Brembo BBK rotor run out - ?

NoLift911 · 01-06-2011, 04:55 PM

Having an issue with some visble rotor runout on one of my Brembo GTP front rotors. Have not run these yet but visibly I have one rotor that has a fair amount of runout. I thought about trying to "index" the hub on the rotor to see if that made things better but am skeptical. Should I try to index the hats on the rotor itself?

Really don't want to have the rotor turned as they are new and not sure that would be the best option at this point.

Anyone else have this? Just don't want any judder when I apply the brakes.

I do not have a dial indicator so I cannot tell how much runout we are talking but it is visible when I spin the assembly on the strut.

Thanks

Steve@Rennsport · 01-06-2011, 07:21 PM

How much runout did you measure?

Did you measure the hubs, too?

Is the area on the hubs where the hat seats, scrupuliously clean?

One needs some specific data to assess whether there is a problem and finding the best solution,....

Jeff Alton · 01-06-2011, 08:21 PM

A couple of things....

I have used the the GTP kit on few cars... And I have got advice from steve in the past with these.....

I would recommend that you invest 40 dollars in a magentic base and a dial indicator. What you want to shoot for is 5 thou or less of runout. Genreally the human eye can detect one to two thou....

That said, even at 10 thou you likely will not experience and shudder in the pedal, but may get some brake noise.... under light braking.

The hats and rotors in these kits are far more "true" than the hub. Most cases of runout issues can be solved by clocking the rotor. If not, a little time with a file on the hub can make the issue go away once you determine where in the 360 degrees of the circle the issue is.

Cheers

NoLift911 · 01-07-2011, 03:16 AM

I hear both of you - going to pick up an indicator adn go from there -

AlfonsoR · 07:08 AM

Steve is right on the money....as always.

Being that the rotors are new, make sure that your hubs are clean enough to eat off of. The rotors should have come with a protective coating on them. It is possible that when the coating was applied on the flange that mates to the hub, that debris got coated on there as well. Make sure you remove this coating on mating surface and you also need to remove from the surface where the brake pads come into contact with the rotor.

Once you are sure everything is clean, be careful on assembly. Make sure that the lugs are not being held out by the stud. In other words, if you are performing the runout check without mounting the wheel and if you are using the standard Fuchs covered lugs, the cover on the lug maybe stopping the lug from screwing down further to properly seat the rotor onto the hub. One way to check that is to remove the rotor and screw on the lug and determine how far it goes onto the stud. If the lug touches the hub, you're good. If it doesn't you need to inspect more carefully, i.e. measure it. Alternatively you maybe able to obtain open lugs??

PS: the 0.005" limit is what I remember. Check your reference material to make sure. If you have more runout than this, you can take your rotors to a shop that machines brake rotors, but don't have them machined, just have them checked for trueness. Your rotors really should be good. If you have a runout issue, I would bet it's in the hub, bearing or something else.

NoLift911 · 01-07-2011, 07:41 AM

OK - thanks guys. I cannot get a dial indicator anywhere today around me so I will not know the measurement until I can get one ordered.

I did do more investigating and attached a few pics. This setup is all new (front suspension rebuild) so gunk on things is not an issue and yes I double checked.

Since the rotors are new they left some witness marks on the face when I turn it so I know where I am high/low etc.

And here is the thing maybe I am making a big deal about nothing - not even sure where my old stock setup stood in terms of runout but I took a few pics...

(And have another question for you experts regarding the coverage of the pad on the rotor - seems to me they could come inboard more - the edge of the pad covers half of the last hole on the face so it seems it needs to be brought in about 3-5 mm? Could be wrong and this may be the way they set. The pads sitting in the caliper are on the very edge, not quite over but real close -

Anyway on to the pics -

Here is the setup: (pretty clean to start with)

The runout: You can see the witness marks on the top - I put red dots on the hub so I know where I am high

Backside (obviously high in the oposite side:

So I will try to "clock the hub" to see what I get

And the other question I had regarding the coverage of the pad on the rotor - both sides are the same, you can see the pad comes in but does not cover the last hole, normal?:

And where the pads sit in the caliper, basiclly even with the edge of the rotor:

So my thought was if needed was to mill down the face of the caliper bracket on the strut a few mm to bring it in? Not needed? Thoughts...

I know Jeff and Steve and Bill have seen installed a ton of these kits - thanks a bunch for the help

Thanks -

KTL · 01-07-2011, 09:30 AM

Agree its worthwhile to clock the rotor + hat assy. on the hub and see what improvement you find. But dial-check it first because the runout you see may already be acceptable. I have some visible runout on one of my Wilwood + simple hat assemblies. I clocked it to get the least amount of runout I could see and it was fine. However my racecar sees all sorts of other mild vibrations due to pickup of track rubber & debris on the tires, in the wheel barrels and in the rotors, as this is very common when you have to drive off-line in a race, where the track is being shared with so many other groups like time trial and DE running on-line most of the time. So it's easy to overlook or accept some vibration that may actually be rotor runout under those circumstances.

