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

Can you help me diagnose what is causing heavy shimmy upon braking?

My '98 4Runner 2WD with about 50K miles is vibrating heavily when braking
at highway speeds. It does not vibrate under any other conditions.

The cause is perplexing me.
Here is all that I know.

- The 2WD 4Runner is not equipped with ABS braking
- The four wheel alignment was done about two years ago
- New tires about a year ago were dynamically balanced when mounted
- The front rotors are smooth with only a single circular scratch in one
- That one rotor scratch is so thin a pen tip won't even catch on it
- The rotors are 0.860 & 0.855 inches thick (min=0.787 inches)
- The pads are about 1/4 inch thick (minimum = 0.039 inches)
- Disk runout was 0.002 & 0.0025 inches (min=0.0028 inches)
- The rear brake drums were not checked
- I did not perform any other tests as I don't know of any other tests

One wierd thing happened while checking disk runout. There was a repeatable
half of a thousanth of an inch "blip" when I rotated the rotors. It was
always in the same spot on the passenger side rotor. I could hear a
scratching sound for a second when I saw the blip on the dial guage. Funny
thing was I could not see any "dent" or imperfection in the rotor at that
point. This rotor wasn't even the scratched rotor so it looked nearly brand
new (even after 50K miles).

Other than that blip, everything seemed normal.

At first I checked runout without removing the pads and without putting the
lug nuts on but the runout was changing until I realized the rotors were
only held on by the lug nuts so I removed the pads and jammed a screwdriver
into the rotor fins so I could torque down (83 foot pounds) the lug nuts
with a washer to prevent cracking the disks.

Do you have any idea what test to run to determine the cause of vibration?

Stu

Sounds like rotors, and it sound like you found your problem with that .005
thickness variation spot on the passenger side rotor you described.

>> Can you help me diagnose what is causing heavy shimmy upon braking?[color=blue][color=green]
>> Do you have any idea what test to run to determine the cause?[/color][/color]
[color=blue]
> You can narrow down which end, if a brake problem, by using
> emergency brake ...[/color]

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

SnoMan <admin@snoman.com> wrote in
news:52s802tsvtenr8i19cu4e4ihqfktv7h0bv@4ax.com:[color=blue]
> 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[/color]

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

"Shep" <djsljsrn@capital.net> wrote in
news:1141136768_9125@sp6iad.superfeed.net:
[color=blue]
> Could also check for rotor thickness variation.[/color]

Thanks Shep.
I did check only one spot since the rotors seemed in good shape visually.
That was when I still suspected runout but when I checked runout, it was
within spec (0.0028 inches).

In hind sight, I should have mic'd the rotors in multiple spots. I did put
a vernier caliper on the rotor but all that did was get the high spot.

I think I'll remove the wheels and mic the rotors in multiple spots again
but this time I think I'll remove the caliper (it's only four bolts ...
these Toyota 4-piston front calipers are beautiful to work on) so I can get
a good spot on the rotor.

Come to think of it, I may as well remove the rotor itself if I remove the
caliper as there is nothing holding them on (it's a 2WD 4Runner) at that
point. Then I can mic it all over the place.

Thanks for the advice, I know what I'll be doing this Saturday!
Stu

"sdlomi2" <sdlomi2@spam.yahoo.com> wrote in
news:gOWMf.1994$Xx6.141@fe06.lga:[color=blue]
> You can narrow down which end, if a brake problem, by using
> the emergency brake--BE CAREFUL--to slow vehicle.
> If shimmy still shows, it's the rear brakes; else, it's the front.[/color]

When I tried this test to isolate whether the brake shudder is coming from
the front or the rear todayI almost skidded out of control. Luckily nobody
was near me and the road was five lanes where I tested it.

I guess I should've waited until the roads were dry (I don't have ABS and
it's been raining for a while now). I'll try again when the roads are dry.

While I'm waiting, do you guys get your brake rotors and pads and shims
from the dealer or do you get them elsewhere? Any recommended Internet
suppliers for northern California?

I looked on froogle for pads, hardware, & rotors for:
- 1998 Toyota 4Runner 2WD 3RZ-FE stock everything
and I found a WIDE range of suppliers, Brembo, RayBestos, Akebono, EBC,
Hawk, etc.

Do you guys go to the dealer for OEM spec brake pads & rotors or do you
have a favorite internet supplier I can order from. Which brand do you go
for?

