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  #11  
Old 11-16-2010, 11:28 AM
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TIMZTOY TIMZTOY is offline
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Originally Posted by subzali View Post
rotors are supposed to be turned on the truck...
Nope. You can do them either way! But On the car lathe is much better and the preferred method.

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  #12  
Old 11-16-2010, 12:27 PM
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Originally Posted by TIMZTOY View Post
Your rotors don't actuall "warp" i believe it is mechanically impossibly for the steel to warp from the low heat tempeture caused by the breaking. The "warp" term is actually brake pad deposit build up. But its easier to just say warped because ppl understand it Better.
I have to disagree (but I would be interested what Gary Krieder says about it).

I have put rotors on a lathe and measured the runout and while that could be measuring deposits on the surface, I doubt it. When the cutting edge was slowly run into the surface it was not cutting evenly, it "skipped' portions of the rotor while cutting into the metal on portions. This indicates to me that the rotor disc was not true to the hub or "warped".

Machining the rotors reduces the amount of metal and ability to get rid of the heat that is caused by braking action ( if you don't think that is much heat run up the hill on I70 and come down, slam on the brakes at Colfax and get out and touch the rotors )
IMO turning rotors can cause the shimmy to return even faster with each machining. When I was at Stevinson the 80 series owners that lived in Genesse had a far greater incidence of vibration under braking then the in-town owners. I can only relate that to the heat induced by the hard braking that can occur rounding that corner at the Morrison exit.

x2 on avoiding Brakes Plus or the brake specialty places. They offer great deals on pads with a "lifetime" warranty but when you go in because the pads are worn you are sold $700 worth of calipers and rotors because "that is what caused the pads to wear out". I can't tell you how many of my customers told me that story when all I wanted to sell them was pads but they went to get them replaced for "free". I can't prove it but I suspect they also cut too much material when they turn rotors so the next time they are "below spec" and can sell you new ones.
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Old 11-16-2010, 12:49 PM
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I think the rule (promoted by various sources) is that 'some who claim to have warped rotors actually have a buildup of pad material on the rotor'. I suspect this is true, but this does NOT mean that no rotor ever warps.

I agree too that overtightening lug nuts would rarely, if ever, cause a warped rotor.

Every manufacturer has cut back on brake rotor thickness and size for ride and fuel economy reasons, and some vehicles are worse than others. When you add mountains and towing to the mix, you find that almost all stock brake systems are inadequate.

The only bright spot in all this is that many of the 'cheap Chinese brake rotors' work just fine - I have used them on 4 vehicles (Mitsubishi Eclipse, Camry, FZJ-80, and F350 diesel) and they have completely solved the braking problems I had. Some folks will still need high performance/drilled/cryo-treated/etc. but if you drive less aggressively and downshift on hills, the cheap rotors can still do the job.
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Old 11-16-2010, 01:08 PM
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Quote:
Originally Posted by Tch2fly View Post
...IMO turning rotors can cause the shimmy to return even faster with each machining...
I agree, which is why i'm hesitant about getting them turned in the first place. I would rather save up some $$ and get new calipers and perform the TSB service.

I have never heard the brake pad deposits thing; so it that something that will come off without taking the rotor to a lathe?

Quote:
Originally Posted by SteveH View Post
I think the rule (promoted by various sources) is that 'some who claim to have warped rotors actually have a buildup of pad material on the rotor'. I suspect this is true, but this does NOT mean that no rotor ever warps.
Again, I've never heard that about the pad material. I ALWAYS thought it was the rotor metal actually warping, which makes sense to me especially if you get a hot spot.

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Originally Posted by SteveH View Post
I agree too that overtightening lug nuts would rarely, if ever, cause a warped rotor.
I agree.

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Originally Posted by SteveH View Post
Every manufacturer has cut back on brake rotor thickness and size for ride and fuel economy reasons, and some vehicles are worse than others. When you add mountains and towing to the mix, you find that almost all stock brake systems are inadequate.
That's my suspicion too, but I'm still amazed that my coworker pulls a very heavy trailer and has no problems while I am pretty much always empty and have problems. I must drive more aggressively than he does, though I try to be light on the brakes...
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  #15  
Old 11-16-2010, 02:23 PM
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Myth's about "warped" rotors

Myth's about "warped" rotors 2
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  #16  
Old 11-16-2010, 03:18 PM
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subzali subzali is offline
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Thanks Tim, That was a very informative article.

Quote:
If the vibration has just started, the chances are that the temperature has never reached the point where cementite begins to form. In this case, simply fitting a set of good "semi-metallic" pads and using them hard (after bedding) may well remove the deposits and restore the system to normal operation but with upgraded pads. If only a small amount of material has been transferred i.e. if the vibration is just starting, vigorous scrubbing with garnet paper may remove the deposit. As many deposits are not visible, scrub the entire friction surfaces thoroughly.
So I should never get my rotors turned ever again I guess? I should vigorously scrub them with garnet paper or get them blanchard ground to get the pad deposits/cementite inclusions off of and out of the rotor?

I believe Toyota uses semi-metallic brake pads already, right? At least for Land Cruisers and Tundras?

