Just because replacing the rotor fixed the problem, does not mean that the rotor was warped. Pulsating due to rotors could also be caused by deposits being left on the rotor by cheap brake pads.
A warped rotor’s runout can easily be measured. Did they do that?
Btw, if you insist on using an impact gun to tighten lugs, it is best to use a torque limiting stick.
A lot of shops replace the front rotors automaically, and I agree with OK4450 that a more in-depth look should be done here.
There are vehicles out there that for design reasons are more prone to rotor warping than others. Do a search for TSBs for this car, and perhaps even look through some GM websites, to see if yours is one.
Additionally, driving environment and driving style matter. If your sister drives in hilly terrain, constantly slowing the car going down hills, the brakes will be more prone to warping. Downshifting going down hills can help this. Or, if she rests her left foot on the brake pedal, this can warp discs. It’s a habit that should be broken if she has it.
But first, as OK4450 said, it should be determined if the discs are actually warped.
db, I did work in manufacturing and we used a variety of air tools. The 3/8 drive ratchets would not torque a tire, they did work for the smaller connections we had, on the larger ones, when the ratchet stopped, it locked so the operator could add a quarter or half turn as needed for the connection. Air impact wrenches would keep hammering on the connection but it would take a long time to get tight, longer than the operator wanted to spend.
For some critical applications, we had some 1/2" drive air ratchets that were preset to 75 ft lbs of torque, again just shy of the needed torque for a tire though.
Currently I buy all my tires at my local Costco. The use an impact wrench to run down the nuts, but the air supply is regulated to a low pressure so it only puts about 25 ft/lbs on the lug nuts. The tires are hand torqued from there. They do a lot of tires everyday.
One of the local Sam’s Club’s here has invited me to never buy tires from them again. Their procedures are supposed to be the same as Costco’s but I noticed that they hammered down the lug nuts with the air impact wrench so much that the torque wrench only just clicked, it did not move the nut. I discussed the proper way to use a torque wrench with the manager but he did not appreciate my valuable advice.
Another tire store that had been recommended by a coworker pretty much ruined the rims on my truck when I took it there for tires. The pin headed moron who installed the tires hammered down on the rims with an air impact wrench with those useless “torque sticks” He did not center the rim properly and with each wheel in an offset from the center, he proceeded to hammer down on the first nut until it deformed the hole on my alloy wheels. I went to the manager about it but they would not take responsibility for their lousy workmanship.
I had to take the truck to Costco and get the tires rebalanced and reinstalled, and it helped, but the wheels still did not quite center on the holes, had to finally remachine the chamfer for the holes myself to get the truck to ride smoothly.
I will give you one thing though, I don’t believe that rotors can be warped by the use of an impact wrench. The only way that over/under/inconsistent torque would warp a rotor would be if it was mounted on a cantilever, which it is not. Just like the over heating theory, I think this is another myth.
Hammering the nuts on with an impact wrench can clearly cause damage, but I’m not sure I subscribe to the theory of it causing warped rotors. More typical damage would be stretched or snapped lugs.
I saw a photo today of an automotive student weilding a crescent wrench with a (no joke) 2 foot handle. Imagine the torque you could get with even just that! Let’s see, I weigh 240lbs, X 2, = 480 foot pounds! That would do the job!
I agree TSM.
On the ratchet vs impact debate, I think a true professional can use either with equal effect and without damaging anything. No doubt there are lazy mechanics out there but I’d hope there are more that apply an impact conscientiously and use the torque setting appropriately.
I run all my lug nuts up using the impact set to its lowest torque setting. Why waste time messing around? And I’m not getting paid by the job either. Done right it’s no more abuse than a 3/8 hand ratchet. They’re just snugged up. Finish with the torque wrench if you prefer, I just use the stubby lug wrench. No way you can over tighten with that.
A lot of posters here point to the use of a torque wrench when tightening wheels but forget to point out needing a star pattern tightening sequence. A circular pattern will cause pulsation very shortly after leaving the shop. Another issue may be at work here. Brake pads, especially metallic ones, will cause localized rusting under the pad if the car isn’t driven very regularly. The rusty spot becomes harder than the rest of the rotor and when it wears a bit causes thickness variation and pulsation. One more ugly problem, some calipers (especially GM calipers) are not very stiff. When the brake is lightly applied a vibration is set up that makes turns the rotor into a waffle! No kidding! Buy aftermarket rotors, good ones from Brembo or ATE, buy ceramic brake pads and hope this cures it. You may have to try different brands of pads to find what works best for her. The is a crappy way to design a brake system but its why GM dumped the Delphi/Delco division that made them and sold them off to the Chinese.
