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Re: MGB Brake rotors

To: gofastmg@juno.com
Subject: Re: MGB Brake rotors
From: mgb.roadster@juno.com (Larry A Hoy)
Date: Thu, 8 Jan 1998 18:32:12 -0700
Well lets see.  Looks like most agree that there is little benefit in
cross drilling brake rotors, there are probably better ways to cool
brakes, and I own two spare paper weights!

Thanks for the info.

Larry Hoy (MGB.Roadster@juno.com)
Denver, CO USA
1969 MGB Roadster
1987 Jaguar XJ6 Vanden Plas
===============================
On Thu, 08 Jan 1998 19:53:34 EST gofastmg@juno.com (Rick Morrison)
writes:
>
>On Thu, 8 Jan 1998 10:52:24 -0700 mgb.roadster@juno.com (Larry A Hoy) 
>writes:
>>I have a "spare" set of front brake rotors for my MGB, I have 
>>considered drilling them for ventilation purposes.  The rotors are 
>>from a 1976 B roadster and my car is a 1969 B roadster.
>>
>>Are these rotors the same?  I think so.
>Yes
>
>SNIP
>
>>What is the minimum thickness specs?  My "spares" measure .290"
>The minimum rotor thickness, per factory manuals is .300". You don't 
>have any spares:, you now have two very large, very heavy 
>paperweights. Sorry
>
>>Do you drill then turn, or turn then drill?
>If you insist on having it done, drill the rotors first, then slightly 
>camfer each hole, then turn them.
>
>>The rotors look OK so do you drill and just put them on (and forget 
>>turning).
> No, see above.
> You will also have to make sure the machinist who drills the rotors 
>does not make the hole pattern too close, or the holes too large, or 
>the pattern symetrical. Any or all of the above WILL lead to cracking 
>of the rotors, starting at the stress raisers, the holes. Also, the 
>drilling removes mass from the rotors which is as important to cooling 
>of the brakes as airflow (possibley more so), So the net gain in 
>cooling is marginal. What you gain in airflow cooling is nearly offset 
>by the cooling due to the mass of the rotors.
>  By the time you pay a competent machinist to do all that is 
>required, plus assuring the rotors stay balanced, you'll find you have 
>spent as much or more than buying a set of new cross-drilled rotors.
> With out some method of getting cooling air to the drilled rotors, 
>the effect would probalby be nil
> A much better solution, and much less expensive, would be to 
>fabricate air ducts to direct a cooling stream of air onto the 
>undrilled rotors. Much more effective than plaine drilled rotors and a 
>lot less expensive. Not to mention a greatly reduced probability of a 
>rotor cracking!
>
>Rick Morrison
>72 MGBGT
>74 Midget
> 
>>TIA
>>
>>Larry Hoy (MGB.Roadster@juno.com)
>>Denver, CO USA
>>1969 MGB Roadster
>>1987 Jaguar XJ6 Vanden Plas
>>===============================
>>
>>
>>

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