Cobra brake upgrade, what went wrong?

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JohnyD05

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Aug 3, 2006

#1

• Aug 3, 2006

• #1

I put the 03 cobra brakes on the front of my 99 GT. its got stainless lines and slotted and cross drilled rotors. I noticed that with a decent brake pedal applied, i get a shimmy/shutter that starts at about 40 mph and continues to about 30 mph. Its not serious just there a little bit. I don't get this if say i brake 35 down. Any ideas of what went wrong. Other than this the brakes are great. I can get on it fast at say 80 and i don't have this problem?!

 

Brute03

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Mar 20, 2006

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Aug 3, 2006

#2

• Aug 3, 2006

• #2

might sound simple but did you remove the protective coating from the rotors?

 

blackfang

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Dec 17, 2001

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39

Richmond, Va

Aug 3, 2006

#3

• Aug 3, 2006

• #3

Have you checked the runout? Maybe the rotor might be making contact with the caliper/pad when braking?

Did you get a caliper bracket to relocate the calieprs being the cobra brakes are larger? Could this be doing it?

 

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JohnyD05

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#4

• Aug 3, 2006

• #4

Brute03 said:

might sound simple but did you remove the protective coating from the rotors?

Click to expand...

The rotors were zinc washed and what i thought i had read was that this would wear off when i seasoned them.

You can see where the pad grabs the rotor because this is a different color than ther rest of the rotor, so i am pretty sure the coating is gone.

 

J

JohnyD05

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#5

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I don't know what the runout is!?

I havn't pulled the wheels off to take a look, i guess thats my fault. The kid came with a caliper bracket that relocated the caliper in relation to the center of the rotor. I will look and see if it looks like they are contacting.

I thought it was wierd that this only happens between 40-30 consistently.

blackfang said:

Have you checked the runout? Maybe the rotor might be making contact with the caliper/pad when braking?

Did you get a caliper bracket to relocate the calieprs being the cobra brakes are larger? Could this be doing it?

Click to expand...

 

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prsrizdgt

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Mar 12, 2004

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St. Louis

Aug 3, 2006

#6

• Aug 3, 2006

• #6

You may only be feeling it at a certain mile per hour, but it could be doing it most of the time to lesser degrees, kinda like an out of balance tire. The condition you describe makes it sound like a warped rotor which is unlikely if they are new, unless they were not seasoned or broken in correctly. I have never seen run-out measured on a rotor, but if you could find a way to mount a dial indicator, you could check it yourself I would think. Are the rotors from a reputable manufacturer? Were the pads and calipers new also?

 

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GodAmGT00

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Jul 28, 2006

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Aug 3, 2006

#7

• Aug 3, 2006

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Do you get an ABS light??



JT

 

J

JohnyD05

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Aug 3, 2006

#8

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Everything was brand new, the rotors are from mustangtuning.com. i did put a new tie rod end on the car when i did the brake job, and it hasn't been aligned, so maybe its that? When i seasoned them i never did the final seasoning where you go back like after the car has cooled off and do the high speed agressive stops to get them up to max temp, wonder if that has caused a problem? I am hoping it just wears in and goes away.

 

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JohnyD05

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#9

• Aug 3, 2006

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No abs light, its only a very slight shimmy/vibration. and I don't feel it through the steering wheel, more through the brake pedal and floor. Because i don't feel it through the wheel ( iam hesitant to say its a warped rotor.) I replaced the brakes before because i had a warped rotor.

 

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prsrizdgt

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Aug 3, 2006

#10

• Aug 3, 2006

• #10

JohnyD05 said:

No abs light, its only a very slight shimmy/vibration. and I don't feel it through the steering wheel, more through the brake pedal and floor. Because i don't feel it through the wheel ( iam hesitant to say its a warped rotor.) I replaced the brakes before because i had a warped rotor.

Click to expand...

Okay, I assumed the vibration was felt more thru the steering wheel.

 

J

JohnyD05

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#11

• Aug 3, 2006

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i need a dial indicator
along with a million other tools.

 

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GodAmGT00

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#12

• Aug 3, 2006

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I've heard of people having issues w/ their ABS, where it would cause vibration, or make sounds when trying to stop...

Something that's free and easy: pull the ABS fuse, and if it doesn't do anything, then it's obviously mechanical..

I was going to ask about your suspension, namely your ball joints, but I would think you'd be able to feel it more pronounced at a higher speed...



JT

 

J

JohnyD05

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#13

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dumb question is the abs fuse in the fenderwell fuse box or the engine compartment one, i am geessing engine compartment.

 

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prsrizdgt

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Aug 3, 2006

#14

• Aug 3, 2006

• #14

JohnyD05 said:

i need a dial indicator
along with a million other tools.

Click to expand...

I'm running slotted rotors on my upgrade, and I know that I immediately noticed the differance in pedal "feel". I'm not talking about improved braking, but more "roughness" or "vibration" thru the pedal. I chaulked it up to being the rotor since it was not smooth like the standard rotor.

 

J

JohnyD05

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Aug 3, 2006

#15

• Aug 3, 2006

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I didn't think of that, maybe its normal?
I noticed a stiffer pedal with the stainless lines. I am gonna keep driving it, cause it stops great, and i will see what happens.

 

R

RochesterGT

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Jul 18, 2006

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Penfield, NY

Aug 3, 2006

#16

• Aug 3, 2006

• #16

My brother bought a Cobra kit recently and he had some vibration under braking. He got new rotors and he hasn't had a complaint since.

 

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BLWNROUSH76

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Oct 1, 2004

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Aug 3, 2006

#17

• Aug 3, 2006

• #17

Warped rotors is what it sounds like! Send em back and get new ones.

 

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GodAmGT00

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#18

• Aug 3, 2006

• #18

The thing is though, if he's only getting the sensation between a certain window of MPH, I'd rule out warped rotors.. I've never had a set of warped rotors that were tempermental w/ speed.

Did you correctly torque your wheel lugs when you put everything back together??



JT

 

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BLWNROUSH76

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Oct 1, 2004

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#19

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• #19

GodAmGT00 said:

The thing is though, if he's only getting the sensation between a certain window of MPH, I'd rule out warped rotors.. I've never had a set of warped rotors that were tempermental w/ speed.

Did you correctly torque your wheel lugs when you put everything back together??

JT

Click to expand...

I've seen it numerous times!! But it may not be the problem.

And having the lugnuts not correctly torqued would not be tempermental w/speed either.

Wish him luck getting it straight!

 

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GodAmGT00

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#20

• Aug 3, 2006

• #20

True about the temperment w/ speed, but it could have prematurely warped his rotors..



JT