Home » Public Forums » GMCnet » Maintaince
| Maintaince [message #288772] |
Wed, 14 October 2015 20:03  |
Jim Galbavy
Messages: 1443
Registered: August 2007
Karma: 7
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Senior Member |
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Came home last week after being out on the road for 3 weeks. The roads
in New Jersey beat the hell out of ANNIE. ChuckB helped keep her together
long enough to get her home. Turns out things were looked into.
1/ The hi strength adjusting bolt for the torsion bar was stripped and
Chuck was able to raise the front end 3 1/2 inches with a good used
bolt and nut. Turns out Chuck was right, the torsion bar was worn out and now
replaced at the COOP.
2/ My brakes sucked on that trip. Chuck seconded that. Turns out the reason
was the hard brake lines had a too large ID. Means after a few uses of the brake
pedal the pedal had to almost bottom out. I just was used to it after 13 years.
Got new lines in the right size from the COOP. Now. ...got brakes.
Lessons learned: With a 43 year old motorhome, don't believe anything that the PO
or his PO did or had done was done correctly. "Trust but verify".
jim galbavy
'73 x-CL ANNIE
Lake Mary, Fl
[Updated on: Wed, 14 October 2015 20:37] Report message to a moderator |
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| Re: [GMCnet] Maintaince [message #288817 is a reply to message #288772] |
Thu, 15 October 2015 15:24  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Darn you, Jim! You kept me awake last night! Thinking about the
"fix" for your brakes.
I hate to break it to you (and probably start an argument), but
changing the lines should not affect the performance of properly bled
brakes. In fact, you could connect them with either 0.010" ID lines
or 1.0" ID lines without affecting anything except response time or
required force on the MC.
Look at it this way: In a sealed system like brakes, a caliper
responds only to the volume of fluid and pressure supplied to it. So,
if the MC supplies 1 ci of fluid, the caliper will receive that 1 ci,
no more and no less, regardless of any intervening rigid container,
such as the brake lines. (The 1 ci is an arbitrary volume --
obviously the caliper will receive only enough volume to move it the
distance imposed by the force applied; the point is that the volume
can only be exactly what's supplied by the MC, in every case.)
I yield the podium.
Ken H.
On Wed, Oct 14, 2015 at 9:03 PM, Jim Galbavy wrote:
> Came home last week after being out on the road for 3 weeks. The roads
> in New Jersey beat the hell out of ANNIE. ChuckB helped keep her together
> long enough to get her home. Turns out things were looked into.
>
> 1/ The hi strength adjusting bolt for the torsion bar was stripped and
> Chuck was able to raise the front end 3 1/2 inches with a good used
> bolt and nut. Turns out Chuck was right, the torsion bar was worn out and
> replaced at the COOP.
>
> 2/ My brakes sucked on that trip. Chuck seconded that. Turns out the reason
> was the hard brake lines had a too large ID. Means after a few uses of the brake
> pedal the pedal had to almost bottom out. I just was used to it after 13 years.
> Got new lines in the right size from the COOP.
>
> Lessons learned: With a 43 year old motorhome, don't believe anything that the PO
> or his PO did or had done was done correctly. "Trust but verify".
>
> jim galbavy
> '73 x-CL ANNIE
> Lake, Fl
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Maintaince [message #288822 is a reply to message #288817] |
Thu, 15 October 2015 16:44 |
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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,
I don't think anyone on this forum can argue with the theories of Blaise Pascal regarding fluid pressure in a closed system; here's
a link to the first in a series of videos that explain his theories:
https://www.youtube.com/watch?v=z5JLF6Bjg4g
Regards,
Rob M.
The Pedantic Mechanic
-----Original Message-----
From: Ken Henderson
Darn you, Jim! You kept me awake last night! Thinking about the
"fix" for your brakes.
I hate to break it to you (and probably start an argument), but
changing the lines should not affect the performance of properly bled
brakes. In fact, you could connect them with either 0.010" ID lines
or 1.0" ID lines without affecting anything except response time or
required force on the MC.
