Brake shake with freshly machined rotors?

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http://www.brakeandfrontend.com/default.aspx
This is the location of the previous Babcox site, and there is a lot of good information if you will dig for it.

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theoretically, but because it is a fleet car, for anything I take it to one of two "approved" shops. If they say it has to go to the dealer, *then* I take it to the dealer.
I really wanted to get my local wrench (near my house) with the program so I could just drop it off there for maintenance/repair, but when I tried to get them on board I inadvertantly caused all sorts of kerfuffle and pissed off my boss, so I won't do that again. There's some things that are worth making a big deal over, and there's times you just grin and say "why yes, of course, I'll come in on Saturday just so I can get my car serviced at the approved shop." Not that I'm bitter or anything. Well, OK, I am, but aside from little PITA stuff like this, I'm legitimately happy to still have a good job these days. The pay's OK and even if it's a PITA to deal with, having a car with gas and maintenance paid for is quite nice - certainly if I were providing my own transportation my old 944 wouldn't cut it, not without a major overhaul first, not with the amount and type (mostly city, with interspersed blasts of high-speed freeway) driving that I have to do. Even if my workload is temporarily doubled because another employee decided that this wasn't the right place for her.
Yes, I am checking Usenet from my desk at work, while waiting for files to download. *sigh* I have no life... (must remember to call Dad later)
nate
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wrote:

Really? So how do they make them in the first place!!! Do you think they just come from the casting bed already machined?
Sounds like you

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Sharky wrote:

Which "the lathe" are you referring to? Have you had bad experiences with the Tyco or Fisher Price offerings?

Perhaps he unevenly "torqued" (with a "torque stick") the wheels or didn't cut the rotors properly, or was using one of the lathes you've had bad experiences with.

If the answer is 'more than 3 mm', what would you say to that?

Probably not; without confirmation, we can assume that this is the average tech doing warranty work here...
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Toyota MDT in MO

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What?
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has

brake,

asked

rotors.

balance was

this

as it

sanding

it

for

ASSumed

of

when

the

typical, and

after

One of your tires is bad. Check for bumps or imperfections in the sidewalls.
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A bad tire will not make the brake pedal shake!
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...nor will a bad tire make the steering wheel shake under braking!
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Here is another link for you, Nate: http://www.brakeandfrontend.com/Article/46342/rotor_runout_check_list.aspx
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Also... there is a tsb that says that rotor runout must be .002 or less... Sounds like an on-the-car brake lathe would be best...
TSB # is 00-05-22-002L
HTH, Ben
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Follow up: I finally got a chance to take the car back today, and the mechanic went for a ride with me and didn't even get the car up to speed, he just got up to maybe 30 MPH and rode the brakes a little, felt a slight pulsing, said "mmm-hmmm," and turned around and went back to the garage. This time they turned the REAR rotors. He said that Impalas were susceptible to rotor warpage, he had one himself and had had the same problem. I'm still trying to figure out how a warped rear rotor(s) could cause the steering wheel to shake but he claimed that you have to turn all four. (I guess this was a different guy than worked on the car last time.) I picked the car up this PM but have not had a chance to try it at speed yet, but the slight pulsing at low speed is gone.
Now I have another question, how does the parking brake work on the newer Impalas, is that a little drum brake inside the rotor hat like a corvette or my old 944, or does the cable just pull the caliper shut like an old VW with rear discs? I'm wondering if setting the parking brake causes rear rotor warpage if the latter, in which case I will be more careful in the future about braking hard when I know I'm going to park soon (I can't avoid using the parking brake, my driveway slopes quite a bit.)
thanks
nate
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N8N wrote:

