How Do You Know When To Replace Brake Rotors? - Drive Accord Honda Forums | radio-pro.ru
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post #1 of 9 Old 08-15-2009, 11:18 PM Thread Starter
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How Do You Know When To Replace Brake Rotors?

I change my own brake pads... How can I tell if it's time to change the brake rotors as well?

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post #2 of 9 Old 08-15-2009, 11:29 PM
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its based on rotor thickness

you shouldnt need to replace your rotors with the pads unless they are too thin or have excessive runout or wear in which case they would need to be turned/refinished or in some cases replaced

if this is your first pad change you should be fine however brake pedal vibration and other signs of rotor warp or wear would indicate the need for rotor service

(if the thickness is ok / you dont have any issue with vibration / and you can run your finger across the rotor and its smooth, you dont feel any ridges you should be ok)

check out this site for some general info:



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post #3 of 9 Old 08-18-2009, 07:45 AM
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- If the rotors are below minimum thickness at the time of pad replacement.

- If the rotors are below minimum thickness after resurfacing at the time of pad replacement.

- If the rotors are cracked and/or show heat damage.

- If you have a lot of lateral runout and/or disc thickness variation that would require heavy resurfacing that would cause the rotor to drop below minimum thickness.

Generally speaking, for most of us, replace the rotors if you are experiencing a pedal pulsation. Or, if you are replacing pads, measure the rotor thickness before installing new pads. A good rule of thumb about rotor thickness-- if you see a "lip" on the edge of the rotors, they need to be replaced.
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post #4 of 9 Old 04-03-2012, 06:32 AM
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If I change the pads at 50% wear will this keep the rotors from having to be replaced? i'm at 80000 miles (40k on the pads) or am I wasting money changing the pads a little too soon?
the mechanic tested the brake fluid and the strip came back purple...but maybe i can wait on this fluid flush til the brakes need replacing?


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post #5 of 9 Old 04-03-2012, 10:19 AM
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Quote:
Originally Posted by knightrdrx View Post
If I change the pads at 50% wear will this keep the rotors from having to be replaced? i'm at 80000 miles (40k on the pads) or am I wasting money changing the pads a little too soon?
the mechanic tested the brake fluid and the strip came back purple...but maybe i can wait on this fluid flush til the brakes need replacing?
No. Changing the pads early has nothing to do with the life of the rotor. You'd just be throwing money away by replacing brake pads that are half used. Rotors usually get warped from excessive heat. Accords have been notorious to warp rotors quickly. I have warped rotors on my car but I don't care much. The brakes are fine and the car stops quickly. When the pulsating gets too much I'll change them.

If you are going to have your rotors turned at a shop make sure you compare prices with the price of new rotors. Sometime the price of new rotors would be the same or less than having them turned. Replacing the rotors are not very hard to do (unless they are rusted on like my old ones were).

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post #6 of 9 Old 04-04-2012, 01:45 PM
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I heard some hondas has a little screw that holds the rotor on and is a pita to get out. Heard many people having to drill it out because they stripped the head.


I will ask is it worth the extra price to get better quality rotors like baer or some of the higher end brake stuff? Or will they warp just as easily? WHY I ask is on my dakota I have 4 wheel disk but my front rotors always warp bad. I was wondering if its worth the extra money to get brands like that?
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post #7 of 9 Old 04-20-2012, 09:02 AM
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Originally Posted by Jecht View Post
I heard some hondas has a little screw that holds the rotor on and is a pita to get out. Heard many people having to drill it out because they stripped the head.
If you are replacing the rotors for the first time they do have screws (2 per rotor) that hold the rotor in place. They can be easily corroded over time and be a PITA to remove. I had to use a drill, crowbar and rubber mallet to get the SOB off the first time. Talk about a mess of rust that fell off.

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post #8 of 9 Old 04-20-2012, 11:01 AM
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Measuring the thinnest part of the rotor with a micrometer against the minimum specification of the rotor will tell you if the rotor is good or bad, but it won’t tell you if your rotors are warped. For this you will need a dial indicator attached to the spindle. Check both sides of your rotors all over the pad surface area. Is your time worth researching these specifications, buying these tools, learning how to use them and then using them on your rotors?

I don’t look at this way. To me, brakes are a big safety item. Vehicle safety items require a higher level of concern. Checking the price at Advance Auto Parts, the price for a front rotor is $31 each and the price for a rear rotor is $21 each. I didn’t shop around and likely you can find cheaper or by using the Advance Auto 25% off $100 discounts this further. Bottom line is, rotors are not that expensive.

