Brake issues

[Wolfgut]

Hey so I hope I'm posting this in the right area.
I have a 2003 jeep grand Cherokee Laredo, recently about once a day when i try to come to a full stop my brakes seem to stutter as in a similar situation to when you try to brake on ice and your ABS engage, but this is happening on clean dry roads. I plan on taking it in but I would like to have an idea what might be causing it before I do.
Don't know if its relevant but my jeep also tends to pull to one side occasionally and I have a mismatched tire which is the same size and such as the others.
I am not a mechanical type of person but I'm trying to learn.

 

[lxskllr]

Should be in the garage subforum. Might be a warped rotor, but that's not so much like abs pulsing.

 

[KB]

I had a similar issue in the past. Turned out it was warped rotors.

Pulling to one side could be a result of this or perhaps bad alignment, or mismatched tire size. The mismatched tires may be the same size but they may be inbalanced.

Have them inspect the rotors and brakes. If they look ok balance the tires and check alignment.

 

[pcgeek11]

Or you may have a caliper piston that is sticking on one side...

 

[boomerang]

Could be something as simple as an ABS sensor ring has picked up a bunch of crap that is generating false signals in the sensor. Semi-metallic pads and the rotors themselves generate dust that can accumulate in the grooves of the sensor ring that can make the ABS computer think that the wheels are turning at different speeds.

 

[mindless1]

^ along the lines of what I was thinking except that I'm wondering if the sensors are working fine and that "mismatched" tire is off just enough to cause the ABS (or through traction control / 4WD) to kick in under certain situations. Different makes and models of tires with the same size # can vary in true size a bit, and as likely the % wear is a little different too.

That might also cause it to pull to one side, or if whatever did the tire in to cause replacement has thrown the alignment off too.

Take the mismatched tire off and example the brake rotor and pad, comparing against the one on the other side of the same *axle*. If either is excessively worn (or both), replace both and the pads. If one is dragging and has done so for a while, you should see accelerated rotor or pad wear.

 

[Meghan54]

In the OP's case, why would what he described as a "mismatched" tire cause any problems? The OP already said the tire was the same size, so it's not a size mismatch....I read it as it's more a brand mismatch. Since the mismatched tire's size is the same as the others, don't see where this has any implication into making the ABS work incorrectly, unless ABS is dependent upon tread patterns matching.

^ along the lines of what I was thinking except that I'm wondering if the sensors are working fine and that "mismatched" tire is off just enough to cause the ABS (or through traction control / 4WD) to kick in under certain situations. Different makes and models of tires with the same size # can vary in true size a bit, and as likely the % wear is a little different too.

That might also cause it to pull to one side, or if whatever did the tire in to cause replacement has thrown the alignment off too.

Take the mismatched tire off and example the brake rotor and pad, comparing against the one on the other side of the same *axle*. If either is excessively worn (or both), replace both and the pads. If one is dragging and has done so for a while, you should see accelerated rotor or pad wear.

 

[mindless1]

^ "Same size" can mean same actual circumference, or just the same numbers stamped on the sidewall.

The tire(s) could be rotated while the brakes are being inspected to see if the problem follows the tire, unless it is a combination of both tire mismatch and alignment off, which seems plausible if an impact damaged the prior tire that this one replaced. I would hope that if the rim itself was deformed that it would have been noticed when the tire was changed.

 

[Raizinman]

Your jeep is known for warping rotors quickly. The only way to tell is to take it into a shop ASAP. It is not a good idea or safe to make brake problems into a guessing game of 'guess the problem'.

 

[mindless1]

^ I don't know if Wolfgut has experienced both, but warped rotors usually feel quite different than ABS modulation sensation, as lxskllr mentioned previously.

Another thought I had was to unplug the ABS module [electrical connector]. The dash may warn of a problem then, which can temporarily be ignored, and this should prevent it from functioning so it can be seen if the effect still happens sans ABS... but I still think the thing to do next is inspect the brakes.

 

[JCH13]

It is highly unlikely that your brake discs are actually warped. The symptoms sound exactly like friction material distribution issues. See this StopTech article. While not all material maldistributions are visible, some are. It can be as subtle as this:

Or even more dramatic than this:

Edit: you can also see hot-spots on the rotor. These indicate high points on the rotor, frequently a result of lumps of friction material.

to fix this you can replace the rotors and properly bed your brakes, or scrub the rotor as described in the StopTech article and re-bed the brakes. The best way to avoid this in the future is to get a different brake pad compound and avoid the offending driving habits.

