frisbee91

I used an impact screwdriver on my brake rotor screws when doing a brake job recently, and it got me thinking...

It was a big help for a few stuck rotor screws. However, while whacking the stuck screws, it occurred to me that it might not be a great idea to impact the wheel bearings. Of course, I did it anyway

My thought is that the hammer blows will be transmitted directly to the wheel bearing (thru the rotor and hub).

I worked with industrial bearings in a previous life, and hammers and bearings don't usually mix. Sharp impacts transmitted to the bearing can dent bearing races and lead to premature bearing failure. Not sure if this applies here.

What type of bearing is in these wheels?

Any opinions on whacking your rotors with a hammer?


P.S. I posted this question in Van's DIY changing brake thread, but I decided to start a new thread instead, just because I'm curious about opinions on this. Still a great DIY!
Also, I like the idea of postulating on a possible bearing failure in a 996.

Mother

My take on it is .... whatever gets it off is alright to me (this includes jumping on a 10ft breaker bar with a extension) however when re-installing care should be taken using the proper Tool/Torque

Barn996

I wouldn't sweat it using an impact wrench to remove the rotor screw. I'll be doing the same thing soon with front brakes.

Zookie

you think your Wheel Bearing does it get it 1000 times worse on the Roads & Bumps? lols

Sneaky Pete

The impact screw driver is correct for the job 1000x over. Don't sweat it.

nick49

Given a large hammer, I'd bet that you could not damage the bearing no matter how hard you tried. Even with successive hard impacts directly to the hub, I think the bearings would do fine. Even hard impacts that will destroy a wheel and suspension components, more often than not will not affect the wheel bearings or hub. They are really tough in that regard.

frisbee91

While I agree that it's probably not a big issue to use the impact screwdriver, I don't think that impacts from road/track driving really compare. Road impacts are transmitted to the wheel bearing through the tires. That would be like trying to dent a hardened metal part with a chunk of rubber. No matter how hard you hit the metal with the rubber, it's not likely to dent.

However, with direct metal-to-metal contact (through the metal screwdriver) it's a different story. Here's a failure analysis for an industrial bearing that was hit with a hammer:
(reference document link)

Also, the wiki for ball bearing installation states "For small bearings ... tapping with a hammer damages both bearing and shaft..."

Many bearing installation guides recommend using a block of wood, rubber hammer, soft brass punch, plastic dead-blow hammer, or an arbor press to avoid sharp impacts to the bearing races.

I still think it's plausible that hammer blows could shorten bearing life.

LC MotorSports

As a fellow Design Engineer... You might be over thinking this one.... Keep in mind that the impact from the small screw being transmitted thru the HUB shaft that is in radial contact with the inner bearing race. Thus the impact load would not be true Point of contact (during many installation guides you are directed to ONLY apply force to the outer race) on the inner race. If you run a FEA simulation on the force transmission you will find the distance and mass of the Cast Iron Hub absorbs the Low impact force applied from the Hammer and Impact driver (which is designed to apply a light/Moderate downward force and a HIGH twisting (radial) force).
So, go ahead and use that impact driver... Just don't go get an Air impact Gun! That is a whole different Game...

frisbee91

Very true. I hadn't considered that the screws are a bit off center, transmitting a high twisting load which can be somewhat absorbed by flex in the hub.

I did use the impact driver without too much worry. Just thinking out loud here...

Wait, did my unnecessarily over-analytical post scream out "engineer". Guilty, I suppose.

LC MotorSports

My father (40 years as a Toolmaker) always tells me, "You over think everything" Just go out and do it!
So, we are both Guilty

ejabour

Is using an impact wrench on lugs which are threaded directly into the hub also that much different in terms of the load transmitted?

pongobaz

When I did my rotors, it did not take a big whack on the impact screwdriver to loosen the screws. Just a mild hit with a dead blow hammer.