Brake problem—do my front rotors need to be replaced?


TJim

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Hey,

Today I did a test. I was going downhill, I put the manual transmission on neutral and cruised in order to check some vibrations.

I was pushing the brakes (neither very lightly nor enough to stop the vehicle). I did this multiply times. I has some vibrations in my steering wheel, when pushing the brake pedal. My uncle told me that this should be EDIT: warped rotors.

Is this correct? Is there any test I can do?

If they need to be replaced any suggestions?
 
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mrblaine

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Hey,

Today I did a test. I was going downhill, I put the manual transmission on neutral and cruised in order to check some vibrations.

I was pushing the brakes (neither very lightly nor enough to stop the vehicle). I did this multiply times. I has some vibrations in my steering wheel, when pushing the brake pedal. My uncle told me that this should be worn rotors.
He is mostly correct but not all the way. Newish rotors can do the same if not treated properly during break in.
Is this correct? Is there any test I can do?
Yes, the test is to coast downhill and moderately apply the brakes to see if the steering wheel shakes.
If they need to be replaced any suggestions?
I highly suggest that you get some that are flat and true.
 

Jerry Bransford

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It's more likely the rotors just have a brake pad pattern built up onto them akin to how a washboard pattern builds up on a dirt road. This is caused by poor braking technique, especially by holding the brakes on hard at stop lights when they're hot. I thought the same thing for several years and was taking my front rotors in to have them turned at the local brake shop to smooth them down. Then @mrblaine informed me what the real problem was and that it wasn't from warped rotors. I changed my braking style to one recommended by Blaine and I haven't had a "warped rotor" since which has been probably 15 years now.
 
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mrblaine

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You can measure runout on each rotor.
You could also mic the rotors, and if within spec, turn them.

Or buy new rotors and measure run out. If they are straight, bolt em on and run them.
It isn't possible for the average person measure even a severe case of Disc Thickness Variation. A but of run-out can be measured but even then, not for the average unless it is really bad. We hold our brake kit conversions to under .003 RO after they are bolted up to new rotors. The scratches in the face from double disc surface grinding are more than half of that amount.

It only takes a thou or so of DTV (high spots) to show up as a severe shake in the steering wheel.
 
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Fouledplugs

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It isn't possible for the average person measure even a severe case of Disc Thickness Variation. A but of run-out can be measured but even then, not for the average unless it is really bad. We hold our brake kit conversions to under .003 RO after they are bolted up to new rotors. The scratches in the face from double disc surface grinding are more than half of that amount.

It only takes a thou or so of DTV (high spots) to show up as a severe shake in the steering wheel.
Now I know. Thank you.
 
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TJim

TJim

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It isn't possible for the average person measure even a severe case of Disc Thickness Variation.
I am below average on brakes so this option is out.

He is mostly correct but not all the way. Newish rotors can do the same if not treated properly during break in.
They are not new at all. In fact, I don't even know if those rotors have ever been changed, since I bought my TJ 2 years ago.

He is mostly correct but not all the way. Newish rotors can do the same if not treated properly during break in.

Yes, the test is to coast downhill and moderately apply the brakes to see if the steering wheel shakes.

I highly suggest that you get some that are flat and true.
So, if this is a stupid question, but what do you mean by true?

Since, I don't live in areas that you ship, can you recommend any rotors that I could get? or maybe some characteristics that I should look for?

There are some many options that it almost chaotic for someone that is a completely beginner.

*I am trying to work on my rig as much as possible, so I am going to replace them on my own, but I just want to be sure I did the right choice of product.
 
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TJim

TJim

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It's more likely the rotors just have a brake pad pattern built up onto them akin to how a washboard pattern builds up on a dirt road. This is caused by poor braking technique, especially by holding the brakes on hard at stop lights when they're hot. I thought the same thing for several years and was taking my front rotors in to have them turned at the local brake shop to smooth them down. Then @mrblaine informed me what the real problem was and that it wasn't from warped rotors. I changed my braking style to one recommended by Blaine and I haven't had a "warped rotor" since which has been probably 15 years now.
So, what should I do? Just hold the brakes lighter at stop lights/ when they are hot?

My uncle told me that rotors can be warped by crossing water (cold) when they are hot as well. Is it true?
 

mrblaine

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I don't recall exactly how Blaine put it but IIRC it was basically don't keep heavy pressure on the brakes at a stop when they're hot which helps avoid brake pad material transfer to the rotor. @mrblaine can give a better explanation or perhaps more ways it can happen.
It's easier to just say don't do that when they are not broken in fully. Do not hold yourself in place with the service brakes when they are hot during the break in period.