Quote:
Depending upon the friction compound, easy use of the brakes for an extended period may lead to the removal of the transfer layer on the discs by the abrasive action of the pads. When we are going to exercise a car that has seen easy brake use for a while, a partial re-bedding process will prevent uneven pick up.
So maybe I should re-bed the pads and drive it hard to hopefully remove any remaining deposits?

Quote:
The procedure is several stops of increasing severity with a brief cooling period between them. After the last stop, the system should be allowed to cool to ambient temperature. Typically, a series of ten increasingly hard stops from 60mph to 5 mph with normal acceleration in between should get the job done for a high performance street pad. During pad or disc break-in, do not come to a complete stop, so plan where and when you do this procedure with care and concern for yourself and the safety of others.
Quote:
In terms of stop severity, an ABS active stop would typically be around 0.9 G’s and above, depending on the vehicle. What you want to do is stop at a rate around 0.7 to 0.9 G's. That is a deceleration rate near but below lock up or ABS intervention. You should begin to smell pads at the 5th to 7th stop and the smell should diminish before the last stop. A powdery gray area will become visible on the edge of the pad (actually the edge of the friction material in contact with the disc - not the backing plate) where the paint and resins of the pad are burning off. When the gray area on the edges of the pads are about 1/8" deep, the pad is bedded.
Is the "proper" way to bed pads for this application to do the 10 60mph-5mph increasingly more aggressive stops, like the article suggested?

Quote:
Other than proper break in, as mentioned above, never leave your foot on the brake pedal after you have used the brakes hard...Regardless of friction material, clamping the pads to a hot stationary disc will result in material transfer and discernible "brake roughness".
Finally, I need to try to never hold the brake pedal down when at a stop (which I try to do anyway)?
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  #17  
Old 11-16-2010, 03:43 PM
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Quote:
Originally Posted by subzali View Post
Is the "proper" way to bed pads for this application to do the 10 60mph-5mph increasingly more aggressive stops, like the article suggested?

Finally, I need to try to never hold the brake pedal down when at a stop (which I try to do anyway)?
First, how do you keep the rig from moving without holding the brake pedal down in an automatice? Shift to park or neutral with the ebrake applied (guessing the rear rotor would be hot too though )

As for the bed in procedure...I use a much less complicated and less Johnny Law attracting process that I found a few years ago. It use to be at this LINK which appears to be dead or messed up now but I found it copied at another forum and will post it below (from Padig USA):

Quote:
BRAKE PAD BEDDING IN PROCEDURE

To ensure maximum performance and customer satisfaction, new brake pads must be bedded in upon installation. Correct bedding guarantees that new brake pads and new rotors work flawlessly together. In order to function optimally, organic brake pads must develop friction coal on its surface. This friction coal develops at a temperature of approximately 280C (537F). It is very important that this temperature is reached continuously and slowly. This gradual process generates temperatures that not only penetrate the surface of the brake discs and pads, but also distribute evenly through the whole disc and pad material. This is essential when using new brake discs, since the disc often shows signs of stress (due to the casting process and fast cooling) in the materials. A steady and careful warming and cooling process guarantees a good release of both materials.

The bedding in/break in procedure should be done as follows:

Drive at approx. 35 mph (60 kmh) for about 500 yards (solid front discs) to 800 yards (vented front discs) while slightly dragging the brakes (i.e. light brake pedal pressure). This process allows the brake temperature to slowly and evenly build up to 300C (572F). Now, if possible, drive about 2200 yards maintaining the same speed without braking. This will allow the pads and discs to cool down evenly. After this cool-down, perform a normal brake application from 35 mph to 0. No panic stops! Now, the friction surface has evenly developed friction coal, the pads have bonded with the disc surface, and tensions in the disc materials will have disappeared.

Only trained master mechanics should perform this procedure before delivering the vehicle to its owner. Do not expect your customer to properly finish your brake job!

This bedding process is only suitable for the front axle - not the rear. This is due to the brake force distribution of front and rear axles. In order to reach 300C (527F) on the rear pads you would have to drive several miles with dragging brakes. However, in that time the front brakes will be glowing red, overheating and thus destroying the front brakes.
Final note dont forget to clean hubs and check the wheel bearings. Also, the brake fluid should be replaced at least every 2 years.
I've done this on both the LX and the 80 and I don't have any braking issues or shimmy problems. Rare for me to perform any work on either truck and not have issues
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  #18  
Old 11-16-2010, 04:16 PM
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im look at the pads right now and i want to say ceramic, but they look like semi metalic/ceramic, because it apeare to have medal in them.. (ours are not labeled) just part numbers.
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  #19  
Old 11-16-2010, 04:32 PM
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I have never seen any evidence to suggest unevenly torqued wheel studs can cause rotor warping. However, it was interesting that the author specifically implies just that at the beginning of his paper on brake performance:

"With one qualifier, presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification, in more than 40 years of professional racing, including the Shelby/Ford GT 40s one of the most intense brake development program in history - I have never seen a warped brake disc.
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Old 11-16-2010, 04:35 PM
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maybe that wouldn't cause warping, but could cause a pulsing or wobbling feeling...
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