Fortification is the Club Magazine of the GT40 Enthusiasts Club
Copyright: GT40 Enthusiasts Club 1997
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The original Mk 1 GT40s kept their handbrakes in about the same location as the
glovebox on most cars: under the left hand side of the dashboard. The "tunnel"
between the seats had a curved top, much like the transmission tunnel in older rear drive
cars, but narrower. By contrast, most replicas have a flat-topped tunnel with the
handbrake sitting on top of it in the conventional position between the seats.
Although I am not fanatical about originality, I wanted my car to be a reasonable replica
in the cockpit. I also just liked the arrangement in the original cars. So the handbrake
had to go under the dash. This was not a trivial job for two reasons. Firstly, the
handbrake mounting has to take high loads. The driver may heave on the lever, and the
mechanism gives a lot of mechanical advantage, so loads in the structure around the
handbrake could easily reach 500 or 1000 lbs. Secondly, the linkage would have to go
around three corners before it had a straight pull on the handbrake cables coming through
the firewall.
I decided to use an open cable running over pulleys. The first job was to fabricate a
subfrarne which would hold the handbrake in the correct location and provide mounting
points for the pulleys. I had bought a cheap(ish) MIG welder and taught myself to use it.
I was confident enough to weld up a subframe, but I did not want to start welding things
to my precious chassis: so the subframe would have to bolt in without having to drill big
holes in the chassis (and thus weakening it).
The basic shape of the subframe is shown in the photographs. The location is quite
critical (low enough to clear the dash without scraping your knuckles, but high enough to
clear the passenger's knees and keep the subframe hidden from view), so make a mock-up
from scrap wood and masking tape, and check it with the dash moulding in place.
When you get to the metal, measure twice and cut once. I used 1" square steel box
section. The plan was to run the handbrake cable down the centre of the box sections, so
that all the serious loads would be taken by the subframe members in compression, so I
made cut-outs for pulleys etc. before finally welding up.
The handbrake itself was from a Triumph Herald. There was nothing special about this
choice, but it was about the right size and looked the part (1960s not 1950s chrome or
1980s Cortina). No doubt someone in the Club knows where the handbrake on the original
cars came from. The mounting brackets were made up from angle iron welded and bolted to
the subframe. The all-important pulleys were a problem. They had to be large diameter (to
avoid damaging the cable by continually forcing it around a tight radius), and they had to
be strong enough to cope with the loads, and durable enough to go on coping year in and
year out.
I eventually used pulleys from the flap system of a light aircraft. Smaller Cessnas and
Pipers use cables for both the main flight controls and the flaps, but the flap cables are
larger at 1/8" diameter. In some light aircraft (e.g. Cessna 180 or 185), the flap
system is operated in much the same way as a handbrake, by heaving on a socking great
lever. Good second hand flap pulleys are sometimes available from aircraft that have been
written off. a friend in the industry managed to find me three without robbing his
employees stock.
No doubt they would be available new, but I have no idea of price. The pulleys were
mounted on brackets running across the corners of the subframe (see drawing):
The only other critical item was the subframe mounting next to the last pulley at the
bottom of the front bulkhead where the handbrake cable emerged to run back to the rear
bulkhead. At this point, the tension on the handbrake cable would be doing it's best to
tear the subframe out. The Tornado chassis has a substantial steel plate welded in here
(supporting the driver and front passenger's heels). A lug was welded to the foot of the
subframe, and this lug was bolted to the steel plate.
The subframe was later modified so that it doubled as a servo mount and tripled as a
heater mount, painted and installed. The finished job (cable by Speedy cables) seems to
work well, but the jury is still out on it as the car has not been MOT'd, and only time
will tell whether the whole set-up will hold up under the years of use.
If I were doing it again, I might experiment with bell-cranks, rods and rod-end bearings
(Rose joints) instead of the pulleys. I might also re-examine the idea of putting the
servos under the dash. It's a neat installation, but access is difficult and it may become
a maintenance problem.
email to sundt@pncl.co.uk
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