Brembo Disk Bell Ring-Hub bolt Failure

[Wess-RA]

No worries, I got the relevance you were drawing. I agree, I do need to consider the level you are at vs. mine. It does become relevant I think. Tons more power and traction creates exponentially more strain on all the components. The only reason I referenced my driving level is because I am already pushing this car pretty hard even though it is new to me. Again more strain, relatively speaking!

Do you feel that I should be concerned about the lack of rotor float due to stack up tolerances?

[panozracing]

not sure about the bolt tolerances. What did PAD stop providing the Brembo part? Is the gold one cheaper, stronger???

I would use the parts that work together even if its more money. Cutting corners to save a buck has never worked for me in racing.

One thing I have always loved on the cars is the brakes. We run top of the line SRF fluid and have always been rewarded with great brakes.

[Wess-RA]

They didn't say why but it was probably to save $'s. On the manufacturing side, not ours. They had it reverse engineered and outsourced. It definitely is not for strength, as it looks to be the exact same design. They stated that the flange thickness that I measured was exactly on nominal to their +/- .005 tolerance. As I stated previously the Brembo part was .010 thinner. The gold anodize is a type II (not a hardened Type III). I checked it! They just changed the color to be able to easily distinguish between the newly outsourced vs original Brembo parts.

I wish they had redesigned it and added 3 more bolt holes to the hat and hub. Based on my experience, that would have been a worthwhile improvement.

[panozracing]

I would buy the brembo part...will they still sell you the brembo one?

[Wess-RA]

Dont know, but I will find out.

[NZGTRA17]

Originally Posted by Wess-RA

I went ahead and replaced the new hat and hardware on the right wheel which broke. I also disassembled the left hub/rotor assembly to inspect the hat to hub bolts and out of these 5 bolts, I found one loose and 2 snapped off completely; which left only 2 bolts holding this rotor in place. Clearly this rotor was just waiting to let go.

Here is a pic of the broken bolts.

My hand was a bit shaky, but clearly these bolts have been snapped for a while now, judging by the rust at the break points.

Uwe, where are the cap screws breaking with reference to the joint that they are securing? Are they breaking just past the joint face within the threaded holes in the hub, or at the joint interface?

I note that the cap screws are threaded for their whole length, this is not very good engineering as they should have a plain shank portion to bear evenly against the sides of the holes in the hat (you will never find this in a well engineered aircraft component thats for sure).

Are you able to drill out the holes in the hats and drill/tap the holes in the hubs to go up a size with the bolts? If you can do this, I would. I would also change to UNF thread form (as the cap screws appear to be UNC) and use an aircraft grade bolt.

Kel.

[Wess-RA]

Kel, Excellent suggestions on the mods. Once I put out some of those other fires I'll circle back to that.

Strangely one bolt broke off 2 threads down into the hub and the other 3 threads down. Both well beyond the parting lines. What are your thoughts on that? I believe it indicates a lot of flexing of the bolts. That makes me wonder if I should actually go up to a harder bolt. A harder bolt could actually snap earlier under repeated flex. These are through, not case hardened.

I'm hoping to get my lift soon. I have a handle on a used Nussbaum (German quality) for about $1900 (new is somewhere around $4.5K) Then I'll have space to put in a manual lathe, Bridgeport mill, parts washer and other small stuff that I have had in storage since I sold the biz. I'm really excited, I feel like an arm has been cut off since I haven't had access to anything. That will give me the opportunity to get into the kind of fixes you are recommending. Then it is only a matter of having the time. I guess we are all feeling that pinch.

[NZGTRA17]

Originally Posted by Wess-RA

Kel, Excellent suggestions on the mods. Once I put out some of those other fires I'll circle back to that.

Strangely one bolt broke off 2 threads down into the hub and the other 3 threads down. Both well beyond the parting lines. What are your thoughts on that? I believe it indicates a lot of flexing of the bolts. That makes me wonder if I should actually go up to a harder bolt. A harder bolt could actually snap earlier under repeated flex. These are through, not case hardened.

I'm hoping to get my lift soon. I have a handle on a used Nussbaum (German quality) for about $1900 (new is somewhere around $4.5K) Then I'll have space to put in a manual lathe, Bridgeport mill, parts washer and other small stuff that I have had in storage since I sold the biz. I'm really excited, I feel like an arm has been cut off since I haven't had access to anything. That will give me the opportunity to get into the kind of fixes you are recommending. Then it is only a matter of having the time. I guess we are all feeling that pinch.

