I have a question for those with some ME background. I'm installing a set of calipers on my track car, and the mounting brackets are made of aluminum (7075).

What is the better mounting scenario - Thread the mounting bolts directly into the aluminum, or use a through hole mounting method with a proper bolt and nut combination?

If I thread the bolt into the aluminum mount, the amount of tension I can preload the bolt with depends on the aluminum, as I'd expect the threads to strip before the bolt yields. If I use a through hole, I can tension the bolt properly.

If I mount the bracket using a through hole, would the bolt need to fit very tighly on both the knuckle and the mounting bracket? Is there an issue with applying to much tension to the bolt and causing the bracket to deform?

I should mention that the OEM caliper mounting bolt is M12 x 1.25 x 21mm and goes through the mounting tabs (10mm) on the knuckle and threads into the bracket. So it only engages about 10mm to 11mm worth of threads on the bracket. Finding longer bolts of equivalent quality has proven quite difficult (if anyone has a source, please let me know, I need something about 25mm to 30mm in length, partially threaded, 10.9 or greater).

 

A hardware store near me almost certainly has them. I don't think they are hard to find. A 25 or 30 mm bolt may be fully threaded, so you might have to buy a longer one and either lathe it down or cut it with one of those water friction saws.

 

Check McMaster for the bolts in your desired length if you want to go with the longer bolts. When all else fails look at what Honda did and match their torque specs on the new piece. If you thread the aluminum bracket and while torquing it down it strips, then you can run the bolt through it and do the nut/bolt combo. Whatever it takes to get the right amount of torque to hold the piece in place.

Who designed the mounting bracket?

 

M12x1.25, class 10.9 or higher, and flanged? What's the name of the store? Is it a hardware store, or a specialty shop? I don't trust hardware bolts for a critical application such as this.

McMaster only has all threaded M12x1.25 bolts, nonflanged, and only class 8.8. Class 8.8 is fairly equivalent to class 5 SAE (http://www.boltscience.com/pages/faq.htm), and I wouldn't feel comfortable using such a bolt in a brake application. Plus I wouldn't want the shear stress to be placed completely on the threaded portion of the bolt.

I've looked at a ton of metric specialty shops, and no one has anything like the Honda bolts. Honda must have them made to their specifications.

I designed the bracket. With the assistance of an ME friend.

 

i wouldnt worry about the threads. id worry more about the heat and strength of the aluminum in place of steel brake parts.

threaded aluminum will be fine. if you really want to worry about it, use threaded inserts.

how would you use a nut anyway.... im not familiar with prelude, but if its anything like civics and integras, theres no room for a nut.

 

Ace hardware in San Carlos. They have a lot of bolts. I can stop by some time to take a look. I can also get a longer bolt and cut it down so that you can have an unthreaded portion. For a nominal fee

 

I'm more worried about thread engagement in the aluminum. Isn't the accepted norm for threading into aluminum 1.5 times the nomial bolt diameter? Right now, the bolt only threads into the aluminum 10 or 11mm.

As for the aluminum bracket, from what I have learned, most aftermarket brake kits use aluminum brackets. Some only use 6061. This is 7075, so I'm confident it is strong enough. Besides the caliper is aluminum.

The bracket mounts on the opposite side as the OEM caliper bracket. The bolt head is on the rotor side of the knuckle, so the nut would go on the opposite side of the bracket, which would be towards the center of the car.

Here's a picture of the bracket:

 

I have a lathe, so I can cut bolts down, no problem.

Ace Hardware - http://www.acehardware.com? We have them all over here. They're run of the mill hardware store bolts. Not something I'd want to use for a brake application, but I certainly appreciate the offer.

 

interesting design.

i would thread the bracket. going thru 2 thru holes introduces twice the amount of free tolerance.

1.5 x the diameter is way too much. its more dependent on thread pitch. given what i see of the thickness of that, youll be fine.

but then again, i withdrew from my 'machine design' capstone class to take a quantum physics and materials class. (perhaps i should have put that in my sig.)

some of those same brackets are known to melt (deform).... just saying.

 

The San Carlos Ace isn't your everyday run-of the mill Ace

 

Do not depend on threaded Aluminum to support the repeated stress of a radial caliper, you are correct most aftermarket brake kits use aluminum brackets however they employ threaded inserts or through hole mounting.

 

That's interesting. The two brands I've seen used neither method. The screws threaded directly into the aluminum. No inserts, no through hole. Do caliper manufacturers do the same? It would seem that the caliper sees just as must stress as the bracket, and the caliper is aluminum....

 

Really? So what happened to the caliper??!

 

For bolts and fasteners look here http://www.metricmcc.com/

2200 Century Circle
Irving, TX 75062

Phone - 972-870-1017 / 800-527-5177
Fax - 972-870-1154

 

Yes, they're local to me. I've used them many times. I've looked on their web site, and I was not able to find exactly what I was looking for. I need to give them a call, but I haven't had time.

 

here is a pic of a stoptech bracket

http://www.digitalsimple.com/TheMCou...h/IMG_6351.jpg

 

It turns out that even the San Carlos Ace doesn't have the bolt you want.
Therefore, I don't think it exists in this world. They came pretty close, though:
1 Correct length and pitch, but not flanged. Also grade 10, whatever that is.
2 Correct length, 10.9, and flanged, but 1.75 pitch.

Your best bet is to get a bolt for some other part of the car that is the size you want. For example, Hondas and Acuras tend to have engine mounting bolts that are 12x1.25, flanged. You can do a search for honda or acura 12x25, 12x26, etc. A RDX has a 12x27 bolt, for example. 93 Integra have 12x25 and 12x30, etc etc.

Your other option is to be a man and get a longer bolt in 1.75 and cut the 1.25 threads yourself.