[Fot] TR4 dual circuit brakes - restrictor valve

[Randall]

> Disk brakes generally need a
> residual
> pressure valve which keeps a bit of pressure on the pucks to prevent
> them from
> being withdrawn too much by seal elasticity.

In the case of the TR3-4, I believe it was done for a different reason: the
front spindles flex enough under hard cornering to push the caliper pistons
back and cause a low pedal on next application.  

I don't recall the change point offhand, but the factory deleted the RPV at
some point (during TR4A production maybe).

Having run for some 25 years with the RPV removed from an otherwise stock
TR3A, I do not believe that seal flex is a significant issue with these
calipers.  But spindle flex definitely is.  For my car and my driving (on
the street), I find that I can just live with a low pedal after hard
maneuvers.  It's never been low enough to need a pump, just enough to be
disconcerting if you aren't expecting it.

I believe it was Jack Drews that came up with the spacer fix instead.

-- Randall