Home » Public Forums » GMCnet » [GMCnet] The Proof is in the Pudding!
| [GMCnet] The Proof is in the Pudding! [message #60287] |
Fri, 16 October 2009 05:46  |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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G'day,
I have had the pleasure of watching the videos of Chuck Aulgur's original
reaction arm system at the Santa Rosa GMCMI convention last year and the
video's of Jim K's production version of that system at Pueblo this year.
From what I saw on both occasions I am satisfied that it works and I think
we all agree with that [not quite sure about Ken H though] ;-). The point
under discussion IMHO is how WELL it works.
If my memory serves me well I remember reading some brake testing that Ken H
did with different brake pads shoes or something. Unfortunately I can't
remember where I read it but I am reasonably confident that it discussed
stopping distances from various speeds.
As I understand there are three coaches with the production system
installed; the design engineer that took Chuck's system and came up with the
production system (I think his name is Rick), Chuck Aulgur's coach, and Jim
K's personal coach.
I would suggest that one (or more) of these three coaches be used to
duplicate Ken's testing so we'd have hard data to compare.
Regards,
Rob "show me the data" Mueller
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
'75 Avion - USA - The Parts Coach TZE 365V100324
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] The Proof is in the Pudding! [message #60352 is a reply to message #60291] |
Fri, 16 October 2009 18:20  |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Ken,
OK so the test procedure should be:
1) take the one of the GMC's equipped with rear disk brakes and the reaction
arm system; run it up to various speeds and slam on the brakes and measure
the stopping distance.
2) take the same coach and remove all the reaction arms and do the same
thing.
3) take a standard coach with drum brakes and do the same thing,
That sound right to you?
Regards,
Rob Mueller
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
'75 Avion - USA - The Parts Coach TZE 365V100324
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Ken Henderson
Sent: Friday, October 16, 2009 10:05 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] The Proof is in the Pudding!
Rob,
I'm 100% convinced that the system will improve braking dramatically,
and have been since before anyone bent any metal. What I'm not
convinced of is how much it will help on the rear wheels. Rigorous
testing is the only way to prove either of those assumptions and the
relative improvement achieved by either or both. But my brake pad tests
are not a baseline for that testing: Those tests attempted only to
compare brake pad performance. That objective did not require testing
the limits of adhesion nor ultimate stopping power. In fact, I could
not have conducted such tests because I didn't have sufficient hydraulic
line pressure to lock up the wheels. To test the 4-link system(s) will
require enough braking force to lock up some of the wheels -- whichever
wheels prove to have the least adhesion. Only at the limit of adhesion
can the relative the benefits of the 4-link suspension variants be
determined.
Ken H.
Rob Mueller wrote:
> G'day,
>
>
>
> I have had the pleasure of watching the videos of Chuck Aulgur's original
> reaction arm system at the Santa Rosa GMCMI convention last year and the
> video's of Jim K's production version of that system at Pueblo this year.
> >From what I saw on both occasions I am satisfied that it works and I
think
> we all agree with that [not quite sure about Ken H though] ;-). The point
> under discussion IMHO is how WELL it works.
>
>
>
> If my memory serves me well I remember reading some brake testing that Ken
H
> did with different brake pads shoes or something. Unfortunately I can't
> remember where I read it but I am reasonably confident that it discussed
> stopping distances from various speeds.
>
>
>
> As I understand there are three coaches with the production system
> installed; the design engineer that took Chuck's system and came up with
the
> production system (I think his name is Rick), Chuck Aulgur's coach, and
Jim
> K's personal coach.
>
>
>
> I would suggest that one (or more) of these three coaches be used to
> duplicate Ken's testing so we'd have hard data to compare.
>
>
>
> Regards,
>
> Rob "show me the data" Mueller
>
> Sydney, Australia
>
> '75 Avion - AUS - The Blue Streak TZE365V100428
>
> '75 Avion - USA - Double Trouble TZE365V100426
>
> '75 Avion - USA - The Parts Coach TZE 365V100324
>
>
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
>
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] The Proof is in the Pudding! [message #60355 is a reply to message #60287] |
Fri, 16 October 2009 19:10 |
zhagrieb
Messages: 676
Registered: August 2009
Location: Portland Oregon
Karma: 0
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Lot of bucks to convert to disks then add Chuck's system. Would be nice to see a side by side against the original drum brakes.
