Hello again Martin,

When you say, "I therefore assumed it could only seize in the off position
if the rear of the car was left up on axel stands with the rear axle
hanging", you're exactly right, which is why they never do seize in that
state, but always in an on or partly-on state, in which you have full or
nearly full braking available at the back. I just had a quick look under one
of our Suds, and found that, with the car empty and at rest, the
valve-actuating lever was not pressing against the valve at all, suggesting
that the valve was completely relaxed and providing full rear braking, i.e.
that any limiting would not start until the rear suspension started to rise
above its static and empty level. I guess the rear brake pistons are of
such small diam that no limiting is needed until this happens.

And when you say, "with our Citroen GS`s ...We used to load up the boots for
the MOT to make sure the rear callipers were doing some work", well, if my
observations under my Sud tonight were right, that wouldn't help in a Sud,
as even with my car empty the valve was already supplying no limiting, i.e.
max braking. It'd be interesting to make some proper tests with jacking up
and loading down the suspension and observing how the valve actuating lever
reacts.

Best rgds,
Graham in NZ

>>>>>>>
Martin wrote...
I always assumed the valve was progressive. That is, when the car was fully
laden with rear passengers and a full boot it was 'off ' and when braking
very hard unladen was 'on' to prevent rear lock up. So under light braking
with no extra load it was about half on (or half off) and this was why the
rear disks rust, as most of the time there is no extra weight on the rear
and so rear braking effort is always partly restricted. I therefore assumed
it could only seize in the off position if the rear of the car was left up
on axel stands with the rear axel hanging...
...with our Citroen GS`s...We used to load up the boots for the MOT to make
sure the rear callipers were doing some work.