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

Reply to
Stuart A. Bronstein
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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

Reply to
Stuart A. Bronstein

Are you sure your rotors are not warped? Can you find a runout gauge and measure the runout? Do you know how to do this? I highly suspect rotor runout.

Maybe it does, but you're not going fast enough for the shockwaves to make it to the passenger compartment.

Bowel Movement

Reply to
MB

You can narrow down which end, if a brake problem, by using emergency brake--BE CAREFUL--to slow vehicle. If shimmy still shows, it's the rear; else, it's the front. And if you find a caring soul who turns rotors, he can, by trial-and-error, fasten the rotor on the lathe so as to minimize the material needed to remove the runout you do have. (While rotors are being turned, it won't hurt to 'plane' your disc pads on a flat concrete surface. I've seen a few times where turning rotors didn't eliminate all the pulsating; whereas, going back and planing the pads corrected it.) HTH, s

Reply to
sdlomi2

You can narrow down which end, if a brake problem, by using emergency brake--BE CAREFUL--to slow vehicle. If shimmy still shows, it's the rear; else, it's the front. And if you find a caring soul who turns rotors, he can, by trial-and-error, fasten the rotor on the lathe so as to minimize the material needed to remove the runout you do have. (While rotors are being turned, it won't hurt to 'plane' your disc pads on a flat concrete surface. I've seen a few times where turning rotors didn't eliminate all the pulsating; whereas, going back and planing the pads corrected it.) HTH, s

Reply to
sdlomi2

Reply to
Shep

You pretty much have a rotor/pad problem here. I had a simular problem with my wifes cherokee. 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. One thing I did do different (as I have with all of my vehicles) is that I do not use hard OEM pads. I use a softer aftermarket one that may wear quicker but they are easier on rotors and do not cause it to want to hot spot as much which can lead to warpage and shimmy. Something has to "give" up there and a hard pad is more senitive to imperfections in rotor surface than softer pads and they tend to cause hooter "spots" on rotor and hard pads cannot "flex" a bit to rotor irregularities and therefore ride on these little high spots more when leads to hot spots and have a different expansion rate than cooler parts of rotor and lead to warpage and brake shudder/shimmy.

Reply to
SnoMan

MB wrote in news: snipped-for-privacy@4ax.com:

Well, I'm not really an expert so maybe I messed up when I did check the runout. What I did was remove the six lug nuts & the wheel, pull the clip and two pad holding pins out and then the anti-rattle spring. Then I removed the pads with their three anti-squeal shims together.

After looking at these 4-piston calipers in amazement (not a single bolt is needed to remove and replace the pads!) I shoved a screwdriver in the rotor fins and let it rotate until it rested against a hard spot on the 4Runner so as to immobilize the freely spinning rotor. Then I put the lug nuts back on with washers under them and torqued them down evenly in a six-pointed star pattern to 84 foot pounds (actually my bending-bar torque wrench doesn't get that accurate so I just went over that number to about 90 or

100 ft lbs).

I tried getting a one-inch micrometer on the rotor but the backing plate was in my way so I shoved it in there and measured the thickness at only one spot (in hind sight, I should have measured multiple spots). My bad.

Then I clamped the vise grips of the dial gauge above the rotor and adjusted the steel neck (which was a pain) until the dial guage stopped moving. I then spun the rotor with my hands and watched the needle flicker. At first, it swung wildly because I didn't have the lug nuts on as I didn't realize nothing was holding that rotor on but when I put the lug nuts on, it swung ever so slightly to about three thousands of an inch.

So, to answer your question, I'm not sure because I'm an amateur, but, I think I measured runout ok. That's the perplexing part. If it isn't runout, what is it?

Symptoms:

- Around town, I do not feel the brake shudder or shimmy upon braking

- On the highway, it shudders mightily upon braking

- Shudder goes away immediately when I let up on the brakes

Housekeeping:

- I switched wheels left to right but the shudder on braking remained

- ABS isn't in the picture as this 4Runner isn't equipped with ABS

- The wheels were originally balanced about a year or so ago

- The four-wheel alignment was done a couple of years ago

So, in summary, I think I measured runout correctly but I may have goofed.

Stu

Reply to
Stuart A. Bronstein

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

Reply to
Stuart A. Bronstein

SnoMan wrote in news: snipped-for-privacy@4ax.com:

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

Reply to
Stuart A. Bronstein

"Shep" wrote in news:1141136768 snipped-for-privacy@sp6iad.superfeed.net:

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

Reply to
Stuart A. Bronstein

"sdlomi2" wrote in news:gOWMf.1994$ snipped-for-privacy@fe06.lga:

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

Reply to
Stuart A. Bronstein

Bad shimmy under braking is a clasic sign of warped brake rotors.

