shadowkahn

So I've had the car at the dealership about 4 times this year trying to get the brake pedal shake figured out. They've shaved the rotors. Twice (no, I wasn't happy about this, but it's warranty coverage, so not much I can do). The last time was 2 weeks ago. They're still shaking when I brake. Assuming they shaved them properly, I don't see any way they could warp so fast.

So I brought it in this morning to have the service manager come take a ride with me. He acknowledged that it was shaking.

Then he said that improperly torqued lugs when I had the tires mounted caused the rotors to twist, which is what's causing the problem.

The problems I have with this are: 1) he hasn't checked the torque of the lugs yet. 2) It's only been two weeks, and that shouldn't be enough time to cause a noticeable pedal shake. 3) The lugs are torqued to within 1lb/ft of 80. I know, because I watched the tire shop guy do it with his hand torque wrench. and 4) it doesn't shake every time I brake. Maybe 7 times out of 10. But the other three times, it'll brake perfectly smooth.

I suspect something else is going on with the brakes. And maybe I'm ignorant, but I have never heard of twisted brake rotors.

It goes in Wednesday for them to "see if the rotors are twisted." I'd like to walk in with some other ideas as to what it could be.


BTW, the last two times they were shaved, they did get around 1000th off on average of all 4. So they were apparently warped.

My suspicion though is that shaving the rotors was treating the symptom without curing the problem.

Turbonut

iTrader: (1)

Well, as they did the rotors, I would assume that they installed the wheels. If that is the case, then they didn't torque them properly.
There has never been a time that I know of when a lathe would remove only 1/1000th of an inch of material to cure out of tolerance rotors. Once cut, the rotors don't last as long as the OE specs, as they will not dissipate the heat quick enough. They should mic the thickness and compare to the minimum allowed, and that is stamped on the rotor.

Not that I agree whole heartedly with the following, but it will give an overview:
http://www.ehow.com/about_5672302_ov...ke-rotor_.html

shadowkahn

Well, after they did the rotors, the tire shop installed the new tires (that whole long saga in the thread I started in the tire forum). So the last one to touch the lugs is the tire shop.

The SM already said that he doesn't care who did it - he'll replace the rotors for me this time and "make it legal," so I'm not worried about assigning blame - - I just have trouble believing that even improperly torqued lugs would cause the rotor to warp within about 70 miles. I haven't even driven it much because the weather's been nice, so I've been in the MR2 mostly. It just seems really fast for them to warp, even if there's a good reason to.

That's why I'm worried that even if they give me new rotors, the problem isn't going to go away. Can you think of anything else in the brake system that could be bad that would cause a shake? Maybe a pad isn't installed properly, or the caliper is damaged so that the pad isn't seated properly and it's fluttering against the rotor? I dunno - just grasping at straws here.

shadowkahn

Well, here's the update, along with my thoughts:

Acura called, and told me that the rotors were warped. Again. 2 weeks after the last time they got shaved. They claim they warped because the tire shop torqued the wheels down too much, and they know this because it took 130lb/ft to loosen the lug nuts.

That's fine, but I've never heard of being able to tell how much torque a tire shop put on by loosening lug nuts, since once static friction sets in, it's going to take more than 80 lb/ft to get them loose, even if they were torqued properly.

I'm starting to suspect that there's a problem with the brakes, and they're just trying to shave the rotors (3 times now) until the warranty runs out. Anyone with me, or am I being paranoid?

Turbonut

iTrader: (1)

All you've got to do is put a torque wrench on the nut and apply pressure and then you'll see when they start to move, that's the current torque.

shadowkahn

I know, but that's not what they said they did. They said "When we took 'em off it took 130 lb/ft to loosen 'em, so your tire shop way overtorqued 'em."

shadowkahn

Update: Picked up the car last night. Was shaking within 7 miles. Took it right back and made them take it back. Today they called: They've replaced the rear rotors, resurfaced the fronts, and it still shakes. "Now it's a treasure hunt. I'm not sure what's wrong with it and we'll just have to start taking things apart until we find what's broken."

I *really* think at this point that there's a caliper or two that isn't releasing properly and is heating up the rotors. I wonder how long it will take them to find it.

I hate cars

That sounds like the best theory aside from a worn or torn bushing.

Just an FYI, you can't measure bolt torque by loosening them as the shop said they did. It takes less force to break them free than it does to tighten them. Tightening them and seeing at what force the torque wrench "breaks" at is the only semi-accurate way.

shadowkahn

I looked at all the bushings I could see with the car on the ground just last week, since I'm now (literally) 3 miles away from the bumper-bumper warranty running out. Wanted to see if there were any that needed replacement on Acura's dime. Didn't see any, but then unfortunately I didn't have time to take it out to my club's garage and get it up in the air, and of course it's possible I missed something anyway.

I explained to them last night about not being able to measure torque by loosening bolts. The tech (it was 9:30, so all the good techs had gone home) said "Yeah, but 130 is really high." I tried to explain that, really, 50lbs extra torque to unstick a bolt (especially if excessive rotor heat has caused uneven metal expansion/contraction between the bolt and the wheel) is really not that much, but he didn't seem to get it.

Of course he also explained to me that it was probably that I was being too hard on the brakes - - he backed off of that position after I explained that I have an MR2 that gets flogged on race tracks and I don't kill rotors in 7, or even 700 miles.

I think your theory is coming into play here - bad diagnosticians. There isn't a computer code for sticking caliper, and so they're having trouble figuring the problem out for themselves.