Rethinking vibration when braking

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MONKEYMAN

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I had terrible vibration last Wednesday when braking most of the time. I could feel and hear front of my 99 SL2 vibrating/shaking.

Thursday night re-torqueded lugs. They seemed too tight.

Friday much of vibration gone.

Saturday I had a dial indicator. I found passenger side hub would not allow me to get runout in spec when installing Wearever or Napa rotors (it was .004"). Interestingly, the new Advance rotors measured having more lateral runout then the Napa rotors I had on car when vibration occured.

I am thinking that lateral runout and proper torque needs more attention when doing a brake job.

I put the old pads and rotors back on after a little sanding. I drove today highway and city driving without much if any vibration.

I will install a shim this week to hopefully get the passenger rotor in spec.

What do you think of these observations?
 
I'm a believer that run out is usually the cause of most brake pedal pulsation and "warped" rotors. A dial indicator is very useful. If inexpensive rotors are adding excessive that's agood reason to avoid them. Sometimes the wheel hub is to blame and on the car braking turning or shims is the only fix.
 
When learning to do brakes run out was not mentioned. I have spent a lot of time and money addressing the problem (pulsation), not the cause (run out). My dial indicator showed me why you want to start with quality rotors. Some lessons in life come at a high price.
 
Some vehicles have continuous pulsation promblems that keep coming back no matter how many times you replace the rotors. Often times it's because the wheel hubs induce excessive run out in the rotors. Without addressing the run out either through indexing the rotor to the hub, shims or turning the rotors on the car the problem will never be permanently fixed.
 
The vibration may have left anyways without your re torqueing.
We will never know.

If it was truly "terrible" , you have other problems.
 
If you are feeling the pulsation through the pedal, most often the cause is not from runout, it is from parallelism. If the surfaces of the rotor is not completely parallel, it will push the brake pedal back towards you. When you have excessive run-out the caliper is basically just sliding back and forth on the slides. You may feel that in the steering wheel, but unless it's horrible you won't feel it in the pedal. Look at runout and parallelism specs and you will see the tolerances for parallelism are much smaller than for runout. Parallelism problems are usually from pad deposition on one part of the rotor. Most often if the problem is re-occurring, it is caused by the drivers driving style.
 
Parallelism is a new term to me. I have never seen a spec for it.

This morning I could hear passenger rotor/pads every revolution of tire. It sounded like a high spot hitting. However, no vibration braking (yet).

I hope to correct hub run-out with shim Thursday. I am interested to see if this corrects all problems.

Scott, based on what you are saying about parallelism I will need to switch out the rotors to the new ones to address that issue.

My driving style changed the last few years since my mom was ill and eventually passed away in March. I was going out of town 2 to 3 days per week. The vibration was most noticeable when slowing down at highway speed. I did hear the out of round sound with every revolution of tire at slow speeds with some rotors.
 
Lack of parallelism or thickness variation is what's likely causing pulsation not the run out per se. But the excessive run out is what leads to thickness variation or lack of parallelism. The excessive rotor run out wears the rotors unevenly after a few thousand miles leading to thickness variation which causes pulsation.

If you have pulsation you will most likely have to correct the rotors (replace or machine), but after that you will need to make sure rotor run out is in spec so the problem doesn't returning. I'm guessing the hub has run out and the shims should fix that.
 
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Can remounting the rotor on the hub in a different position correct run out? Indexing, as mentioned above?
 
Originally Posted By: doitmyself
Can remounting the rotor on the hub in a different position correct run out? Indexing, as mentioned above?


I tried indexing. It worked to get drivers rotor to .002". But with passenger side the hub was keeping it at .004" or more. I will index when I get the shim (hopefully with good results).
 
That shim will have to be about 0.0005" or so.
It's dimension will be magnified by the rotor's outside diameter being so far away.
 
Originally Posted By: mechtech2
That shim will have to be about 0.0005" or so.
It's dimension will be magnified by the rotor's outside diameter being so far away.


I did not know that when ordering from Rock Auto. I bought the 0.003" size due to arrive Thursday. On Rock Auto's Website it says "Will Correct 0.003" Rotor Runout". The 0.006" size seemed like it would be too thick.

Monday had a heavy downpour. Since then my brakes have been very quiet. Still no noticeable vibration when braking.

I noticed when my car was washed in the past braking vibration would be reduced. Could that be from removing some brake material off the rotor?
 
If you are .002" - .004" out, then put in a .003" shim, you will overcompensate.
The .003" is tripled in magnitude at the rotor's edge vs. the hub where it is installed.
 
Originally Posted By: mechtech2
If you are .002" - .004" out, then put in a .003" shim, you will overcompensate.
The .003" is tripled in magnitude at the rotor's edge vs. the hub where it is installed.


The OP claimed the listing said it would correct a .003" runout, which seems to indicate that it takes into account the distance (at least a rough estimate of the distance) from the hub.

I haven't used one of these shims before, but that's my understanding from what the OP posted.
 
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This is a learning experience. My experience is that learning comes at a price....

I am thinking the shim to correct 0.003" will be closer to the dimensions Mechtech2 listed. I am not very experienced with technical language, so sometimes I get descriptions wrong.

I read similar StopTech articles on warped rotor myths which are referenced a lot when posting that you have pulsation. I was not able to correct pulsation doing some hard stops as some recommend.

Last Wednesday I had the most vibration and pulsation when braking I ever experienced with my Saturn. Today my brakes had no pulsation and worked well.

I am not feeling well so I am going to wait to install the shim. My brakes working well has bought me some time for now....
 
If the brakes are not pulsating then don't worry about it for now. Although they usually don't correct themselves it's possible if run out and the resulting thickness variation is slight.

Rotor correction shims come in part numbers applicable to a vehicle model and are usually listed as .003 or .006 correction to correct .003 to .006 run out as measured at the rotor's edge.

This site has a good explanation of the run out correction process: http://www.nucap.com/products/hardware/brake-align/ . Check out the video. It's pretty good and covers most all the steps.
 
I installed brake align shims tonight. Dial indicator was reading .005" on passenger rotor. I watched the video and tried to follow instructions, but even with shim it was a little over .002". I then tried a Wearever rotor. Same result. I was getting frustrated not ordering the larger shim. I then just put the other Wearever rotor on and first try it was right at .002 or a little under with the shim. On drivers side lowest reading was .003" with Wearever rotor. After shim .0015. I was impressed. If I have problems in the future I know to buy a correction shim for .006" run out. I think I would have gotten a better reading. I re-used Raybestos Ceramic pads after some light sanding. Advance gave me the wrong pads. Tomorrow I will try every thing out before I go to see my Stepfather for Father's day. Thanks for all the help! I learned a lot. I will never change rotors without testing run out first. Happy Father's Day!
 
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