Andy,
A subject very similar to this came up last year on the Triumph list, and
generated a great deal of heated debate. I'm sure my response will generate
another round, but I must respond. If one installs a set of disk brakes into
the rear of a Spitfire, I believe one is left with three alternatives:
1) Upgrade the front brakes to maintain the front to rear brake bias,
2) Add proportioning valve in the brake line to the rear to reduce the braking
power to approximately the same as with the original drum brakes, or,
3) Get your affairs in order and prepare to die.
Manufacturers spend a great deal of engineering time to balance the braking
system front to rear to prevent the rear brakes from locking up before the
front brakes do. If the rears lock up first in a panic stop, the rear end has
the unfortunate tendency of trading places with the front of the car. It is
extremely difficult to control the direction of travel when you are looking
where you've been. There is a great deal more to it than that, but you get
the idea.
I am not a brake engineer, but I have been doing a lot of research on this
subject for my TR6/Ford 302 project. By default, I wound up with 11 X 2 inch
drum brakes on the rear in place of the factory 9 X 1 3/4 inch drums. I am now
looking into option 1 or 2 (option 1 is preferable, option 3 is not
acceptable). Before taking my word for it, I recommend reading one of the
many books avialable with this type information. In particular, I recommend
"Brake Handbook" by Fred Puhn, HP books, ISBN 0-89586-232-8.
I don't know of any other readily available books just on brakes, but many of
the Street Rod or Hot Rod publications have material on this subject, and it
comes up often in the various rodding magazines. Without exception, the
articles warn against letting the rears lock up first.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
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