Date: Sat, 3 Jul 2010 17:17:54 -0700
Reply-To: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Subject: Re: Pedal Pressure & Brake Lights
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=response
well,
they just repsond to pressure, wherever it comes from.
ideally that pressure only gets developed in the brake lines from your foot
pushing on the brake pedal, and the booster amplifying that pressure ..or
'foot force' into the lines, developing pressure.
sure...if say, things were dragging building up heat, that could deveope
pressure ..
but dragging brakes would be more of an issue than brake lights being
activated by dragging brakes,stuck caliper etc.
about brake master cylinder push rod length ...
that is a critical adjustment in my opinion.
I can say this for sure ...if you adjust it so it's too long ..
it will hold on the brakes some, or can.
but the brake switches are passive ..
they only know when brake pressure exeeds the threshold at which they make
contact.
they have no idea where the pressure comes from.
If there was 'stuck on residual' pressure ...
enough to keep the brake light switches activated, you'd know it from
dragging brakes I would think...
and it would not affect when the brake lights come on.
I've yet to hear of any vanagon people measuring actual brake line pressure
..
but that is a fancy diagnostic tool...
and ...there are even caliper piston force measuring guages...
just saw a tool for race cars for just that ...about $ 200 .
when you have really weird problems you start thinking about actual brake
line pressure in psi ...
and how much force is actually getting applied to the brake pads, etc.
my point is ....................btw, .is it marked on the switches...what
pressure they activate at in bar ..?
we should look into that.
surely they must come in different pressrure ratings.
and yeah...really old ones sure might need more pressure to make contact.
On my vans, the brake lights just work when I stomp on the pedal medium
hard.
and it's always seemed to me that if using a pedal-holder-down tool to
erergize them...it seems to take a fair amount of pressure on the brake
pedal.
I'll get a couple of new ones and try them out sometime when it seems to
take a bit extra pedal pressure to make them make contact.
s.
----- Original Message -----
From: "David Beierl" <dbeierl@ATTGLOBAL.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, July 03, 2010 12:19 PM
Subject: Re: Pedal Pressure & Brake Lights
> At 02:48 PM 7/3/2010 Saturday, neil n wrote:
>>installed ~4 years ago. Would an improperly adjusted push rod (on
>>booster) affect amount of pedal pressure needed to turn brake lights
>>on?
>>
>>What else would could be at fault here? Design flaw?
>
> Neil, they're pressure switches. They haven't a clue that you're
> moving the pedal, but they know when the brakes start to push back on
> the hydraulic fluid, and that's when they switch. If they're not
> switching on reliably by the time the first perceptible braking
> occurs, they're bad. If they're switching on *before* the brakes
> actually engage, you've got stuck calipers or some other mechanical issue.
>
> Yours,
> David
