Brakes Broke!

[MacShee98]

Hi All, Happy St. Patricks Day (everybody's Irish today)!

I just had all four rotors resurfaced under warranty due to a lateral runout condition: there was a slight pulsation under light to moderate braking.

My 2002 Pewter Coupe developed this condition in less than 4000 miles of light to moderate driving: I never womp on a car until its had a decent chance of getting a proper "break in". 5000 miles should be enough.

My questions are these:

1) Has anyone else had to have brakes redone (under warranty or not) because of lateral runout?

2) What causes lateral runout on a car that has been pampered?

Your response will be much appreciated. Thanks!

 

[c4c5specialist]

Hi there,
Well, sometiimes, at the factory, the torque guns may not be perfect, and it is our job, as service technicians, to retorque the lugnuts, on the predelivery inspection.
My guess is that this was not done.
I am sure you will be fine after this point, besttoyou, c4c5

 

[MacShee98]

Thanks for responding!

I have what might seem to be the dumbest question you've fielded in a while, but I'm going to ask it anyway on the firmest belief that the dumbest question is one you never asked because you were afraid it was too dumb...

...how do you remove the plastic lug nut caps?

Next question. If my rotors were warped from the get-go, say at the factory,
then run-out is an inevitable consequence of improper torqueing. Put another way, there was nothing in my braking technique, or lack thereof, that caused this condition to occur. Correct?


Any tips on proper break-in, burnishing, etc. now that the rotors are true?
How many more re-surfacings can I expect (typical) before the rotors exceed the minimum allowable thickness? Does re-surfacing degrade proformance, heat dissipation, increased fade?

Last question: do braided-stainless lines increase braking sensitivity, feel? Do they reduce spongieness. Would they void my warranty?

Thanks in advance!

 

[c4c5specialist]

Hi there,
The first 100 miles are the most critical, for brake pad break in of new resurfaced rotors.
Unless you are doing autocross, you will be fine, with the performance of the rotors being turned, and it will not degrade the surface, or the performance.
As for the plastic lug nut caps, they are usually on pretty tight, just twist them off, using a 19 mm socket, and you will be fine.
Brakelines will help a little, however, unless you are autocrossing, I really dont think you will use them.
I cannot justify the cost, because for most instances, you will not feel the difference.
Besttoyouall, c4c5

 

[David-F]

Hi, first it's not lateral run out that gives you brake pulsation, but thichness varation that gives you brake pulsation, you have sliding calipers so if it woved side to side a little so would the caliper and you wouldn't feel it. But if you have thich and thin spots on the rotor you would have places that would grip better than other places and this is what you feel. How does this happen? well there are a few theories out there so would be uneven lug nut torque, maybe even not in sequence and there maybe something to this, but from what we have seen I think the bigest problem is the not true rolling of the hub bearings. If the rotor while turning on the hub moves a little side to side, like when running down the road what happens is the brake pads will drag a little harder on some spots of the rotor then on other spots there by thinning some spots more than others and over time you get brake pulsation. Now what we do is to resurface the rotors on the car there by truing the rotor to the rotation of the bearing and from we have be able to see over the past 3 years or so is that this makes a big difference people who would come in just about every 4 or 6,000 miles never come back, so what we have been able to tell is that there has to be something to this and as far as I am concerned on car turning is the only way to go.

David Fulcher

 

[rjsmith]

Thanks for responding!

...how do you remove the plastic lug nut caps?

The same size socket you use for the lugnuts. Turn counter-clockwise to remove. They should be hand-tightened and then apply about another 1/4 turn with a socket with a short ratchet. Don't over tighten them. If done properly you won't lose any.

If you are careful you won't nick them. If you are going to be removing the wheels a lot (say to put autocrossing tires on every other weekend) they will start to look less than pristine. If so, just buy another set from the Chevy dealer. Thay are not very expensive.

Ray

 

[MacShee98]

Thanks to all for the info. I really appreciate it. I guess that's one of the reasons I'm here on CAC, to get really good feedback. Thanks again to all.

 

[rjsmith]

Last question: do braided-stainless lines increase braking sensitivity, feel? Do they reduce spongieness. Would they void my warranty?

I installed braided stainless steel brake hoses on my '90 coupe because I was autocrossing and the advertisement made sense. Basically the ad said that rubber hoses "bulged" on heavy braking and this made the pedal travel further (because the amount of brake fluid sent from the master cylinder increased if ever so slightly). This, so the ad claimed, produced the "sponginess". I never noticed any difference but thought, what the heck, they look cool. I'm not implying that they don't work, just that I never noticed any difference. I never even bothered to put them on my '92 coupe which had the larger diameter rotors included with the Z07 option.

