Yes, Bob was right, it was a year ago this month when we broke a brake ro= tor at an autocross.
It was a clean, round break, completely around the circumference of the p= lane where the rotor mounts onto the hub. As a result, the rotor itself staye= d in place. Although the noise it made was real scary, it didn=92t do any oth= er damage except chip a little paint off the inside of the dust shield. And= , since the rotor remained captive there on the hub, the pads didn=92t pop = out and I didn=92t loose any braking effort at the other three corners.
The funny part was that it was a brand new rotor, that hadn=92t been on t= he car for much more than six or seven months . . .
My brake rotor story actually begins in December, 1990. I was ordering s= ome stuff from Vicky-Brit., and I noticed that they had brake rotors listed i= n the catalog. <YA-YA, I know . . . But this was 1990 . . . we didn=92t have n= o Tiger-list back then . . . And how was I to know they were THE Vicky-Brit= .?> Anyway, even though I didn=92t need =92em right then, I knew I would some= day, so I ordered a pair. <$99.50 each, in 1990.> They went on the shelf in the s= hed, and remained there until sometime in the spring of =9297.
Then in April of 1995, I was ordering some other stuff from Rick, and I noticed that he had brake rotors listed in the catalog. Even though I di= dn=92t need =92em right then, I knew I would someday--two Tigers are surely goin= g to need two pairs of brake rotors someday, right?--so I ordered a pair <$67.= 00 each, in 1995 . . . get the message here boys =92n=92 girls?> They too w= ent on the shelf in the shed.
Then, in the spring of =9297, I started fooling around with the brakes on= the autocrosser. Bought some of those high-tech carbon-kevlar pads from Dale= , and decided that now was the time to swap in a pair of new rotors. The old o= nes weren=92t all that bad, and could have been turned, but hey, I had new on= es on the shelf. So I grabbed a pair off the shelf and went about trying to le= arn how to drive with the much-improved brakes.
Shortly after that, in preparing the street car for a trip somewhere, I determined it was time to repack the front wheel bearings . . . might as = well swap in some new rotors, no? So on went the second pair.
(This is sort of related, because at this point, I didn=92t know which pa= ir had come from where. I had a pair of new rotors on the autocrosser, and a pa= ir of new rotors on the street car. One pair had come from Rick, the other fro= m Vicky-Brit. But I didn=92t know which was which.)
The first indication that something wasn=92t quit =93right=94 with the si= tuation was the response I got when I called Rick=92s place to order another rotor fo= r the autocrosser. =93We don=92t carry new brake rotors any more,=94 she said= . =93We have some good used ones . . .=94
=93Well, hrumph!!! I already have a shed full of good used ones; I need a= nother new one! . . . And why doesn=92t Rick have =92em any more? Curt has =92e= m. Yucky- Brit. has =92em. And somebody told me the club in England has =92em? Wh= at=92s wrong with Rick???=94
Now it just so happened that last summer I was in the middle of a complet= e rebuild of the front crossmember for the Series II soon-to-be pointy-fin- racer. I needed new rotors for it, but nobody listed rotors for the Seri= es I & II Alpines. I was just beginning to think about the possibility of tak= ing a pair of later Alpine/Tiger rotors and turning them down to fit the Series= II. If that would work, I might as well get three from Curt--a replacement fo= r the busted one and a pair to modify for the Series II. <That, it turned out, would not work, but that=92s yet another story.>
So, before ordering three rotors from Curt, I decided to call Dan Walters= and see what he had to say about the possibility of using the later rotors on= the early car. I opened the conversation with something like =93Hey Dan! We= broke a brake rotor at Devore last week and I was thinking about . . .=94
As soon as he heard about the broken rotor, he wanted to know ALL about i= t. Was it old/new? Where did I get it? How did it break? You know how Dan= is; he=92s not like the rest of us--you and me. I see a busted rotor, and I = think =93Wow! I need another rotor!=94 Dan sees a busted rotor, and he thinks= =93Why did that rotor break?=94
And the reasons for Dan=92s concern:
1. According to Dan, about a year before that, Dale had discovered a crac= ked brake rotor on Jeff Queen=92s vintage race Tiger. It hadn=92t broken, bu= t it was cracked . . .
2. Then, maybe five or six months before that, according to Dan, Tom Saka= ii had broken a rotor while engaged in a vintage race.
Under =93investigation,=94 Dan discovered that the rotor on Tom=92s car h= ad been machined improperly. The surface on the inside of the =93hat=94 where th= e bolts go through to mount the rotor onto the hub had been machined out too far. This made the little funnel-shaped surface that joins the disk part of th= e rotor with the mounting surface too thin. This is most noticeable, Dan s= aid, when you install the things on the hub. On an original/OEM rotor, you ha= ve a tough time putting a socket over the bolt because there is hardly enough = room between the bolt head and the inside surface of the =93hat.=94 This too = was a new rotor, and after checking a number of others, Dan determined that all suc= h new rotors were improperly machined in this area.
Per Dan, I compared my busted rotor with some used/OEM rotors from the sh= ed, and the bad news is that the diameter of the inside portion of the =93hat= =94 where the disk joins the mounting surface is approximately:
o 4.180 inches on a used/OEM brake rotor o 4.320 inches on a new brake rotor
The difference, nearly an eighth of an inch, substantially reduces the thickness of the material that joins the disk to the mounting surface of = the rotor.
According to Dan, it was when he called Rick and explained the situation = that Rick stopped selling the things.
I called Rick to verify the story, and he did. According to Rick, all of= the new brake rotors that have been available for a very substantial period o= f time came from the same supplier. He also said that the supplier claims = to have manufactured the rotors EXACTLY to match a brand-new Girling rotor .= . . ???
When I checked the new rotors on the street car, they were identical to t= he broken rotor on the autocrosser, which means that these things have been = on the market since as early as December of 1990, as near as I can tell, and quite possibly earlier, though my records do show that the ones I bought = from Vicky-Brit. were back-ordered for a couple of months and didn=92t actuall= y ship until February of 1991.
So, should we go into a =93panic=94 mode if we have these new rotors on o= ur cars? I don=92t know. All of the failures I=92ve heard of have been in competi= tive driving situations--haven=92t heard of one breaking on a street car. I r= eplaced =92em on the autocrosser with resurfaced originals, but I still have =92e= m on the street car . . . Yes we still drive the street car--drove it to Pleasanto= n to have a peek at Bo=92s really neat-o garage a couple of weeks ago--but do = have a funny feeling about aggressively Tigerin=92 down a twisty mountain road w= ith =92em . . .
The new rotors bear casting numbers of =93BDC48C=94 and =93R1=94 (or perh= aps "RI") 180 degrees apart on the inside =93hat=94 surface.
The End
Ramon