What is this? Wire in slotted rotor

FChat experts,
This is my first post! I've been lurking for a while and so far you've all answered just about every single one of my questions in the regular posts w/o having to submit replies or new posts. Thank you!!!

So I'm in the middle of rebuilding the CV joints on both half shafts, and as I was putting a screwdriver into the slots of the rotor on one of the last bolts, I came across this bizarre little wire buried in the slots of the rotor.

In the picture, I'm holding it in front of the rotor. However, I originally found it *in* the slots--in the same orientation that I'm holding it. In other words, each "lobe" of the wire was in a separate slot and the bottom of the wire was bridging between them. That bridging was nearest the hub, not on the outside of the rotor--which would have probably flung it out of the rotor a long long time ago. I had to rotate the affected rotor slots to the opposite side of the caliper to find room to wiggle it out from the inside of the rotor near the hub.

So what is it? And how long has it been in there? It's definitely not a paper clip (metal gauge too thick). And the shape makes me think it was intentional. The "mild" surface rust had adhered it to the inside of the slots and had to do a bit of poking to loosen it. So it's been there a while.

Also, again many thanks for the excellent info contained in these pages. It's made things fairly straightforward to debug. I do wish the search function was a bit more advanced...but, well, it seems this forum is the only thing that's free about owning a Ferrari, so I'm really not complaining.
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I believe it's for balancing. Newer rotors have material ground off the outer edge.

 

Balancing would be my guess as well, ……..although the process to spin a bare rotor and determine the location rather boggles the mind...and that wire can not weigh much....

Thinking about it I would hazard a guess a parts guy stuffed it in there to have a place to mount a Part Number tag??

That's really odd, have never seen one and I have stacks of spare rotors lying around....of course I will have to look in the morning!!!

 

It's a balancing hair pin, very common. More recently MFG switched to milling.

 

Wow--I've never seen a balancing wire for a rotor before either.

So next question: Does this mean I should try to put it back? Similar to @BigTex note, I find it difficult to believe that the mass of this little wire actually makes a difference to the balancing of the rotor esp given the years of oxidation on both the rotor and the wire itself. You'd think that both the oxidation and the rotor wear have changed whatever "balance" this little guy was trying to hard to achieve.

But if you folks think I should put it back, well, back it shall go.

 

I've seen this a few times in older cars/rotors. Yep, for balancing.

 

Are you going to remove the rust/oxidation?

 

@thorn no immediate term plans to clean up or resurface the rotors. It would be *way* down the list.

 

Welcome to Ferrarichat

 

Afternoon Jason and welcome to ferrarichat,
My 1987 328 has the same wire on the rotors, balancing purposes? Beats me, yet makes sense. Although with such small mass(the wire) and small rotor diameter(centrifugal force) I really don't believe that you would notice any vibration if it was removed.

Just my opinion,

John.

 

Was it for final balance or balance during surfacing at the manufacturing process?

 

I would guess final balancing; as SMG noted, more modern rotors have an area that's cut/ground off to balance it. Balance (or lack of it) isn't really a thing when you're dealing with resurfacing a rotor - at least not that I've ever heard/seen nor done.

 

The reason I asked was that the speeds at which they are spun during manufacturing is probably a lot faster than what we think of when resurfacing and therefore that little bit of weight might be more significant ? Just a guess.

 

brake wear indicator

 

It was always my understanding they were an anti harmonic noise spring, designed to stop ringing noise under braking

 

For balancing. I just replaced my original factory rotors and they had that pin. The (OEM Brembo rotors) had the same pin. I would leave it in IMHO.

 

Put it back in the same place you removed it

 

Hmmm...just wondering - if it's for balancing, did the manufacturer have a supply of different size (weight) clips for every possible balancing need or were all the rotors equally OUT of balance based on the manufacturing process so that only one specific clip was was necessary? BUT...seems like if they were all manufactured equally OUT of balance, they could have just as easily been all manufactured equally IN balance.

Not saying it isn't for balance but it seems an odd way to do it. I would think some spot-grinding or drilling would be more effective...

 

I found one in my 308's Brembo so I called them. They confirmed its for balancing.

 

Funny, I was going suggest they were NOT for balancing based on Brembo's web site which includes this statement re rotor balancing:

"All discs are checked and, if necessary, balanced automatically during production.

Discs are checked on an electronic test bench which spins the disc and measures any imbalance. If any imbalance is detected, the excess material is ground away to balance the disc perfectly.

Not all discs need correction, and the majority are already perfectly balanced, making it unnecessary to machine material from the outer edge. This means that some discs may have a notch while others do not."

Since they don't mention anything about clips, I ASSUMED they are not there for that purpose. My assumption, could, of course, be erroneous and that these clips were used back in the '80's but the idea of such a clip for balance still seems odd to me. It's not like the 1980's were an era of 'stone knives and bear skin rugs' (thank you Mr. Spock). If they could measure the balance during the manufacturing process, they could perform the necessary grinding to adjust the balance on a rotor rather than sticking a clip on it, as did the common rotor manufacturers. Again, did they produce a variety of these clips in different weights? Makes no sense to me.

 

I may have been unclear in the above post and the 20 minute limit to revise had occurred.

I said this: "If they could measure the balance during the manufacturing process, they could perform the necessary grinding to adjust the balance on a rotor rather than sticking a clip on it, as did the common rotor manufacturers."

In re-reading it, I realized that it could be taken as saying the common rotor manufacturers used a clip. I meant the opposite, the common rotor manufacturers back then (and now) balanced rotors if necessary by grinding, not by using clips.

Sorry for poor composition

 

Still unclear what you are trying to say.


A. How they balanced rotors in 1980 is and imagine this "Different than how it is done now"

B. The wire is a balance weight.....Period.

And C to the original poster. That is not a slotted rotor. A slotted rotor is something very different. It is a ventilated rotor.

 

What I'm trying - unclearly - to say is:

In the 1980's (and much earlier) standard production rotors made by the common rotor suppliers in the USA were balanced then as they are now - by grinding/milling as necessary. It is (was) hard for me to imagine that Brembo, who from what I understand, was supplying brakes for Ferrari F1 cars back then, did not have the technology to balance brakes accurately by machining.

I can certainly understand the IDEA of using the clips - pretty much like balance weights on a wheel. It just seems 19th century crude, especially for a vehicle capable of 150+ MPH but if that's how they balanced them, then that's the end of the discussion and my confusion over the clip's purpose!

 

Mill balancing is how it's done now, not that it wasn't possible then but the technology wasn't exactly in place. Instead the balancing was done with hairpins, much like wheels today with weights. With advances in CNC etc, the marriage of milling and balancing is possible, faster and more accurate.

Keep in mind that rotors are cast, there's going to be imperfections, always. Loss rates are high as well due to this.

 

I am sure its robotics at this point and remain untouched until unboxed by the installer. Not done that way in 1980.