Home » Public Forums » GMCnet » [GMCnet] Residual pressure valves
| [GMCnet] Residual pressure valves [message #270814] |
Fri, 30 January 2015 09:54  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Senior Member |
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I noted with interest a recent post about installing residual pressure valves to cure the low brake pedal issue when changing over to six wheel disk brakes. I was not familiar with these so started digging. Here is what one site has to say:
"Residual Pressure Valves are used in a both front and rear brake system as follows:
• 2 PSI Valves - These valves are used in a disc brake system only and are required when the master cylinder is at, or below, the height of the calipers. It's purpose is to act as an anti-siphon valve preventing the brake fluid from siphoning back into the master cylinder when the brake pedal is released. Even if the master cylinder is even or slightly above the calipers, put one in anyway. If you don't and you park on a hill, fluid will siphon! These valves are cheap insurance - put them in!
• NOTE: You will know if you need one of these valves if you had to pump the pedal twice to get a good pedal. See illustration for more.
• 10 PSI Valves - These valves are used in a drum brake system to prevent air from being ingested into the hydraulic system when you release the brake pedal. Typical wheel cylinder seals only seal when there is pressure behind them. Rapid release of the brake pedal creates a vacuum in the system which causes the seals to relax and air is ingested into the wheel cylinders. Maintaining 10 PSI in the system at all times prevents this. Some disc/drum master cylinders have 10 PSI residual pressure valves installed internally, some don't. If you're not sure, call us and we can tell you how to check. Also, some new style wheel cylinders have cup expanders which negate the need for the residual pressure valve. Either way, if you are not sure whether you have one or not, put one in. They are not cumulative and it won't hurt anything if you have two. Don't worry about brake drag, it takes roughly 75 PSI to overcome the return springs."
I could not find info on why they would be necessary when our master cylinder is way higher than the calipers front and rear. Can anyone shed more info on the benefits or lack there of from the use of these valves in the six wheel disk brake set up? If they would be helpful for our six wheel disk system, how many and where should these be installed?
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
Visitors always welcome!
glwork@mac.com
http://jerrywork.com
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] Residual pressure valves [message #270816 is a reply to message #270814] |
Fri, 30 January 2015 10:14  |
GMC.LES
Messages: 505
Registered: April 2014
Karma: -2
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Senior Member |
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My opinion regarding their use on our coaches is that we shouldn't need something more than what GM fitted at the factory to obtain decent brakes. The proof of this is how many coaches are still running out there with totally stock brakes and they have acceptable braking. Adding a valve to fix a problem is just masking that problem. Yes the valve might be the easier fix, but the cause is still present and unfixed.
Les Burt
> On Jan 30, 2015, at 10:54 AM, Gerald Work wrote:
>
> I noted with interest a recent post about installing residual pressure valves to cure the low brake pedal issue when changing over to six wheel disk brakes. I was not familiar with these so started digging. Here is what one site has to say:
>
> "Residual Pressure Valves are used in a both front and rear brake system as follows:
>
> • 2 PSI Valves - These valves are used in a disc brake system only and are required when the master cylinder is at, or below, the height of the calipers. It's purpose is to act as an anti-siphon valve preventing the brake fluid from siphoning back into the master cylinder when the brake pedal is released. Even if the master cylinder is even or slightly above the calipers, put one in anyway. If you don't and you park on a hill, fluid will siphon! These valves are cheap insurance - put them in!
> • NOTE: You will know if you need one of these valves if you had to pump the pedal twice to get a good pedal. See illustration for more.
> • 10 PSI Valves - These valves are used in a drum brake system to prevent air from being ingested into the hydraulic system when you release the brake pedal. Typical wheel cylinder seals only seal when there is pressure behind them. Rapid release of the brake pedal creates a vacuum in the system which causes the seals to relax and air is ingested into the wheel cylinders. Maintaining 10 PSI in the system at all times prevents this. Some disc/drum master cylinders have 10 PSI residual pressure valves installed internally, some don't. If you're not sure, call us and we can tell you how to check. Also, some new style wheel cylinders have cup expanders which negate the need for the residual pressure valve. Either way, if you are not sure whether you have one or not, put one in. They are not cumulative and it won't hurt anything if you have two. Don't worry about brake drag, it takes roughly 75 PSI to overcome the return springs."