Glenn
Glenn Giere, Portland OR, K7GAG
'73 "Moby the Motorhome" 26'
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| Re: [GMCnet] The Proof is in the Pudding! [message #60379 is a reply to message #60352] |
Fri, 16 October 2009 22:06 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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No, Rob,
It's not quite that simple.
First we need to define the purpose of the tests. If it's to evaluate
the improvement in braking with the reaction rods, we do one set of
tests. It it's to compare the effectiveness of 2- vs 4-wheel reaction
rods we do another. There may be some overlap, but it's much more
complex than your proposal.
As a very rough test plan, here are some of the steps:
1. Configure the test coach with disc brakes which will slide all 6
wheels -- no small feat in itself, which may require PowerMaster or
HydroBoost. New/broken in brake pads should be used. A position marker
for when the brakes are applied and a controlled, measured, and
recorded brake pedal application device should be used (like my paint
gun and pneumatic pedal puller).
2. Run sufficient tests in configuration 1. to establish the minimum
stopping distance (with no sliding wheels)(disabling the rear brakes may
be necessary).
3. Reconfigure the test coach with reaction rods on the center wheels.
New/broken in brake pads should be used to duplicate configuration 1. as
closely as possible.
4. Run tests as in 2., preceding.
5. Reconfigure with reaction rods added to the rear wheels and again
renew the brake pads.
6. Run tests as in 2. & 4., preceding.
7. Reconfigure by returning the center wheels to OEM configuration and
again renewing the brakes.
8. Run tests as in 2., 4., & 6., preceding.
Only with all of that data accumulated and charted will everyone
(including me) be completely satisfied (no, that's not so -- there will
still be something to question).
I doubt that anyone, including me, will be willing to go through all of
that effort and expense, but that's what's really needed. Just
determining the minimum no-lock-up stopping distance in each
configuration will require a lot of test runs.
1.--6. is probably the minimum worth fooling with.
JMHO,
Ken H.
Rob Mueller wrote:
> Ken,
>
> OK so the test procedure should be:
>
> 1) take the one of the GMC's equipped with rear disk brakes and the reaction
> arm system; run it up to various speeds and slam on the brakes and measure
> the stopping distance.
>
> 2) take the same coach and remove all the reaction arms and do the same
> thing.
>
> 3) take a standard coach with drum brakes and do the same thing,
>
> That sound right to you?
>
> Regards,
> Rob Mueller
>
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| Re: [GMCnet] The Proof is in the Pudding! [message #60383 is a reply to message #60379] |
Fri, 16 October 2009 22:27 |
Bmac91724
Messages: 35
Registered: August 2009
Location: Covina CA
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| GMCWiperMan wrote on Fri, 16 October 2009 20:06 |
No, It's not quite that simple.
|
Stock coach then add the 4 wheel discs - then the reaction arms then go back to the drums with the reaction arms and make sure the weight and conditons don't change for all the tests.
By the way who is buying the tires for all this testing?
Brett Mac Donald
1974 23' Canyon Lands
[Updated on: Fri, 16 October 2009 22:28] Report message to a moderator |
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| Re: [GMCnet] The Proof is in the Pudding! [message #60384 is a reply to message #60379] |
Fri, 16 October 2009 22:28 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
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All I can say is Ugh, I hate stopping distance tests.
Ok I'll say more. Stopping distance is a poor measure of true brake performance. I'm sure there is a little bit of improvement with the reaction arm, but stopping distance is missing the point of good brakes.
A better test is back to back 60 to zero fade tests. This test measures the whole brake system. How well it cools the rotors, how well it handles the heat and even how long it takes to stop.
I want brakes that after 3 hard stops still haul the beast down using the Honda in front of me as a doorstop.
I also don't think it's necessary to get all Design of Experiments about it. All I'd like to see is the same coach using the same tires 1 set using stock brakes, 1 set using disk brakes and one set using the front and rear reaction arms.
3 as close to lockup as possible stops per setup. 9 tests.
Measure each stopping distance.
That will tell what the improvement is.
Keith
who thinks about brakes way too much
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: [GMCnet] The Proof is in the Pudding! [message #60387 is a reply to message #60384] |
Fri, 16 October 2009 23:01 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Senior Member |
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Keith,
I don't understand that attitude.
