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Automobile brake maintenance question
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daddy-o
Joined: 12 Apr 2004
Posts: 3307
Location: Springfield

2/13/13 6:05 AM

Automobile brake maintenance question

A few months ago I put on 4 new tires. Less than 2000 miles later I heard the brake pad warning grind. I was pretty irritated that the tire shop didn't point out that my pads were thin, but I justified why they didn't and took it back to them. They told me I needed new rotors, these were scored, too thin to dress. I wasn't happy but agreed. That tire shop was recommended by another (foreign car) shop I've found to trust.

Fast forward to last week. I heard the grind again when I was pulling into a parking place. About 30 gentle mile later, most of it highway, I took it somewhere else more convenient for the circumstances. They did the same thing, only they said the rotors were "near spec" iirc .994" actual vs .935" replacement. I approved it just because they had me in a tight spot and I'd rather be conservative. I didn't know the new-spec to compare.

The car has 55K and these were the first replacement pads.

When I asked to see the rotors, the mechanic and the manager came up. It went like this:
Me: There's no scoring, what's current thickness and factory spec to replace?
Them: 994/935, "it was getting close."

Them: Factory originals are thin these days
Me: Are these replacements more robust?
Them: Not really
Me: So I need to replace rotors every time I replace the pads from now on?
Them: Not necessarily, it depends on how hard you drive.
Me: I got 55,000 miles out of these pads, it sounds like I'm easy on them.
Them: Yes
Me: Why do they make them thin?
Them: To save weight for gas mileage.
Me: WHAT!? How many ounces out of a 1 ton car are they going to save on brake rotors? I pointed out "of all the places to save weight"

There's more, but I thought that was the best.

Cut to the chase
How does this sound right?
How do I find OEM specs for the rotors? --So I can tell what the real wear is. An hour on google didn't help.

A good shop is hard to find. 2 down, 100 to go.

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Pat Clancy
Joined: 13 Jan 2004
Posts: 1353
Location: Manchester, CT

2/13/13 7:30 AM

Maybe true

I've heard the same thing - that to save weight rotors have become essentially disposable items on many cars. It's also probably a matter of convenience as well. Rather than investing in a rotor lather and taking the time to turn them, or waiting while an outside machine shop does them, they can slap new rotors on in minutes.

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Sparky
Joined: 08 Dec 2003
Posts: 19063
Location: PDX

2/13/13 10:22 AM

I just go for new ones, especially with the pads I like to use which eat rotors with sintered/metal etc.

Rotors have become cheap enough, and I find cut rotors just warp faster as the metal seems to have a 'temper', so to speak. Give me fresh steel I have not heated into oblivion. Although I am a lot better with the lead foot on both the gas and brakes in my un-youth. ;)

But literally, YMMV

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Sparky
Joined: 08 Dec 2003
Posts: 19063
Location: PDX

2/13/13 10:26 AM

On a [sorta] side note, a while back Rob Coapman hit metal and was trying to not drive and drive very light, etc. So as not to ruin the rotors so they could be cut when it got it to the brake place...

I said, go to O'reily, pick up rotors and pads and get over here, we will pop on and then go for a bike ride..

So if I hit metal, i just keep driving and get new rotors and pad when I can get to it.

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Andy M-S
Joined: 11 Jan 2004
Posts: 3377
Location: Hamden (greater New Haven) CT

2/13/13 10:47 AM

Don't most pads...

...include a "chirp" mode, so that you can get the pads replaced and not get the "Titanic meets iceburg" sound that's generally your next warning?

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Sparky
Joined: 08 Dec 2003
Posts: 19063
Location: PDX

2/13/13 10:51 AM

Chirp'

In Robs case the inner pad wore faster, and chirper was on the outer pad well clear of touching. I have seen this fairly often when doing brakes. Which I started doing a lot more once both boys got cars etc...

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 5094
Location: Nashua, NH

2/13/13 11:59 AM

It's not worth machining rotors

Depending on the type of vehicle you have, front rotors can be as cheap as 25 bucks each. "Deluxe" rotors may run $50-$60 for the same vehicle, but I've found that they do tend to be better quality. As for life, it depends on how you drive and what type of driving (city/highway). I would say that 60K miles is decent for a city driver, with longer life if you do mostly highway. That said, the "usable life" can be shorter than the "optimum life". My rotors are still within spec, but they're warped or worn unevenly enough that I feel it when braking. When the current pads are shot, I'll replace the rotors, too.

BTW, on many cars, replacing the rotors is a snap and it's a good DIY job, along with replacing the pads.

