Front brakes get hot on highway.

Outdoors_Guy_88 · April 15, 2023

2015 K1500 Sierra with 5.3L

Driving around town in stop and go traffic, my brakes seem fine. Nice smooth firm pedal.

If I get on a highway and drive more than 10 miles and as I slow down to get off at an exit, I get brake pulsation, like a warped rotor. I check and only the front brakes are hotter than usual, but not smoking. I am guessing slightly overheated brakes in front, (but I was cruising on the highway and not using them). I don't notice and real dragging or pulling to one side. Everything seems OK at low speeds. No pedal pulsation and overheating after driving a couple miles under 40 mph.

I already pulled both front calipers and pads. I removed, cleaned and regreased the calipers and caliper pins with the green high-temp caliper grease. Only 1 was a little sticky. Pads were good.

I reassembled and still the same problem persists. Funny how it seems to be both front wheels. The drivers side seems slightly hotter.

Any other parts that I could check why the fronts seem to be getting hot?

Brake fluid level is good, clean, and not low or losing fluid. Suggestions where to look next?

I have a new set of OEM pads and rotors, but I am reluctant to put them on, because nothing looks wrong with the current ones. They are at 75% thickness.

Edited April 16, 2023 by Outdoors_Guy_88

mikeyk101 · April 17, 2023

Is it possible there are aftermarket pads on there?

A couple months back, I tried to save a few dollars and went with front brake pads from O'Reilly's. That turned out to be a big mistake. I had same issue but it was obvious the pads were not releasing from the rotors. They were what I felt was to tight when fitting into the caliper mounting bracket. I had some smoke coming out of the wheel wells and could smell the heated brake pads. I then thought maybe the brake caliper mounts were the issue so I bought some remanufactured ones and the fitment of the pads was still an issue. I took the pads back to O'Reilly's as they had a lifetime warranty and exchanged them. This replacement set fit a lot better but not perfect. These to wouldn't fully release and would still drag a bit. I gave up on those and purchased OEM pads and right from the beginning, they fit like they should. Lesson learned, problem solved but ended up costing a lot more than if I had just gone OEM in the beginning. At least I had the good sense to go with OEM rotors...

Outdoors_Guy_88 · April 17, 2023

Thanks for the suggestion. Pads and rotors are all OEM (They are only 1 year old.) and calipers are original. I pulled the calipers and pads about 3 months ago due to the same problem and checked the fit in the shims and greasing (for debris and dirt. Still moved well and only 1 caliper pin was a little sticky. I also pressed the caliper pistons in at that time and they move fine (and no leakage)

I now have found several posts on here now about front brakes freezing. So it appears to be a common problem. I am now suspecting bad flex lines or something in the hydraulic system. Also strange how it happened to both front brakes at the same time.

KARNUT · April 17, 2023

I had a similar problem on a 20 year old Chevy Silverado. After replacing everything else the only thing left was the brake lines to the calipers. It threw me off because it was both at the same time.

Outdoors_Guy_88 · April 18, 2023

14 hours ago, KARNUT said:

I had a similar problem on a 20 year old Chevy Silverado. After replacing everything else the only thing left was the brake lines to the calipers. It threw me off because it was both at the same time.

@KARNUT Any good way to tell if it is the flexible brake lines or the calipers? I'll definitely replace the lines, but I hate to trash good calipers, because they seem to retract smooth without binding when I press them back in.

The "Hill Start" assist system could possibly be another bad item. If that system can apply the brakes, then it also has the possibility of not releasing all the way. Anyone know if Hill Assist is front or rear or both? (Or any troubleshooting)?

KARNUT · April 18, 2023

15 minutes ago, Outdoors_Guy_88 said:

@KARNUT Any good way to tell if it is the flexible brake lines or the calipers? I'll definitely replace the lines, but I hate to trash good calipers, because they seem to retract smooth without binding when I press them back in.

The "Hill Start" assist system could possibly be another bad item. If that system can apply the brakes, then it also has the possibility of not releasing all the way. Anyone know if Hill Assist is front or rear or both? (Or any troubleshooting)?

I’ve owned many vehicles. That’s the first time I encountered that problem. It was the first time I’ve even had replaced calipers. Even though it wasn’t the problem. I don’t have much experience with hill assist only that I had a rental once in a hilly area. It down shifted when I was going down a mountain pass.

mikeyk101 · April 18, 2023

3 minutes ago, KARNUT said:

I don’t have much experience with hill assist only that I had a rental once in a hilly area. It down shifted when I was going down a mountain pass.

I believe you are thinking about hill descent control. Hill assist is different. It happens when you are stopped at an uphill angle with brakes on. When you release the brakes, hill assist will continue to hold the brakes until you start to accelerate to keep from rolling backwards.

Grumpy Bear · April 18, 2023

:lurk:

KARNUT · April 18, 2023

8 hours ago, mikeyk101 said:

I believe you are thinking about hill descent control. Hill assist is different. It happens when you are stopped at an uphill angle with brakes on. When you release the brakes, hill assist will continue to hold the brakes until you start to accelerate to keep from rolling backwards.

Ok, I don’t notice if I ever did. Once pass antilock brakes they have too many driver assist for me.

asilverblazer · April 18, 2023

Are you sure its not just a warped rotor and you just aren't noticing it at lower speeds?

How do you know the front brakes are hotter than 'normal'?