In my opinion, stopping distance is THE important measure -- it's the
one that determines whether you use a Honda as a doorstop in a panic
situation. Now if you're foolish enough to repeatedly approach the
doorstop rapidly enough to be concerned about fade in repeated stops,
your position makes sense. Sports cars tend to lull drivers into that
habit. But in a vehicle as heavy as the GMC, with wheels so small that
they restrict the size and consequent cooling capacity of the discs,
it's not likely that you'll ever achieve good fade resistance. Even in
mountain driving, fade resistance, while nice to have, is not a major
consideration; the transmission and judicious braking will control speed
on the steepest mountain I've climbed or descended -- which covers a lot
of them, from the Alps to the Rockies.
Good judgment will control fade better than any feasible brake
configuration. Stop hard, fast, and short when you MUST; otherwise use
brakes sparingly.
JMHO,
Ken H.
Keith V wrote:
> All I can say is Ugh, I hate stopping distance tests.
>
> Ok I'll say more. Stopping distance is a poor measure of true brake performance. I'm sure there is a little bit of improvement with the reaction arm, but stopping distance is missing the point of good brakes.
>
> A better test is back to back 60 to zero fade tests. This test measures the whole brake system. How well it cools the rotors, how well it handles the heat and even how long it takes to stop.
>
> I want brakes that after 3 hard stops still haul the beast down using the Honda in front of me as a doorstop.
>
> I also don't think it's necessary to get all Design of Experiments about it. All I'd like to see is the same coach using the same tires 1 set using stock brakes, 1 set using disk brakes and one set using the front and rear reaction arms.
> 3 as close to lockup as possible stops per setup. 9 tests.
> Measure each stopping distance.
> That will tell what the improvement is.
>
> Keith
> who thinks about brakes way too much
>
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| Re: [GMCnet] The Proof is in the Pudding! [message #60404 is a reply to message #60379] |
Sat, 17 October 2009 01:58 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Ken,
Hypothetical situations:
I am approaching an intersection and the light is green, out of the corner
of my eye I see a driver approaching from the left who is on his cell phone
and not paying attention. Two seconds later he runs the red light and enters
the intersection. I hit the brakes in my standard drum braked GMC. The nose
dives, the middle rear brakes raise the rear end causing the rear wheels to
skid and I plow into the car!
During the rebuild of my GMC I decide to install all wheel disk brakes and
the reaction arm system which will improve my braking. Damned if a month
after I get the GMC back on the road another idiot does the same bloody
thing. This time when I hit the brakes the front dives but the rear end
stays put and the rear most wheels contribute to the braking and I stop
before the intersection and not run into the second idiot.
Rob Mueller
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
'75 Avion - USA - The Parts Coach TZE 365V100324
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Ken Henderson
Sent: Saturday, October 17, 2009 2:06 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] The Proof is in the Pudding!
No, Rob,
It's not quite that simple.
First we need to define the purpose of the tests. If it's to evaluate
the improvement in braking with the reaction rods, we do one set of
tests. It it's to compare the effectiveness of 2- vs 4-wheel reaction
rods we do another. There may be some overlap, but it's much more
complex than your proposal.
As a very rough test plan, here are some of the steps:
1. Configure the test coach with disc brakes which will slide all 6
wheels -- no small feat in itself, which may require PowerMaster or
HydroBoost. New/broken in brake pads should be used. A position marker
for when the brakes are applied and a controlled, measured, and
recorded brake pedal application device should be used (like my paint
gun and pneumatic pedal puller).
2. Run sufficient tests in configuration 1. to establish the minimum
stopping distance (with no sliding wheels)(disabling the rear brakes may
be necessary).
3. Reconfigure the test coach with reaction rods on the center wheels.
New/broken in brake pads should be used to duplicate configuration 1. as
closely as possible.
4. Run tests as in 2., preceding.
5. Reconfigure with reaction rods added to the rear wheels and again
renew the brake pads.
6. Run tests as in 2. & 4., preceding.
7. Reconfigure by returning the center wheels to OEM configuration and
again renewing the brakes.
8. Run tests as in 2., 4., & 6., preceding.
Only with all of that data accumulated and charted will everyone
(including me) be completely satisfied (no, that's not so -- there will
still be something to question).
I doubt that anyone, including me, will be willing to go through all of
that effort and expense, but that's what's really needed. Just
determining the minimum no-lock-up stopping distance in each
configuration will require a lot of test runs.
