heli-coil

blksc

Registered User
Hey gang. im working on the womans taurus and found that the spindle has a stripped thread so that i cant fasten the caliper onto it. I bought the thread insert kit, and the insturctions seems pretty straight forward:

1. drill out oil
2. tap oil
3. insert coil thingy

My question is what size to drill the hole for a 9.9mm bolt ? Also should the hole be slightly smaller than the tap bit ? or should the tab bit fit into the hole ??

Please help
 
Okay David. I bought this kit from autozone, so i will take a peek at the instruction to see if it lists what size drill bit to use.
 
Yes, for Heli-coil's (a brand name) you must use the exact bit size they say. Any thing else and the thread repair will fail.

They actually make oversize self cutting caliper bolts that will do a similar thing.

You may want to loc-tight the heli-coil in as you turn it in. But don't loc-tight the caliper bolt. Otherwise you'll just pull the heli-coil out. Use Anti-Sieze on the caliper bolt and make sure you don't tighten it more than what the specification calls for.
 
Don't use a cheap drill bit. Use a numbered bit if it specifies a number and have it sharpened so you don't make a rough hole. I hope you're doing this with a drill press, also. Heli-Coils are quite easy to install, they're just pickey about the hole you screw them into...
 
What is a numbered drill bit ? and i am not doing it on a press. I dont have the know out to disassemble the front end suspension stuff to have it drilled out somewhere.
 
Carlos,
Any GOOD heli-coil kit comes with the proper sized drill bit. At least all the ones I've bought.

Mike
 
Crap. Mine came with the tap, the tool to insert the coils and thats it... Maybe im missing something :rolleyes:
 
While we're talking about 'heli-coil' does anyone know of a good source. I've been trying unsuccesfully to find an M10x1.0 for my PBR calipers. I stripped the banjo bolt thread in the caliper casting. I forgot it was alum. and used the regular torque amount by mistake. In fact can you use a heli-coil on alum?.
 
Thanks a lot for the info. I'm surprised about your corrosion comment though, because the pistons in those PBR alum. calipers are also stainless. Nevertheless if I get that right size 'helicoil' I'll use some zinc primer first.
 
Galvanic Corrosion occurs when two dissimilar metals come in contact with each other. So the stainless steel will react with the aluminum.

I'm not sure about the piston in the aluminum bore. Are they not kept away from the walls by some sort of gasket? It's possible brake fluid contains something that limits this. Or that the issue is not something to worry about in such an application. Stainless steel pistons are used on high performance brake systems to prevent corrosion from the piston being exposed. They don't use dust boots on such calipers as the rubber would become damaged from the high heat experienced by the caliper. So they use stainless steel pistons that won't be damaged by corrosion due to water.
 
I'm not sure I would worry about the corrosion in this application. There was after all a steel bolt in an aluminum hole to begin with!

We also pulled up the threads on one of my Cobra (PBR as well) calipers and had to heli-coil it. Still holding some three years later! Of course, I have not tried to remove it! LOL
 
Joisey Jim said:
Thanks a lot for the info. I'm surprised about your corrosion comment though, because the pistons in those PBR alum. calipers are also stainless. Nevertheless if I get that right size 'helicoil' I'll use some zinc primer first.

Galvanic corrosion will only occurr if there's an electrolyte in contact with both metals. Brake fluid contains cleaners that are also dessicants and keep water and other electrolytes from coming into contact with either metal electrically. If you put some sort of lithium grease (lithium is a stronger metal than aluminum, chemically) on the threads, they will not corrode. Zinc primer might scratch/vibrate off in this application and may also make the bolts hard to get out.
 
Yeah, I didn't think about the likely hood of the issues.

In general it's not a serious issue. The information I've read dealing with that really came out of the Aerospace industry where they do worry about that type of thing much more.

I feel the key thing to deal with Heli-Coils is to use a thread locker when installing them. (Though they claim they don't need them). And use an Anti-Seize for the bolt you are installing. Make sure you use the appropriate torque on the bolt as well. That will help to ensure the heli-coil doesn't back out when trying to remove the bolt later.

p.s. I'm dreading removing the drain plug from the aluminum transfercase in my ranger. A steel plug in the aluminum case has caused obvious signs of corrosion around the plug. I think it's going to come out hard.
 
Thanks Guys - I'm going to helicoil the caliper and then push the pistons out to flush the inside. Any recommendations on torque George, because I think that's what did mine in the first place - I forgot they were alum. and used the regular settings (45 ft.lbs I think it was).
 
Torque for just about any aluminum threads is snug + 1/4 to 3/8 turn... no more. You use a lock washer on applications that need a higher torque usually. I wouldn't even bother with a torque wrench on your calipers as they'll likely just strip again.
 
Ouch, 44ft lbs is too high for many caliper bolts that go into steel. Those on my Durango are at 28ft lbs. And even then they have pulled threads out.

If it's a concern, use a lock washer as already suggested.
 
The lock washer is a good idea in most applications, however do not use one on the banjo bolt we are talking about here! Only use the little copper washers for sealing. I like new ones!

I don't usually use a torque wrench on those banjo bolts, so the snug + a little more that thebigslide suggested would be about the torque I would use.
 
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