Outdoors_Guy_88 · April 18, 2023

7 hours ago, asilverblazer said:

Are you sure its not just a warped rotor and you just aren't noticing it at lower speeds?

How do you know the front brakes are hotter than 'normal'?

If I accelerate to 65 mph and then slow down immediately, this doesn't happen. If I drive 10 miles on the highway and then slow down, the pedal pulsates until the brakes cool off. Driving at 40 mph or less doesn't seem to heat them up to cause vibration. Driving 1/2 hour at 55 mph just starts to cause it. Driving several miles at 65 mph causes it whenever I exit. (This is cruising and then gentle braking on the exit ramp, not hard braking).

They pulse/vibrate (like a warped disc) when I am slowing down on an exit ramp and at the first stop or two. I get out and I can feel the heat coming off of them and the stock steel wheels are hot to the touch. I also checked with an IR gun. If I pull over and stop for 5-10 minutes, the pulsation is gone. When I drive 10 miles in stop and go city traffic they don't seem to get hot (just warm like normal brakes) and no pedal vibration, even though I am actually using the brakes more.

Seems they only drag enough to generate significant heat at highway speeds. Like they just aren't quite releasing.

Edited April 18, 2023 by Outdoors_Guy_88
more information.

asilverblazer · April 19, 2023

19 hours ago, Outdoors_Guy_88 said:

If I accelerate to 65 mph and then slow down immediately, this doesn't happen. If I drive 10 miles on the highway and then slow down, the pedal pulsates until the brakes cool off... Driving several miles at 65 mph causes it whenever I exit. (This is cruising and then gentle braking on the exit ramp, not hard braking).

I would try to more controlled testing to get some more concrete data/temperatures.

A set of 'cold' tests; first record temperature prior to starting, drive 1 mile at 65 mph stop with "x" amount of pressure or within "y" feet. Record temperature, then let brakes cool to beginning temperature and repeat several times. Record all the temperatures and pulsation experienced.

A set of 'hot' tests; first record temperature prior to starting, drive 10 miles at 65 mph stop with "x" amount of pressure from previous test or within "y" feet, same as above. Record temperature, then let brakes cool to beginning temperature and repeat several times. Record all the rotors temperatures and pulsation experienced.

ANY brake applications other than the application to stop voids that test.

The only difference between the test is the time/distance at 65mph for the brakes to heat up prior to stopping.

If the brakes are dragging, the 'hot' test will show a repeatable measurable difference in temperature.

How does each side compare to the other, is one side heating up more than the other? You mentioned the drivers side seeming hotter and a sticky pin, but not where it was. Your tests above should confirm this.

What are the rear brakes doing temperature wise?

Then - How does this compare to another truck? Run the same test in a loaner, rental, test drive, buddy's truck as similar to your own as possible. The comparable truck will either not drag like yours or build up heat like yours.

If your truck is heating the brakes more than another - the calipers and guides or collapsing brake line are the likely component in the braking system that could cause it. Also, could something be preventing the proper amount of air getting to the rotors to cool them off? Aftermarket wheels, modifications that would alter the aerodynamics...

If your truck isn't heating the brakes up more, are your parts more susceptible to 'something' causing a vibration due to 'normal' heat build up than others? The pads might have something in them that cause normal heat to make them 'stickier' or the rotors might be warping abnormally... in either case, parts changing, again, would be the only solution.

The test/temperatures will tell us a bunch more to diagnose.

Edited April 19, 2023 by asilverblazer

swathdiver · April 19, 2023

@Outdoors_Guy_88

Did you use a thermal temperature gun to measure the differences between cold and hot, normal and abnormal?

How many miles on the truck?

I did rotors and pads for the 2nd time on one of mine (135K) and then a year later (154K) had a piston get stuck in one caliper that smoked the brakes. Had to do it all over again and with new lines and calipers and while apart, rebuilt the rear calipers.

These trucks last so long and can be driven so far that clean brake fluid is essential to proper operation and longevity.

Outdoors_Guy_88 · May 15, 2023

Problem solved. Bad flex lines on both front brakes at 60 k miles. Replaced flex lines, calipers (solid rubber-like particles were coming out with the fluid from the driver side bleeder, so I didn't trust them and replaced the calipers),

(and also replaced the fairly new rotors and pads due to overheating the sticking pads caused). Pads were probably OK, but decided not to chance it.

The driver side flex line was so constricted that no fluid would flow by gravity down from the master cylinder when I pulled the calipers - It did drip at the rigid line once I pulled the bad flex line.

Replaced it all, bleed the system, gravity, first, then the 2-person method and good to go. Still working after 2 days driving.

KARNUT · May 15, 2023

1 hour ago, Outdoors_Guy_88 said:

Problem solved. Bad flex lines on both front brakes at 60 k miles. Replaced flex lines, calipers (solid rubber-like particles were coming out with the fluid from the driver side bleeder, so I didn't trust them and replaced the calipers),

(and also replaced the fairly new rotors and pads due to overheating the sticking pads caused). Pads were probably OK, but decided not to chance it.

The driver side flex line was so constricted that no fluid would flow by gravity down from the master cylinder when I pulled the calipers - It did drip at the rigid line once I pulled the bad flex line.

Replaced it all, bleed the system, gravity, first, then the 2-person method and good to go. Still working after 2 days driving.

Yup, just as I thought