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rear rotor question

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Guys, I just installed a new set of DBA T3 4000 Rear rotors. Sense then I now have a vibration coming from the rear on my test drive. It starts at 65 mph and very noticeable. The vibration was not there before the rotor swap. The rear rotors were the only thing that changed.
lugs on wheels are tight
no weights missing on rims
there was no right / left markings on the rotors. could there be a L & R?
Rotors looked in perfect condition. cleaned with brake cleaner to remove oils
brakes are smooth
I know I can reinstall the OEM rotors to see if its the rotors but figured I ask the pros first.
where could I have gone wrong?? any and all help is welcome.
If anyone will know it will be the BMO members...HELP
Thank You
 

TMSBOSS

Spending my pension on car parts and track fees.
7,530
5,247
Exp. Type
HPDE
Exp. Level
10-20 Years
Illinois
superhero said:
Guys, I just installed a new set of DBA T3 4000 Rear rotors. Sense then I now have a vibration coming from the rear on my test drive. It starts at 65 mph and very noticeable. The vibration was not there before the rotor swap. The rear rotors were the only thing that changed.
lugs on wheels are tight
no weights missing on rims
there was no right / left markings on the rotors. could there be a L & R?
Rotors looked in perfect condition. cleaned with brake cleaner to remove oils
brakes are smooth
I know I can reinstall the OEM rotors to see if its the rotors but figured I ask the pros first.
where could I have gone wrong?? any and all help is welcome.
If anyone will know it will be the BMO members...HELP
Thank You

Directional/ right or left. I checked the KNS site. These are Not directional and therefore it should not maker which side they are on. A good indication of a directional rotor is the asymmetrical pattern of the grooves and the direction of the venting inside. All directional rotors I have used, Girodics and DBA have all been clearly marked.

Can you check for runout?? This is the wobble or our of true rotation of the rotor. If there is excessive runout there will be a vibration. If the rotor does not spin true, thats your problem.
Run out can come from a manufactures defect or from warping related to heat...a lot of heat.

Have the rotors been on Track?

Did you change pads and bed the new pads?

Its not common but sometimes debris can get between the rotor and axel causing a wobble.

Swapping back to the stock rotors will give you an indication of runout.

Did you rotate the caliper pistons back into the caliper when you did the swap?
 
TMSBOSS said:
Directional/ right or left. I checked the KNS site. These are Not directional and therefore it should not maker which side they are on. A good indication of a directional rotor is the asymmetrical pattern of the grooves and the direction of the venting inside. All directional rotors I have used, Girodics and DBA have all been clearly marked.

Can you check for runout?? This is the wobble or our of true rotation of the rotor. If there is excessive runout there will be a vibration. If the rotor does not spin true, thats your problem.
Run out can come from a manufactures defect or from warping related to heat...a lot of heat.

Have the rotors been on Track?

Did you change pads and bed the new pads?

Its not common but sometimes debris can get between the rotor and axel causing a wobble.

Swapping back to the stock rotors will give you an indication of runout.

Did you rotate the caliper pistons back into the caliper when you did the swap?

Rotors have not been tracked. Just a test drive of 60 miles

Pads were not changed. Still OEM

No rust on axles and OEM rotors came off with ease

Did not rotate piston back in because I did not remove pads. Is this OK? I thought that if I dont remove pads I would not have to rotate the pistons. True or You screwed up...Lol
 

DEye

You can't get there from here...
If you were able to get the calipers back on without compressing the cylinder, it begs the question - why did you change the rotors?

But that aside sounds like the rotors my be out of true ?
To the crowd, Would it be possible to detect the defect by placing them on a flat surface ?

Don
 

TMSBOSS

Spending my pension on car parts and track fees.
7,530
5,247
Exp. Type
HPDE
Exp. Level
10-20 Years
Illinois
But that aside sounds like the rotors my be out of true ?
To the crowd, Would it be possible to detect the defect by placing them on a flat surface ?

Don
[/quote]

Highly unlikely, unless they were manufactured with a serious warp.

Another indication of a out or true rotor is an increase in free travel before the brakes grab. I had 4 warped rotors at RA and there was over an inch of "Extra" travel before braking. Did you notice any difference in where the brake pedal is when the brakes bite?
 
DEye said:
If you were able to get the calipers back on without compressing the cylinder, it begs the question - why did you change the rotors?

