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

> 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?

I forgot to mention that I evenly torqued down all six lug nuts to around
90 foot pounds (the specs call for 84 foot pounds but I can't get that
close of a granularity with my bending-bar-style torque wrench).

There is SOMETHING causing that vibration.

I guess I could shoot in the dark and have the rotors turned or replaced.
I don't mind that if they were the culprit. Or, I could shoot again and
have the alignment and wheel balancing done again.

But, like most of us, I'd like to actually diagnose what the CAUSE of the
problem is before I just start replacing & aligning stuff.

Any ideas how to diagnose the cause of a shimmy that only occurs during
breaking at highway speeds (it does not occur during normal around-town
driving).

Thanks in advance for your advice,
Stu

"Shep" > wrote in
:

> Could also check for rotor thickness variation.

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" > wrote in
:
> 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.

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 > wrote in
news
>>Do you have any idea what test to determine the cause of shimmy?
> 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.

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.

> 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

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

MB "> wrote in
news
> Are you sure your rotors are not warped?

Apparently rotors don't warp.

What people think is warped rotors isn't warped rotors.

I found that phD discussion he
http://www.performanceoiltechnology....ingsystems.htm

Now I have to rethink the cause and cure of my wobbly braking.

Stu

Scott in Florida > wrote in
:
> Your local Toyota dealer....or if price is a problem....order from a
> Toyota dealer that sells via the Internet.

Based on the Babcox (http://www.babcox.com/editorial/bf/bf100326.htm) and
PerformanceOil (http://www.performanceoiltechnology....ingsystems.htm)
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

Skip > wrote in
:

> My 2000 Tundra developed the same thing, starting at about 35,000
> miles. I asked the Toyota dealer's service manager about it and was
> told that some of the Tundras had brake systems that were too light
> duty for the PU. He also told me there was a TSB on the problem

I couldn't find that Toyota TSB for the 1998 4Runner but I did find that
the main cause of brake shimmy is brake material buildup on the rotors.

http://www.zeckhausen.com/avoiding_brake_judder.htm
says "Despite the popular myth, brake judder is not caused by warped
rotors. Judder is the result of a thickness variation in pad buildup on
the rotors' surfaces."

So, I'm replacing the pads and rotors but that is not a long term solution.
I need to find how to test and eliminate the four pistons from sticking in
the caliper. Pads won't solve the problem. Since nobody can tell the
quality of aftermarket pads (which was proven in the preceeding threads)
I'm going OEM (it's the only way one can go and have any given truth) which
means the brake shudder will likely re-occur at the 50,000 mile mark
regularly unfortunately.

There's no other way as far as we can see yet.
Stu

"Stuart A. Bronstein" > wrote in message
. com...
> Skip > wrote in
> :
>
>> My 2000 Tundra developed the same thing, starting at about 35,000
>> miles. I asked the Toyota dealer's service manager about it and was
>> told that some of the Tundras had brake systems that were too light
>> duty for the PU. He also told me there was a TSB on the problem
>
> I couldn't find that Toyota TSB for the 1998 4Runner but I did find that
> the main cause of brake shimmy is brake material buildup on the rotors.
>
> http://www.zeckhausen.com/avoiding_brake_judder.htm
> says "Despite the popular myth, brake judder is not caused by warped
> rotors. Judder is the result of a thickness variation in pad buildup on
> the rotors' surfaces."

That site is talking about a problem when you change from
street brakepads to racing brakepads without changing the rotors.
If you are not doing such, it is simply not a cause for your problem.

Brake rotors DO warp.
The "warping" also known as "lateral runout", is caused mostly
by an incorrect tightening of lugnuts when a tire/wheel is changed.

It can also (rarely) be caused by overheating in areas where the rotor
has a problem with uneven cooling such as blocked vent holes in some rotor
styles.


> So, I'm replacing the pads and rotors but that is not a long term
> solution.
> I need to find how to test and eliminate the four pistons from sticking in
> the caliper. Pads won't solve the problem. Since nobody can tell the
> quality of aftermarket pads (which was proven in the preceeding threads)
> I'm going OEM (it's the only way one can go and have any given truth)
> which
> means the brake shudder will likely re-occur at the 50,000 mile mark
> regularly unfortunately.

If a proper brakejob is done, and you ALWAYS tighten lugnuts correctly.
no problem will arise later except the fact you will need
to replace worn pads and "worn" rotors. (usually pads only if no excess
wear of the rotors has occured)
and..
Yes rotors also wear so later on you will need to replace them also.

These websites you are finding that state "a rotor can not warp" might as
well be saying "steel can not be bent".
In short,, those website experts... are bent.

--
James M Driscoll Jr
Spaceman

"Spaceman" > wrote in
:
> Brake rotors DO warp.
> The "warping" also known as "lateral runout", is caused mostly
> by an incorrect tightening of lugnuts when a tire/wheel is changed.
> It can also (rarely) be caused by overheating in areas where the rotor
> has a problem with uneven cooling such as blocked vent holes
> If a proper brakejob is done, and you ALWAYS tighten lugnuts
> correctly. no problem will arise later except the fact you will need
> to replace worn pads and "worn" rotors.
> Rotors also wear so later on you will need to replace them also.

Hi James,

I understand that rotors "can" wear out once they reach their wear limit.

However, it's interesting that everyone "says" the wear limit is for heat
dissipation but (according to the articles I've quoted), it's not. The wear
limit is imposed to reduce the risk of the pistons falling out. Amazing.
What I've thought for so many years is wrong.

In addition, I've also learned that while I could true the rotors, I should
(and will) replace the rotors and the pads with OEM rotors and pads, mainly
because there are absolutely no standards that aftermarket rotors and pads
have to meet yet which OEM braking systems must meet (FMVSS 105 and FMVSS
135 for example).

Furthermore, I've learned that I should go to one of the two best Internet
Toyota dealerships because they offer OEM parts at more than 25% less than
my three closest Toyota dealerships did (I checked a dozen suppliers and
found this to be true. In fact, one local dealership charged 5% MORE than
list! Obviously I'll never go to him for parts!).

However, even after all that research, I've learned that the brake judder
(aka brake shudder, shimmy, vibration, pedal pulsation, etc) problem WILL
RETURN if the real cause is the brake pistons sticking in their calipers.

So, if the root cause is really do to the brake pistons "sticking", then
I'll have the problem all over again in a few thousand miles! So, now I've
moved on to researching how to tell if a piston is sticking (see a separate
thread on that which concludes, so far, there is no instrument out there
that will provide measurable values for brake piston sticking).

The net is that if I just do as you said, then I could get the brake judder
again in just a few thousand miles. That's why I'm doing all this research!

Thanks for all your help for me and others,
Stu