>
> I could not find info on why they would be necessary when our master cylinder is way higher than the calipers front and rear. Can anyone shed more info on the benefits or lack there of from the use of these valves in the six wheel disk brake set up? If they would be helpful for our six wheel disk system, how many and where should these be installed?
>
> Jerry
> Jerry Work
> The Dovetail Joint
> Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
> Visitors always welcome!
> glwork@mac.com
> http://jerrywork.com
>
>
>
>
>
>
>
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| Re: [GMCnet] Residual pressure valves [message #270817 is a reply to message #270814] |
Fri, 30 January 2015 10:31 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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Non-GMC opinion/experience.
I installed a 10 psi in my VW buggy, right off master cylinder. It has 4 wheel drum brakes, running off one reservoir.
from what I can tell, it just makes up for piss poor adjusted drum brakes in my case. keeps a very tiny amount of pressure on the wheel cylinders to hold the brake shoes against the drums. So when I apply the brakes, the pedal does not need to travel as far before real pressure hits the shoes to give me some braking power. I can't tell you for sure if it is a real improvement, because over all, my brakes in that buggy are very poor at best.
Now it did help my VW, but again, they are generally not always well adjusted, abused, and I am sure my drums are over turned. This is for my off road buggy. I do not see a huge need for the valve, unless the brakes are not adjusted or being adjusted properly.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: [GMCnet] Residual pressure valves [message #270819 is a reply to message #270817] |
Fri, 30 January 2015 11:16 |
Hal StClair
Messages: 971
Registered: March 2013
Location: Rio Rancho NM
Karma: -12
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Senior Member |
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My brakes are not stock with the addition of rear disc's and the one ton front end as well as the 34mm m/c. The two lb residual valve mounted in the rear brake line at the m/c, with no other changes moved the brake pedal up from an inch above the floor to about an inch below the top. I see no detrimential issues using the valve and on the contrary a huge improvement in pedal/braking. Unless there is more runout in the rear disc's than I observed with the Manny system one wouldn't see a need for the valve but in reality it works great. Our brakes work so well I'm afraid someone is going to plow into us from behind during an aggresive stop.
Just my observations, Hal
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."
1977 Royale 101348,
1977 Royale 101586, Diesel powered,
1974 Eagle Bus 45',w/slideout,
Rio Rancho, NM
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| Re: [GMCnet] Residual pressure valves [message #270821 is a reply to message #270819] |
Fri, 30 January 2015 12:08 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Hal, there will always be the discussion between the group that have stock
brakes and are determined to remain that way, and the group that realizes
that with traffic the way it is today with smaller, lighter, vehicles with
vastly improved braking systems mixed up with our 12,000 pound vehicles
with 40 year old braking systems on the road. Combine that with cell
phones, GPS, heavy instrumentation, and other distractions from driving,
and you have a recipe for accidents. I figure that we need all the REAL
IMPROVEMENTS that we can equip our coaches with. But, some of the
"improvements" are not that at all, but a hazard. If your coach has a
spongy pedal, it needs to be remedied. If your coach has excessive pedal
travel before any braking takes place, it needs to be fixed. I have heard
of, and personally seen braking systems, that had half of the brakes
disabled, and the owners traveled great distances like that. One coach that
I worked on had the rear brake hard lines crimped off entirely. Scary
stuff. Please guys, for your own safety, and for those around you on the
highway, Do not accept less than the best braking you can have.
