I asked this in another thread, but apparently it's not getting enough attention.

After bolting, what are the thoughts of welding the conversion bracket to the spindle?

I spoke with Scott over at Big Brake Upgrade, and he was concerned that welding the brackets might make them brittle.

I don't like how Ed does his with the smaller hardware to clear the abutment. Scott uses 12MM bolts, but he threads them in from the rear (counter bore the spindle) into the bracket, but 5/16" thread engagement is not even close to enough for a 12MM bolt.

I could of course just bolt them in Scott's way, and weld the bolt to the bracket after it's tightened, but I'm curious what the issue would be welding the whole bracket to the spindle.

-- Joe

 

Same issue that always comes up when welding mild steel to cast iron. If you know how to do it properly, then it shouldnt be an issue

Since you're thinking that far into it, why not design and new carrier that mounts directly to the spindle skipping the custom bracket entirely

 

I don't have the equipment to pull that off.

Making an aftermarket spindle out of plate stock would probably be easier, one that would have the 4 bolts to mount an LS1 hub, and take a bolt on steering arm.

But I don't have the jigs for that stuff or the desire to mock it up. It's something Racecraft should consider.


-- Joe

 

Joe,

I'll reiterate what we talked about in PM.

The standard is 1.0 or 1.5 * the thread size for minimum thread engagement length. The goal of this spec is to make sure the bolt breaks before the internal threads strip. That is the safer and easier failure mode. Now this is the general guideline that works for "all" engineering materials (steel, titanium, cast iron, aluminum, etc..). It covers your butt for all situations.

One thing you can do to lower the thread length is to use a material that has better strength. The spec is really driven by the weaker materials like aluminum and cast iron. If you use a stronger material you can get away with less engagement. Most brackets I have seen are made of mild steel. Mild steel holds a thread pretty well. I use stainless and it holds a thread well as well. Even better options would be chrome moly, 17-4, ect....

Yet another option would be to use a helicoil. The helicoil itself is 200ksi stainless which is stronger than the bolt. Of course it also uses larger threads in the bracket which gives it more strength.

After testing, I have made myself comfortable with the thread engagement of a 3/8" thick bracket and 7/16-20 hardware. In testing I took a single hole tapped in 3/8" stainless with 75% threads and torqued a bolt stronger than grade 8 at double the torque spec, 5 times. That is 150 ft lbs in a 7/16" bolt!!! There was no sign of damage to either the bolt or the internal threads. I am sure you could do this hundreds of times with a helicoiled holes as they are much more resistant to wear when tightening and un-tightening.

I would also advise anyone straying away from the guidelines to do their own testing. The numbers I get are based on my manufacturing process. I am very careful to do everything right, drill and ream holes for a 75% thread engagement, use only a drill press to drill and tap to ensure all holes are straight, ect...

So with that said, I support the plan to run the bolt backwards and tap the bracket. That assumes a 3/8" bracket. You mentioned 5/16". That would make me sit back and think about a number of things for a while, and not just thread strength. I thought a 3/8" bracket works for the LS stuff?

John

 

Hey John,

Didn't see this post.

I thought they were 3/8" as well, but after doing some research, Ed and Scott (both whom make the brackets) state 5/16 for the LS1 bracket. The C5 setup, while better in every way won't work with my 16" formula wheels so it's not an option. (but that does use a much thicker bracket, and doesn't have abutment clearance issues).

12MM in a 5/16 for me is a whole other ballgame.

A friend of mine brought up a good point. The abutments are bolted to the knuckle on an LS1 car with 12MM hardware, yet the calipers are bolted to the abutment with what an 8mm bolt?

-- Joe

 

Joe maybe you could use a the C5/C6 caliper on the LS1 rotor?

 

I must have missed it. Which conversion are you refering to? 4th gen calipers and rotors (typically called LS although as I understand even a V6 4th gen came with LS calipers)?
Just wondering as I've done that particular conversion (with 12mm hardware) and in comparison to the rest of the OEM components (as in your 8 mm reference) I'm far ahead of the game.

 

Got a picture of the lower bracket to spindle connection?

 

No I don't but would I be mistaken if I said one of the options was a 12mm button head bolt? This is bracket to (modified) spindle. The second bolt was a conventional 12mm hex bolt and washer. If I recall the button head was needed to provide clearence relative to the caliper.

Edit: I just double checked my notes and I've modified my spindle for 12mm x 1.75mm fasteners.
Ed Miller at Flynbye supplied a mix of metric and imperial for the bracket to spindle hardware when I purchased my brackets. I opted for 12mm all around.
I found this picture at LukeSkaff.com

 

I saw that picture on Lukes site as well, but many people have reported the bolt head hitting the carrier/abutment.

For example:

https://www.thirdgen.org/forums/post...668-post5.html

Are you saying that on your LS1 brake swap you used normal 12x1.75 bolts and the head on the bottom bolt didn't hit the carrier?

-- Joe

 

I would not trust that photo without a caliper mounted. I can't imagine that bolt head wouldn't get in the way.

What Joe is trying to avoid I think is using the button head for good reason.

