The spec is actually "12 inch pounds of torque" to rotate the bearing when the bearing is properly loaded by the hub bolt. If the shim is too tall, you will get less resistance. If the shim is too tight, you will get more--or even lock up the hub.
Interestingly, I had a long conversation with Carroll Smith right before he died about this very problem. He said it plagued the cars in the 60's--seems to still be a problem.
That is why the auto makers have come out with the Gen 1, Gen 2, Gen 3, and now Gen 4 hub assemblies. All four "gen-sets" are still in use today. The Porsche set up is a Gen 1. A while ago, we quit using the Porsche bearings as they were getting impossible to get a hold of. So, we switched to a Lexus bearing--also a gen 1 set up.
Unfortunately, you can NOT convert ORIGINAL hubs to the Gen 1 set up. There is no place to machine the lip into the upright as the seal area of the upright has been machined down to avoid the drive pin nuts.
Now, I am not really sure what Shelby is doing on your car as who knows what bearings they are using now. Take some pics and post them and I will let you know what I think--but I doubt they can be changed.
Your choices are buy a completely new Kirkham set up (you would not be the first)--expensive, but solves the problem completely. We have had NO bearing hub failures...and I hope it stays that way!
Option 2:
Get a local machine shop THAT IS REALLY GOOD to do the set up measurements. We did the set up measurements at 5 tons. You will need to make the spacers out of a HARDENABLE material. Then, they should be rough machined to size in the initial set up. You will have to make them TOO TALL because they will MOVE in heat treat and likely not be parallel when they come out. Then you will have to GRIND the shim FLAT AND PARALLEL to the required dimension. They will have to grind them to +/- 0.0005 inches. It is a nasty trial and error procedure. If you don't grind the shim parallel you will side load the bearing and it WILL prematurely fail...seen that one too.
It is a pain, but it can be done. The shims should be Rockwell 55 C when done. That means they must be heat treated and then quenched to get the required hardness so they will need to be made out of some good steel...not mush metal (I have seen that one too). Sorry to be the bearer of bad news. But there is a reason why no one does this any more. This is not the first time I have had this conversation and as long as people keep doing this it will not be the last.
I am happy to walk you through the procedure if you want in much more detail.
David
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