Depending on the road conditions where you live road rutting might be causing your to pull to a side. I know that it certainly does with two of my cars.

 

[mindless1]

It is highly unlikely that your brake discs are actually warped. The symptoms sound exactly like friction material distribution issues.

It's not all that unlikely. Even the article you linked, mentioned an issue, one commonly present when some kid at a shop improperly torques your lug nuts on one at a time, all the way as tight as their air wrench will go instead of using a torque wrench and proper sequence.

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.

No matter how an expert tries to state it, warping is a real thing and not uncommon. Here's another example of how information can be misleading: http://www.hendonpub.com/resources/article_archive/results/details?id=1787

Brake rotors do not warp from heat, even when driven by the most aggressive traffic officer. Instead, they wear unevenly. This uneven wear is caused by the brake pads themselves as they intermittently touch an out-of-true rotor...

... The unevenly torqued rotor, even with the correct amount of torque, will not be bent when the rotor is cold. However, as the rotor heats up in normal use, it will expand unevenly. The most uneven area will, of course, be near the first tightened and last tightened lugs. As the rotor heats up and expands, a runout will be caused, i.e., a high spot on one side and a high spot on the other side. These high spots will come into intermittent contact with the retracted pads during normal driving, i.e., without brake pedal pressure.

In other words, they don't warp from heat, except they do warp, when heated, if a certain, not uncommon situation exists.

- It is possible his rotors are warped when the pulsating happens and this is leading to uneven wear.

- It is possible they instead have material deposits, or a combination of the two, which over time has caused uneven wear.

- Neither of these things tend to pull the vehicle to one side if minor enough that the pulsating symptom disappears for most of the day as described "recently about once a day when i try to come to a full stop".

It all starts with an inspection, trying to isolate which wheel is the problem. If it's pulling to the side with the mismatched tire then I'd suspect an undersized tire compared to the rest, or drag on the brake system on that side.

If pulling to the side opposite the mismatched tire, I'd suspect a larger tire than the rest, or a brake issue on the opposite side, or in either case, a wheel misalignment. It could be a combination of any of the above.

 

[JCH13]

It's not all that unlikely. Even the article you linked, mentioned an issue, one commonly present when some kid at a shop improperly torques your lug nuts on one at a time, all the way as tight as their air wrench will go instead of using a torque wrench and proper sequence.



No matter how an expert tries to state it, warping is a real thing and not uncommon. Here's another example of how information can be misleading: http://www.hendonpub.com/resources/article_archive/results/details?id=1787



In other words, they don't warp from heat, except they do warp, when heated, if a certain, not uncommon situation exists.

- It is possible his rotors are warped when the pulsating happens and this is leading to uneven wear.

- It is possible they instead have material deposits, or a combination of the two, which over time has caused uneven wear.

- Neither of these things tend to pull the vehicle to one side if minor enough that the pulsating symptom disappears for most of the day as described "recently about once a day when i try to come to a full stop".

It all starts with an inspection, trying to isolate which wheel is the problem. If it's pulling to the side with the mismatched tire then I'd suspect an undersized tire compared to the rest, or drag on the brake system on that side.

If pulling to the side opposite the mismatched tire, I'd suspect a larger tire than the rest, or a brake issue on the opposite side, or in either case, a wheel misalignment. It could be a combination of any of the above.

I didn't see any information about the rates of brake pulsing being related to improper torquing. I find it considerably more plausible that the average driver routinely rides the brakes from a high speed to stop, such as an interstate off-ramp ending in a stop sign, than a large number of mechanics out there mis-torquing wheels. Admittedly this is a hand-waving argument. However, my experience is directly in-line with the article I linked. I've always found pad-shaped blotches of friction material on brakes where people were complaining about brake pulsing. I'm not a professional mechanic, but I do wrench more than your average bear.

A closer inspection of the rotors and their wear patterns will provide solid evidence about what is happening. If the rotor is 'warped' i.e. improperly installed, we'll see wear with a matching pattern on the back-side of the rotor (i.e. 12 o'clock on the outside, 6 o'clock on the inside). If it's pad transfer there will likely be blotches, maybe shaped like the brake pad, somewhat randomly distributed around the rotor.

