[DeTomaso] Trying to diagnose weak brakes
Mike Drew
MikeLDrew at aol.com
Sat Feb 17 14:37:27 EST 2018
Mike,
In answer to your last question:
Yes, you are nuts. I think your car was great when I rode in it ten years ago or so and it has only gotten better over time, I think. If it was a POS then tearing it apart might be justified, but it’s not, so it’s not.
Drive it and enjoy it! :)
We all know people who started with perfectly good cars and ‘improved’ them to the point of complete immobility. It takes rather a lot of the fun out of it.....
Mike
Sent from my iPad
> On Feb 17, 2018, at 11:33, Mike & Elizabeth Thomas <mbefthomas at comcast.net> wrote:
>
> Not really. Since I replaced my master some years ago, the brakes have
> never been what I would call `stellar', and starting just such a thread
> to get them figured out has been on my mind, but more pressing fixes
> were needed. Now that the rest of the car is running better then it
> ever has, this is at the top of the list.
>
>
> `Course, doesn't it make sense that after years of tinkering this and
> that, everything seems to be coming together just as I'm contemplating
> a full tear down for a restoration of the metal/paint. Am I nuts . .
> . ?
>
>
> Thanks
>
> Mike T.
>
>
> From: Jeff Cobb [mailto:jeffcobb1 at me.com]
> Sent: Saturday, February 17, 2018 11:03 AM
> To: Mike & Elizabeth Thomas <mbefthomas at comcast.net>;
> DeTomaso at server.detomasolist.com DeTomaso at server.detomasolist.com
> <detomaso at server.detomasolist.com>
> Cc: Jeff Cobb <jeffcobb1 at me.com>
> Subject: Re: [DeTomaso] Trying to diagnose weak brakes
>
>
> Mike,
>
> Something strikes me as being out of order in the problem-cause and
> effect diagnosis of understanding and fixing your brake pedal travel
> problem in reading these back and forth mails. You write as if these
> problems just appeared.
>
>
> Seems that your real stated problem is;
>
> -1-perceived or really too much pedal travel.
>
> -2-cannot lock up wheels
>
> Also:
>
> -1-more brake dust on rear wheels versus the fronts.
>
>
> My questions are simple.
>
> -1-When this problem start?
>
> Not when you first noticed or recognized it, but when it first showed
> up.
>
> -2-Was this first time problem right after someone worked on it?
>
> -3-Has someone done any adjusting to the pedal unit?
>
>
> My brake work fixing history has taught me:
>
> --Your #1 and 2 make sense.
>
> --This type of problem #1 and #2 does not just show up
>
> --Also more rear dust than fronts indicates a brake bias imbalance.
>
> NEVER do rears have more dust than fronts on any car because of
> laminar air flow.
>
> The fronts always run hotter which emits more gas and powder.
>
> --That GM masters NEVER give a tight brake pedal unless they are p/s
> pumped hydraulic boosted power brake function or
>
> using a vacuum booster with an electric motor vacuum pump.
>
> The vacuum should be between 16 to 21.
>
> My thoughts to cure your two stated problems.
>
> -1-Make sure the brake pedal to booster pushrod does not have any slack
> caused by wear and giving sloppy joints,
>
> That the first pushrod is set correctly so that the pedal is correct
> height from floor.
>
> the vacuum booster pushrod to master does not have too much
> clearance--Should be about .020".
>
> -2-Then bled your brakes in the correct order; RR-LR-RF-LF.
>
> while watching for air bubbles and any type of pad to rotor air
> clearances/movement so to give reasons.
>
> If doing above work makes no difference "which I would be surprised".
>
>
> -3- then you need to plug off the master outputs and see if master
> travel is non and rock hard.
>
> When all above is correct and still note problems then you problem is
> in the fluid/caliper/pad space.
>
>
> -4-If you had rubber lines you could pinch them off with vise grips and
> find the soft one.
>
> Since you do not then a temp gun and some hard 60mph stops will give
> you your temp rise to grip performance function.
>
> Do 3 stops then measure/record then do 6 or so more and read and
> write again.
>
> Axle temps should be same and fronts are always more.
>
> The lowest temp unit will be your problem.
>
>
> Thoughts:
>
> -1-I have had brake problems caused by owners spraying tire shine shit
> on their wheels. That crap coats and greases the rotors which then
> kills the pads from gripping.
>
> -2-Also calipers with rubber piston boots that retract the pads more
> than .002" will cause problems.
>
> -3-Also if the rotors are not dead center to caliper then weird stuff
> lives on. Calipers can be shimmed to center them.
>
> Jaguar did that on all of their XJS v12 cars and when I recently
> removed my Mangustas L rear caliper, mounting shims were present. Which
> was it first ever removal, so the factory did the shims because of
> manufacturing differences.
>
>
> If none of this allows the car to stop better then maybe your pads
> function temp range is not right for you.
>
> Take care,
>
> Jeff Cobb
>
>
> On Feb 17, 2018, at 10:45 AM, Mike & Elizabeth Thomas
> <[1]mbefthomas at comcast.net> wrote:
>
> 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 [[2]mailto:julian_kift at hotmail.com]
> Sent: Saturday, February 17, 2018 8:20 AM
> To: Joseph F. Byrd, Jr. <[3]byrdjf at embarqmail.com>; 'Mike &
> Elizabeth
> Thomas' <[4]mbefthomas at comcast.net>; 'List DeTomaso Forum'
> <[5]detomaso at server.detomasolist.com>
> Cc: 'List DeTomaso Forum' <[6]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 <[1][7]detomaso-bounces at server.detomasolist.com> on
> behalf
> of Joseph F. Byrd, Jr. <[2][8]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
> [[3][9]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 [[4][10]mailto:MikeLDrew at aol.com]
> Sent: Friday, February 16, 2018 9:04 PM
> To: Mike & Elizabeth Thomas <[5][11]mbefthomas at comcast.net>
> Cc: List DeTomaso Forum <[6][12]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
>
> <[7][13]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][8][14]www.panterasnorthwest.com
> References
> 1. [9][15]http://www.panterasnorthwest.com/
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