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Discussion Starter · #1 ·
I think I have had a warped rotor(s) for a while now and am tired of living with the annoying shimmy it is making. I am not certain this is the culprit, but am leaning toward front brakes over driveshaft/ujoints, wheels/tires, or lift, or alignment as the main problem. What I feel is a shimmy that I really don't notice at all until about 40+MPH. It tends to come and go past that speed. As speed increases it does not necessarily shimmy more/harder. It just seems to be rythmic after about 40mph. The steering wheel shakes some as I brake from these speeds, and at lesser speeds. There is no real noticeable pull to either side. The alignment is ok now as it drives straight, no pull, and the tires are wearing ok.

Is there a way that anyone has used to check the rotor for warping?

They both appear fine (no hotspotting) and appear to still have plenty of thickness (I do have about 40K on the rotors/pads now). Anyone have any thoughts on rotor turning? I am getting ready to pull hub/rotors, repack wheelbearings, and put new pads on. I also will be replacing the outer tie rod ends and will then probably go have an alignment done. I would just like to be able to figure out if these rotors are causing my problem so I can take care of this all at once. The idea of like an AutoZONE turning my rotors has me a bit worried, I have heard yea and nea on the turning subject. Since I am doing the work, I have half a mind to just try to figure out the condition of the rotors and if they appear to be the problem, just go buy new ones and forget the turning.
 
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Um............I've never experienced rotors causing a shimmy anytime except for braking. When you apply the brakes the vehicle should shimmy, the pedal will probably pulsate, and you'll almost surely feel it thru the steering wheel.

I think your tires need to be balanced.
 
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If you go to a good shop there is nothing wrong with turning the rotors. As long as they are not turned passed their limits. You should always turn your rotors and drums when you do a brake job. You should also rebuild or replace caliphers and wheel cylinders. Another good idea is before you start bleed the brakes that way you have good clean fluid when you reinstall the parts. IMHO if you are going to do a brake job think seriously of changing over to silicon brake fluid with all new or clean and rebuilt parts. Silicon fluid does not attrack water and stays clean longer if you use silicon you don't have to rebuild parts you can just slap on new pads and shoes. The military uses silicon in all of their vehicles for these and other reasons. The cost is a little more but it lasts longer and you don't have to replace or rebuild parts it works out cheaper. Hope this helps and Good Luck,
 

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Brake Rotor test

Jack up the wheel you THINK is the problem and one of the rears. Remove the front wheel, lock it into 4, CHOCK BOTH WHEELS that are still on the ground, crank it, & put it in gear. DO NOT USE THE BRAKES - they might make the truck lurch off the jackstands. If it tries to move, pull it out of gear BEFORE hitting the brake pedal.

Once you have the front rotor turning, you can hop out, and look at it to see if it's warped. Gauge it against the caliper BRACKET, not the caliper, which may be following the warp & therefore moving, too.

If your diffs are BOTH open, this will work.
If either diff is locked/LS, you'll have to lift both wheels on that axle.
 

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if you got a shimmy and you are not pressing the brakes then you might have a ball joint or a tie rod end going out on you, not the brakes. If it is the brakes you can really feel it during braking.
 

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use a mag-base dial indicator to check the runout... the specs should be listed in Haynes. if this is a non-braking issue though i doubt the rotors are the culprit... make sure you have no mud stuck to the inside of your rims.
 

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Pilotrick is right...surfacing your drums/rotors is standard procedure when doing a brake job. It's ~$5-$10 per wheel and it's cheap insurance for smooth brake operation. I'll admit that I've skipped a few times, sometimes been lucky, sometimes not and had to pull 'em apart again for surfacing.

This doesn't sound like your immediate problem...if it's shaking without the brakes applied, look elsewhere first.
 

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Discussion Starter · #8 ·
So, consensus is probably not brakes, check elsewhere first. I do have the shimmy independent of the brakes being applied. It is speed related. And it is weird rythmic, at speeds greater than about 40-45mph it begins. It kinda comes and goes, but is always there to some extent. My original thought was that a warped brake rotor, as it turns with the speed of the wheel, can cause the shimmy, regardless of the brake being applied, was this flawed thinking?