But that aside sounds like the rotors my be out of true ?
To the crowd, Would it be possible to detect the defect by placing them on a flat surface ?

Rotors were change because I'm slowly get the car ready to hopefully go to the track next year. As for now I dont want any type of track pads for just cruising around town. I'm doing things slowly. In this case i'm glad. If I would of change a few things at once it would be harder to figure were I went wrong.

I know how to detect defects (run out) I think.
I would need to use a dial indicator. that's one tool I don't have. I was wondering if by some slim chance that JUST maybe there may be something inside one of the cooling veins left from machining. Slim chance I know, I'm just trying to think of anything that could cause this. I know the rotors will have to come off in the long run. Just trying to put a check list together.

Thank you guys.
Just sucks that something so simple can go wrong. My problem is that I only have a rock driveway or a garage that is filled with so much crap that my car just fits. This is why I'm pissed at myself. But life goes on. What I would give to have a garage like some of them members here have. Maybe in my next life on planet earth.
Please keep any ideas coming.
 
TMSBOSS said:
But that aside sounds like the rotors my be out of true ?
To the crowd, Would it be possible to detect the defect by placing them on a flat surface ?

Don


Highly unlikely, unless they were manufactured with a serious warp.

Another indication of a out or true rotor is an increase in free travel before the brakes grab. I had 4 warped rotors at RA and there was over an inch of "Extra" travel before braking. Did you notice any difference in where the brake pedal is when the brakes bite?

No extra brake travel. Brakes are smooth when applied. No difference with Parking brake.
 

302 Hi Pro

Boss 302 - Racing Legend to Modern Muscle Car
2,009
441
Southeast
Hi SuperHero:

From reading over your posted information, I get the sense that your brake operation is fine, and that you are experiencing a high speed vibration at highway speeds of 65 mph.

I would suggest that you remove the rear wheels and inspect the wheels and tires first. Start with the easy things first. Missing wheel weights, tire damage etc. then make sure your rotors and wheels are seated properly.

You might have a rotor manufacturing issue, but chances are it's just something simple, like wheel/tire balancing. Did you reuse the factory rotor clips on the wheel studs? They have been known to interfere with wheel seating.

Good luck and let us know what you find.
302 Hi Pro
 
302 Hi Pro said:
Hi SuperHero:

From reading over your posted information, I get the sense that your brake operation is fine, and that you are experiencing a high speed vibration at highway speeds of 65 mph.

I would suggest that you remove the rear wheels and inspect the wheels and tires first. Start with the easy things first. Missing wheel weights, tire damage etc. then make sure your rotors and wheels are seated properly.

You might have a rotor manufacturing issue, but chances are it's just something simple, like wheel/tire balancing. Did you reuse the factory rotor clips on the wheel studs? They have been known to interfere with wheel seating.

Good luck and let us know what you find.
302 Hi Pro
This is what I was thinking too. Are you using the stock wheels? Maybe some grit got inbetween the hub and wheel. One time I changed from my track wheels back to street wheels and forgot to remove my centering ring. I crushed the ring installing the stock wheel and didn't notice it was on until after I drove the car and got a vibration at high speed. It's worth checking.
 
Nothing on the car changed except the rotors. Wheels and tires are in perfect condition. I did not reuse the rotor clips. The wheels that came off are the same ones that went on.
Braking is smooth at any speed.
No difference in brake pedal oe E-brake
65mph I get the vibraition all the way up to 80. Does not get worse from 65 to 80. And you can feel it is coming from the rear. Steering wheel is smooth with no vibraition.

I'm just as stumped as everyone that has tried to help me. Bottom line is that I will have to pull the wheels off and play dective to see if anything is wrong. I'm sure it will end up being my fault some how. I just have a hard time thinking that a New rotor would be out of ballance. A warped rotor is completely different story. Bottom line is everything was fine with OEM rotors and I changed them to the DBA rotors and I have a problem. These are the joys of Moding.
 

Grant 302

basic and well known psychic
There's also the chance that tire balance is causing the issue and maybe through the drivetrain. Before you changed the rotors, the wheels/tires were clocked relative to each other in some position, and it's likely they are not in the same relative position. So where they may have been able to cancel a slight imbalance, it may be exaggerating one now. Total long shot, but that's the only other thing I can think of.

