Actually, both trucks AND nearly all cars had the master cylinder under the
floor until the mid-'50s.  (Chrysler switched to pendulem-mounted brake
pedals with firewall-mounted master cylinders in 1955.)  Some cars' master
cylinders were more accessable than others.  (Ever to try to top off a 1953
Cadillac?  Takes nearly an hour, IF you've done it before and know how.)

I've always thought under-floor mounting was not a good idea.  The master
cylinders are subject to mud, road grim, salt and other contaminations that
can cause the linkages to bind and the fluid to be compromised.  Putting
things inside the passenger compartment and under the hood definately
increases safety and reliability.

I've switched my Vanagon over to DOT 5/silicon fluid, with excellant
results.  I wouldn't reccommend doing this unless one REALLY knows the
proper procedures, but using DOT 5 does alleviate concerns about spilling a
caustic fluid behind the dash of a Vanagon when doing brake service.  (Did
this to my '53 Cadillac, too.)

Mark in Westminster, CO

>
> Some vehicles do have their brake master cylinders underneath the floor pan,
> it was common on trucks in the 1950's. A lot of street rods built today also
> place them there, it make for a more clean looking engine compartment,
> especially after stuffing a big V-8 where a 4 cylinder used to go. The linkage
> is pretty straight forward, it just goes down instead of up, and power
> boosters will work also.
>
> Mark in AK