MGB and GTV8 Front brake upgrade
Geoff King in Kincardineshire has sent in a useful
upgrade to the front brakes on his V8 Roadster conversion. (May
Powerful four piston calipers with vented discs can easily be retrofitted
to the MGB or GTV8 using components from specialists such as Wilwood,
however, the following notes refer to a cheaper alternative using
readily available standard parts.
Four piston calipers with vented discs. (Photos: Geoff King)
Four piston Rover SD1 calipers (see above) or the calipers
from an Austin Princess bolt directly on to the MGB or MGBGTV8 stub
axle; both calipers have the same distance between mounting holes
but thin wall sleeves or stepped bolts are required for the metric
holes. Special hoses are also required with an imperial fitting on
one end and metric at the other to connect the Metric caliper to the
existing Imperial MGB hydraulic system. Sleeves and hoses are available
from Dave Vale at V8 Conversions. The dust shield can be left off,
to increase cooling, or it can be cut slightly to clear the larger
caliper. The calipers bolt up with no other modification and it looks
as if that was how MG built it originally.
MGB and GTV8 discs are 10 ¾ inch diameter (273 mm), Peugeot
505 Turbo vented discs are also 10 ¾ inch diameter (273 mm)
with the correct offset to centre in the Rover SD1 or Princess calipers
and simply require re-drilling for the MGB bolt PCD. The disc spigot
bore is very slightly larger than the MGB hub and ideally it should
be sleeved to minimise the risk of radial runout of the disc.
RV8 vented disc is smaller at 10 5/8 inch (270mm) diameter and the
Rover SD1 vented or solid discs are considerably smaller at 10 1/8
(258 mm); fortunately neither will fit the MGB hub as the offset is
The area of the four Princess caliper pistons is the same as the
two MGB pistons, therefore, pedal travel is unaffected. The SD1
has slightly larger pistons which need more fluid to move the same
distance so there will be an increased pedal travel if used with
the original master cylinder, although, in practice this additional
pedal travel would probably go unnoticed. The late rubber bumper
MGB master cylinder with the integral servo has a larger bore and
is a better match for SD1 calipers but to fit this to an earlier
car it is necessary to change the whole pedal box assembly.
Four piston calipers are bigger and heavier than the MGB ones so
unsprung weight is increased, however, the difference is not huge
and for road use can be ignored - and anyone concerned about unsprung
weight should try weighing a rear axle assembly, but that is another
Although the calipers and discs fit on the stub axles very easily
care must be taken when fitting the wheels. SD1 calipers won't fit
behind Rostyle wheels without using ¼ inch spacers, so trial
fit and check for clearance if using wire wheels, aftermarket alloys
or original GTV8 wheels.
With any front brake upgrade the front/rear brake balance should
be considered and the use of the smaller roadster rear brake cylinders
in a GT backplate would reduce premature rear lock-up.
Finally, no matter how good the brakes are they will only be as
good as the tyres at stopping the car. To avoid compromising safety
renew old tyres, even if they have considerably more than the legal
tread depth. The tyre might look brand new, but rubber degrades
over time irrespective of whether it is being used or not, the tyre
will lose flexibility and handling and grip will be reduced.