     Correct me if I'm wrong, but I believe this is the first mention of a pulsing that can be felt in the brake pedal at low speed?     You are now asking if this could have been caused by something you have done, but previously you said the car had the problem when you first got it.
    You didn't actually tell us what they did to fix the problem with the rear brakes. It sounded like you maybe don't know for sure. You did say the mechanic said they should have done all 4 rotors at the time of the first visit but that was before he took it apart and did the work. Did they tell you what they did? I agree the second guy is definitely more competent. He probably test drove the car after doing the work. The first guy obviously didn't.
    My wild guess would be that the origins of the problem are sticking rear calipers due to sitting. that might well have something to do with the parking brake that may have rusted up from sitting. believe you said it sat for 4 months over the winter.
    I would also guess you are going to find the brakes now do a lot better job of stopping the vehicle at highway speeds.
    Having a pulse in the brake hydraulics that is felt in the pedal thaqt is caused by one wheel is going to carry to the other 3 wheels also. So there is no mystery about how it got to the front wheels.
-jim
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jim wrote:

I didn't mention it because it is very faint, inoffensive and hard to notice unless you're deliberately looking for it... if that were the only problem I wouldn't have taken it in. The steering wheel shaking violently when braking from high speed... yeah, that's a problem.

No, I'm just asking if the parking brake design is such that it clamps the pads to the rotors, *in which case* in the future I'll take care to try to not have to use the parking brake immediately after having put a lot of heat in the brakes. Yes, the car did exhibit these symptoms when I first got it and it's only gotten worse over the few thousand miles I have driven it, but it was previously used by other drivers before I got it. I'm certainly not taking responsibility for "causing" the issue even if parking brake use is the actual cause because I would consider applying the parking brake after stopping the car to be normal operation and the car should be able to accept it.

They resurfaced the rear rotors.

Yes. on the first visit they resurfaced the front rotors. On the second visit they resurfaced the rear rotors. That's apparently it, other than on the first visit they also balanced/rotated the tires at my request, and also changed the oil.

Not sure exactly how long it sat, but yes, the last previous user of the car left the company last year, so it did sit for several months, some of them such "winter" as we get here. My original thought was uneven rust on the rotors (I've seen cars that didn't move *at all* for a long time develop rust on the rotors, but when you roll it forward you find that the area under where the pads sat isn't rusted at all) I figured it'd wipe off after a few hundred miles, but it didn't. Nobody mentioned anything about a stuck caliper, so if that is in fact the root cause, either it's unstuck itself or the problem is going to come back :(
Along the same lines, *while* the car was in the shop, I ended up having to unexpectedly make a speed run to a job site (apparently the easiest way to ensure that you have to leave the office is to schedule for your car to be in the shop...) and ended up taking another ex-employee's car that's waiting to be reassigned (same year/model, maybe 20K more miles, sitting for 2-3 weeks) and I did in fact hear evidence of rust on the rotors for the first few stops, but by the time I got back to the office (maybe 70 miles later?) it was braking fine. Please don't ask why we have so many ex-employees, it seems to be only one position that it's hard to get someone to fill long-term, and I can't explain it either.

I try not to have to test the ultimate stopping power, but they *feel* a lot better now :) Yes, I did take the highway home from work and tried some light braking from speed, and I didn't see any of the steering wheel shake that I experienced before.

it just seems odd to me that the predominant symptom was a shake in the steering wheel. You'd think that if there were hydraulic effects that carried to the other wheels I would notice non-smooth braking, but that it would be equal on all wheels, so no steering effects. Or, in other words, the steering wheel shaking would point to a fault with the *front* brakes, not the rears. Not so, I guess.
nate
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Nate Nagel wrote:

I wasn't interested who to blame. I was saying the picture you painted wasn't as clear as it could have been that's all. I had assumed there wasn't any pulsing in the pedal since you hadn't said anything about that . I don't think using your parking brake will warp the rotors even if they are hot. But it might contribute to the rear brakes getting stuck if you park it for months.

The braking surfaces should be rust free in five minutes if the calipers were working as they should. The rust on the braking surface never seems to be as deep as the rust on other surfaces. Don't know exactly why that is but the rust on the braking surfaces is usually very thin. Often if you hear scraping from rust it is on the surfaces next to where the pads contact that have blossomed with rust and it is rubbing against the sides of the pads.

