Dangerous brake pulsing on long downhills

[swild]

When descending significant grades at altitude, like 8% grade for 10 miles at 7,000+ feet, my GX front and rear brakes will pulse when I apply the brakes. It's so bad it feels dangerous. The steering wheel wobbles, and the rear bounces. I had to shift into Sport mode, downshift, and use engine braking to keep the brakes from going wild.

What do you think is overheating? The rotors? The fluid?

 

[Poop Bubbles]

You should always be downshifting in that scenario, whether your brakes are pulsing or not. This keeps them from overheating which is more than likely what is happening. Once you have overheated rotors a few times, it's very hard to get rid of this pulsing. It could be pad buildup on the rotors, but given your description I doubt it.

 

[swild]

You should always be downshifting in that scenario, whether your brakes are pulsing or not. This keeps them from overheating which is more than likely what is happening. Once you have overheated rotors a few times, it's very hard to get rid of this pulsing. It could be pad buildup on the rotors, but given your description I doubt it.

But what was making the pulsing? The rotors? Boiling water in the fluid? I haven't changed the brake fluid in about 4.5 years.

 

[Poop Bubbles]

It's the rotors more than likely. Old, overheated fluid won't pulse... it just won't hold pressure as well.

 

[swild]

It's the rotors more than likely. Old, overheated fluid won't pulse... it just won't hold pressure as well.

Damn. I replaced the front rotors about a year ago too.

I'm starting to think the brakes on the GX aren't up to par with other SUV's I've driven on that same road.

 

[Arailt]

I think GXs have an inherent problem with the front brakes. It's one of the few flaws in the design. I've changed my front brakes twice and I still get brake pulsing from time to time. Not all the time, but easily a few times a week. I remember it being worse in Pagosa Springs last March, in scenarios like you describe. Friends of mine with GXs and 5th gen 4Runners experience the same thing. I have one buddy who swapped out the factory rotors and calipers for aftermarket units. He said that fixed the issue.

 

[Poop Bubbles]

Damn. I replaced the front rotors about a year ago too.

I'm starting to think the brakes on the GX aren't up to par with other SUV's I've driven on that same road.

What brand rotors did you use?

I had a lot of pulsing, was swapping pads or rotors annually.. then I switched to the Powerstop rotors and Z36 pads. No issues yet.

Regardless of brake brand/age, you should be downshifting on steep grades. This is heavy vehicle driving 101.

 

[swild]

I replaced the OEM rotors with OEM rotors.

I've heard other GX owners talk about wimpy brakes on the GX, and now I believe it. I've taken Surburbans down this grade multiple times, loaded with people and gear, and never had to use engine braking.

 

[xychromosome]

I'm on OEM rotors and pads and I get that pulsing/shudder from time to time. I think it's more to do with uneven brake pad residue that builds up over time. I go through a 'bed-in' process from time to time which seems to help. Basically get the brakes hot by doing a series of hard stops from speed. Of course, a straight empty road is the best place to do this!

Watching GX Bob's brake service video where he talks about the importance of replacing caliper pins and clips may also play a role as well.

 

[jdam]

I replaced the OEM rotors with OEM rotors.

I've heard other GX owners talk about wimpy brakes on the GX, and now I believe it. I've taken Surburbans down this grade multiple times, loaded with people and gear, and never had to use engine braking.

I don't think it has to do with brake size - they're adequate for the job. It's more that IFS Toyotas are sensitive to rotational balance in the front. I'd either get the rotors replaced or turned, then learn the proper process for rebedding. You can also get higher temp brake pads which will help.

You can build up deposits on the rotors by dragging the brakes for long periods which gets them super hot, then if you stop at all, the pads start to adhere to the hot rotor and build up unevenly on the rotor.

 

[swild]

When I bought the GX almost 4 years ago, the front rotors had to be warped as they pulsed whenever I braked.
I replaced the rotors and did the bed-in process to a T. I've had zero problems until this trip and started braking on steep long grades.

 

[TheBussman]

it's the rotors, on these trucks sometimes i have to go back and cut the rotors an extra time during the pads life. usually it's just the front. Hopefully you have a good place that can turn them for you.

