Bad shimmy upon heavy braking Toyota 4Runner (why?)

[Stuart A. Bronstein]

Can you help me diagnose what is causing heavy shimmy upon braking?
Do you have any idea what test to run to determine the cause?

You can narrow down which end, if a brake problem, by using
emergency brake ...

Ah, Excellent idea. I didn't think it was the rear only because they have
drum brakes and I didn't think brake shudder could be caused by drum brakes
(how?).

But this is a good isolation test if it works.

Is this the test:
- Drive on the highway in a safe spot with no traffic
- Press on the brakes (brake shimmy will occur)
- Let up on the brakes (brake shimmy stops)
- Pull hard on the emergency brake
- If the brake shimmy occurs, the problem is in the rear
- If there is no shudder, the problem is in the front

Is that the way to isolate the front from the rear as the cause of the
brake shudder?

Stu

[Stuart A. Bronstein]

The rotors were pretty flat when cold but
warped up when they got hot and caused a bad shimmy.
I replaced rotors and pads and the problem has never come back.
I do not use hard OEM pads. I use a softer aftermarket one

You may be on to something here SnoMan!

I bought the 4runner new and it has over 50K miles on it yet the pads are
thick as Ronald Reagan's hair. I was amazed at the condition of the pads
given the number of city miles that are on this vehicle (I don't take many
long trips so it's mostly around town driving). Maybe my Toyota OEM brake
pads glazed something somewhere to cause the brake shudder at highway
speeds.

Also, I had not thought about the runout being different when the rotors
are hot vs when they are cold. I guess I could drive hard and then quickly
stop and remove the wheels and check the runout but probably that is a
losing cause as they'd cool pretty quickly I'd think.

I'm getting closer and closer to just replacing the rotors and pads just to
see what happens although I don't like just replacing stuff that I didn't
diagnose as being faulty. I don't mind replacing faulty parts. But it feels
bad to replace good parts just on a whim.

Thanks for the advice.
Stu