[DeTomaso] Trying to diagnose weak brakes

jtaphorn at kingwoodcable.com jtaphorn at kingwoodcable.com
Sat Feb 17 12:44:24 EST 2018 

Mike

The brake issue you describe may also be caused by a stuck piston in one of your calipers.  

JT
---- Stephen Nelson <steve at snclocks.com> wrote: 

=============
Having gone the Wildwood route - hey, maybe it is overkill for a road car -
but it is good overkill.  Can one have too good of brakes?

 

I am very happy with the brakes on 5332 - went with a kit from Pantera
Performance - and kept the original back caliper for the emergency brake.

 

Thought I'd throw in a shot of our car, pulled the a/c compressor, dryer and
expansion valve last weekend, will be flushing the system and bolting it all
back together this week.  And putting on the 10 inch rims I found here
locally.  Then we will be READY FOR SUMMER!

 

And yes, I know it is crap picture, but I think it just plain looks cool -
like it is flying!

 

Hey Mike - drive on down - we'll put it up on the other rack and sort out
those brakes.

 

Stephen - 5332

 

-----Original Message-----
From: DeTomaso [mailto:detomaso-bounces at server.detomasolist.com] On Behalf
Of Mike & Elizabeth Thomas
Sent: Saturday, February 17, 2018 8:45 AM
To: 'Julian Kift' <julian_kift at hotmail.com>; 'Joseph F. Byrd, Jr.'
<byrdjf at embarqmail.com>; 'List DeTomaso Forum'
<detomaso at server.detomasolist.com>
Cc: 'List DeTomaso Forum' <detomaso at server.detomasolist.com>
Subject: Re: [DeTomaso] Trying to diagnose weak brakes

 

Thanks all.  I am planning a full-on restoration of the car in a year or
two, and running of fresh brake lines, master, etc. even if I do retain the
original Girling brakes, will be on the list.  I will try a proper bleeding,
and it may not be a bad idea to upgrade to whatever master I intend to use
after the restoration.  I may consider going the full Willwood route, but as
I never intend to track the car, that may be overkill.  If I stay with the
Girling calipers, I'll certainly have them properly rebuilt.

 

 

Mike Thomas

 

 

From: Julian Kift [ <mailto:julian_kift at hotmail.com>
mailto:julian_kift at hotmail.com]

Sent: Saturday, February 17, 2018 8:20 AM

To: Joseph F. Byrd, Jr. < <mailto:byrdjf at embarqmail.com>
byrdjf at embarqmail.com>; 'Mike & Elizabeth Thomas'

< <mailto:mbefthomas at comcast.net> mbefthomas at comcast.net>; 'List DeTomaso
Forum'

< <mailto:detomaso at server.detomasolist.com>
detomaso at server.detomasolist.com>

Cc: 'List DeTomaso Forum' < <mailto:detomaso at server.detomasolist.com>
detomaso at server.detomasolist.com>

Subject: Re: [DeTomaso] Trying to diagnose weak brakes

 

 

Your diagram refers to the shuttle valve, the proportioning valve is the
hunk of metal in front trunk also but plumbed purely to the front brakes
limiting output pressure by about 20% of input. It does much the same as a
stepped master cylinder in compensating for woefully undersized rear
calipers. It was installed based on tires of the day etc. but modern rubber
especially 335 on the rear significantly alters brake balance and wheel
lockup front to rear. 

 

 

Although referring to the wrong valve your postulation that air is trapped
in it might be a very valid one, that or it's probably the master cylinder
going bad. I have a Motive pressure bleeder and it makes the task an easy
and one man operation, with no fear of running the reservoir dry during
bleeding (yes we've all done it!).

 

 

As a general note removing or gutting the proportioning valve should be
evaluated along with any brake component upgrade (note Mike said he has an
aftermarket master cylinder). It is hard to get all the components matched
perfectly right to ensure the front brakes lock up just before the rears,
hence installation of a more modern adjustable brake proportioning valve can
provide the fine tuning to ensure that. I would strongly recommend everyone
test their brakes for lockup periodically on a very quiet and wide stretch
of asphalt, not only is that a basic safety test it also provides you a
measure of what pedal force locks up the brakes, if only under the road
conditions prevailing at the time

 

 

Julian

 

  _____  

 

From: DeTomaso <detomaso-bounces at server.detomasolist.com

< <mailto:detomaso-bounces at server.detomasolist.com>
mailto:detomaso-bounces at server.detomasolist.com> > on behalf of Joseph F.

Byrd, Jr. < <mailto:byrdjf at embarqmail.com%20%3cmailto:byrdjf at embarqmail.com>
byrdjf at embarqmail.com <mailto:byrdjf at embarqmail.com> >

Sent: Saturday, February 17, 2018 8:06 AM

To: 'Mike & Elizabeth Thomas'

Cc: 'List DeTomaso Forum'

Subject: Re: [DeTomaso] Trying to diagnose weak brakes 

 

 

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>
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> mailto:MikeLDrew at aol.com]

Sent: Friday, February 16, 2018 9:04 PM

To: Mike & Elizabeth Thomas <
<mailto:mbefthomas at comcast.net%20%3cmailto:mbefthomas at comcast.net>
mbefthomas at comcast.net <mailto:mbefthomas at comcast.net> >

Cc: List DeTomaso Forum <
<mailto:detomaso at server.detomasolist.com%20%3cmailto:detomaso at server.detomas
olist.com> detomaso at server.detomasolist.com
<mailto: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

< <mailto:mbefthomas at comcast.net> mailto: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] <http://www.panterasnorthwest.com> www.panterasnorthwest.com <
<http://www.panterasnorthwest.com> http://www.panterasnorthwest.com>

> 

> References

> 

>   1.  <http://www.panterasnorthwest.com/>
http://www.panterasnorthwest.com/ 

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