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Why machine brake rotors? 5
- Thread starter BobM3
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GregLocock
Automotive
BPM, that article sounds reasonable, but is fixated on friction material buildup on the rotor, which is not generally an important problem with production brakes.
Cheers
Greg Locock
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Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
BiPolarMoment
Mechanical
Greg: Okay, but the next logical question would be if all those things are reasonable for a race brake system, would "warping" ever occur--at all--on a street car? I'm thinking no considering the differences in brake temperatures observed.
GregLocock
Automotive
I wouldn't say it /never/ occurs, just that I've not had to work on it, ie DTV is practically far more important than runout by itself.
If the callipers are sliding then they will accomodate warping reasonably well, whereas DTV has to be reacted by the hydraulic circuit, or by flexure in the calliper itself.
Cheers
Greg Locock
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If the callipers are sliding then they will accomodate warping reasonably well, whereas DTV has to be reacted by the hydraulic circuit, or by flexure in the calliper itself.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
In light of the article I feel obliged to correct my termonology... at least re define it as I see it.
When I refer to a "warped" disc I am refering to that pulsating brake pedal and shake in the steering wheel. The actual cause is technically not a 'warping' but rather a variation in thickness around the pad surface the disc.
I have only had one personal experience on a street car and that was the above mentioned LHS which was eventually traced to metalurgical problems as I recall and not to an actual warped cast iron rotor. I deal with race brake problems almost exclusively and with racing people and I just "assumed" we were all on the same page which, apparantly, we are not. Sorry for my part of any confusion.
PS: My current, ongoing problem with the wifes Lincoln turned out to be a rather sever runout problem on the left front...I already bought new Brembo discs and EBC Greens so I will eventually change then anyway...Oh well, never too old to learn to 'look before you leap', I guess.
Rod
When I refer to a "warped" disc I am refering to that pulsating brake pedal and shake in the steering wheel. The actual cause is technically not a 'warping' but rather a variation in thickness around the pad surface the disc.
I have only had one personal experience on a street car and that was the above mentioned LHS which was eventually traced to metalurgical problems as I recall and not to an actual warped cast iron rotor. I deal with race brake problems almost exclusively and with racing people and I just "assumed" we were all on the same page which, apparantly, we are not. Sorry for my part of any confusion.
PS: My current, ongoing problem with the wifes Lincoln turned out to be a rather sever runout problem on the left front...I already bought new Brembo discs and EBC Greens so I will eventually change then anyway...Oh well, never too old to learn to 'look before you leap', I guess.
Rod
GregLocock
Automotive
"When I refer to a "warped" disc I am refering to that pulsating brake pedal and shake in the steering wheel. The actual cause is technically not a 'warping' but rather a variation in thickness around the pad surface the disc.
"
Exactly. Disc Thickness Variation. Here's a paper written by my partner in crime, Mr Leslie, aka Bubba:
Mathematical Model of Brake Caliper to Determine Brake Torque Variation
Associated with Disc Thickness Variation (DTV) Input
AU LESLIE A C, (Ford Motor Co. Australia Ltd.)
SO SAE Tech Pap Ser (Soc Automot Eng) SAE-2004-01-2777
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
"
Exactly. Disc Thickness Variation. Here's a paper written by my partner in crime, Mr Leslie, aka Bubba:
Mathematical Model of Brake Caliper to Determine Brake Torque Variation
Associated with Disc Thickness Variation (DTV) Input
AU LESLIE A C, (Ford Motor Co. Australia Ltd.)
SO SAE Tech Pap Ser (Soc Automot Eng) SAE-2004-01-2777
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
patprimmer
New member
Rings are quite hard.
Brake pads are reasonably soft by comparison, so the bore wears to the rings, but the pads wear to the rotor. In that case your logic suggests you should hone the pads, not the rotors.
I don't see how work hardened rotors causes pull, unless the rotors are obviously damaged from metal to metal contact.
Knock back and shudder can result from warped disks, but that would be obvious from a road test before the pads were replaced.
Bedding in pads takes about 2 minutes of road test while left foot braking. I think that is faster than aching, and the cost of the job is less than half, or cost of job is the same, but you use premium pads.
Regards
eng-tips, by professional engineers for professional engineers
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Brake pads are reasonably soft by comparison, so the bore wears to the rings, but the pads wear to the rotor. In that case your logic suggests you should hone the pads, not the rotors.