I do remember that they interfered with something in the wheel-well. It might have been the wheel-speed sensor cables. The braided hoses were a little bit too short and they chaffed the cables (sorry, that was about 12 years ago). I simply put some heat-shrink tubing over them at the point of contact and replaced it periodically.

As to the warranty, my dealer never said anything, but then I never needed any serious warranty work. If they want to make a case to avoid performing warranty work I suppose *anything* that is not GM or GM-approved will give them grounds.

What I discovered was more important than hoses was the fluid used. We went autocrossing at the Dagget airport in Barstow, CA. It's in the Mojave Desert, and it was September, and it was hot. After a few runs I was negotiating a chicane at the end of a fairly long (for autocrossing) straight when the pedal went completely to the floor. It turns out what caused this was the fluid in the calipers boiling and forming bubbles. Bubbles are gas which is compressible (the fluid, for all intents and purposes, is not). The brake fade was due to putting much too much heat into the caliper for the fluid that is installed at the factory.

I flushed the brake system and refilled it with Motul 300C (buy two cans). It is designed to not boil at temperatures at or below 300 degrees centigrade (572 degrees Fahrenheit). It woked well for autocrossing. It might be overkill for normal driving, but it will not hurt. It is DOT 3 fluid.

Disc brakes work better when they are warm (the rotor expands when it gets warm decreasing the distance the pistons/pads need to travel) and what I have noticed about my Z06 is that because of the efficiency of the brake cooling ducts, the brakes stay too cool sometimes. This makes the first use after a long non-braking period less steller than the normal 3-wire-grabbing effect the system normally provides. It takes a few brake applications to get some heat into them, after which they work as you would expect. For autocrossing (Solo II), or Solo I track use, they are probably very effective. And they look cool.

Above a certain temperature the brake pad material becomes gaseous at the surface where it is in contact with the rotor. The gas causes the pad to "float" over the rotor. The effect is similar to coating the rotor with 5W-30 motor oil: it lubricates. This can be ameliorated (but not eliminated in extreme use) by switching to racing-grade pads (which squeal loudly when cold and produce prodigious amounts of caustic brake dust) or by cross-drilling the rotors. The holes let the gas escape. The problem with drilling is that it produces points where metal fatigue can begin. Cross-drilling stock rotors is not a good idea. Cars (such as some Ferrari models) are delivered with cross-drilled rotors made from steel designed to better handle stress cracking (although it can not be totally eliminated). You can purchase after-market rotors which are cross-drilled and made from the approriate grade of steel. Have a defibrillator ready when you get the invoice.

I used carbon-kevlar pads made by Porterfield Racing in Costa Mesa, CA (they were heavily into Trans-Am racing at the time and are located about a block from the Road & Track Magazine offices where you can see exotic cars being examined in the parking lot). Suprisingly, I discovered that they cost about as much as stock pads from the Chevy dealer. While autocrossing they worked wonders. They gripped extremely well. But driving back and forth to work was not so pleasant. They squealed loudly and covered the front wheels with heavy black dust after only a few miles. Even the rear brakes, which do not normally do that much work (brake bias directs more force to the heavily loaded front brakes and less to the rears because they tend to lock up easily as a result of weight transfer to the front during deceleration) generated enough dust to blacken the wheels. I didn't mind cleaning them virtually every day after work, but I discovered that they were eating the clear-coat on the wheels. Bye-bye racing pads.

There is a special paint you can buy which, when applied to the outer edges of the rotor, will change color depending on the highest temperature it is exposed to. You then compare the color to a chart which comes with the paint to determine *approximate* maximum rotor temperature. This is applied across the thickness of the rotor (along the cooling vanes), not on the area swept by the pads. You apply the paint using a small (1/8th inch) brush to create a very narrow band. You can do this many times, such as after an autocross run on a certain course, to see if changes you make to the brake system are helping to reduce temperature.

This may be more information than you wanted but it may be of use to someone else.

Ray

Got Torque?

 

[rjsmith]

...but from what we have seen I think the bigest problem is the not true rolling of the hub bearings. If the rotor while turning on the hub moves a little side to side, like when running down the road what happens is the brake pads will drag a little harder on some spots of the rotor then on other spots there by thinning some spots more than others and over time you get brake pulsation. Now what we do is to resurface the rotors on the car there by truing the rotor to the rotation of the bearing...

