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Spitfire brake rotors

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N

number6

Jedi Trainee
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Having decided to rebuild the front suspension of my 79 Spitfire, I ordered all the parts. A friend who's
garage I using said I should turn the new rotors for better balance. He said his dealer told him this is done as a matter of course on brake rebuilds. I am not buying this. Anyone heard of this? Can't imagine
new parts are that far out to need this done. Am I missing something?
Tom S.



1979 Spitfire
1969 MGC
1967 Rover 2000 TC
2004 Jaguar X-Type
Sunbeam Harrington
 
Having access to a brake lathe, I have checked this myself. You'd be surprised how often I have found new rotors that are not perfectly straight. I am sure there is a tolerance they work to , so they are not often dead nuts. Sometimes 001"-.003" out. I like to check just for piece of mind.
 
Your friend is "wrong" stating that this would be done for balance. It would be done to address runout. Runout can be felt as a pulse in the pedal when you apply the brakes.

As Scot said above, check the runout of the new rotors and then make your decision. If you use a dial indicator to check disk runout, be aware that the hubs have an acceptable horizontal endfloat. My Bentley manual says endfloat is 0.002" to 0.008" while Haynes says 0.003" to 0.005". Spin the disc carefully to measure runout without applying horizontal force or you may mistake endfloat for runout. Regardless, do not have the rotors turned "just because" as the disks also have minimum thickness specification. You don't want to start with "narrow" rotors if you don't have to.
 
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