Look at it this way: In a sealed system like brakes, a caliper
responds only to the volume of fluid and pressure supplied to it. So,
if the MC supplies 1 ci of fluid, the caliper will receive that 1 ci,
no more and no less, regardless of any intervening rigid container,
such as the brake lines. (The 1 ci is an arbitrary volume --
obviously the caliper will receive only enough volume to move it the
distance imposed by the force applied; the point is that the volume
can only be exactly what's supplied by the MC, in every case.)
I yield the podium.
Ken H.
On Wed, Oct 14, 2015 at 9:03 PM, Jim Galbavy wrote:
> Came home last week after being out on the road for 3 weeks. The roads
> in New Jersey beat the hell out of ANNIE. ChuckB helped keep her together
> long enough to get her home. Turns out things were looked into.
>
> 1/ The hi strength adjusting bolt for the torsion bar was stripped and
> Chuck was able to raise the front end 3 1/2 inches with a good used
> bolt and nut. Turns out Chuck was right, the torsion bar was worn out and
> replaced at the COOP.
>
> 2/ My brakes sucked on that trip. Chuck seconded that. Turns out the reason
> was the hard brake lines had a too large ID. Means after a few uses of the brake
> pedal the pedal had to almost bottom out. I just was used to it after 13 years.
> Got new lines in the right size from the COOP.
>
> Lessons learned: With a 43 year old motorhome, don't believe anything that the PO
> or his PO did or had done was done correctly. "Trust but verify".
>
> jim galbavy
> '73 x-CL ANNIE
> Lake, Fl
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GMCnet mailing list
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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] Maintaince [message #288828 is a reply to message #288827] |
Thu, 15 October 2015 17:36 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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Senior Member |
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Yeah, Rob, but how much of "all" have you forgotten?
HAR!
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ Since 30 November '53 ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ Member GMCMI and Classics ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ ~ TZE166V101966 ~ ~ ~ ~
~ ~ ~ '76 ex-Palm Beach ~ ~ ~
~~ k2gkk + hotmail dot com ~~
~ www.gmcmhphotos.com/okclb ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
______________
|[ ]~~~[][ ][]\
"--OO--[]---O-"
> From: robmueller@iinet.net.au
> To: gmclist@list.gmcnet.org
> Date: Fri, 16 Oct 2015 09:28:26 +1100
> Subject: Re: [GMCnet] Maintaince
>
> Mac,
>
> I didn't watch the whole first section as I've been working with pressure for 50 years since I was 18 and a Mechanical Accessories
> Repairman in the USAF, so I know it all! ;-)
>
> I believe at the end of the first section there will be a link to watch the next.
>
> Regards,
> Rob M.
> The Pedantic Mechanic
>
> -----Original Message-----
> From: D C _Mac_ Macdonald
>
> Hi, Rob.
>
> Are you planning to send all 16 sections?
>
> ~~ ~ D C "Mac" Macdonald ~ ~~
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| Re: [GMCnet] Maintaince [message #288832 is a reply to message #288817] |
Thu, 15 October 2015 18:05 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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Ken Henderson wrote on Thu, 15 October 2015 16:24Darn you, Jim! You kept me awake last night! Thinking about the "fix" for your brakes.
I hate to break it to you (and probably start an argument), but changing the lines should not affect the performance of properly bled brakes. In fact, you could connect them with either 0.010" ID lines or 1.0" ID lines without affecting anything except response time or required force on the MC.
Look at it this way: In a sealed system like brakes, a caliper responds only to the volume of fluid and pressure supplied to it. So, if the MC supplies 1 ci of fluid, the caliper will receive that 1 ci, no more and no less, regardless of any intervening rigid container, such as the brake lines. (The 1 ci is an arbitrary volume -- obviously the caliper will receive only enough volume to move it the distance imposed by the force applied; the point is that the volume can only be exactly what's supplied by the MC, in every case.)