I could have the rotors turned at a cost of $12 each, but then I’m depending on the machinist to properly measure and machine my old rotors. Which also requires me to deliver these dirty rotors to a machinist and then pick them up hours later. As someone who has turned hundreds of drums and rotors, it is possible to screw up turning a rotor or drum.

When I do a brake job for my car I ALWAYS replace the rotors. To me it is cheap insurance.

NOTE 1: To remove the screws holding the rotor on, ONLY use an Impact Driver with a screwdriver Phillips bit. An impact driver is a sort of a screw-driver with a spring-loaded twisting action that works when the handle is hit with a hammer. Make sure the Phillips bit fits perfectly tight in the screw. This will work 90% of the time. If this doesn’t work, get out the drill.

NOTE 2: Put just a dab of anti-seize compound on the screw thread (or new screw) for ease of disassembly at your next brake job. If you do this, the impact driver will 100% work on these screws next time.

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post #9 of 9 Old 04-20-2012, 06:16 PM
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As part of my crusade to persist until every serious driver understands what really causes judder - and it's not "warped rotors" - I offer the following from a much earlier post;

Quote:
I understand the attraction of warped rotors as an explanation. Until I was involved in brake rotor development, I thought judder was cause by "warped rotors." Then a bunch of us looked at the situation in terms of what was happening.

The short answer is that floating calipers accommodate any "warping" (which I define as an out-of plane surface.) The suspension on your car acts very much like a floating caliper on a brake. The suspension allows the wheel to travel up-and-down significantly to absorb the variations in the road without transmitting shock to the rest of the vehicle. A gently rolling road is like a warped rotor - at least one surface of it. As the car drives down the road, the suspension adjusts for the SMOOTH. CONTINUOUS CHANGE IN THE PLANE OF THE ROAD. The effect is a smooth ride. So it is with floating calipers on a rotor of constant thickness which may have two faces out of plane with each other. The calipers accommodate that variation without transmitting any vibration.

Now let's look at another metaphor. When a potato chip is cooked, it usually curves or "warps." Does the potato chip change thickness appreciably? No. So even if a rotor "warps" (and a calculation of the forces required says it takes a lot), the calipers accommodate the change in planarity, if you will.

Let's go back to the car and road example. What happens if you're on a perfectly flat road but run across a pothole, rumble strips, or a speed bump? You get a lot of vibration. Why? Because the suspension cannot accommodate the SUDDEN, DISCONTINUOUS CHANGES in the surface.

From the perspective of the car's suspension. the rolling terrain is effectively smooth, but not perfectly flat. The rumble strips are effectively flat, but not perfectly smooth. It is this sudden, effectively discontinuous change in smoothness (the technical term is differential thickness variation, or DTV) that causes judder.

The overwhelming reason that high DTV arises on metal rotors is local variation in the rotor metallurgy. Brakes work by the pad and rotor working together to form a third body friction film on the rotor surface. If the metallurgy variies (perhaps a car was parked immediately after a series of hard stops and the heat from the pads "cooked" the rotors at that one spot where the car was parked), the friction film may be more or less apt to build up at that place. That local discontinuity is a high DTV. When you turn "warped" rotors, you change the smoothness but not the metallurgy, and the high or low spot regenerates. Many explain this as "A turned rotor is even thinner, and even more susceptible to warping."

Why am I so sure of this? The brake rotors I was involved with were ceramic composite motorcycle rotors. We made them by laying up plies of carbon fabric and infliltrating them with a liquid that turned to silicon carbide. Because the liquid lost volume in converting to ceramic, we had to repeat the process several times. Imagine trying to fill in all the voids in a sponge using latex paint and you get the picture. Any way, at some point, these rotors had to be ground to a smooth surface. At some level, the rotor blanks weren't perfectly uniform. The shrinkage of the liquid converting to ceramic introduced stresses. In addition, the outside of a rotor could be more dense than the inside, because it got harder for the liquid to make it to the center of the rotor, not unlike a Tootsie Roll pop. Sometime - quite often, actually, the process of grinding the surfaces smooth took more off one side than the other, creating differential stresses that were high enough to cause the rotors to "potato chip" as much as 0.030" out of plane. But as long as they were of uniform smoothness, they did not judder. Sometimes, the rotor blank wasn't uniformly thick and the grinder ground down one part more than another, but as long as the transitions in thickness were smooth, the rotors did not produce judder. If however the thickness between two points 60 degrees apart on the rotor varied by more than 0.004" any rider could feel it, and some riders could detect judder at a DTV of 0.002."

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