Just remembered I owed you a picture of that 930 rear caliper hard line plumbing...... I'll get that for you this weekend.

Don't sweat that pad location on the rotor. It's fine to have a bit of rotor surface exposure on the bottom. You'll find a ridge will establish itself down there as the rotor wears. No big deal. Actually acts as an unintentional indicator of rotor wear.

AlfonsoR · 10:47 AM

I can't answer the question on "should the pad cover the last hole", I am sure Steve W or one of the other experts will be able to. It's difficult to compare with the picture your posted, but here's a similar installation, maybe you can compare

rpm north dot com /blog/2010/03/porsche-996-turbo-brembo-big-brake-kit-installation/

How are you identifying the runout? Is it just visual observation as you turn the rotor? You are stacking components, so without checking each piece with a dial indicator, it's difficult to pin point where the problem is.

PS: can not seem to copy link to where it will work with one click, but you can copy and paste and remove the blanks, change "dot" to ".", then it should work.

NoLift911 · 01-07-2011, 10:35 AM

Thanks guys - I have no idicator so I am kinda pissin in the wind at this point - I did clock the rotor and it seemed better - more like the other side.

Again just doing a visual so I have no reference - I was using the caliper/pad assembly as a reference so yeah - not high tech and I may be worried about something for nothing.

I will get an indicator and see where I am. Just wanted run this stuff by folks that have done it before.

Jeff Alton · 01-07-2011, 02:47 PM

I think these are the pics Alfonso was mentioning

Wil Ferch · 01-07-2011, 04:47 PM

I'm surprised at the amount of run out quoted. Let me explain.

At the "other" end of the automotive/price spectrum sits my ages-old Geo Prizm ( aka "Toyota Corolla")....and I needed to buy front rotors. The most dirt-cheap Chinese made rotors ( that I've used before....remember, the car's got over 250k miles on it) have given me perfect service and are really, really cheap to buy. They quote 4 thou "max guaranteed" runout. I'm talkin' $15 or so for one rotor . The "identical" looking NAPA part costs $30 ( still cheap), but offers a longer warranty and they say 2 thou runout max. There are rotors that can cost up to $130/each or more for the Prizm, and they don't offer better specs ( but more bling). At first blush this 4 thou runout concerned me but in practice.... the Chinese cheapos never pulsed or gave bad street service. Some pretty hard service and certainly thru all manner of muck and mire for Buffalo winters.

Compare this to Jeff Alton saying 5 thou or less and maybe up to 10 thou is OK.....really? Isn't this a bit high for a premium product?

Jeff Alton · 01-07-2011, 05:19 PM

Wil,

I did not say 10 thou was OK, I said you MAY not notice a problem.....

Who said the runout was located within the rotor hat assembly? It may be, but the run out may also be (likely) in the hub, which is a few years old now and of unknown history, as well not just the rotor.... Also, the bigger the diameter the more runout that will be noticed at the OD if the error is closer to the ID.

Did you measure the run out in the Toyota rotors? I am interested to know if they met there advertised claim.

NoLift911 · 01-08-2011, 07:01 AM

All good info - according to Brembo a runout should not exceed 0.07 or (0.003) inch...which is pretty small. The whole reason this came up for me is that yes these are huge rotors and in my mind a slight runout will cause some vibration, bearing wear etc.

My guess is it is the hub assembly - so whatever my dial indicator says (when I get it) I will know where I am.

Has anyone seen this? Brake Align Runout Correction Plates – Product Information

Saw a video and it basically took runout down to 0.000....

Didn't see an application for 911.

Wil Ferch · 01-08-2011, 08:33 AM

Jeff:

Methinks thou potesteth too much....

I wasn't being critical ...I was "just askin".

Fine....5 thou to 10 thou, then....in any case much bigger numbers than plebian stuff on the market. No...I didn't check runout on the cheapo Chinese rotors (as I said) since I had purchased these a few times before and their perfect "feel" ( no pulsing, etc), made such a check unnecessary. True enough, total runout can be stack-up of influences starting with the rotor itself and going thru all the stack-up of pieces with their own characteristics.

NoLift911 · 01-14-2011, 10:32 AM

Ok so I got a runout gauge(been needing one forever so good opportunity) anyway I get .01 runout and brembo says anything over .007 is bad soooo.

Everything is spotless - clocked the hub on the hat and each time get the same result.

I can identify the high spot is it worth it to take "some" material off of that area on the hub?

Since Carrera hubs are NLA - little bit hesitant about taking stuff off of the hub.

So there is the rotor (which I can't check easily by itself) the hat (same) and the hub.

First step is to check runout of the hub and see whats what...but if one of the petals is high or has more material will that really show witha dial indicator?

Has anyone successfully taken material off and have the runout zero out? Or is this just a bit of a hack solution?

Thanks -