I yield the podium.
Ken H.
Ken,
This not an argument. It is merely another look at the entire picture.
While I also don't believe that the root cause has been correctly identified in this case, there could be an issue with brake lines that are too thin a wall. Please note that I am not talking about the tubing ID in this case. Tubing ID comes in only because the OD of the tubing is controlled by the related hardware. There have been cases where the tubing did expand under load and cause those involved serious headaches until the issue was identified. Brake lines do expand, this fact was used for an electric brake controller that failed in the market place in the late 60's. It was a line pressure responsive control that starred a strain clamp that was placed on a line out of the master cylinder and electronics with adjustable gain to convert that to a signal for the trailer brakes.
Another case I am most familiar with was a small diesel engine (DB OM328) family that had a smoke issue when it should not have had same. While the pressures were higher than GMC brakes, I am sure that the case is still valid. In this case, the injection lines were 6mm OD and 2mm ID. With some very expensive equipment we demonstrated that the fuel injection rate did not match the high pressure pump output curve at many loads. They had to be changed to a 1.5mm ID.
How could this be? The injectors opened a the correct pressure? Yes, but nobody had counted on the elasticity of the injection line. So, as the fuel line pressure rose, it did not get to the cracking pressure of the injectors when it should have, it was late.... And, when the injectors did finally open, the balloon effect of the fuel line caused the delivery of gobs more fuel in the early part of the cycle than the burn process could manage. Worse still was that the technician that set up the engine had realized that timing was wrong, so he cranked the pump ahead a couple of degrees.
Now, if this sort of a situation existed in a vehicle service brake, it would result in an always soft pedal and not a declining pedal height. The only way it could cause the symptoms as described would be is the steel line were continuously deforming. I believe that any common metallic line that did so would fail in relatively sort order. It would also be very visible, much as when a copper water line that gets frozen.
If all he has changed the steel lines and absolutely nothing else, I still do not believe that the case is closed by any means. Were line deformation a real root cause, I would start by looking at the flexible components first, their elasticity has a way lower threshold than any steel line at all. I did work in foundation brakes for a little while, and we measured this sort of stuff for certification.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Maintaince [message #288841 is a reply to message #288832] |
Fri, 16 October 2015 07:36 |
Jim Galbavy
Messages: 1443
Registered: August 2007
Karma: 7
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Senior Member |
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Guys, we are out on the road again.. ......and all I can say is that I now have
a good hard brake pedal with half the pedal travel. Brakes are the best I can
remember in 13 years. Go figure.
Coach is really improved. ....both handling and stopping.
Maybe it is just magic......... 
Oh, and Chuck had the oil sample analyzed with the engine showing no wear or problems
after 13 years. Everything showing normal.
jim galbavy
'73 x-CL ANNIE
Lake Mary, FL
[Updated on: Fri, 16 October 2015 07:39] Report message to a moderator |
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| Re: [GMCnet] Maintaince [message #288851 is a reply to message #288841] |
Fri, 16 October 2015 13:00 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Jim,
Did he change out all of the rubber brake lines at the front calipers and at the rear bogies too?
JR Wright
GMC Great Laker MHC
GMC Eastern States Charter Member
GMCGL Tech Editor
GMCMI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan
> On Oct 16, 2015, at 8:36 AM, Jim Galbavy wrote:
>
> Guys, we are out on the road again.. ......and all I can say is that I now have
> a good hard brake pedal with half the pedal travel. Brakes are the best I can
> remember in 13 years. Go figure.
>
> Coach is really improved. ....both handling and stopping.
>
> Maybe it is just magic......... ;)
>
> jim galbavy
> '73 x-CL ANNIE
> Lake Mary, FL
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
_______________________________________________
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] Maintaince [message #288855 is a reply to message #288851] |
Fri, 16 October 2015 14:38 |
KB
Messages: 1262
Registered: September 2009
Karma: 0
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Senior Member |
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another theory: the lines were reversed front to rear at the master cylinder during the swap. As Albert B, Dave Lenzi,
and others have recently demonstrated, the capacity of the piston in the master cylinder is different in the front vs rear
(not just the reservoir, the volume available in the piston itself).