I don't see how work hardened rotors causes pull, unless the rotors are obviously damaged from metal to metal contact.
Knock back and shudder can result from warped disks, but that would be obvious from a road test before the pads were replaced.
Bedding in pads takes about 2 minutes of road test while left foot braking. I think that is faster than aching, and the cost of the job is less than half, or cost of job is the same, but you use premium pads.
Regards
eng-tips, by professional engineers for professional engineers
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Pat, even severely damaged disc usually won't pull once the pads are bedded in. Knockback is usually a 'runout' problem (or an engineering problem as we have noted in other threads). The 'shudder' is probably DTV in origin. I'll stick on message...If it's bad enough to need machining, it's bad enough to need replacement.
Rod
Rod
patprimmer
New member
Typo in my last post
"Bedding in pads takes about 2 minutes of road test while left foot braking. I think that is faster than (aching should be machining), and the cost of the job is less than half, or cost of job is the same, but you use premium pads."
Rod
I agree entirely. If the groves are so deep that you cannot bed the pads via driving while left foot braking in less time than it takes to machine the rotors, the rotors need replacing.
I think that someone who uses A$15.00 a set pads is not going to replace rotors. My pads for my Honda Integra cost about A$40.00 with trade discount.
Regards
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"Bedding in pads takes about 2 minutes of road test while left foot braking. I think that is faster than (aching should be machining), and the cost of the job is less than half, or cost of job is the same, but you use premium pads."
Rod
I agree entirely. If the groves are so deep that you cannot bed the pads via driving while left foot braking in less time than it takes to machine the rotors, the rotors need replacing.
I think that someone who uses A$15.00 a set pads is not going to replace rotors. My pads for my Honda Integra cost about A$40.00 with trade discount.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
I'm with Pat and others, in recommending that rotors never be replaced unless they have an obvious and severe defect, or if the brake pedal pulsates when applied: that is a sign of rotor thickness variation (NOT runout) and will be caused by variations in thickness that are undetectible with a micrometer.
Having worked in brake engineering at a *former* Big Three firm, I saw a number of pedal pulsation complaints caused by thickness variation.
This thickness variation problem cropped-up most frequently in cars that were built, driven briefly, and then sat on a storage lot for several weeks or months before being sold. The rotors got wet and/or salty, then rusted everywhere except where the pads were. Once they were driven for a few thousand miles the softer rust wore down leaving high spots where the pads had been parked.
I also frequently saw newly-turned rotors that the technician only succeeded in making worse, by introducing runout and/or thickness variation and creating a noise or vibration problem where none had existed before.
With my own vehicle, one having grossly under-sized brakes, the front pads wore out at 15,000 mile intervals, so I got quite good at replacing them, and could do the job in 20 minutes, working in my driveway. The rotors finally required replacement at about 160,000 miles (and 20 years).
Having worked in brake engineering at a *former* Big Three firm, I saw a number of pedal pulsation complaints caused by thickness variation.
This thickness variation problem cropped-up most frequently in cars that were built, driven briefly, and then sat on a storage lot for several weeks or months before being sold. The rotors got wet and/or salty, then rusted everywhere except where the pads were. Once they were driven for a few thousand miles the softer rust wore down leaving high spots where the pads had been parked.
I also frequently saw newly-turned rotors that the technician only succeeded in making worse, by introducing runout and/or thickness variation and creating a noise or vibration problem where none had existed before.
With my own vehicle, one having grossly under-sized brakes, the front pads wore out at 15,000 mile intervals, so I got quite good at replacing them, and could do the job in 20 minutes, working in my driveway. The rotors finally required replacement at about 160,000 miles (and 20 years).
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patprimmer
New member
20 min for the full job sounds about right for fronts to me. A\ little longer for rears if they have to be wound in for the park brake mechanism
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
Twenty minutes sounds about right for an experienced tech.
I just replaced the front discs (Brembo) and all four wheel pads (EBC Greens) on the 01 Lincoln LS @ 134,000 miles...took me about an hour, total, but I have a full shop with all (well, mostly all) the proper tools (finally, after 50 years)...
Pat, a little fab time, a 3/4 nut and long bolt, a little plate steel...voila...neat little gizmo for winding in rear pads in about 30 seconds.
Rob, I think I had one of those cars from Canada...I know the brakes went bad after only a few thousand miles, unacceptable for the 'flagship' of the company.