1.--6. is probably the minimum worth fooling with.
JMHO,
Ken H.
_______________________________________________
GMCnet mailing list
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http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] The Proof is in the Pudding! [message #60407 is a reply to message #60404] |
Sat, 17 October 2009 06:12 |
Gary Casey
Messages: 448
Registered: September 2009
Karma: 0
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Rob's comments started me to thinking, not a good thing, as it usually ends up costing money :-). First, the objective of any braking systems is to have all wheels arrive at a locked-wheel condition simultaneously. The fact that Rob slid into the car isn't the whole story - which wheels were locked? The rears and fronts, or only the rears? I assume the middles didn't lock. If they were all locked, even though the rears locked early, the brakes had done all they could do. Granted the leading-trailing arm rear suspension is not a good thing and the parallel-arm conversion is certainly in the right direction - but expensive. The real problem is not that the rears are contributing less than their share of braking (stay with me for a minute on this), it's that the center wheels don't contribute their share. To look at it the other way, the rears don't contribute their share of traction, but they have more than enough braking. In other words, let's
take it as a given that the middles carry much more of the weight (during braking) than the rears. This is a predictable and reproducible effect.
What is the normal way to compensate for this in a braking system? Change the proportioning of the brakes to match the weight carried. Bottom line - change the wheel cylinder diameters. Put larger cylinders in the middle brake and smaller ones in the rear. Result is that the rears would be less prone to lock up and the middles would absorb more of the braking effort. Certainly not as good of a solution as the parallel arms, but a lot cheaper. As the rear drums use standard parts different wheel cylinder diameters might be readily available - and cheap. Has anyone done this?
There would be (at least) two disadvantages with this approach. First is that with the middles doing more of the braking they would get hotter than before and might fade when being used aggressively. The second is that with unequal torque between middle and rear, the rear of the coach would rise on braking. I don't know whether or not this effect would be noticeable or detrimental. It might be that a modest change would make the problem manageable - not fix it, but make it just okay.
Gary
________________________________
From: Rob Mueller <robmueller@iinet.net.au>
To: gmclist@temp.gmcnet.org
Sent: Sat, October 17, 2009 12:58:19 AM
Subject: Re: [GMCnet] The Proof is in the Pudding!
Ken,
Hypothetical situations:
I am approaching an intersection and the light is green, out of the corner
of my eye I see a driver approaching from the left who is on his cell phone
and not paying attention. Two seconds later he runs the red light and enters
the intersection. I hit the brakes in my standard drum braked GMC. The nose
dives, the middle rear brakes raise the rear end causing the rear wheels to
skid and I plow into the car!
During the rebuild of my GMC I decide to install all wheel disk brakes and
the reaction arm system which will improve my braking. Damned if a month
after I get the GMC back on the road another idiot does the same bloody
thing. This time when I hit the brakes the front dives but the rear end
stays put and the rear most wheels contribute to the braking and I stop
before the intersection and not run into the second idiot.
Rob Mueller
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
'75 Avion - USA - The Parts Coach TZE 365V100324
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| Re: [GMCnet] The Proof is in the Pudding! [message #60408 is a reply to message #60404] |
Sat, 17 October 2009 07:06 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Senior Member |
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Exactly. That's the whole point of Chuck's endeavors -- to save us from
idiots (regardless of which vehicle they're driving).
The only question remaining in my mind, which I believe you're trying to
probe, is whether those rear-most wheels are significantly less likely
to break loose with the reaction arms on them. If, with the reaction
arms on the middle only, I can stop 1/4" short of the idiot instead of
1/2" short, I may be tempted to save $1500+ of my kids' inheritance.
Now if that 1/4" will put me in front of him...
Ken H.
Rob Mueller wrote:
> Ken,
>
> Hypothetical situations:
>
> I am approaching an intersection and the light is green, out of the corner
> of my eye I see a driver approaching from the left who is on his cell phone
> and not paying attention. Two seconds later he runs the red light and enters
> the intersection. I hit the brakes in my standard drum braked GMC. The nose
> dives, the middle rear brakes raise the rear end causing the rear wheels to
> skid and I plow into the car!
>
> During the rebuild of my GMC I decide to install all wheel disk brakes and
> the reaction arm system which will improve my braking. Damned if a month
> after I get the GMC back on the road another idiot does the same bloody
> thing. This time when I hit the brakes the front dives but the rear end
> stays put and the rear most wheels contribute to the braking and I stop
> before the intersection and not run into the second idiot.