If the caliper can't slide then it puts a tremendous uneven bending load on the rotor. It doesn't have to be stuck very long to damage the rotor. If it had stayed stuck you wouldn't have been driving it for months before getting it fixed. Once it starts I have never seen a brake rotor get better on it's own - it's all down hill from there.

The point was if the problem was tires it wouldn't reduce braking power until you brake to the point where the tires start to let loose of the pavement. Lousy tires aren't going to make a noticeable difference when "light braking"

I think it was reasonable to assume it was from the front because that would be more likely on most cars, but they should have test drove it afterwards. If the pulse is still there then obviously it is coming from the back. And because the pulsing will carry to the other wheels it could lead to uneven wear in the other rotors after a while. So when it has been happening for a long time it probably is a good idea to do turn all of them.
-jim
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jim wrote:

Right, but I'm still curious now as to which design it uses... if it is a caliper parking brake it hypothetically could cause warpage... I'm still at a loss as to how a rear rotor could warp, seeing as the rear brakes on a typical car do about jack in normal use.

I agree, I was just hypothesizing that it might cause uneven wear patterns even after the rust was gone. Have never actually had that happen though, even on my Scirocco which sat almost as long at one point.

if you're talking about the slides being stuck, I ASSume that that would have been identified/fixed while turning the rotors... I hope... (this is why I really prefer working on my own cars myself; I won't do it on a company car though. My boss would have my head on a platter if I munged something up, waaaaaaaaaay too much liability.)

well I maybe put 1K miles or so on it in the 10 days between 1st and 2nd trip to the mech (there's a reason why it took so long to get it in, and it's that I had lots of places that I *had* to be...) front rotors still look "just surfaced" so I don't think I managed to mung up the new job. I hope.
I'm planning on putting some "personal use" miles on it this weekend (finally! a weekend without work!) so I ought to know by Monday whether it's 100% good or not.
It's actually not a bad driving car, now that it's sorted, except for the awful OEM tires. Pleasantly surprised. The other car I drove had apparently already had the tires replaced, that one felt even better despite the higher mileage.
nate
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Nate Nagel wrote:

Nope, they use a "monoshoe" inside the rotor hat. It's a horseshoe shaped friction lined assembly that flexes toward the inner drum surface when actuated, making roughly 270* of contact.

I haven't noticed that scenario play out, but I guess it's possible.

Normally, that would be true. I've seen some rare cases on 4WD vehicles where apparently the rear vibration is sent through the driveshaft in the form of uneven rotational speed (shaft minutely speeds up/slows down in accordance to the rotor thickness variation while braking). Perhaps if I had test driven your car I might have describe the complaint differently. Assuming I would have concurred that there was indeed a brake shudder directly affecting steering oscillation, it's possible they might have returned your front rotors on-car (without telling you this time) to cure the last off-car machine intolerance. Otherwise I'll assume the vibration was just more noticeable in the steering wheel, though it was a chassis vibration coming from untrue rear rotors.
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Toyota MDT in MO

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Toyota MDT in MO wrote:

thanks for satisfying my curiosity. I will no longer worry about using the parking brake :)

y'know, I think I may have just figured it out... if it's a *diagonal split* system, that would make sense.
Now whether it is or isn't I'm not sure how to find out without either a) purchasing the factory shop manual or b) draining one circuit I dunno, seeing as it has 4-wheel ABS and all the lines enter/leave a big machined block of aluminum.
nate
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Nate Nagel wrote:

The RM's system description indicates this is a split diagonal setup, but for what you are concerned about, that applies only during standard braking where the EBCM/BPMV tandem doesn't cut off, boost, or cycle pump pressure to any of the 4 wheels during brake assist, electronic proportioning, traction control, ABS, or vehicle stability operations.
Good luck on draining the fluid as a reverse engineering measure. You might need to borrow a capable scan tool to bleed the system afterwards :-)
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Toyota MDT in MO wrote:

I'm aware of this, that is why I was speaking in hypotheticals :)
that makes sense, actually. will have to file that away in the "weird automotive crap that can fake out your butt dyno" section of my brain...
nate
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A perfect summary of your Usenet career. Unfortunately, you've consistently chosen wrong.
nate
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