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ErikS
Joined: 19 May 2005
Posts: 8337
Location: Slowing boiling over in the steamy south, Global Warming is real

2/13/13 6:03 PM

Hahahaha

Chevy got one thing right on my Tahoe. The OME breaks just got replaced at

108,000 miles! I did not require rotors. I had at least 15k left on the pads but replaced them anyway.

I drive easy but not that easy. I suspect the brakes are over built for heavier Suburbans and trucks. So they last a long time on lighter Tahoe.

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Pat Clancy
Joined: 13 Jan 2004
Posts: 1353
Location: Manchester, CT

2/14/13 9:29 AM

Improvements

It's worth noting how far cars have come in terms of maintenance. Between improved designs and better materials, many things we used to routinely do - change plugs, replace points, check the timing, tune or rebuild the carb(s), are all things of the past. Brakes, although discs have been common for decades, are also greatly improved. I don't remember the last time I had to do a brake job prior to 75,000 miles.

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Dave B
Joined: 10 Jan 2004
Posts: 4511
Location: Pittsburgh, PA

2/14/13 5:59 PM

Spelling!


quote:
The OME breaks just got replaced at....

Come on, you know better then that!

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Andy M-S
Joined: 11 Jan 2004
Posts: 3377
Location: Hamden (greater New Haven) CT

2/14/13 8:59 PM

Word Order

O.E.M!

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April
Joined: 13 Dec 2003
Posts: 6593
Location: Westchester/NYC

2/14/13 10:19 PM

cut vs replace, inspection, etc

It depends a lot on what kind of driving.

When I lived in California, the rotor "predictably" warp at around a year. So much of my driving was on curving mountain roads that goes straight down! The brakes heat up and warp the rotor. (It's also in California I experienced the first time a brake fade due to overheating!) While we actually live in the valley, the mechanics said people live up in the foorhills (say, Saratoga), their rotor don't even last a year!

In those cases of warp rotors, it can be cut once between replacements. So it's new rotor every other year, cut once to smooth out the warping midway through its lifespan.

In NY state, cars needs to be inspected every year. So I never get to the point of metal on metal. Each inspection, I get a report of how much brake is left and I would know if the next inspection would include new brakes (or I have to do it ahead of time at a different shop). Here in New York, I don't seem to get so much rotor warp as I did in California (same car), just wearing thin, evenly. So far, I've notice I need new rotor for every 2 pad replacement.

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ErikS
Joined: 19 May 2005
Posts: 8337
Location: Slowing boiling over in the steamy south, Global Warming is real

2/15/13 3:05 AM

Yeah, brakes and OME. fat fingers and 20 waking work/school hours a day this week.

It has been a tough week, that is my excuse.

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daddy-o
Joined: 12 Apr 2004
Posts: 3307
Location: Springfield

2/15/13 4:27 AM

Informed decision though?

How do I find out the original rotor thickness? --to judge how much actual wear, internet sources I found were no good

From that I might be able to tell what .994 measured vs .935 minimum means in terms of wear.

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ErikS
Joined: 19 May 2005
Posts: 8337
Location: Slowing boiling over in the steamy south, Global Warming is real

2/15/13 5:32 AM

Either the manufacture's manual or a Haynes manual will have the correct thickness.

Even if you have fairly new car with a warranty still in place, you should have a repair manual for it. That way you have a reference for maintenance that you get done. Plus, you may find some repairs are easy and you can do them yourself.

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Andy M-S
Joined: 11 Jan 2004
Posts: 3377
Location: Hamden (greater New Haven) CT

2/15/13 5:56 AM

Repair Manuals

I've bought a repair manual for each car I've owned, and either because the systems are getting more complex or the publishers lazier, there is less and less information on adjustment and repair in each one I buy. Disappointing, but not unexpected.

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 5094
Location: Nashua, NH

2/15/13 6:01 AM

Check online

Car manufacturers commonly put their factory repair manuals online these days.

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KerryIrons
Joined: 12 Jan 2004
Posts: 3234
Location: Midland, MI

2/15/13 7:42 PM

Downshifting


quote:
So much of my driving was on curving mountain roads that goes straight down! The brakes heat up and warp the rotor. (It's also in California I experienced the first time a brake fade due to overheating!)


Every time I drive in the mountains I am amazed that nobody seems to realize that they should downshift rather than burn the brakes all the way down. I can drive Big or Little Cottonwood Canyon, Rabbit Ears Pass, etc. without hardly touching the brakes. The guy in front of me is braking so much I can smell his pads burning.

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April
Joined: 13 Dec 2003
Posts: 6593
Location: Westchester/NYC

2/15/13 8:26 PM

engine braking

In the hot weather of California summer, engine braking isn't always desirable.

Besides, rotors are cheap after all. As long as one is aware of it, that is.