>
> Rob Mueller
> Sydney, Australia
> '75 Avion - AUS - The Blue Streak TZE365V100428
> '75 Avion - USA - Double Trouble TZE365V100426
> '75 Avion - USA - The Parts Coach TZE 365V100324
>
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| Re: [GMCnet] The Proof is in the Pudding! [message #60410 is a reply to message #60407] |
Sat, 17 October 2009 07:26 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Senior Member |
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Gary,
There have been a LOT of attempts to properly proportion the braking
force between the center and rear wheels. Some of them have been very
successful, with both drum and disc brakes. BUT, with the swing arms on
the center wheels, the rear of the coach is lifted so much that the
portion of total adhesion left available at the rear wheels becomes
minus zero -- thus my removal of the rear brakes to properly proportion
them. Granted, I don't have effective enough brakes on the center
wheels to slide them, so I'm not providing them with their proper
portion.
Point is, proportioning just becomes too extremely biased to the center
with the OEM suspension.
Ken H.
Gary Casey wrote:
> ...As the rear drums use standard parts different wheel cylinder diameters might be readily available - and cheap. Has anyone done this?
>
> There would be (at least) two disadvantages with this approach. First is that with the middles doing more of the braking they would get hotter than before and might fade when being used aggressively. The second is that with unequal torque between middle and rear, the rear of the coach would rise on braking. I don't know whether or not this effect would be noticeable or detrimental. It might be that a modest change would make the problem manageable - not fix it, but make it just okay.
>
> Gary
>
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| Re: [GMCnet] The Proof is in the Pudding! [message #60411 is a reply to message #60408] |
Sat, 17 October 2009 07:27 |
|
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Ken,
OK, glad to read we're both on the same wave length!
Now it's time for me to go to bed!
Regards,
Rob Mueller
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
'75 Avion - USA - The Parts Coach TZE 365V100324
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Ken Henderson
Sent: Saturday, October 17, 2009 11:07 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] The Proof is in the Pudding!
Exactly. That's the whole point of Chuck's endeavors -- to save us from
idiots (regardless of which vehicle they're driving).
The only question remaining in my mind, which I believe you're trying to
probe, is whether those rear-most wheels are significantly less likely
to break loose with the reaction arms on them. If, with the reaction
arms on the middle only, I can stop 1/4" short of the idiot instead of
1/2" short, I may be tempted to save $1500+ of my kids' inheritance.
Now if that 1/4" will put me in front of him...
Ken H.
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] The Proof is in the Pudding! [message #60419 is a reply to message #60410] |
Sat, 17 October 2009 10:00 |
Gary Casey
Messages: 448
Registered: September 2009
Karma: 0
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Senior Member |
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Ken,
I agree, there is probably no way to "solve" the problem just by changing the proportioning, but reducing the rear wheel cylinders by 10% and increasing the middle by 10% might make enough difference to at least improve it. Or not.
Gary
Gary,
There have been a LOT of attempts to properly proportion the braking
force between the center and rear wheels. Some of them have been very
successful, with both drum and disc brakes. BUT, with the swing arms on
the center wheels, the rear of the coach is lifted so much that the
portion of total adhesion left available at the rear wheels becomes
minus zero -- thus my removal of the rear brakes to properly proportion
them. Granted, I don't have effective enough brakes on the center
wheels to slide them, so I'm not providing them with their proper
portion.
Point is, proportioning just becomes too extremely biased to the center
with the OEM suspension.
Ken H.
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| Re: [GMCnet] The Proof is in the Pudding! [message #60421 is a reply to message #60419] |
Sat, 17 October 2009 10:28 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Senior Member |
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Gary,
Try http://www.gmcmotorhomeinfo.com/brakes.html#anal for information on
the various options.
Ken H.
Gary Casey wrote:
> Ken,
> I agree, there is probably no way to "solve" the problem just by changing the proportioning, but reducing the rear wheel cylinders by 10% and increasing the middle by 10% might make enough difference to at least improve it. Or not.
