather way as long as the tapered part of the tap passes through to make an even threaded hole. you can install the coil on wich ever side you want, but make sure the tang (the small end that the tool snags up to install) is broken off properly to avoid snagging on bolt. and once its in there its like any other threads. Once in a while we encounter a coil that snags and hangs on to the bolt opon removal,, this is a bitch but once out just reinstall another one if threads are not damaged.