warped rotor - front or rear

[Donald]

I got a new to me 2001 Jeep Cherokee Laredo and while the prev. owner said he had just done the brakes, there is a pulsing in the brakes that comes from a warped rotor or more correctly when the rotor is not of uniform thickness.

I do not have a dial gauge to measure things so how does one tell. I'd like to order pads/rotors ahead of time before I get into it, but want to order either front or rear.

 

[tom slick]

does the vibration happen with light braking or only during moderate to heavy braking?

 

[Donald]

I would guess more moderate braking.

 

[The Critic]

You don't need a dial indicator to check for warped rotors. Pedal pulsation is caused by disc thickness variation, which is often caused by runout.

If you have a micrometer, measure the disc thickness in eight different spots on the rotor. If there is more than 0.001" of thickness variation, that could a pedal pulsation.

 

[Chris142]

If you feel it in the steering wheel its the front. If you feel it in the seat it's the rear.

 

[Big Jim]

If the parking brake uses the rear calipers there is another way to pin it down. If the parking brake is a drum type brake built into the "hat" of the rear disc it won't work though.

If the pulsation is present using the park brake to stop the car (rear brakes only, assuming park brake is not the "hat" style), the problem is in the rear. If not present present using the park brake, the problem is in the front.

 

[PT1]

My guess would be the person who did the brakes did not resurface the rotors...or if they did they failed to clean off and lubricate the hub before putting the rotor back on. If you take the rotors into your auto parts store they will measure them for you. Then you can decide to re-surface or replace. Just be sure to replace them in pairs and clean the hub/rotor mating surface with a wire brush completely. Then coat the hub face with permatex synthetic brake lubricant before reassembly.

 

[tomit]

Donald,

The first thing I would do is loosen and re-tighten all the wheel bolts/nuts to the factory recommend torque. Problem might go away.

Tom

 

[Donald]

Originally Posted By: tomit
Donald,

The first thing I would do is loosen and re-tighten all the wheel bolts/nuts to the factory recommend torque. Problem might go away.

Tom


Good idea. I was going to bring it to Sams where they rotate and balance for about $12 total (4 wheels). That assume you did not buy tires at Sams. If you did its free.

 

[Gary Allan]

Originally Posted By: Chris142
If you feel it in the steering wheel its the front. If you feel it in the seat it's the rear.


That would be my first self diagnostic. There should be nothing happening at the steering wheel if it's the rears.

 

[The Critic]

Originally Posted By: Donald
Originally Posted By: tomit
Donald,

The first thing I would do is loosen and re-tighten all the wheel bolts/nuts to the factory recommend torque. Problem might go away.

Tom


Good idea. I was going to bring it to Sams where they rotate and balance for about $12 total (4 wheels). That assume you did not buy tires at Sams. If you did its free.

They'll probably overtighten your lug nuts.

 

[Donald]

So I took the vehicle to Sams Club and had them do the $15 tire balance and rotation. The tech told me there are new pads on the front but one of the rotors needs replacing and on the back one rotor also need replacing. Whats the chance the rotors can be machined rather than replaced? Can the front pads stay or will a bad rotor have ruined them by now and they need replacing along with the rotors?

 

[Donald]

Originally Posted By: The Critic
Originally Posted By: Donald
Originally Posted By: tomit
Donald,

The first thing I would do is loosen and re-tighten all the wheel bolts/nuts to the factory recommend torque. Problem might go away.

Tom


Good idea. I was going to bring it to Sams where they rotate and balance for about $12 total (4 wheels). That assume you did not buy tires at Sams. If you did its free.

They'll probably overtighten your lug nuts.


Sams uses those torque limiting color coded bars to tighten things.

 

[wantin150]

Pads are cheap. If there is enough thickness on the rotors, I don't see why they can't be turned. Worst case, you buy a set of cheapy rotors (if that suits you) and drop less than $100 an axle (provided you do the work yourself).

 

[The Critic]

Originally Posted By: Donald
Sams uses those torque limiting color coded bars to tighten things.

The accuracy of the torque sticks is going to depend on the input of the impact gun.

However, torque sticks are still very effective as they are very consistent. It's actually better to have all five lug nuts tightened to the same torque value (even if it's overtightened) than to have 3 lug nuts tightened to the correct value and 2 under tightened. GM issued a service bulletin explaining this a while ago.

 

[Donald]

So if the rotors when people saw warped are not really warped but rather no longer of uniform thickness, how does this happen? Is the iron softer in some areas? I don't see how pads would wear it so its no longer of uniform thickness. If a rotor was truly warped I could see that might have happened from overheating.

 

[Gary Allan]

Uneven pad application. It can occur due to bound up sliding channels. Happens more often with newer (my term for "newer" - which is a few years longer than our neo-brake would be guru, The Critic has graced the face of the earth

) assemblies.

 

[PT1]

Originally Posted By: tomit
Donald,

The first thing I would do is loosen and re-tighten all the wheel bolts/nuts to the factory recommend torque. Problem might go away.

Tom


Or just hit em with the impact gun until it starts smokin..

 

[Donald]

So if one has the caliper'ssliding pins lubricated, and the rotors machined should this happen again, unless the sliding pins stick again?

 

[wantin150]

That's a starting point. Clean everything up REALLY well and grease the pins.