More important to use the brake "intelligently" instead of dragging it the entire 30 minutes it takes for the descend.

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dddd
Joined: 11 Jan 2004
Posts: 3345
Location: NorCal

2/15/13 11:34 PM

As far as the wear limit spec is concerned, it's not a problem if the wear limit is exceeded between service intervals.

Only when putting new pads in does the wear limit serve as a "go, no-go" dimension which is approved for the expected service interval (the life of the new set of pads).

A brake repair shop should know this, and if the the rotors were supposedly "so close" to the wear limit, then a comparison must also be made to the thickness of new rotors, to be at all meaningful in terms of a decision to replace.
One might then conclude that the rotors were not so very worn at all, or that they were indeed very close to the service limit for use over the full lifespan of a new set of pads.

The (likely Chinese) replacement rotors are not very expensive on standard cars, but I would rather have an OEM rotor turned than use aftermarket parts even if there was no difference in price.

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daddy-o
Joined: 12 Apr 2004
Posts: 3307
Location: Springfield

2/16/13 7:00 AM

"it's not a problem if the wear limit is exceeded between service intervals"
"Only when putting new pads in does the wear limit serve as a "go, no-go""

That was my logic, and I paid for not arguing it. The work was at a Goodyear shop, last minute decision because of the noise and convenience. The guy at the front counter is paid to sell. Because I was distracted I didn't ask the right questions, and... I paid.

At least I didn't buy the "flush the brake fluid" recommended service pitch.

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Dave B
Joined: 10 Jan 2004
Posts: 4511
Location: Pittsburgh, PA

2/16/13 8:40 AM

Please Explain


quote:
In the hot weather of California summer, engine braking isn't always desirable.

Why not?

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 5094
Location: Nashua, NH

2/16/13 9:13 AM

Engine braking is hard on transmissions

In manuals, it puts a lot of strain on the gears in the opposite direction that they are designed to work in, which if nothing else, increases the wear on them.

In an automatic, you have the additional concern that you can cook the transmission fluid which will trash the transmission. A transmission oil cooler can help, but at slow descent speeds, it may not be enough.

Unless the vehicle is equipped with a heavy-duty transmission designed to handle the extra loads and wear, extensive engine braking pretty much guarantees that you're going to need a tranny rebuild or replacement during the vehicle's life. It takes a lot of brake rotors and pads to equal that cost.

The only time I use engine braking is if it appears that the brakes will not be up to the task and even then, I use both, sometimes together, sometimes alternating. Well, there is one other situation...if I'm in a rental car. ;-)

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April
Joined: 13 Dec 2003
Posts: 6593
Location: Westchester/NYC

2/16/13 9:51 AM

Primary concern is transmission overheating.

Though I always thought manual will do fine for engine braking. It's automatic that's a bit funky.

The one time I encounter brake fade, I wasn't driving. The driver was actually also a reasonably experienced driver who grew up driving manual cars. But she's been driving automatic cars for so long she plain forgotten about engine braking. More over, the grade we were descending wasn't all that steep. Not the sort of grade one worries about braking power. But we were caught in stop-n-go tourist traffic leaving Yosemite (very long if mild descend, something like 20 miles descend). About 1/2-1 hr into that slow crawl, she commented the brake (my car) felt really soft, that I might want to have it looked at when we got home. So I asked her to use some engine braking to help get us down to the valley safely. (yes, we were also worried about cooking the tranny in the 100 degree weather too) After we got down the valley, the brake was no longer "soft" any more. That's when we realized what was actually happening on that long descend.

When caught in stop-n-go traffic in a mountain road on a hot summer day, it's a balancing act of alternating normal braking and engine braking to keep both working. What I sometimes do is simply put the car in "park" until the car in front of me had moved more than a car length, instead of inching forward while riding on the brake the whole time. It's also less wear and tear on my calf muscle too.

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dfcas
Joined: 11 Jan 2004
Posts: 2815
Location: hillbilly heaven

2/17/13 10:04 AM

I've used engine braking on manual transmissions since 1972, and have never had a manual transmission failure or repair. The highest mileage I've had was just under 200K. Every time you let off the gas in a manual vehicle you are engine braking. I do not engine brake on automatics, since heat shortens their lifespan.

I've also never had rotors "wear" thin. Warping is a problem, and cutting them back to true weakens them, ultimately leading to another failure in my experience.

Do the big chain auto parts stores still offer "lifetime" warranties on rotors? In a vehicle that warps rotors, thats the way to go.

I had a GM Astro van that warped rotors. Never had a set last over 3 months, and I always said they used the leftover Chevette brakes on those,ala parts bin engineering.

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