Thanks,
Stu

Don <don@NO-SPAMdonsautomotive.com> wrote in
news:ol5a0254f3rlqqiaitr3ku60bgomtpnovd@4ax.com:[color=blue][color=green]
>>Do you have any idea what test to determine the cause of shimmy?[/color]
> A half thousandth thickness variation will induce brake pulsation.
> Check the rear drums unless the problem includes steering wheel wobble
> induced while braking in which case it is the front brakes for sure.
> You can check the rears by applying the parking brake at speed.[/color]

Thanks Don for your advice and thanks everyone else too!
I had never thought of these two tests:
- Use the rear brake to isolate the location of the shimmy
- Note whether the steering wheel or just the brakes are affected

After test driving just now I can emphatically say that not only does the
shuddering not occur with the rear wheels, but, with all this rain, I would
never recommend jamming on the rear brake at speed on the freeway as I
skidded sideways more than a few times during my 80 mph tests.

Also, the Toyota high-speed brake shudder DOES affect the steering wheel,
although I can feel the front end body of the 4Runner shake with the seat
of my pants more than I can feel it in the steering wheel. Still, I can
feel the shimmy ever so slightly in the steering wheel.

So, now it's time to turn them or replace them. I'm inclined to replace the
Toyota rotors as they've got 50,000 miles on them already and that's more
than they typically last according to the Toyota dealership when I priced
them today.
[color=blue]
> Buy quality rotors such as Mountain or Brembo brand or Toyota OEM.
> Rotors should NOT be resurfaced out of the box.
> Shipping and handling does NOT knock rotors out of round[/color]

I hate to buy without knowing what I'm buying. I already know there is no
government or private standard for brake pads so they could put toilet
paper in there and call it friction material. It's all advertising.

Is it the same with rotors? Is there a government or private standard for
rotors that I can rely on (like that of tires, oils, greases, etc.)?

Stu

"Beloved Leader" <Kim_Jong_Il@volcanomail.com> wrote in
news:1141225411.516053.262350@e56g2000cwe.googlegroups.com:
[color=blue]
> Brake fluid has a FMVSS number stated on every container. I
> find it unlikely that brake pad material does not have to conform to a
> FMVSS too.[/color]

AFAIK, there is a standard for almost everything EXCEPT brake friction
materials and rotors.
[url]http://www.nhtsa.gov/cars/rules/standards/FMVSS-[/url]
Regs/pages/Part571SD101to139.htm

From my research, it seems there are braking (not brake, but braking)
standards which are sometimes not met. For example, the National Highway
Traffic Safety Administration (NHTSA) Vehicle Research Test Center (VRTC)
has reported evidence of rotors losing their ABS tone ring tooth profile
due to corrosion causing the ABS to fail.

REF: [url]http://www.doe.state.in.us/safety/pdf/ODINotice-prn.pdf[/url]

That article refers to a FMVSS 105 which is apparently a braking standard,
not a brake pad or rotor standard. Digging more, I see mention of an FMVSS
135 brake performance standard but again, it seems these standards are for
the braking operation of a new vehicle, and not for replacement pads and
rotors.

REF [url]http://www.741limo.com/show_press.cfm?press_id=3[/url]

Now that I know the braking performance standard, I found a description at
for FMVSS 105 at
[url]http://www.nhtsa.gov/cars/rules/standards/FMVSS-Regs/index.htm[/url]

Given that there are no standards to protect the consumer, and given that
that means (by definition) that there is nothing to protect the consumer
from shoddy materials, does anyone have a recommended trustworthy honest
Internet supplier of Toyota friction materials and rotors?

I'm going to replace the pads and rotors and the wheel bearings just to
ensure I get rid of this horrible 4Runner rattle & wobble when I brake.

Stu

Scott in Florida <MoveOn@outa.here> wrote in
news:r4sd021jt2n4c17kj8ej61jugk1efvcj73@4ax.com:[color=blue]
> Your local Toyota dealer....or if price is a problem....order from a
> Toyota dealer that sells via the Internet.[/color]

Based on the Babcox ([url]http://www.babcox.com/editorial/bf/bf100326.htm[/url]) and
PerformanceOil ([url]http://www.performanceoiltechnology.com/brakingsystems.htm[/url])
articles, it seems going OEM is the ONLY way.

For example, we could go to the local parts store and ask for ceramics and
get the exact same pads as someone who asks for semi-metallics!

That makes the local parts store useless from a trust standpoint.
It leaves only OEM at the dealership.

For my Nissan, there is one dealership in the USA that stands above all
others in garnering the loyalty and trust of those who work on their own
cars. This dealership of choice sells Nissan/Infiniti parts for 20% to 40%
lower than any other dealership in America (including tax and shipping),
and is the dealership of choice that we all partonize. We want HIM to stay
in business because he actually cares about US (I've spoken to him many
times and he's great!).

Is there a similar Internet dealership of choice who actually cares enough
about us in the Toyota/Lexus world to give us the mechanic's discount every
day?

Stu