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brake drum cracked!!??

To: vintage-race@autox.team.net
Subject: brake drum cracked!!??
From: " christopher h. kang, md" <chkangmd@earthlink.net>
Date: Tue, 31 Jan 2006 13:44:26 -0800 (GMT-08:00)
I need some input on a prob. i just found (just getting to do winter 
maintenance, was waiting for it to get cold outside).

the rear drums on my car cracked in a linear pattern across the diameter 
(almost completely in half!), going through  the two small 3/8" holes that are 
for  holding the drum to the hub.  i took a photo  but don't have any place to 
post it.

info: hubs are 3 yrs old. bought  from Rimmer Bros. in England, are from a  GT6 
early model rear brakes, I'm using them on my  '72 lotus Europa TC (wt 1550#). 
new pads from carbotech (alittle harder than the ones I used last year).  the 
backing plate uses twin cylinders as was used in the front of the triumph 
herald sedan. This set up has been used by prior racers w/o problems. The only 
problem I've had w the rear brakes was related to trying to use after market 
wheel cylinders which was corrected this year by have the originals resleeved.

any ideas as to why? this is what my friend who helps me work on the car 
thought:

>Very interesting, and it suggests that there was either a stress
>riser, or poor casting.  The linearity of the break suggests an over
>tension by the brake shoes, though I can't understand why unless the
>shoes locked in position while the drums cooled, but then why right
>across where the holes are?  I think you are right in that the crack
>must have started at the small holes and propagated outwards.  I assume
>the wheel nuts were tight, and the shoes retracted? 


christopher




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