> Gary
>
>
>
> Gary,
>
> There have been a LOT of attempts to properly proportion the braking
> force between the center and rear wheels. Some of them have been very
> successful, with both drum and disc brakes. BUT, with the swing arms on
> the center wheels, the rear of the coach is lifted so much that the
> portion of total adhesion left available at the rear wheels becomes
> minus zero -- thus my removal of the rear brakes to properly proportion
> them. Granted, I don't have effective enough brakes on the center
> wheels to slide them, so I'm not providing them with their proper
> portion.
>
> Point is, proportioning just becomes too extremely biased to the center
> with the OEM suspension.
>
> Ken H.
>
>
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| Re: [GMCnet] The Proof is in the Pudding! [message #60427 is a reply to message #60407] |
Sat, 17 October 2009 11:23 |
Tin Gerbil
Messages: 236
Registered: October 2006
Location: Vancouver Island, B.C.
Karma: 0
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Senior Member |
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Gary;
From what I read in the archives, many people have done the wheel
cylinder change. Some have tossed the rear wheel cylinders altogether.
My coach has this change documented in the accompanying operators
manual. I can still lockup the rear wheels and did lockup the rear on
the drivers side, in some highway grit, on my return from the last rally
I attended. Having driven over a million miles in my heavy trucks, I
would say, my coach stops very well, much better than any of my trucks
either empty or loaded. Comparing a GMC to, or trying to make it stop
like a car is an admirable undertaking. Some driver training might be a
whole lot more cost effective. You can see over most vehicles while
driving your GMC. Learning to not follow vehicles you can't see over is
a good place to start. Quit driving your GMC like a car and look as far
ahead as you can at all times. Once you have moved 50-100 tons on a
truck, you will have a very different perspective on driving. As a
passenger, you will continually be wondering what the hell your driver
is thinking about, if they are thinking at all. Gas, brake, gas, brake,
gas, brake. NOT!
Gordon
Gary Casey wrote:
> Bottom line - change the wheel cylinder diameters. Put larger
> cylinders in the middle brake and smaller ones in the rear. Result
> is that the rears would be less prone to lock up and the middles
> would absorb more of the braking effort. Certainly not as good of a
> solution as the parallel arms, but a lot cheaper. As the rear drums
> use standard parts different wheel cylinder diameters might be
> readily available - and cheap. Has anyone done this?
>
> There would be (at least) two disadvantages with this approach.
> First is that with the middles doing more of the braking they would
> get hotter than before and might fade when being used aggressively.
> The second is that with unequal torque between middle and rear, the
> rear of the coach would rise on braking. I don't know whether or not
> this effect would be noticeable or detrimental. It might be that a
> modest change would make the problem manageable - not fix it, but
> make it just okay.
>
> Gary
>
>
>
> ________________________________ From: Rob Mueller
> <robmueller@iinet.net.au> To: gmclist@temp.gmcnet.org Sent: Sat,
> October 17, 2009 12:58:19 AM Subject: Re: [GMCnet] The Proof is in
> the Pudding!
>
> Ken,
>
> Hypothetical situations:
>
> I am approaching an intersection and the light is green, out of the
> corner of my eye I see a driver approaching from the left who is on
> his cell phone and not paying attention. Two seconds later he runs
> the red light and enters the intersection. I hit the brakes in my
> standard drum braked GMC. The nose dives, the middle rear brakes
> raise the rear end causing the rear wheels to skid and I plow into
> the car!
>
> During the rebuild of my GMC I decide to install all wheel disk
> brakes and the reaction arm system which will improve my braking.
> Damned if a month after I get the GMC back on the road another idiot
> does the same bloody thing. This time when I hit the brakes the front
> dives but the rear end stays put and the rear most wheels contribute
> to the braking and I stop before the intersection and not run into
> the second idiot.
>
> Rob Mueller Sydney, Australia '75 Avion - AUS - The Blue Streak
> TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426 '75
> Avion - USA - The Parts Coach TZE 365V100324
>
>
>
> _______________________________________________ GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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Gordon
'74 Canyon Lands "Tin Gerbil"
Vancouver Island, B.C.
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| Re: [GMCnet] The Proof is in the Pudding! [message #60473 is a reply to message #60427] |
Sat, 17 October 2009 20:13 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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Senior Member |
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| Gary Casey wrote on Sat, 17 October 2009 04:12 |
... First, the objective of any braking systems is to have all wheels arrive at a locked-wheel condition simultaneously. ...
|
No.
