Brakes "shudder" when light braking so did a Brake Rotors Runout Inspection

**thewagon** · 11-20-2008, 02:19 AM

Using OEM rotors and pads

Ok, my brakes "shudder" typically under light braking, most of the time. Installed new set of pads, still shudder.
Installed a different set of stock rotors, still shudder.

Is the runout indicated a cause of the brake shudder? Would the R1 rotors run truer than this?

The dealer mentioned even new oem rotors could not be true and they recommend cutting the NEW rotor on the car when first installing them...$150 for the fronts. WTF?

Dealership says to check runout, here is what I found:

Setup like this

Dial indicator

Video of the variation on the rotor surface

**Phil Hunter** · 11-20-2008, 01:25 PM

I assume you checked your tie rode ends to make sure that none of them are worn. A bad tie rode end can also cause the shudder you are experiencing. Just another thought.

Phil

**Junior** · 11-20-2008, 01:32 PM

Interesting test. I wonder what the normal "good" rotor tolerances are? I mean they're not perfect down to the micron - I wonder what the range is.

Are we looking at .055" right there? 55 thousandths? One full revolution on the main dial would be 100 thousandths, or .100"? Do I have that right?

**Monster** · 11-20-2008, 03:31 PM

The runout looks to be about .005" - .006" from what I see on the video. This is about the thinkness of 2 pieces of paper. I'm not really sure if this is bad or within tolerances. If I were to guess, I would say that it looks good. Everything has a tolerance, nothing is zero tolerance. And the way that the needle moves slowly over a long section of the rotor and not a quick jump from high side to low side.

Andrew, you might want to check the inside surface of the rotor too. One side could be fine, but the other side be bad.

BTW Andrew, I think the shudder your feeling is from those dead bodies that you have rolling around in the back. Try securing them better and your troubles will go away.

J/K

**r1concepts** · 11-20-2008, 07:18 PM

Those numbers looks good, and shouldn't be making the car "shudder". Do some inspections on your tires/tie rods/joints. The LX platform is known to have these issues,especially on the 05's.

**Mighty Noid** · 11-20-2008, 07:50 PM

r1.... thanks for stopping by and giving us that info...

**Todd TCE** · 11-21-2008, 11:37 PM

Didn't look at a video but .005-.006 is not outrageous. Over .010 and I'd have some concerns. I'd like to see some pics of the rotors, both sides of them to make more comments. Does the pulsation come and go? Was it there after something that was done such as alternate rotors, pads or even wheels with centering rings?

If that dial indicator was set at 0 and is now at .055 that's huge!

**Mighty Noid** · 11-21-2008, 11:45 PM

Hey Todd... I forgot to wish you a Happy Birthday yesterday!!! My bad!!

Also thanks for stopping and letting us know what you think and giving him so more things to check out!!

**OLJustice** · 11-21-2008, 11:49 PM

Interesting test. Where do you guys get these wonderful toys??

**fnkychkn** · 11-22-2008, 12:10 AM

brake rotor runout will eventually cause thickness variation. rotor thickness variation will cause brake shudder. runout, on it's own, should not cause shudder. ensure mounting surface is clean and turns true. might have to match-mount the rotors.

btw, front rotor specs for '05 RT (18") are 0.0014" for runout and 0.0004" for thickness variation.

**srtjohn** · 11-22-2008, 02:33 AM

Originally Posted by r1concepts

Those numbers looks good, and shouldn't be making the car "shudder".

i disagree with this!

Originally Posted by fnkychkn

brake rotor runout will eventually cause thickness variation. rotor thickness variation will cause brake shudder. runout, on it's own, should not cause shudder. ensure mounting surface is clean and turns true. might have to match-mount the rotors.

btw, front rotor specs for '05 RT (18") are 0.0014" for runout and 0.0004" for thickness variation.

i have seen rotors that have exesive runout and no thickness varation that have caused brake pulsation! i do agree that left unrepaired rotor runout will cause thickness varation. but brake pulsation is casued by imperfections in the rotor pushing the pads back. could be runout or variation.
i would check all 4 rotors, also 0.05inch isnt ok- if you have replaced rotors and it still pulstates i would remove rotors and measure hub runnout (where rotor mounts to hub) also its recomended that while measuring runout that the dial indicator be mounted to the car!
if hub runout is good than try match mounting.

**sulzerdrone** · 11-22-2008, 02:45 AM

5 thou. runout on your rotors shouldn't be a problem. We allow 2 thou. shaft runout on a pump for a nuclear reactor.

**Mighty Noid** · 11-22-2008, 02:46 AM

I think that Andrew needs to take his Magnum down to Torrance... LOL

**thewagon** · 11-22-2008, 03:46 AM

Thanks everyone for your input. I would like to add some more info but I need to get ready for tomorrow first. A bunch of us are going trap/skeet shooting in about 7hrs. I'll add the info and thoughts Saturday afternoon.

You guys all