 

[r2m]

That pulsing and shaky steering wheel absolutely is your rotors. It will also affect your ABS and cause to to skid rather than control your braking. Ask me how I know.
And yes, it does seem the GX's are kind of hard on brakes. I never have to replace brakes but have had to turn (true) my brakes once already in 5 years.
You don't need to replace the rotors if they're only a year old, you just need to true them. Should cost about $100.00 for all 4 rotors.

When you get the trued, THEN, when you're on a down hill grade, slap your shifter to the left and start bumping it up and down for manual shifting.
I've become so use to this I sometimes even use it to slow down when coming to a stop from freeway speeds or down hills.
I always have the lever to the left and am sifting when I'm in the mountains on grades and/or off roading.
Part of it is, I miss manual transmissions, but also for saving the brakes.

 

[ericm979]

When descending significant grades at altitude, like 8% grade for 10 miles at 7,000+ feet, my GX front and rear brakes will pulse when I apply the brakes. It's so bad it feels dangerous. The steering wheel wobbles, and the rear bounces. I had to shift into Sport mode, downshift, and use engine braking to keep the brakes from going wild.

What do you think is overheating? The rotors? The fluid?

You should be downshifting on grades like that even when your brakes are perfect!

You have warped rotors. Probably one or both front rotors. Mine did that when I bought it even though the rotors and pads were not worn much. I replaced the rotors and pads and bedded the brakes in properly. No shudder and it stops much better too.

It can be tough to find a shop that will remove, turn and replace rotors. You might be able to find a machine shop that will turn them if you bring them in but even that is tough these days. OE rotors are well under $100 each.

 

[ace10]

Which wheel/tire combo are you running?

 

[185]

I would do a brake inspection. Check for irregular pad transfer, check the the runnout on the hub and rotor surface, and generally inspect the calliper for failure or need of a good r&r service.

Sometimes its simple as some missing lubrication but other times its time for new parts. But dont just assume its this part or that.

Fluid boiling over simply equals loss of braking performance or look for an exit. Lexus has this pegged at 3/36 interval change.
Rear bouncing is weird phenomom, really dont know if thats a bad description, or indicative of something like a sticking caliper or handbrake, but you will find out with the brake inspection.

Side note
Toyota is known to undersize their braking parts, in an effort of cost reduction and gaining mpgs. That kind of elevation drop, i would try to also consider upfitting brake rotor size, and going metal brake pads rather then ceramic. More dust but improved performance.

 

[xychromosome]

Wouldn't bother with turning or machining the rotors. They are only ~$70 each at Bell Lexus and a set of news pads are about the same price. They were even cheaper at their last sale a month ago.

 

[swild]

Which wheel/tire combo are you running?

Stock rims and Michelin Defenders. All stock sizes.

 

[Arailt]

Wouldn't bother with turning or machining the rotors. They are only ~$70 each at Bell Lexus and a set of news pads are about the same price. They were even cheaper at their last sale a month ago.

I installed new factory rotors and pads on mine early this year. Old ones had like 60k. Same pulsing happened in my new rotors after a few thousand miles, and I don't drive aggressively or do anything crazy that would cause that kind of uneven wear. My tires are road force balanced. Butter smooth. Nothing out of the ordinary.

 

[Poop Bubbles]

I replaced the OEM rotors with OEM rotors.

I've heard other GX owners talk about wimpy brakes on the GX, and now I believe it. I've taken Surburbans down this grade multiple times, loaded with people and gear, and never had to use engine braking.

Did you break them in properly with new pads? Different pads have different break in periods and it all has to do with bedding them on the rotors.

Performance pads usually call for heavy acceleration/full stop full force braking over and over (high, fast heat).

Passenger pads usually call for slow heating, accelerate to 45, slow to 25 over and over.

Always follow the instructions included with the pads. If they don't include instructions on break-in, find better pads.

I installed Z36 pads and powerstop slotted rotors on mine. It's been smooth sailing with good braking ever since. I'm also about 1,000 lbs over on curb weight. They do get residue on them from time to time and pulse.. after dragging the brake for a ½ mile or so it goes away. It's happened twice in 10k miles with very frequent trips up and down I-70 West of Denver.