Rod
I just replaced the front discs (Brembo) and all four wheel pads (EBC Greens) on the 01 Lincoln LS @ 134,000 miles...took me about an hour, total, but I have a full shop with all (well, mostly all) the proper tools (finally, after 50 years)...
Pat, a little fab time, a 3/4 nut and long bolt, a little plate steel...voila...neat little gizmo for winding in rear pads in about 30 seconds.
Rob, I think I had one of those cars from Canada...I know the brakes went bad after only a few thousand miles, unacceptable for the 'flagship' of the company.
Rod
Yep, 20 minutes for the whole job, from walking out my backdoor with new pads in one hand and toolbox in the other; but as I said, I got a *lot* of practice at it!
High-Lift jack under the brushguard ('roo bar, to you, Greg!) lifts both front wheels off the ground, removing one bolt gets the caliper off the slider after prying the piston all the way back into its bore. Wirebrush the rust off the slider ways, file the paint off the edges of the pads, drop 'em in, bolt the caliper down and you're done.
The only hazard is if you forget where you put your beer down and kick it over!
Cheers!
High-Lift jack under the brushguard ('roo bar, to you, Greg!) lifts both front wheels off the ground, removing one bolt gets the caliper off the slider after prying the piston all the way back into its bore. Wirebrush the rust off the slider ways, file the paint off the edges of the pads, drop 'em in, bolt the caliper down and you're done.
The only hazard is if you forget where you put your beer down and kick it over!
Cheers!
patprimmer
New member
I found that insisting who ever owned the car, or from time to time wanted to borrow my stood there and held the beer for me, passing it to me on demand. This removed certain risks.
I also strategically placed the wheels under the car, so I had half a chance if the jack failed.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
I also strategically placed the wheels under the car, so I had half a chance if the jack failed.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
clayndwoods
Computer
Almost 85k miles ago I put a set of chinese made rotors on a Grand Cherokee. They were much heavier units than the stock one's, quite a bit thicker. The dudes at the parts house measured the factory ones and said, yep, they were original and never been turned and couldn't be turned.
The point I'm making is, the factory units lasted about 40k. The chinese units have over twice the mileage on them, and the brakes don't fade under constant load like they did with the factory units. They factory units were replaced because they had small cracks in them (from the heat).
That said, I don't drink beer below the car. I make up for it when I get back up. The brake drum idea is a good one. I often use a piece of tree trunk for a secondary safety stand.
Of course, my F-body is real sensitive about where I "stand" it.
JayMaechtlen
Industrial
I've had brake pedal pulsation and steering wheel shake from brakes on about 2/3 of the cars I've had.
Maybe I drove them too hard, or too inconsistantly?
'89 Aerostar- don't recall mileages, but definately had rotors turned to alleviate the problem. Usually helps for quite a while.
Ditto '89 and '93 Buicks. All the above have kinda puny brakes for how I drove them.
No probs yet with 03 Regal- original pads went 75k miles, don't recall if I turned the rotors or not. Probably did out of paranoia.
Now that rotors are pretty cheap, replacing them makes a lot more sense. The older cars, where the rotor included the wheel hub, were much more expensve to replace the rotors.
The worst fade I ever had was going down a steep fire road in the Aerostar. Had to ride the brakes, because even first gear wasn't low enough to slow the vehicle. Wasn't going fast enough to get any air flow through the rotors. Bad news- just barely got stopped (still on the hill) before they faded completely.
Could have used an electric cooling blower on each corner!
cheers
Jay
Jay Maechtlen
Maybe I drove them too hard, or too inconsistantly?
'89 Aerostar- don't recall mileages, but definately had rotors turned to alleviate the problem. Usually helps for quite a while.
Ditto '89 and '93 Buicks. All the above have kinda puny brakes for how I drove them.
No probs yet with 03 Regal- original pads went 75k miles, don't recall if I turned the rotors or not. Probably did out of paranoia.
Now that rotors are pretty cheap, replacing them makes a lot more sense. The older cars, where the rotor included the wheel hub, were much more expensve to replace the rotors.
The worst fade I ever had was going down a steep fire road in the Aerostar. Had to ride the brakes, because even first gear wasn't low enough to slow the vehicle. Wasn't going fast enough to get any air flow through the rotors. Bad news- just barely got stopped (still on the hill) before they faded completely.
Could have used an electric cooling blower on each corner!
cheers
Jay
Jay Maechtlen
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