Frankly, it doesn't really matter one way or the other though. The solution is the same in both situations: have the rotors turned and reinstall them, or replace the rotors outright.

FWIW - OP didn't say that the pulling was happening consistently in one direction, or even that it was happening under braking.

 

[mindless1]

I didn't see any information about the rates of brake pulsing being related to improper torquing.

It's there, read the links, or what I quoted out of one "... The unevenly torqued rotor, even with the correct amount of torque, will not be bent when the rotor is cold. However, as the rotor heats up in normal use, it will expand unevenly. "

It's fairly obvious that high and low spots cause pulsation.

I find it considerably more plausible that the average driver routinely rides the brakes from a high speed to stop, such as an interstate off-ramp ending in a stop sign, than a large number of mechanics out there mis-torquing wheels.

... and yet, they claim heat doesn't warp rotors. Riding the brakes doesn't necessarily cause a problem, if it's going from a constant speed down to a lower speed without applying gas. It's still friction enough to slow the vehicle down an appropriate amount, except spread out over time so the rotor and pad heats up less. I don't see a lot of people riding the brakes with one foot while pushing the gas pedal with the other.

Admittedly this is a hand-waving argument. However, my experience is directly in-line with the article I linked. I've always found pad-shaped blotches of friction material on brakes where people were complaining about brake pulsing. I'm not a professional mechanic, but I do wrench more than your average bear.

Rotor warp is more common on vehicles with undersized brakes, like back when they were putting 14" wheels on full sized american sedans, or 15" on supposed sports cars, but it can happen with the average vehicle driven aggressively. I almost never see those blotches pictured, but often see sort of a darker rainbow color from overheating.

A closer inspection of the rotors and their wear patterns will provide solid evidence about what is happening. If the rotor is 'warped' i.e. improperly installed, we'll see wear with a matching pattern on the back-side of the rotor (i.e. 12 o'clock on the outside, 6 o'clock on the inside). If it's pad transfer there will likely be blotches, maybe shaped like the brake pad, somewhat randomly distributed around the rotor.

Agreed, except that the pattern isn't always obvious because when warped, 2 opposing sides get more contact, but when they cool down, those are now low spots so the rest of the rotor gets more contact. Sometimes excess brake material gets deposited on the high spots, but other times it is scrubbed off.

Frankly, it doesn't really matter one way or the other though. The solution is the same in both situations: have the rotors turned and reinstall them, or replace the rotors outright.

FWIW - OP didn't say that the pulling was happening consistently in one direction, or even that it was happening under braking.

Yeah we have very little info and no inspection information... sort of a waste of time to speculate further until some attempt is made to find out what's going on. We don't even know how many miles on on the current pads and rotors, could be that it's time to replace them regardless of other symptoms.

 

[JCH13]

It's there, read the links, or what I quoted out of one "... The unevenly torqued rotor, even with the correct amount of torque, will not be bent when the rotor is cold. However, as the rotor heats up in normal use, it will expand unevenly. "

It's fairly obvious that high and low spots cause pulsation.

Read what I asked: there is nothing about the rate of causation. I believe that improper torquing can result in excessive run-out of the rotor. This is exacerbated by un-even heating of the rotor because the run-out causes extra contact/wear in a few spots. However, there is no information that says "xx% of brake pulsing symptoms are correlated to excess run-out and xx% is related to bad frictional material transfer."

... and yet, they claim heat doesn't warp rotors. Riding the brakes doesn't necessarily cause a problem, if it's going from a constant speed down to a lower speed without applying gas. It's still friction enough to slow the vehicle down an appropriate amount, except spread out over time so the rotor and pad heats up less. I don't see a lot of people riding the brakes with one foot while pushing the gas pedal with the other.

Not sure why you're talking about riding the brakes/gas at the same time...

Having stationary pads clamped on hot rotors leads to frictional material transfer, which exhibits virtually all of the same symptoms of 'warping' but the bulk metallic material of the rotor is not actually warped. There are high spots created by the extra frictional material that would measure, feel, and behave like a 'warped' rotor. It is important to recognize this as a possibility, otherwise a driver will just bitch about bad lug torquing or crappy rotors instead of changing their driving style slightly to stop the problem preemptively.

