Brake rotor wear and wheel nut torque consistency


#1

I had a realization the other day, based on a Porsche 944, that the “set screw” holding brake rotors are more for the assembly process but are not actually what accounts for the fastening of the rotor on the hub. instead, the 130 Nm torque on the five wheel nuts that sandwich the rotor between the hub and wheel do this.

… if the torque on the nuts is uneven, but the assembly is otherwise secure, wouldn’t one prediction of this be uneven brake rotor wear?


#2

Over-torqueing often causes distortion of the rotors, which causes vibration when braking. If no nut is over torqued, and some are under, I would say that would not cause excessive wear.

However, for safety all nuts must be equally tightened.

Vibration due to techs using air wrenches is a common complaint.


#3

My wifes 96 Accord had screws that held the rotors in place. When I had to replace them at about 200k miles I had to drill the screws out. Obviously they never went back in. The only thing holding the rotors/tire on were the lug-nuts. Which is common.


#4

I’ve never actually owned a vehicle with retaining screws for the rotors, so it’s always the lugs.

And yes, the torque matters and will cause problems, as will rust buildup between the hub & rotor. This typically make a problem after removal and reinstallation if the surfaces don’t get cleaned up. I also use a thin film of grease on the hub/rotor mating surface to discourage such things.


#5

My son in-laws Honda has the retaining screws. I bought a impact driver from Harbor Freight and actually twisted the bits into a spiral, cheap Chinese steel. Then I bought a Klein reversible and it worked great. Klein Tools 70220 Reversible Impact Driver Set from Amazon. I have resorted to drilling them out before. I put the rims on with a torque wrench to keep the rotors flat and flush. Also, I want to be able to get them off if there is a flat.


#6

The phillip head screw in Asian brake drums serves the same purpose as the tinnerman nuts on domestic brake drums. They held the drum in place until the wheel was installed.


#7

Oh geez…My Odyssey has those screws holding the rotors on the hubs. I had one of those impact drivers from Sears and those screws twisted the phillips bit onto a spiral! My BIL got them out with a screwbuster, a tool with a lever on a bit used with an air hammer. Yeah, if you drill them out, the wheel nuts will hold everything together just fine.


#8

The screws are there just to hold the rotor in place while the wheel is being removed. It isn’t necessary to really crank them down as the lug nuts supply the actual holding power when in use and are therefore critical to proper torque when mounting the wheel. I would think that some anti seizing compound could be put on the threads. I have ordered a removing tool which you use one end to prepare a screw head and the other with a reverse thread to wined out the screw. Hopefully it will eliminate the need for drilling out a screw and ruining the threads.


#9

The screws holding the rotors on are there to help prevent warping, but not by themselves. The screws are there to keep the rotor tight against the hub when the wheel is removed for tire service/rotation. Without that screw, there is a chance that rust or debris may fall between the rotor and hub, then when reassembled there would be an uneven mating surface that may cause warping of the rotor.

Uneven or excessive wheel lug torque can contribute to rotor warping. Some cars seem more sensitive to this than others.


#10

My escort has retaining screws for the drums in the rear. I get them out with my air impact with the appropriate sized phillips bit and socket for it.


#11

New cars used to use a thin metal spring washer that slipped over a lug bolt to hold the brake drums on while the chassis went down the assembly line. Kept them from slipping off and landing on someone’s toe (or head). When they switched to rotors, they switched to a screw that indexes the rotor so that it goes on in the same orientation that it came off. I am not sure that is all that important since I don’t think they spin balance the rotors in place on the car.

As for lug nut tension, that is all about heat transfer. A lot of heat transfers from the rotor to the hub and to the wheel. Heat transfers more effectively around a tighter lug nut. Several thousand cycles of uneven heating and cooling tend to warp the rotor.

As has been pointed out here before, a lot of tire shops claim to use torque wrenches to tighten the lug nuts, when in fact, the use the torque wrench only to double-check that they have tightened all the lugs. By the time they pick up the torque wrench, they have already over-tightened and unevenly-tightened all the lugs with their impact wrench. That is why I carry loose wheels to the tire store and mount my wheels myself.