Yes, like you I am thinking that the failures are related to cyclic fatigue of the bolts. The failure point is probably the point of flexure given the tolerance/fit of a UNC type fastener. This convinces me that going up in fastener cross sectional area (edge distances allowing) is the best fix Uwe, in combination with using a top quality fastener with a plain shank portion for dealing with brake torque bearing loads.

Kel.

[Wess-RA]

It'll be awhile before I get back around to that, considering some of my other fires. In the short term I'll keep a seriously close check on the bolts. I think you are 100% right on with the fix. I'll check to see what up-sizes we have clearances for.

[panozracing]

I agree with the changes except one problem. Dont you think Brembo knows what they are doing and designed something that works? Maybe you had a previous owner that decided to use his own hardware in lieu of paying out the nose for Brembo hardware?

[NZGTRA17]

Originally Posted by panozracing

I agree with the changes except one problem. Dont you think Brembo knows what they are doing and designed something that works? Maybe you had a previous owner that decided to use his own hardware in lieu of paying out the nose for Brembo hardware?

Brian, great idea regards checking that the hardware used is actually correct, I have assumed this to be the case. Does your car have fully threaded cap screws fitted such as Uwe has found in his? If so I would not be happy to run this fastener setup in my car, period.

Regards your question about Brembo's design capabilities, I cant answer that as I am a first time Brembo owner and have had no issues as yet. There are 2 observations that I would make though;

1. The GTRA has a higher spec attachment system (8 bolts) than what is now on the GTS (5 bolts) and I find that intriguing given the far higher load that the GTS brake system operates under.
2. There are countless manufacturers out there in the racing world producing products which fail in the environment for which they have supposedly been designed to operate in. I.e. no manufacturer is immune to design shortfall. I have seen this many times in the aircraft world as well.

Kel.

[Wess-RA]

You both make vary valid points. I wonder who actually spec.'ed these 5 bolts in question. The hardware on these didn't come from Brembo but rather from Coleman. Remember these are old technology Impala style hubs. It does make sense to have a shouldered bolt if I can find one of the proper shoulder length. I never posted close up photos of the failed hat. The threads were imprinted on the Brembo hat flange holes. Presumably this happened when the 2 bolts snapped and the hat tried to spin and therefore dug into the sides of the screw threads. I dont know what types of loads were induced upon these Impala hubs in the day or what they were designed to withstand. Needless to say I'll be inspecting these bolts often now. Hopefully I wont have any more failures to report; nor anyone else.

[Rich F]

You guys are a great resource for a new guy. I replaced my mounting bolts yesterday. All were rusted near the bolt shoulder and 1 snapped as soon as I put a wrench on it.

Would not have thought to check them without this site.

Thanks to all.

Rich

[Wess-RA]

Rich, I'm glad these discussions helped you. This is definitely a safety issue. Great that you caught it before an incident. I was told by PAD that they hadn't heard of this failure. That means most everyone has been doing the replacements on a correct schedule. Unfortunately yours and mine hadn't been done in time.

[jmimac351]

Originally Posted by NZGTRA17

Uwe, my RA had the standard rotors/pads/calipers on it when I got it. I have changed to rotors locally CNC'ed from blanks cast in Italy (half the price of using PFC rotors). I am also running Carbotech endurance compound pads.

I think that the additional load generated in a GTS is probably related as much or more to the torque compound of the pad being used. Remember that the RA comes with PFC 97's which are a low torque pad. Similarly the endurance pads I run are not as high torque as what you will run in a GTS for sprint type racing. I note a couple of comments about RA brakes being lower spec. The only major differences are the pads/lack of bias adjuster/larger rear master cylinder, all other components are essentially the same as the GTS as far as I am aware.

On the design side though Uwe I point out with interest that the RA brakes use 8 aircraft grade bolts to attach the disc hub to the wheel hub. There are 8 floater bobbins and bolts between the disc and disc hub. I see that the newer brakes use only 5 bolts between the disc and the disc hub/hat. The reduction from 8 to 5 bolts will mean that there is a less efficient clamp between the parts requiring a larger dia bolt and a higher torque loading to prevent fatigue. What dia are the 5 bolts and what is the torque loading on them?

Personally I am happier with the 8 bolt arrangement and will not be going out of my way to change this anytime soon !! (especially given your experiences).

Kel, you may have shared this but can you provide more info about the rotor blanks you're using? Where did you get them, etc.? A few of us are shopping for rotors for the GTRA and this is an issue.

Thanks,
Jim