It's possible to bottom out one half of the piston (and hence have low pressure on one half) while still having
functional brakes on the other half. More an issue with all-disc systems, but could happen in other circumstances.
Just a wild guess, which may not apply here. As JR suggested, it could also be that the rubber brake lines were changed at
the same time and that those were the real problem. Bulging, spongy, or collapsed lines will play havoc with your brakes.
Karen
1975 26'
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| Re: [GMCnet] Maintaince [message #288857 is a reply to message #288855] |
Fri, 16 October 2015 15:14 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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However the front and rear have different size fittings at the master cylinder so they cannot be reversed.
Emery Stora
> On Oct 16, 2015, at 1:38 PM, KB wrote:
>
> another theory: the lines were reversed front to rear at the master cylinder during the swap. As Albert B, Dave Lenzi,
> and others have recently demonstrated, the capacity of the piston in the master cylinder is different in the front vs rear
> (not just the reservoir, the volume available in the piston itself).
> It's possible to bottom out one half of the piston (and hence have low pressure on one half) while still having
> functional brakes on the other half. More an issue with all-disc systems, but could happen in other circumstances.
>
> Just a wild guess, which may not apply here. As JR suggested, it could also be that the rubber brake lines were changed at
> the same time and that those were the real problem. Bulging, spongy, or collapsed lines will play havoc with your brakes.
>
>
> Karen
> 1975 26'
>
>
> _______________________________________________
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| Re: [GMCnet] Maintaince [message #288864 is a reply to message #288857] |
Fri, 16 October 2015 17:01 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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As I have the Dave Lenzi brake layout on my stretch coach with 80MM front, 80MM with 12 1/2” Ford rotors (Leigh Harrison Brake setup on Mid bogy) and Stock drums with 15.16” slave and carbon metallic shoes, I run with the reversed lines as the rear re has a larger volume than the front along with the longer rear stroke. You have to see the demo that Dave does with the Master cylinder and it does in deed have a longer stroke! I also have the sensitized booster and matched master cylinder by DL along with the pressure sensor adapter that allows to see only the brake booster pressure and the new Ford hi-volume vacuum pump. I run my pressure switch at 18 in vac, I may reset for 20” vac in the future after I cure some vacuum leaks in the HVAC side of the vacuum system. I have the best brakes that I have ever had in 18+ years in 2 coaches and the avion with also have this system upgrade.
Now for the adapters to swap the lines on the master cylinder.
or
http://tinyurl.com/pjwj4br
and
or
http://tinyurl.com/pzbl8mw
This is my results, yours may vary.
JR Wright
GMC Great Laker MHC
GMC Eastern States Charter Member
GMCGL Tech Editor
GMCMI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan
> On Oct 16, 2015, at 4:14 PM, Emery Stora wrote:
>
> However the front and rear have different size fittings at the master cylinder so they cannot be reversed.
>
> Emery Stora
>
>> On Oct 16, 2015, at 1:38 PM, KB wrote:
>>
>> another theory: the lines were reversed front to rear at the master cylinder during the swap. As Albert B, Dave Lenzi,
>> and others have recently demonstrated, the capacity of the piston in the master cylinder is different in the front vs rear
>> (not just the reservoir, the volume available in the piston itself).
>> It's possible to bottom out one half of the piston (and hence have low pressure on one half) while still having
>> functional brakes on the other half. More an issue with all-disc systems, but could happen in other circumstances.
>>
>> Just a wild guess, which may not apply here. As JR suggested, it could also be that the rubber brake lines were changed at
>> the same time and that those were the real problem. Bulging, spongy, or collapsed lines will play havoc with your brakes.
>>
>>
>> Karen
>> 1975 26'
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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