Adding heat to a part that has lots of run-out from bad clamping/fastening will exacerbate the run-out. This is what I think they mean by 'expand unevenly' which is a technically incorrect way to phrase what happens, but is more understandable to the average person.

Rotor warp is more common on vehicles with undersized brakes, like back when they were putting 14" wheels on full sized american sedans, or 15" on supposed sports cars, but it can happen with the average vehicle driven aggressively. I almost never see those blotches pictured, but often see sort of a darker rainbow color from overheating.

See above. Smaller brakes = hotter brakes = more frictional material transfer. Can have blotches that look like brake pads, but not always. Sometimes the material transfer is effectively invisible, as described in a few articles, including the StopTech one. Sometimes these high-spots of frictional material cause localized overheating.

Agreed, except that the pattern isn't always obvious because when warped, 2 opposing sides get more contact, but when they cool down, those are now low spots so the rest of the rotor gets more contact. Sometimes excess brake material gets deposited on the high spots, but other times it is scrubbed off.



Yeah we have very little info and no inspection information... sort of a waste of time to speculate further until some attempt is made to find out what's going on. We don't even know how many miles on on the current pads and rotors, could be that it's time to replace them regardless of other symptoms.

 

[mindless1]

Read what I asked: there is nothing about the rate of causation.

Your statement was too vague. Nobody has data on every vehicle and brake problem on earth, nor do any articles. I can only tell you that in fact, rotors do warp.

I find it considerably more plausible that the average driver routinely rides the brakes from a high speed to stop, such as an interstate off-ramp ending in a stop sign, than a large number of mechanics out there mis-torquing wheels.

It has been my experience that there are more instances of mis-torqued wheels than properly torqued wheels. Literally, I expect them to screw that up and am constantly encountering cases where passenger vehicles needed 200 lb ft or more to break lugs loose, and I mean soon after work was done, not after years of corrosion. They're often driving the nuts on with an impact wrench and that's all, no torque wrench involved because that's more work and takes longer, and it's not their vehicle.

Not sure why you're talking about riding the brakes/gas at the same time...

You were implying that riding the brakes matters. It is no greater stress in brakes to "ride them" to stop more gradually, than to stop faster with more pressure. Either way you're slowing the vehicle down, unless you're also giving it gas during the process.

Having stationary pads clamped on hot rotors leads to frictional material transfer, which exhibits virtually all of the same symptoms of 'warping' but the bulk metallic material of the rotor is not actually warped. There are high spots created by the extra frictional material that would measure, feel, and behave like a 'warped' rotor. It is important to recognize this as a possibility, otherwise a driver will just bitch about bad lug torquing or crappy rotors instead of changing their driving style slightly to stop the problem preemptively.

I never stated it wasn't a possibility, only that it's incorrect that brake rotor warp is uncommon. It's only uncommon in a perfect world where everything else is right, but if everything else is right then your brakes have NO problems.

Stationary pads are on hotter rotors if someone tries to stop quickly rather than gradually. I really don't know why you think riding the brakes is common anyway because vehicles have things called brake lights. I usually only see that happening when someone is tailgating, and in that case they aren't just slowing down but rather continually speeding back up too.

Adding heat to a part that has lots of run-out from bad clamping/fastening will exacerbate the run-out. This is what I think they mean by 'expand unevenly' which is a technically incorrect way to phrase what happens, but is more understandable to the average person.

A change in dimensions is warping if not a uniform expansion. People are trying to pretend it isn't, only because it's temporary while hot, but the wear and brake material deposits are evident after it cools down.

See above. Smaller brakes = hotter brakes = more frictional material transfer. Can have blotches that look like brake pads, but not always. Sometimes the material transfer is effectively invisible, as described in a few articles, including the StopTech one. Sometimes these high-spots of frictional material cause localized overheating.

Yes, you're describing one kind of problem, but failing to understand what warping is. Now we have wasted even more time on a topic that is not solving anything.

 

[JCH13]

I'm sorry that you can't take the time to slow down and comprehend what I'm writing. You clearly are fixed in your way of thinking and consider any dissenting opinion or information to be false or misleading, making further discussion pointless. Have a good day!