David Fulcher

David,

Very clever solution to true the rotor in the plane of rotation caused by the non-true rotation of the hub bearing. I'm sure there is is reason for using this technique, but I would have thought that replacing the hub bearing would solve the problem without the need to cut the rotors. Is it the cost that makes this technique preferable? Or is it that the rotor needs to be cut anyway to correct the damage done by the uneven wear (and if so why bother to replace the bearing)?

Is this bearing problem common? If so, is it common on the C5? Is it, in your opinion, a manufacturing flaw in the bearing, improper assembly, or is it caused by abuse (i.e., hitting curbs, big potholes, etc.)?

Ray

 

[David-F]

I think there are a lot of posible reasons for this , first no bearing run true they will all move a little, but what I think we have here is metalic pads and soft rotors, and I mean this in a relitive sence. I have heard that some aftermarket rotors don't seam to have this problem, but before you just say GM should just change the rotors you have to remember there is more to it then just make them harder, different compositions of rotors do different things, if you where to remember back to 84(if you can remember back then) the 84 Corvette had a problem with squeeling brakes the fix was to change the rear rotor composition, was it harder or softer? I don't know all I know is that what they had made a noise and what was replaced with did not. Also different pad composition makes a difference in wear on the rotor also. I had a friend that used to road race(time trials) his 89 he used a Performance Friction pad for this because the stock pad would not hold up, well the pad lasted a lot longer but the rotor wore real fast. So if we take a look at just these two examples we can come to some understanding just why we probably have the problem we have on the C5 Gm has gotten the brake effect they want but to do this has maybe gone with a softer rotor which makes it more prone to wear when the pad drags on it then say other years, there has been some changes in pads on the newer cars so maybe this will become a thing of the past but only time will tell.

David Fulcher

 

[MacShee98]

Ray,

Thanks for the excellent info - you can *never* have too much information, well...about the Vette anyway.

Ray, I may skip the braided lines since I'm not autocrossing and according to all accounts it would only make a difference of about 1/10th inch (?) in pedal depth under HARD braking - not something I'm likely to get euphoric about. The stock lines don't feel spongy, if fact, they feel, well, like the best brakes I've ever put my foot on.

After consulting the 2002 GM Service Manuals brake section (yeah, I went and bought 'em), their preferred method of rotor latheing is ON VEHICLE and, yes David, I fully agree with that.

I could be wrong about this, but when you remove the rotor and resurface it off the car, you've also removed the bearing/hub variable, which will be re-introduced as soon as you reinstall the rotor to the car. It may cut straight on the lathe - but will it be straight once it's back on the hub? Only a second check of lateral runout with a guage once the rotor is back on the hub would tell you if you've eliminated the runout altogether. With the right "ON CAR" brake lathe, and done properly, ie torque values exact during turning, you should have eliminated all runout.

I think I may have just figured out what caused the runout on my "pampered" Coupe: the dealer installed the wheel locks! Here's a guess: they installed the locks, but didn't re-torque 'em to spec! That would do it, wouldn't it.

I've got about 150 miles on the re-turned rotors and they now feel true. I'm guessing that they were lathed OFF the car, due to some careful rotor/caliper inspection - looks like the calipers were removed indicating OFF car turning.

Thanks again to all for your expert advice. And, Ray, nice post on your brake experiences. I'm sure many will benefit from it: Vette Brakes 101.

Have a Great and Safe Weekend!
Michael

 

[David-F]

The caliper has to come off even if they are turned on the car. If you turn the rotors off the car they will probably last about 6,000 miles it has very little to do with how hard you drive your car. I have been there before back in 97 when this was first coming to light we first started to turn off car but it didn't last so we decided to start to do it on car and that was the only way it seemed to last. We had many owners that babied their car but still had pulsation problems so it has nothing to do with your driving and don't let them tell you otherwise. I use a torque scoket when reinstalling the wheels and do it in a star pattern they are GM required tool(this is my own scoket) so again there is no excuse for not having them torqued correctly, GM has had a push for correct wheel tightening for about 12 years now so again there would be no excuse on this point either. I do hope you have better luck if they have done it off car then we have had in the past but I'm sorry if I just don't feel that is the case what I think happens in so many cases is they turn it once then after that you're on your own or maybe they give you new rotors again only thing this does is buy time to a point when you need brakes or someother thing comes up. What I would do is if it comes back you take the shop manual with you and ask if they did it on the car like what is recomended and see what happens, but hopefully they have done it on car and you will not have any other problems.

David Fulcher