Improper lug nut installation may not be the only cause of pulsing brakes but it’s best to install lug nuts correctly to eliminate that as a possible source of the problem.
For the doubters and others, search “pulsing brakes lug nut torque” to see some other views on this topic.
You don’t need to use a star pattern for tightening, thats another myth. The wheel is not cantilevered so it doesn’t matter what tightening order you use.
What is an issue is the initial snugging of the lug nuts. You snug the first one, then snug one on the opposite side of the wheel, that centers all the studs in the holes so when the lug nuts are tightened/torqued, the hole or lip of the hole doesn’t get deformed.
This is critical on some GM vehicles as the wheels do not have tapered seats in the holes, but the lug nuts do have tapered seats. It wouldn’t be so bad except that the lug nuts they use are made form a soft steel, so it is easy to deform the seat on the lug nut so that it wants to push the hole off center.
A small burr on the mating surfaces of the rotor or the hub will hold the rotor askew resulting in the same wobble as a warped rotor. Likewise, a burr on the rotor or the mounting hardware on a brake lathe will cause the rotor to be cut askew. There are many causes of a rotor being lop sided/warped/askew, whatever. I have seen many rotors discarded because they were cut beyond the minimum thickness by poorly trained or inept mechanics who blindly threw them on the holding fixture, set the depth and let the machine cut while it was obvious that the cut was bad. I have heard rotors being cut into scrap iron from across the shop, above all the normal racket of a busy shop. It is really just that obvious.
@keith Star pattern torquing is not a myth! I worked as an engineer GM during the days of the warped rotors and I have seen the data. It will most assuredly warp the rotors on these cars. It isn’t the cantilever or the centering, it is the fact that the hub is rather thin and the rotor hat is very thin and pulling down the stud torque deforms the wheel surface and pulls the hat and hub into the aluminum. Circular pattern tightening deforms the assembly unequally. Star pattern helps prevent this.
As you say, snugging it down before torquing helps prevent this but when is the last time you saw a mechanic do this rather than hammering them all home with an impact wrench each in turn?
An air wrench can be used (and usually is) when installing lugs and it will create no problems at all. It all depends on the person using it. Someone who has ham fists and keeps the adjustment on 10 all of the time can certainly create some prroblems but constant use of an air wrench by someone allows them to develop a feel for things and this will not be a problem.
That feel will allow someone to be close to the torque called for anyway as many torque specs have a wide range. Some have a 20-25 Ft. Lbs. spread, as in 67-82, 60-80, and so on.
As to air ratchets, I’ve never seen or even heard of someone using one to install wheel lugs. Maybe there’s something like this used on an assembly line but out in a repair shop this would be news to me. I was under the impression that an assembly line used what is essentially a multi-socketed air wrench tool that installs all lugs at once. The car makers are certainly not torquing lugs when they build the cars.
About the most torque one is going to get out of a 1/2" air ratchet is about 60 Ft. Lbs. and most mechanics use 3/8 and 1/4 drive air ratchets which produce nowhere near 60 Ft. Lbs. Slamming lugs home with an air ratchet even at torque like that is going to be very tough on the gear head mechanism and the user’s shoulder when that lug bottoms and the ratchet whiplashes around.
I separated a shoulder out in the shop once with less leverage than that being applied and which led to a hopital visit along with a minor chronic problem that still exists to this day.
Even a smaller capacity air ratchet with much lower torque applied can be hard on the knuckles and wrist if attempting to ram a fastener home and I can’t imagine hanging onto a 1/2 ratchet at 60 Ft. Lbs.
My GM Factory Service Manuals For Our Late Model Cars Contain Admonitions For Wheel Lug Tightening. It Shows Star Tightening Patterns For 4, 5, 6, 8, And 10 Lug Wheels. It Warns That Improper Tightening Can Cause “Brake Pulsation” And “Expensive Brake Repair”.
