It's a *very* common issue that's been beaten to death on these forums... but...:
(Regarding my 2001 4Runner, owned since 2003)

Long ago, I suffered "warped rotors", steering wheel shimmy during braking, getting worse and violent as the brakes heated.
Did a brake job, and it was fixed ... for a couple years ...

"Warped rotors" again, same thing. Did a S13WE TBU, and it was fixed ... for a couple years ...

"Warped rotors" again, did a 13WL TBU, and it was fixed ... for a couple years ...

So, is it really "warped rotors"?? I now suspect steering rack bushings.

Sure, right after a brake job, everything is straight, smooth, well behaved. But, after a while, things wear. Even the best disks/pads will lose their perfection.
I think as that happens, it introduces small vibrations into the steering linkage (no duh). And, the rest of the steering system can either damp out, or amplify, the vibrations.

I recently changed out my old degraded rubber steering rack bushings for new polyurethane. Unfortunately, I also did yet another brake job (disks, pads). It would have been interesting to see if the new bushings solved an existing "warped rotor" issue.

I've seen countless threads on "warped rotors" and the TBU solutions. Yeah, I thought so, too, right after the job. But, it doesn't last, IMO. I haven't seen any other thought on those topics (maybe I missed it).

I'll report back in a few years

I dont know how you drive or where to make you go through so many brake systems. I have had three 3rd gens.. The first and third had or have the TBU. I live in the hils, Ive worn out pads but not rotors. I suspect you have something else going on.

Yikes. Well, some possibilities, sticking calipers causing the rotor to overheat. Or rack bushings. You can check by prying on the rack back and forth. Or lay under the car and have a buddy w/engine off but key on turn the wheel back and forth. You'll see play.

It is almost *never* warped rotors. It is nearly always unevenly deposited pad material on the rotors. The right pads for the driving conditions will probably fix it up, as would the correct bedding procedures and minor modifications to your driving style. A minor change you can make to help - avoid coming to a complete stop at the end of a hard braking event. Nearly stop about one car length short and creep slowly with light brake pressure to 'smear' the hot friction material evenly around the rotor. Holding hot pads on one location of the rotors causes the uneven deposits.

When I got my 4Runner (it was in the family since new, Dad, then sister, then me) it had 'warped rotors' that I was able to fix with just driving style. Yes, really. I was even running the 15" wheel brakes on 32" tires, so *smaller* than the stock 16" wheel brakes.

I have since upgraded to the larger Tundra calipers - and it is nice that I don't have to be so careful about brake usage...

https://www.wilwood.com/Pdf/Misc/Pad...ding_Steps.pdf

-Charlie

I've searched and followed lots of advise. Everything I could find that seemed well thought out.

There was a superb article by a track team guy about mis-diagnosed warped rotors almost always being uneven brake deposits. Makes perfect sense. So, for the past couple times, I followed proper break-in/bedding procedures.

*No* I did not wear out my brakes these times. I got so fed up with the "warped rotor" symptoms that I was chasing a better fix. *No*, these were not sticking calipers. The calipers were swapped out with new/refurb each time.

99% of driving is on level ground and light braking. No issues present.
"Warped rotor" symptoms happen under more intense braking situations and temperature changes.

If you want to test yours, the most reliable place is driving down the East side of CA Hwy-120 Tioga-Pass from summit to Hwy-395. It's a 3000' drop in about 6 miles. Or, likewise CA Hwy-108 Sonora-Pass, about 3000' in 4.5 miles. I travel both of these passes relatively frequently.

There's exactly your issue. Your 99% driving removes the transfer layer of pad material on the rotor, then they aren't ready for the 1% conditions.

You may already know this, but engine braking is your friend, as is "pulsing" the brakes. Never hold them constantly on. Pick a 10mph or so range and brake from the topo of the speed range to the bottom each application. Similar to how the TFL Truck guys to their "worlds toughest towing test" thing...

What pads are you running (material/type)? A semi-metallic will be better for this, probably...

And that is a fun grade... Haven't had the pleasure in the 4Runner yet, but have done it in other cars.

-Charlie

Have your rear brakes ever been touched? Often conveniently forgotten on these since drums suck.

T4R2014: Yes, I did my rear brakes probably around the time of the first TBU because of a leaking axle seal and oil saturated shoe. Are you saying this could introduce steering wheel shimmy somehow?

phattyduck: Ever since reading the detailed article on brake deposits and proper bedding (2009'ish), I've been very conscious of standing with hot brakes. In those possible situations, I do try to keep slow rolling. But, I'm skeptical of your diagnosis. If true, then almost every vehicle on the road has this problem. I'd bet that if you asked 10,000 drivers, only a few would even know that's a thing. And, I've driven my wife's old Honda Civic, and been passenger in other cars, over those passes with no noticeable issues.

I am convinced 4Runners (3rd gen) suffer a high rate of "warped rotor" steering shimmy problems. That's pretty well documented. The overwhelming response is that the front brake system is under-sized. Solution = TBU. I just don't buy that, anymore. A TBU is an excellent upgrade. It's just not usually the primary culprit or fix for this problem (IMHO, YMMV).

Is there any rust on the hub, where the rotor sits? And between the rotor and wheel? Lug nuts torqued?

No. No. Yes.

Yes, the 3rd gen 4Runner does have undersized brakes (especially compared to anything more modern - it was 'ok' at the time it was designed). Upgrading the brakes does make it much less likely to overheat the brakes and risk the wobbles. I'm happy that I no longer have to pay attention to this with the TBU.

My 4Runner (before I got it) 'warped' rotors all the time. After I got it, without changing the brakes and adding a bunch of weight and larger wheels/tires never 'warped' them again... Ok, actually - I could get them to start the 'wobble' after a single hard braking event on the freeway (coming off down a downhill offramp) - and it took some work to get them smooth again over the next drive or two.

This effect is also highly dependent on pad material. When the pads are matched to the driving conditions, the 'warping' issue is much reduced...

And TONs of cars have this issue. Our Odyssey is known to 'warp' rotors too and it is ~15 years newer. More aggressive pads (semi-metallics) is usually the longest lasting fix. More dust on the wheels and noise, but those pads rely less on the even transfer layer that ceramic pads require. But again, I still run the factory pads with no issues there...

-Charlie