How old are the tires and how long ago were they last balanced?
 
Grant 302 said:
There's also the chance that tire balance is causing the issue and maybe through the drivetrain. Before you changed the rotors, the wheels/tires were clocked relative to each other in some position, and it's likely they are not in the same relative position. So where they may have been able to cancel a slight imbalance, it may be exaggerating one now. Total long shot, but that's the only other thing I can think of.

How old are the tires and how long ago were they last balanced?

Tires have 3400 miles and were balanced at 3100 miles when I switch to LS rims.
I had no problem with new rims or tires when I installed them.
Hopefully my schedule will give me some free time to pull the wheels off so I can inspect the wheel weights. If all looks good then then the rotors will get taken off and looked at very closely. At that point I will have to make a choice to put the OEM or DBA back on.
I have DBA rotors on the front with no issuies. Installing the rears, was just me trying to complete the full DBA package.
 
173
38
When I changed my Boss to the GT500 six piston setup I had a similar issue but in the front.
One of the new Brembo front rotors was incorrectly machined.The inner and outer face of the rotor at the hub were not parallel with 4-5 thousandth runout.
A new set of rotors were the cure.
This was not easy to figure out,but a dial indicator was the solution.
Good Luck!
 

drano38

Wayne
1,130
318
Superhero,
If all else looks to be in good condition, put the stock rotors back on as mentioned in your first post. If that solves it, you found the issue. Looks like you've covered all other potential issues.

Keep your stock rotors for the future. They actually last just as long (and maybe longer) than higher cost performance brands. But I'll admit that slotted front and rear do look nice.
 
Guys, I had a thought / vision..Lol and need to poll the BMO members for advice.
Sense I dont have a dial Indicator to check to see if the rotors have a machineing problem.
My question to the guys are:
If I removed the rotors and put them on a tire ballancing machine and spin them, would that tell me if the rotors are ballanced.

I dont even know if this is doable. Will I be able to mout the rotors on the wheel ballancer?

This Idea came to me with the help of Beer. So I dont know if I'm kidding myself or need to drink more beer.
its just very fustrating and I'm the type of person that needs to know the answer. My wife says I'm my worst enmeny when it come to things like this. I over think things! Shes right. I think?
I just want to know that maybe its the left rear rotor thats out of ballance by 1 1/2 oz or what ever.

What say the sober BMO members.
Wheel ballancer.......Yea right / Good luck
Wheel ballancer.......Thats a tough one / Maybe
Wheel ballancer......Never thought of that / good idea let us know if it works
Wheel ballancer......It will work / that should give you your answer

Only reason I ask is because I have access to a digital wheel ballancer. And dont want to put OEM rotor back on only to find out it was the DBA rotors. Then Get the DBA rotors replaced and do it all over again.

Thank you for any help.
 

TMSBOSS

Spending my pension on car parts and track fees.
7,530
5,247
Exp. Type
HPDE
Exp. Level
10-20 Years
Illinois
Never thought of that.

Could it work?? Don't know. The rotor has a max diameter of 12 inches. Our tires are in the 27 inch range. Will the wheel balancer see a out of balance issue? Maybe. Will it be 100%? Don't know.

If you are taking the rotors off anyway, put the factory rotors on and take a drive.
 

302 Hi Pro

Boss 302 - Racing Legend to Modern Muscle Car
2,009
441
Southeast
SuperHero:

If the rotors were out of round, I would think you would have some viberation or shimmy type feel in the brake pedal. Also, I've seem cars with terrible brake pedal shimmy from out of round front rotors that had no effect on driveability at any speed, until you hit the brake pedal, then the steering wheel would vibrate out of your hand.

As far as the wheel balancer, you won't know until you try it. But check the balance of your rear wheels and tires first. You might not need to mount the rotors.

302 HP
 
I ballanced the rear tires today.
before i started, i observed that all piror wheel weights were there. I removed all weights and put the tires on the machine. the old location of the weights were very close to the new weights. The olny difference was. one tire had 3oz of weight on it and when we reballanced it we only installed 1oz. Thats what the machine called for. both rear wheels zero out. Tonight I will have them back on the car and maybe this week end I will be able to test it.
Hopefully all will be good and a cheap fix. Otherwise next step is to remove the new rotors that were installed and put the OEM's back on.
 

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