I've looked at numerous past threads on this issue, but there's very little that's definitive from people who have actually fixed the problem themselves. A lot of opinions on what causes it.

Any help before I invest serious dollars.

The problem: When braking at highway speed, shimmy from front end which shakes the steering wheel back and forth. Most noticeable when going downhill (50 – 70 mph or so) and applying light to moderate braking to reduce speed. Does not pull to either side. Steering wheel shales fairly violently (enough that its a little scary), but the vehicle doesn't really shake.

Notably, a very similar steering wheel shake at low speed (5 mph or less) on dirt with minor bumps/washboards. Wheel shakes more than would be expected form the road conditions.

Tires recently roteted and balanced. Vehicle tracks straight on pavement. No vibration at any speed when not braking. Vehicle has 250K miles, Dobinson's suspension and new LCAs installed a couple of years ago. Front brakes done and left caliper replaced about 30K ago.

Brakes? Suspension? Steering? Where to start? I recognize that this may become a series of fixes.

Worn parts. Replace anything worn.

If you haven't replaced your rotors when you did the front brakes, start there. I would stick with OEM or brembo blanks.

There is an interesting app called Smoothride Pro by Pro-Cut that might give you some information. It helps distinguish between rotor thickiness variation (i.e. warped rotors) and wheel balance issues. Have used it and found it to be pretty accurate. Good to use it to get a baseline before you have issues but suggest you give it a go. Kind of sounds like rotor related issue. If you replace them, clean the hub well and verify rotor run-out in spec with a dial indicator.

Smoothride PRO | Pro-Cut On Car Brake Lathes

Anything in particular? At 20 years and a quarter million miles there’s a lot of worn parts…

Have you checked for frozen calipers? These 4th Gens eat stock or auto zone type. I went with Powerstops my last round and haven’t looked back.

Also, could be a hub going bad.. Around 200K the average on them. If you do one, do both.. But these normally make noise when going bad.

All Worn Parts.
MAGA!

I had a mild wiggle on braking, with zero noticeable play when I jacked it up and shook the wheel/tire. I'd also replaced all bushings + ball joints + the shock + pads/rotors/calipers in the last 5k or so to help improve the ride and that brake issue persisted.


Finally replaced both front hubs and ta-daa, the issue was gone immediately and the bearings were definitely crusty and slightly corroded when I got them out to look. Given the age/mileage mentioned here I'd be checking tie rods, and strongly considering either pulling a hub to check or just replacing them for the hell of it.

Classic cause is rotor problems. Usually by switching brands of pads and not turning rotors to get old pad material off. You could have an pad material uneven buildup on your rotors -often called warped rotors.
Also bed-in your pads on refinished rotors to apply an even coating of pad material onto rotors.
My 2 cents.

Also had a similar issue at very similar conditions to yours (shimmy when braking at speed).

Turned out my upper control arm (JBAs) ball joints and bushings were worn. I could feel a bit of play through the steering knuckle.

Replaced both and things felt tight again.

My vote goes to a sticking front caliper piston/uneven inside/outside rotor wear. Also, torque the wheel nuts by hand with a torque wrench set to 83 ft.-lbs.

Same symptoms. Sticky calipers. Powerstops solve it

This sounds like warped brake rotors: you can take them to an auto shop and have them measure the run-out and potentially face them.

Or you can buy new rotors.

I had a similar issue, rotors are worn most likely and I would check for a seized caliper as well. Power stop makes a great replacement caliper.

I had a powerstop caliper seize up after only 2 years. The red is real pretty but I learned my lesson... only OEM for me if available.