[Geoff Dowdle]

Geoff,



Although I have not done this conversion myself I believe a rear disc
from a Mercedes 300TD can be fitted to the front hub of a 400 - 403 with
very little modification (possibly just enlarging the stud holes). It is
approx 11inch diameter x 1/2 in thick with correct offset & PCD .



A caliper carrier must then be made to suit . Note the 403 uses a sway bar
and the caliper can hit the vertical sway bar link on full lock . Also
select a caliper that is not to bulky as you need clearance on the wheel . I
used a Girling #17 caliper from a Humber Hawk post 1960, they use a larger
pad than the 406 Dunlop calipers. There are probably many calipers available
that would fit but most modern calipers are designed to fit thick ventilated
discs and are not suitable to use with the MB 300TD disc.

Bristol used 7/8in diameter rear wheel cylinders when converting 400 - 405
to Dunlop front discs .If you don't reduce the diameter you could get severe
rear brake lock up on panic stops.
OR
You could retain the original rear wheel cylinders and fit a adjustable
brake proportioning valve in the line to the rear brakes to get the correct
brake balance between front & rear.

I suggest you get some advice from a brake specialist who prepares
race/rally cars.

The 406 brakes front & rear on my 400 with Girling #17 front calipers
certainly makes the car stop as well as most modern cars.
Good luck ,its a worthwhile update .

Geoff D