 

No. I used a 12mm x 1.75 grade 10.9 button head bolt. IIRC, there may not have even been enough room for a washer. The top bolt is a conventional hex head.

Precisely. I can't imagine that the components would fit together without the additional clearence provided by the button head.

 

Ok. We're all on the same page. Thanks Skinny z!

Button head bolts scare me to death. They are not meant for forces involved in something like a carrier bracket.

87350IROC, what are your thoughts on 37* structural fasteners like the picture below ? Do you think a 5/16" plate has enough material to machine a concave to receive a bolt like this?


C5 calipers won't work with LS1 rotors, and a C5 swap won't fit under my factory wheels. The reason C5 calipers clear that bolt is because they are another inch away from the center.

-- Joe

 

For what it's worth, I believe the button head bolts I'm using are the same grade as the OEM hardware. My local fastener house had them in stock.

 

The grade of the shank of the bolt yes and they have the same sheering strength.

The problem is the bolt head, does not have the same clamping strength as a hex head.

-- Joe

 

Here are 10mm versions of the bolts I've used (I only purchased enough 12mm button bolts to do the job so I don't have any pics). These in 12mm with red loctite in grade 10.9.
I can't say for certain however it appears as though the underhead area of both fasteners is about the same. Is this the area regarding the clamping force you're referring to?

 

I'd have to see the fastener detail sheet on both, but I'm assuming the clamping force of the bullet head will be much less than the larger hex head.

I had a conversation with ARP about this over the summer, because some SFI flywheels were so thick the flywheel bolts were hitting the coil hub of the clutch disc. ARP offers a shallow 12point head with minimal losses in clamping force, but a straight up bullet/convex head wasn't considered strong enough for this application.

-- Joe

 

Interesting stuff. I've noticed that ARP's flexplate bolts are also a low profile design.
Regarding the fastener I'm using, you can see a circular ridge that keeps the edges of the hex from making contact. While it appears that the detail under the head of this hex head bolt limits it's area of contact to that of the similarly sized button head I can understand how that doesn't mean it has the same properties.
Once the warmer weather arrives, I'll be back in the shop for the annual pre-season maintenance routine. I intend to check on the condition of all the hardware I've installed.
The last thing a person needs is to have his caliper break off when he's coming off the hiway!

 

Button heads are not rated for structural applications in the engineering world.

The problem is they have a tiny hex socket with limited engagement. A M12 button head uses a tiny M8 allen with less than 3/16" engagement. This means you can never tighten the bolt to its nominal torque spec without stripping the head. For this reason torque specs on button heads are usually lower, leading to lower clamp up.

Since they are not used for structural applications, they are not forced to comply with the normal specifications. Basically you don't know what you have, that is my biggest problem with them.

 

I have looked at the countersunk fasteners. The head size on these is huge for the size of thread. When I was playing with these it was for a Camaro SS brake bracket, which is quite similar to the LS1. If I would have used those fasteners, it would have made the bracket to big and would have interfered with caliper.

Also I see to recall the thickness of the bracket even at 3/8" was not enough for the countersunk bolts. Let me check my reference.

I can't find the exact reference right now, but the head for M12 is somewhere in the neighborhood of 0.3" thick and there is a spec for how much remaining thickness needs to be left. I can't find the spec right now.

I would imagine that picture you have linked, he is using bolts smaller than M12. The heads on these are truly huge.

Are you sure the C5 calipers won't work? Obviously they would need a custom bracket. I think it would be close. I have all the components laying around, I can take a look one of these days.

John

 

For what it's worth I had no trouble torquing these button head bolts to the recommended value which I believe was about 90 ft/lbs with loctite (wet).
As for structural applications (I'm no engineer though) the millwrights in this (automation) shop use conventional socket head, hex head and button head bolts interchangeably. This is for assembling machines and equipment for (primarily) the auto industry. Our fastener supplier keeps the bins stocked and as far as I'm aware, the specs for all of these fasteners is the same given a similar grade.

 

Interesting. I am always up for some good testing, maybe I'll pick a few up and do some testing.

 

If you do get around to it, I'd like to see what your results are. As I had mentioned earlier, I don't need my caliper separating itself from the rest of the car.
I'd be happier to find out that my execution of this swap is sub-standard through these forums rather than after I've called a tow truck because I've totalled my car.
If I get the opportunity, I'll make a trip to my industrial supplier and see if can't get the spec of the bolts I've used. I know what I asked for but....

 

I bolted the bracket in. The top I threaded to 12x1.75, the bottom however I nut and bolted it with a 1/2" grade 8 assembly. (because I didn't have any long enough 12MM in the shop, and it is snowing so I'm not going out).

To run a nut in the back you have to counter bore the hole. It's flat in the back, but there is a clock face casted into the spindle exactly where the nut would be, so it wouldn't have an even clamping surface.

After bolting together, I took .020" off the bolt head, and about .020" off the abutement/carrier. This leaves about .010-.012" clearance between the bottom bolt head.

I welded the bolt heads to the bracket, and nut to the spindle. (rather than using loctite).

I also changed struts, tubular a-arms, and moog springs. I'm very tired.

-- Joe

 

you can look up a lot of these specs on www.mcmaster.com