[DeTomaso] Trying to diagnose weak brakes

Joseph F. Byrd, Jr. byrdjf at embarqmail.com
Sat Feb 17 11:06:49 EST 2018


Forgive me, but after having to participate in several “Fault Tree” evaluations where we thought of ridiculous scenarios that could be possible.
Given;
~3 inches of travel before braking
Rear doing the most braking
The proportional valve is gutted
Assume;
 Air is trapped in the proportional.  This would cause the first master cylinder piston to travel while not establishing front caliper pressure to move the second piston.   After 3” of pedal travel, the first piston makes contact with the second and now the rear caliper pressure is devolved with majority rear braking.
However, one would expect the differential valve to give failure lamp.

-----Original Message-----
From: DeTomaso [mailto:detomaso-bounces at server.detomasolist.com] On Behalf Of Mike & Elizabeth Thomas
Sent: Saturday, February 17, 2018 10:37 AM
To: 'Mike Drew'; 'List DeTomaso Forum'
Subject: Re: [DeTomaso] Trying to diagnose weak brakes

Thanks, certainly the cheapest and least invasive approach.

-----Original Message-----
From: Mike Drew [mailto:MikeLDrew at aol.com]
Sent: Friday, February 16, 2018 9:04 PM
To: Mike & Elizabeth Thomas <mbefthomas at comcast.net>
Cc: List DeTomaso Forum <detomaso at server.detomasolist.com>
Subject: Re: [DeTomaso] Trying to diagnose weak brakes

Mike,

Another note. If the Les Schwab people are so dumb that they don’t know that DOT4 is just DOT3 with a higher boiling point, I.e. an improved product that is 100% interchangeable, I wouldn’t trust them to do a proper job of filling and bleeding your brakes. 

I suspect there is nothing really wrong. Carefully drive to a friend’s house, one with good mechanical aptitude and an appetite for the beer you will bring on the passenger seat, and together just bleed the brakes properly using a quality brake fluid. (I like ATE Typ 200, available from Tire Rack, Summit and Amazon to I suspect). I have a feeling they will be perfect afterwards....

Mike

Sent from my iPad

> On Feb 16, 2018, at 18:50, Mike & Elizabeth Thomas <mbefthomas at comcast.net> wrote:
> 
>   I've been working through trying to figure what seems like a weakness
>   in my brakes on 6328.
> 
> 
>   How do they feel now?  There seems like a fair bit of pedal travel
>   before they start to hook up.  Once they hook, they're fine when I'm
>   just in normal traffic and stop and go.  If I have to stomp down on
>   them, it just doesn't seem like they're biting very well.  If I have to
>   really stomp on them, I can't get any wheel to lock up at all.
> 
> 
>   Current setup:  the brakes are stock Girling, rebuild in 2004. they've
>   been fully bled at Les Schwab 6 months ago with DOT 3 (they wouldn't
>   use DOT 4 as it was not spec).  Yes, they were aware that there were
>   two nipples on the front, the tech that handled me has 2 or 3 Panteras
>   that come in through the year.  The flex lines were replaced with
>   stainless lines in 2004 when all of the calipers were rebuilt.  The
>   vacuum line from the engine to the tube and tube to booster is recent,
>   about 3-4 years ago.  So far as I know, the proportioning valve has
>   been gutted, but not really sure nor know how to be sure.  The master
>   is an early `80's GM/Cadillac replaced about 10 years ago, the same was
>   in the car when I bought it in `04.  I've just replaced the Porterfield
>   R4S pads.  It was rather cold day when I went out to burn them in so
>   first speculation is that they are not fully `seasoned'.  However, they
>   feel about the same as the previous 10-yr old R4S's, and that wouldn't
>   explain the pedal travel.  The booster is original so far as I know.
> 
> 
>   First question, how much pedal travel should there be before the pedal
>   feels resistance the brakes start to take up?
> 
> 
>   So, what else can I check/do out to figure out why my brakes seem so
>   lazy.  I will try to re-season them when the weather gets warmer, but
>   that won't deal with pedal travel.  When brake booster starts to fail,
>   how does that happen?  Gradually or all at once?
> 
> 
>   Your input is appreciated and eagerly awaited.  I'd like to get this
>   figgered before the season starts as everything else is running a well
>   as it ever has.
> 
> 
>   Thanks
> 
>   Mike Thomas
> 
>   Pres., Panteras Northwest
> 
>   206-795-3302
> 
>   Yellow '74 #6328
> 
>   [1]www.panterasnorthwest.com
> 
> References
> 
>   1. http://www.panterasnorthwest.com/ 
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