A well designed brake system should lock the FRONT wheels BEFORE the rears. The reason for this is when a wheel is sliding it provides no control. If you slide the front wheels, the vehicle tends to keep going straight. The driver can feel this and back off on the brakes to regain control. BUT if you lock the rear wheels, you loose directional stability... the vehicle tends to spin. When the driver feels this... backing off the brakes is only ONE of the things needed to recover!
If you have a system that is set so that "all wheels arrive at a locked-wheel condition simultaneously", you are leaving it up to other conditions to determine if you go straight or spin.
This is the one reason that I thought Ken's idea of disconnecting the very rear brakes has merit.
| Tin Gerbil wrote on Sat, 17 October 2009 09:23 |
... Gas, brake, gas, brake, gas, brake. NOT!
|
Besides the obvious safety issues, many people do not seem to realize that anytime you use any controls, it costs money. (At least with an automatic.) Pressing the gas uses more gas, pressing the brake eats up momentum that you paid for. Turning the steering wheel also eats momentum. Easy on the controls will get you the most for your money. It is amazing to see all the brake lights coming on for no reason.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] The Proof is in the Pudding! [message #60475 is a reply to message #60473] |
Sat, 17 October 2009 20:19 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Senior Member |
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Mike,
You're right about wanting the fronts to lock first, in general. There
probably can be a good case made for letting one of the rear pair lock
with or before the fronts, leaving the other rear pair turning for
directional stability, as you suggest in commenting on my removal of the
rear brakes.
I ignored the front-first rule in my pseudo test plan because one of the
objectives is to evaluate relative performance of all wheels. Once
that's determined, it should be relatively simple to control which set
of wheels slides first.
Ken H.
Mike Miller wrote:
> Gary Casey wrote on Sat, 17 October 2009 04:12
>
>> ... First, the objective of any braking systems is to have all wheels arrive at a locked-wheel condition simultaneously. ...
>>
>
>
> No.
>
> A well designed brake system should lock the FRONT wheels BEFORE the rears. The reason for this is when a wheel is sliding it provides no control. If you slide the front wheels, the vehicle tends to keep going straight. The driver can feel this and back off on the brakes to regain control. BUT if you lock the rear wheels, you loose directional stability... the vehicle tends to spin. When the driver feels this... backing off the brakes is only ONE of the things needed to recover!
>
> If you have a system that is set so that "all wheels arrive at a locked-wheel condition simultaneously", you are leaving it up to other conditions to determine if you go straight or spin.
>
> This is the one reason that I thought Ken's idea of disconnecting the very rear brakes has merit.
>
>
> Tin Gerbil wrote on Sat, 17 October 2009 09:23
>
>> ... Gas, brake, gas, brake, gas, brake. NOT!
>>
>
>
> Besides the obvious safety issues, many people do not seem to realize that anytime you use any controls, it costs money. (At least with an automatic.) Pressing the gas uses more gas, pressing the brake eats up momentum that you paid for. Turning the steering wheel also eats momentum. Easy on the controls will get you the most for your money. It is amazing to see all the brake lights coming on for no reason.
>
>
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| Re: [GMCnet] The Proof is in the Pudding! [message #60483 is a reply to message #60475] |
Sat, 17 October 2009 21:27 |
Gary Casey
Messages: 448
Registered: September 2009
Karma: 0
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Senior Member |
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That may be true in general, but I think the discussion was how to improve stopping distance. Since the traction coefficient slightly higher just before the wheels lock by allowing one to lock first it will be doing a little less than it would do if still turning. But for controllability, yes, keeping it going straight is generally preferable to having the rear tending to come around. Stopping distance isn't everything, for sure. Unless you are about to hit something.
Gary
________________________________
From: Ken Henderson <ken0henderson@gmail.com>
To: gmclist@temp.gmcnet.org
Sent: Sat, October 17, 2009 7:19:08 PM
Subject: Re: [GMCnet] The Proof is in the Pudding!
Mike,
You're right about wanting the fronts to lock first, in general. There
probably can be a good case made for letting one of the rear pair lock
with or before the fronts, leaving the other rear pair turning for
directional stability, as you suggest in commenting on my removal of the
rear brakes.
I ignored the front-first rule in my pseudo test plan because one of the
objectives is to evaluate relative performance of all wheels. Once
that's determined, it should be relatively simple to control which set
of wheels slides first.
Ken H.
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