Reply to
Jeff Strickland

99% of these are rotor problems.

Irrelevant. When ABS kicks in you know it.

Irrelevant

Irrelevant if problem occurs only on braking.

Scratches are irrelevant.

So they could be turned if you choose that route.

Pad thickness is irrelevant to pulsation problems.

Surely you meant MAX=.0028 inches. What is the thickness variation? That's more critical than runout.

Check the drums unless the problem includes steering wheel wobble induced while braking in which case it is the front brakes for sure.

Now you are looking at the problem! Get the rotors turned or replace them.

Its not easy to see half a thousandth. But a half thousandth thickness variation will induce brake pulsation.

You could check the rears by applying the parking brake at speed. Its sort of tricky to do safely. Just get the rotors turned or replace them and be done with it. If you replace them it will be a lot longer before the pulsation comes back. Quality rotors such as Mountain or Brembo brand or Toyota original equipment will go MUCH longer before developing annoying pulsation than cheap units made in China. Quality rotors should NOT be resurfaced out of the box. If somebody tells you "See they have runout and need to be machined!" what is really happening is they have a worn spindle or cones on their lathe and they will machine runout into what was a quality piece. Shipping and handling does NOT knock rotors out of round as was tested by Brake and Front End magazine several years ago.

Don

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Reply to
Don

Don wrote in news: snipped-for-privacy@4ax.com:

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.

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

Reply to
Stuart A. Bronstein
**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.**

Are you sure? I'm not trying to argue with you, but that sounds awfully unlikely. Quoting:

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**The National Highway Traffic Safety Administration has a legislative mandate under Title 49 of the United States Code, Chapter 301, Motor Vehicle Safety, to issue Federal Motor Vehicle Safety Standards (FMVSS) and Regulations to which manufacturers of motor vehicle and equipment items must conform and certify compliance. FMVSS 209 was the first standard to become effective on March 1, 1967. A number of FMVSS became effective for vehicles manufactured on and after January 1, 1968. Subsequently, other FMVSS have been issued. New standards and amendments to existing standards are published in the Federal Register.**

And so on. 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.

Reply to
Beloved Leader

MB wrote in news: snipped-for-privacy@4ax.com:

Apparently rotors don't warp.

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

I found that phD discussion here:

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

Stu

Reply to
Stuart A. Bronstein

Federal Motor Vehicle Safety Standards generally specify performance standards, not methods of achieving the desired performance. This allows vehicle designers to develop new methods that deliver the desired performance. For example, the regenerative braking provided by some hybrid vehicles might not be covered by the use of conventional friction materials, and specifying a certain metal hardness for the rotor would not account for ceramic or composite rotors. Future braking technology might use induction to stop or slow down a vehicle with much less heat generated.

San Francisco street cars use long blocks of wood pressed against the tracks to provide additional braking in addition to the brakes on the wheels.

Lighting standards now allow for the use of high intensity discharge and LED lights in addition to the incandescent bulbs that are now in wide use.

Toyota passenger vehicles, including your 4Runner, do not use the brake rotor to generate an ABS speed signal. The principle behind measuring wheel speed for ABS is pretty simple. The sensor is a reluctor - magnet, and as the tooth passes by the sensor, it sends a pulse signal to the electronic control unit (ECU), and the faster the teeth pass by the sensor, the faster the ECU detects pulses. The ECU compares how fast the pulses are coming from each wheel, and if the pulses come at the same rate then no ABS is needed. If the pulses from one or more wheels slow down more quickly or vary from the other wheels, then the ECU tells the ABS actuator to "let up" on the brakes for the wheels that are slowing down too quickly until the wheel speed for all the wheels equalize. The ABS actuator that Toyota uses can pump the brakes for each wheel indpendently at a much more rapid rate than a human is capable of doing, and the pumping action is what causes the pulsation and noise when the ABS is activated. Some automakers use a less expensive ABS system on front wheel drive vehicles that have 1 speed sensor on the output shaft of the transmission and 2 sensors for the rear wheels.

There is a wide variance in the quality of aftermarket brake pads, shoes, drums, and rotors. Some are excellent and some are cheap parts with marginal performance and/or life. They can cause more or less brake dust than OEM rotors and make more or less noise. The only way to know for sure is to try them all out. For me personally, I do not have the time or the money to experiment with brakes, and since OEM parts usually only need replacement every 3 or 4 years, I stick with OEM parts, which it looks like you intend to do as well.

Reply to
Ray O

Your local Toyota dealer....or if price is a problem....order from a Toyota dealer that sells via the Internet.

Reply to
Scott in Florida

Scott in Florida wrote in news: snipped-for-privacy@4ax.com:

Based on the Babcox

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and PerformanceOil
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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

Reply to
Stuart A. Bronstein

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