[DeTomaso] Trying to diagnose weak brakes
Julian Kift
julian_kift at hotmail.com
Sat Feb 17 11:20:13 EST 2018
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> on behalf of Joseph F. Byrd, Jr. <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] 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/
> _______________________________________________
>
>
> Detomaso Email List is not managed by POCA Posted emails must not
> exceed 1.5 Megabytes DeTomaso mailing list
> DeTomaso at server.detomasolist.com
> http://server.detomasolist.com/mailman/listinfo/detomaso
>
> To manage your subscription (change email address, unsubscribe, etc.) use the links above.
>
> Members who post to this list grant license to the list to forward any message posted here to all past, current, or future members of the list. They also grant the list owner permission to maintain an archive or approve the archiving of list messages.
_______________________________________________
Detomaso Email List is not managed by POCA Posted emails must not exceed 1.5 Megabytes DeTomaso mailing list DeTomaso at server.detomasolist.com http://server.detomasolist.com/mailman/listinfo/detomaso
To manage your subscription (change email address, unsubscribe, etc.) use the links above.
Members who post to this list grant license to the list to forward any message posted here to all past, current, or future members of the list. They also grant the list owner permission to maintain an archive or approve the archiving of list messages.
-------------- next part --------------
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> on behalf of
Joseph F. Byrd, Jr. <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 [[1]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 [[2]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. [3]http://www.panterasnorthwest.com/
> _______________________________________________
>
>
> Detomaso Email List is not managed by POCA Posted emails must not
> exceed 1.5 Megabytes DeTomaso mailing list
> DeTomaso at server.detomasolist.com
> [4]http://server.detomasolist.com/mailman/listinfo/detomaso
>
> To manage your subscription (change email address, unsubscribe, etc.)
use the links above.
>
> Members who post to this list grant license to the list to forward
any message posted here to all past, current, or future members of the
list. They also grant the list owner permission to maintain an archive
or approve the archiving of list messages.
_______________________________________________
Detomaso Email List is not managed by POCA Posted emails must not
exceed 1.5 Megabytes DeTomaso mailing list
DeTomaso at server.detomasolist.com
[5]http://server.detomasolist.com/mailman/listinfo/detomaso
To manage your subscription (change email address, unsubscribe, etc.)
use the links above.
Members who post to this list grant license to the list to forward any
message posted here to all past, current, or future members of the
list. They also grant the list owner permission to maintain an archive
or approve the archiving of list messages.
References
1. mailto:detomaso-bounces at server.detomasolist.com
2. mailto:MikeLDrew at aol.com
3. http://www.panterasnorthwest.com/
4. http://server.detomasolist.com/mailman/listinfo/detomaso
5. http://server.detomasolist.com/mailman/listinfo/detomaso
More information about the DeTomaso
mailing list