I would trust OK4450 to properly torque the wheels on my car, but he is very experienced in using an impact, knows his wrenches and knows the feel. When I torque my wheels I use a star pattern and tighten in 2 stages, 60-70 pounds and then the 100 pounds, specified.
I will say that from my experience, certain makes and models are possibly more susceptible to problems from improper torque techniques than others. For example, when I worked for a Volkswagen dealer I saw brakes screwed up this way. I’ve not had the problem on my cars.
CSA
First, I did not mean to say that anyone should use an air ratchet for wheels. What I was trying to convey is that an impact wrench can leave a loose fitting. granted, we used lock washers in the connections and impact wrenches just don’t tighten up a lock washer or a belvil washer worth a darn. an air ratchet worked under those conditions. Wheels do not have lock washers or belvil washers but I still don’t want an impact wrench used on my wheels.
To Mustangman, you claim to be an engineer at GM, then you should know that the pattern used to tighten down the lug nuts did NOT warp the rotors, you and I know why they warped, I worked for a supplier to GM as well. And there is no aluminum in a lug nut, hub or rotor.
CSA, that admonition by GM is them trying to duck responsibility. It appears that I am far more anal about how my wheels are mounted than you are. First I snug all the nuts by hand. Then I use a socket with a short extension, no handle, to further tighten the lug nut as I hit the wheel while spinning it. This makes sure that the nut is absolutely centered. Then I go to 25 ft lbs and then to final torque. I don’t worry about the pattern.
It is better to go from 25 ft lbs to final than it is to go from 60 or 70 to final. 25 to 100 or final is about a quarter turn and that is about what each stage of torque should take. The problem with getting too close to final is that you can get a false torque that is too low. The force it takes to restart the nut moving again after reaching 60 or 70 ft lbs can higher than the final torque because of starting friction. You only get the proper clamping force if the nut (or bolt) is moving smoothly when final torque is reached.
Anybody Use Craftsman Microtork “Clicker” Type Torque Wrenches ?
I own and have used beam type torque wrenches, a 3/8" inch-pounds and a 1/2" foot-pounds one.
Sears just had the clicker wrenches on sale for 50% off, $40 each, instead of $80 for Christmas.
I bought one 3/8" inch-pound ( 0 - 20 foot pounds ) and one 1/2" foot-pound ( 20 - 150 foot pounds ) wrench.
I no longer enjoy crouching down and leaning over to read the scale on the old beam type wrench when I tighten lugs with the vehicle on the ground, so I thought the clicker would be nice.
Anybody Use Craftsman Microtork “Clicker” Type Torque Wrenches ?
Are these things any good ? Do you know who makes them ?
CSA
@commonsenseanswer, this is what I use, when I’m doing a cylinder head
Expensive, but worth every penny.
" db4690 "
That’s a beauty, but for my limited use I don’t want to go $500+. If I were a pro I wouldn’t hesitate. I’m just wondering what to expect with my new $80 wrenches. I haven’t even opened the packaging, yet.
CSA
If you’re not earning your living with the tools, Craftsman is more than adequate.
I keep Craftsman tools in my personal garage for sidejobs and weekend repairs on my personal vehicles. They haven’t let me down yet.
Excellent value for the price.
In the factory, the Craftsman torque wrenches didn’t hold up well, not even as well as some of the cheap torque wrenches from Harbor Freight tools. But there is a slight problem with all click type torque wrenches that I noticed when performing the monthly calibration check, as soon as the head clicks, the torque wrench “bumps” the fastener with almost twice the applied torque.
This probably doesn’t have any significant impact on the fastener because the duration is so short, but the torque calibrators are so sensitive that it is very difficult to check the calibration of click type torque wrenches. Dial torque wrenches are the best, but very expensive.
If you're not earning your living with the tools, Craftsman is more than adequate.
I have a whole bunch of Craftsman hand tools. Never had to replace even one of them.
My tools are a mixed bag; from Snap-On, Mac, Cornwell, Craftsman, and quite a few oddities that came from various sources including the aircraft salvage. The pile includes a Snap-On torque wrench like dbs along with half a dozen others including a pricy and very accurate German made 1/4" drive torque wrench with a dial indicator on it.
Craftsman hand tools are great tools for the money but a lot of their electrics, jacks, VOMs, and so on have become, or are becoming, Chinese junk.