Incidentally, when tires are skidding on the pavement, you are not stopping
at the greatest rate of decelleration. Brakes that lock up tires are not an
ideal system.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Fri, Jan 30, 2015 at 9:16 AM, Hal StClair
wrote:
> My brakes are not stock with the addition of rear disc's and the one ton
> front end as well as the 34mm m/c. The two lb residual valve mounted in the
> rear brake line at the m/c, with no other changes moved the brake pedal up
> from an inch above the floor to about an inch below the top. I see no
> detrimential issues using the valve and on the contrary a huge improvement
> in pedal/braking. Unless there is more runout in the rear disc's than I
> observed with the Manny system one wouldn't see a need for the valve but
> in reality it works great. Our brakes work so well I'm afraid someone is
> going to plow into us from behind during an aggresive stop.
> Just my observations, Hal
> --
> 1977 Royale 101348,
>
> 1977 Royale 101586,
>
> 1974 Eagle Bus 45',w/slideout
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Residual pressure valves [message #270824 is a reply to message #270821] |
Fri, 30 January 2015 12:36 |
Daniel DeLuca
Messages: 120
Registered: June 2014
Karma: 0
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Senior Member |
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I really think people who are “new” to these coaches don’t know what to expect when it comes to braking a 35 year old 12,000 pound 6 wheeled vehicle. I certainly don’t. When I redid the brakes this summer, I replaced the master cylinder, the fronts got the 80mm “upgrade” rears got new shoes, lines and cylinders but otherwise stock. Frankly, I was less then impressed when all was said and done. Adjusting the rear brakes helped immensely, and now that they have begun to ‘seat’ I would call braking ‘adequate.’ Having never driven another coach, I have no real way of knowing. I could have the best brakes in the world or the worst. I passed NJ state inspection so at least the government thinks they are safe.
Dan
Allentown NJ
78’ Eleganza
> On Jan 30, 2015, at 1:08 PM, James Hupy w
>
> Hal, there will always be the discussion between the group that have stock
> brakes and are determined to remain that way, and the group that realizes
> that with traffic the way it is today with smaller, lighter, vehicles with
> vastly improved braking systems mixed up with our 12,000 pound vehicles
> with 40 year old braking systems on the road. Combine that with cell
> phones, GPS, heavy instrumentation, and other distractions from driving,
> and you have a recipe for accidents. I figure that we need all the REAL
> IMPROVEMENTS that we can equip our coaches with. But, some of the
> "improvements" are not that at all, but a hazard. If your coach has a
> spongy pedal, it needs to be remedied. If your coach has excessive pedal
> travel before any braking takes place, it needs to be fixed. I have heard
> of, and personally seen braking systems, that had half of the brakes
> disabled, and the owners traveled great distances like that. One coach that
> I worked on had the rear brake hard lines crimped off entirely. Scary
> stuff. Please guys, for your own safety, and for those around you on the
> highway, Do not accept less than the best braking you can have.
> Incidentally, when tires are skidding on the pavement, you are not stopping
> at the greatest rate of decelleration. Brakes that lock up tires are not an
> ideal system.
> Jim Hupy
> Salem, OR
> 78 GMC Royale 403
>
> On Fri, Jan 30, 2015 at 9:16 AM, Hal StClair
> wrote:
>
>> My brakes are not stock with the addition of rear disc's and the one ton
>> front end as well as the 34mm m/c. The two lb residual valve mounted in the
>> rear brake line at the m/c, with no other changes moved the brake pedal up
>> from an inch above the floor to about an inch below the top. I see no
>> detrimential issues using the valve and on the contrary a huge improvement
>> in pedal/braking. Unless there is more runout in the rear disc's than I
>> observed with the Manny system one wouldn't see a need for the valve but
>> in reality it works great. Our brakes work so well I'm afraid someone is
>> going to plow into us from behind during an aggresive stop.
