So it was brought to my attention in a previous thread of mine https://www.northamericanmotoring.com/forums/showthread.php?t=157077 that one can operate without the torx bolt that retains the rotor to the hub... While this seems perfectly acceptable in theory, since the lug bolts serve the same function, I noticed that in reality there is considerable slack in the assembly using only the lugs:



This allows the rotor to rotate back and fourth slightly on application of the brake and / or throttle, which I could imagine would put undue stress on the lug bolts. Theoretically this would be limited by the frictional force on the rotor from being sandwiched between the wheel and the hub, but I can't believe that would be enough to entirely counteract the rotation.

Has anyone safely run their car without the torx bolts on the rotors? The reason I ask is because I snapped the bolt attempting to extract it, and the dealer is closed today so I can't get a replacement.

 

Race cars don't use them. Most aftermarket BBKs don't have them. Just a convenience when using a bolts style wheel rather then studs, like you said.

 

I wouldn't leave it out for the same reason, the potential for the rotor to bang back and forth on the lug bolts.

 

The MINI uses a Hub-centric setup, so when the wheel is installed and the lugs/nuts are set at the right TQ the rotor will not be moving around behind the wheel. If the Rotor is moving the lugs are too loose and the wheel will fall off before the rotor does any damage to the bolts or lugs.

 

Rotors don't bang back and forth. Once the brakes are applied hard for the first time, if they move at all, this is the one and only time they do.

 

I have a theory about this kind of thing: Car manufacturers first and foremost wish to make a profit so they can make more and better cars.
Manufacturers of sporty/fuel-efficient cars want to save weight.
Why on earth would they add to the cost and weight (ounces, I know, but nontheless...) by putting something on the car that has no purpose? If you don't know what is there for, don't assume it's not needed.
There's a nickel's worth of (probably useless) opinion.

 

I know that, generally speaking, the rotors don't move once the lugs are properly torqued but, IMHO, why take the chance? What if the next person to work on the car doesn't tighten the lug bolts/nuts properly? That screw probably doesn't weigh more than an ounce so why leave it out? It's cheap insurance if nothing else.

 

My thoughts on the bbk kits not using them is that perhaps the openings for the lugs are smaller, and thereby don't allow any slack?

I agree that the rotor should move only once, with the one exception of a badly matched heel / toe downshift, whereby you would be applying too much gas while operating the brake simultaneously, which could allow the hub to spin back slightly while the rotor is held by the brakes - it's unlikely, but it could happen.

As far as the manufacturer's intention for the bolt, it could go either way. I wouldn't doubt for one second that it could be there for some form of movement-eliminator based on the rather loose tolerances the OE rotors use around the lugs, but at the same time it could purely be for ease of assembly because it was quite a pain to put the rotor on without it. I may give my local dealer a call tomorrow and have a chat with the service dept. about this. I'm hoping its really just for retaining the rotor while the wheels are off though... I actually snapped a fairly robust easy-out in half trying to pull the remainder of the bolt out.

 

Update: I spoke with a MINI SA today regarding a noise that has developed after this brake job. During the conversation, I brought up the torx bolt: I couldn't really get him to commit one way or another to whether or not it was actually a critical component, but his basic response was that he always uses them with OE rotors because the factory put it there.

 

ive never taken that torx bolt off but is that the only thing holding the rotor to the hub?

My thinking is, if what i said earlier is the case, then the reason for that bolt is to prevent the rotor from falling off everytime you take the wheel off.

 

The rotor won't fall off when you remove the wheel because the caliper has it lightly clenched between the pads. Set your parking brake the rears will be even tighter. My opinion is keep the torx bolts on. I did even when I had a stud conversion kit. The factory put it there so leave it there. But hey, that's just my opinion.

 

The factory uses it to hold the disc on before the calipers go on.