I'm not sure there is logic involved, but there is some evidence - 3 cars in
my club, including mine have experienced this. It doesn't make a lot of sense
to me, but it seems too coincidental to have switches fail completely or
become much less sensitive to pedal pressure to stop working, and its been
after a switch to Dot 5. Dot 4 flushing/refresh, typical maintenance etc and
I don't know of an issue. Possibly its related to having some air trapped in
the switch, but in my thinking that would just lead to a spongy pedal feel,
not failure - pressure would be transmitted in the switch through the air
too.
In my case I was still using an older switch so possibly the newer Napa or
equivalent replacement might behave better.
> Date: Fri, 13 Jun 2014 07:34:18 -0700
> From: binduni@gmail.com
> To: triumphs@autox.team.net
> Subject: Re: [TR] Brake light woes
>
> Not sure I follow the logic of the Dot 5 fluid - I've used this in at least
> a dozen cars I've restored and have never had an issue because of it. I
> have, however, learned that the mechanical pressure switch is a finicky
> bugger, and have also learned that if I fill the pressure inlet with fluid,
> it will push the air out that is trapped in there. Remember, if you have
> air in your brake lines, the brakes don't work so well. Same goes for the
> switch. You need to "bleed" the air out of it before installing it. I'm not
> claiming that the switch works exactly like a mech switch, but pretty
> close. If there is enough pressure to engage the brakes, the lights should
> come on.
>
> Of course, this is assuming the switch is new, which is an absolute must!
>
> Brian
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