I am beginning to think about the weird rythmic variation: How about, since many of you are thinking tires, if two or more of the tires are out of balance through either nicely bent lips or loss of weights then as they rotate they could be phasing in and out with each other, creating a shimmy that comes and goes at speed as the tires rotate. The tires don't exactly rotate at the same amount, so the phasing is a possibility?????

Oh, and someone mentioned tie rods, and yes, I will be doing those regardless. It's time for a tire rotate and I have been wanting to make the swap to some 15 x 8 steels, same offset, so I think I am going to do this first, mount/balance, and see where that gets me.
 
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You're on the right track Juice. Do the tires first and go from there. I've had unbalanced tires give a "rythmic" vibe.....
 

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You would quickly lose and gain the phasing each and every turn you made. Basically you would have a big vib going and not a shimmy. Normal shimmys are hard part stuff. You could have a blister that causes a shimmy though. Jack up the tires and give each one a spin and look for out of round condition. Front would be my guess.
 

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If you think it's tire related,rotate the front tires to the back and see if the vibration moves or changes.I've seen belts slip in tires causing a vibration.If that's not it I would suspect something in the driveline.


Billy
 

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definitly think its the tires to check the drive shaft take note of eng rpm when it is doing it at 45 and then leave the tranny in 2nd gear and run up to same eng rpm if it is not there then it would most definitly be the tires because the drive train would be spinning at the same speed isnt this right guys
 

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Discussion Starter · #13 ·
Shilo, wouldn't be so bad if the rythm happened to correspond to the tunes I was playing at the time.


Havack, I don't know, I'm thinking it would slowly go in and out of the phasing. Let's say both tires are "rated" at 550 revs./mile due to their size. Now, if because of small variations in actual size, and PSI, they spun just ever so slighly off, say 10 or 15 revs./mile, wouldn't that cause misbalanced tires to slowly come and go in the way they match up with each other?

It I just had one unbalanced tire, this probably would not happen as the single tire is always out of balance and a constant shimmy would be felt. But with two or more and the above scenario.....hmmmmm
 

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TheJuice
When did all this "shimmying" start?
After you took the top off?

Reason I ask, and maybe it's somehow related:
Mine's been off for 4 weeks now.
I've got a harmonic vibration between 40 and 50mph.
It goes from front to rear, opposite sides. ie: LF to RR or vice-versa.
Nothing major, but it's there. Could be described as a "shimmy" in your terms.
It's non-existent at slower or faster speeds.
In addition, the harmonic was most certainly not there before I took the top off.
I know it's not the new tires since they were on quite a while before that.

BTW, I've experienced this in the past while running "topless".
I'm sure the structural integrity is reduced somewhat with the top off.
Good reason to put in a roll bar.


I'm with the other folks.
You'll definitely feel a warped rotor through the brake pedal.
 

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Discussion Starter · #15 ·
I know what you are saying. The shimmy was there before the top came off. It was there before these wheels started to get buggered all up, but not nearly as noticiable. It comes and goes at really any speeds above say about 40mph. It has gotten worse over the last 6 months. In that time, the wheels (all 4) have suffered mild dings and 2 pretty heavy lip bends, to the point I was a bit surprised they held the bead (and are still not leaking). The top off does seem to add to it as well, and affects the ability to brake straight, since I have changed the front/rear weight bias of the vehicle (adding weight in front, deducting from rear.)

It all adds up to why you won't see The Juice heading to the trails at a "cozy" 80 mph!!!!
Reminds me of Muddy's story about the wheel coming off and passing by and heading into the tall weeds.
That one still makes me smile thinking about it.
 
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WD40
I have the same problem with the "shimmy" between 40 and 50 mph it is almost nonexistant at any other speeds. I don't know if it has anything to do with the top being off though I take the top off and on all of the time. It does it with the top on or off. If you find it is something when you put the top back on let me know.
 
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