Please note that I didn't say anything about a failure of differential pressure switches.
In fact, I've personally never heard of one failing (I guess it's possible, but probably
very rare).
What I was saying was that if a BRAKE CIRCUIT fails, it triggers the switch and when these
switches are triggered (ie, piston moved off center) they have to be reset by recentering
the piston. Perhaps I should have mentioned that these switches were DESIGNED specifically
so that they would have to be reset. The original idea was that having the failure light
remain on after a brake circuit fault would serve as a continuing reminder to anyone
operating or working on the vehicle (including a safety inspector) that work was needed.
This would be more important in fleet or rental vehicles where there are multiple
operators or customers who don't communicate with each other regarding mechanical problems
and who might not be accustomed to the way a vehicle is "supposed" to feel.
I really don't think that a brake circuit failure light is a "gimmick," any more than an
oil pressure guage or light is a gimmick. Further, under certain circumstances (perhaps
rarely, perhaps not your own circumstances), it just might save someone's life.
I partially agree with your opinion about being able to detect a circuit failure by the
way the vehicle responds. In an earlier part of this thread, I opined that a failure of
either brake circuit would usually be noticeable (especially the front circuit) in almost
any non-power-assisted system. However, a rear circuit failure in a power-assisted brake
system might very easily go unnoticed for some time. Depending on the vehicle, road
conditions, and loading, the front brakes do about 60 to 85 percent of the stopping work.
If you have a vehicle with a high level of power assist, particularly if it has a short
pedal travel design (where a failure of a circuit may cause only a slight change in pedal
height), the loss of the rear circuit (especially if it was a gradual loss due to leakage)
could certainly go undetected. A person could hop into an unfamiliar vehicle with
non-functioning rear brakes, and for all he or she knows, that vehicle could be handling
normally.
Finally, these switches are standard in all factory dual-master-cylinder systems. If you
don't like the switch, I suppose you could remove it. I personally see no reason to remove
it but several reasons for having it there, including possible liability reasons in the
case of a conversion. Let's say you do a conversion and the brakes fail while someone is
driving your car. It might be argued that you didn't do a proper conversion because you
failed to install a safety warning device that is standard in factory automobiles. Maybe
that argument would hold water, maybe it wouldn't. But why not go ahead and put the switch
in? It doesn't cost much and the switch itself should not reduce the reliability of the
system itself. Worst case is that you have to take a little time to reset it after it has
done its job.
What we DO seem to agree on completely is that we both perceive a significant safety
benefit from having a dual master cylinder. This brings us back to the original intent of
the first posting...to get feedback about the potential value, problems, technical
considerations, etc., of converting an M37 to a dual master cylinder system.
I'd still like to get some feedback regarding the actual "nuts and bolts" of the
conversion itself.
Thanks for your comments.
Regards,
Alan.
jonathon wrote:
> >For those of you who haven't had the pleasure of dealing with these switches...
>
> I find these silly switches to be utterly useless. I NEVER put them in and
> anything I have every owned that had one never worked. It should be very
> easy do get the feel of something wrong with the brakes both by the feel of
> the pedal and how the vehicle is behaving. But then, if you like gimmicks,
> go right ahead. I do believe that the safety benefit of a dual master
> cylinder (with or without the switch) far outweighs any statistically
> insignificant failures of them.
> je
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