Brake Pedal Pulsation- How to prevent it
So you do your own brake jobs and you’re proud of it. Then you slap the wheels on and crank down the lug nuts so it takes a 1” drive impact wrench and 2,000ft/lbs of torque to get them off. And you wonder why your rotors warp and you’ve got pedal pulsation?
Proper lug nut torque is CRITICAL to maintaining true rotors. Yup, that means you MUST use a torque wrench. I’m not a big fan of those cheapies you can buy at Harbor Freight. But, if you buy one of those, at least you can hope that each of the lug nuts will be tightened to the same torque (or close to it.)
In a recent GM seminar, an engineer disclosed that if you under-torque a single lug nut, you can cause up to .003” of lateral runout. That’s three times the maximum spec allowed by GM.
So here’s the best way to prevent it:
1) Use a wire brush to clean rust off the hub and wheel.
2) To prevent rust from forming again, apply a thin coat of anti-seize on the face of the hub. Do not EVER lubricate the studs!!! This is EXTREMELY important. If the lug nut is hard to install on the stud, get a new lug nut or replace the stud—it means the threads are distorted.
3) Install the wheel and torque the lug nuts in a star shaped pattern to one-half the specified torque. This is known as pre-stretch. Then reset your torque wrench to the specified torque and tighten them all to full torque. It’s a two-step process.
I know. I know—nobody does it that way. Then again, everybody complains about warped rotors, too.
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© 2007 Rick Muscoplat
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This is a good idea, but how about all those times when you get a tire rotation/repair or new tires, and the mechanic doing the work zips it on with his pneumatic wrench. Those things are not torque regulated, and can deliver way more torque than most manufacturer’s settings which are in the 70-100 ft-lb range. So, it doesn’t make sense to fuss about it much, just try not to overtighten them and ask mechanics to put lug nuts on manually.
Some mechanics use “Torque Sticks” on their impact wrenches. These are specially designed spring steel sockets that are about a foot long. They’re designed to twist when the nut reaches the proper torque. Each torque stick is rated for a certain torque level. HOWEVER, the instruction for these sticks say that the impact wrench should NOT be set to maximum torque or the torque stick will not operate properly. The majority of rookie techs do not follow that last piece of advice. So, if you ask them to manually torque your lug nuts and they say they use a torque stick, make sure they’re not using maximum torque setting on their impact wrench.
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