>> Just my observations, Hal
>> --
>> 1977 Royale 101348,
>>
>> 1977 Royale 101586,
>>
>> 1974 Eagle Bus 45',w/slideout
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
> _______________________________________________
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> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Residual pressure valves [message #270869 is a reply to message #270824] |
Sat, 31 January 2015 13:35 |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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Daniel DeLuca wrote on Fri, 30 January 2015 13:36I really think people who are "new" to these coaches don't know what to expect when it comes to braking a 35 year old 12,000 pound 6 wheeled vehicle. I certainly don't. When I redid the brakes this summer, I replaced the master cylinder, the fronts got the 80mm "upgrade" rears got new shoes, lines and cylinders but otherwise stock. Frankly, I was less then impressed when all was said and done. Adjusting the rear brakes helped immensely, and now that they have begun to 'seat' I would call braking 'adequate.' Having never driven another coach, I have no real way of knowing. I could have the best brakes in the world or the worst. I passed NJ state inspection so at least the government thinks they are safe.
Dan
Allentown NJ
Dan,
When the GMC coaches hit the street, one of the things that they were heralded for were the remarkable brakes. At the time, not even all the passcars were disk front and radial tires did not yet have that great market penetration. If you drive any six ton vehicle it will not stop like your little passcar.
As good as they can be, they are nothing like what a passcar can do today. For a while, I drove a 1987 Ford Turbo-coupe with 4 wheel anti lock disks. A tail light got cracked in a parking lot. When I called the local scrappers to look for a replacement, I was laughed at. Finally I asked one what was so funny. He told me that with those brakes, they were getting rear-ended regularly. When he got one (which was rare - he allowed) he could sell it that day for twice what he would expect for the standard model.
Back to the subject at hand. You have an additional problem - NJMVC. You have to have a parking brake to pass. To that end, and even if you were to move to NY (for an additional consideration - you pass inspection) I will suggest that you consider
what they call reaction arms here. In the motorcycle world, they were called floating brakes for years. We fit a set on our coach some years back, and the change was immediate and remarkable. AND, we no longer worry about flat spotting the rear tires. My wife (she drives most) still tries to provide the required space to make a safe stop, but when the stupid little toy car jumps into that space, it no longer requires panic and evasive maneuvers too keep from flattening the idiot. Ours is a very light coach - by TZE standards, but still a full panic can lock a rear tire and often as not it has been and intermediate when I had the chance to figure out which locked.
It is a brake upgrade that I routinely recommend. If you install the kit and later want to go to disk rear (when you leave NJ), JimK can supply the parts to do that - too.
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] Residual pressure valves [message #270875 is a reply to message #270869] |
Sat, 31 January 2015 14:01 |
Dolph Santorine
Messages: 1236
Registered: April 2011
Location: Wheeling, WV
Karma: -41
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Senior Member |
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Matt:
I currently have one of these mounted, and it seems to do just fine.
Last summer, I drove a young man’s S-10 that was heavily modified at the vehicle dynamics area at PittRace.
Big brakes (lots of pistons), and made them good and hot - with one of these:
http://sddimage.com/originals/sdd/speeddaddyebay//HANDB-T1-BL.jpg
In the motorhome, it gives me an “emergency” brake, as well as a parking brake (well, parking, as long as it takes me to motivate my fat ass and put the chocks in place).
I know some people will take issue with it. That’s fine.
It’s safe, and it works for me.
Dolph
DE N8JPC
Wheeling, West Virginia
1977 GMC 26' Palm Beach
TZE167V100820
1976 GMC 26' Donor Coach
TZE166V101610
> On Jan 31, 2015, at 2:35 PM, Matt Colie wrote:
>
> Daniel DeLuca wrote on Fri, 30 January 2015 13:36
>> I really think people who are "new" to these coaches don't know what to expect when it comes to braking a 35 year old 12,000 pound 6 wheeled
>> vehicle. I certainly don't. When I redid the brakes this summer, I replaced the master cylinder, the fronts got the 80mm "upgrade" rears got new
>> shoes, lines and cylinders but otherwise stock. Frankly, I was less then impressed when all was said and done. Adjusting the rear brakes helped
>> immensely, and now that they have begun to 'seat' I would call braking 'adequate.' Having never driven another coach, I have no real way of
>> knowing. I could have the best brakes in the world or the worst. I passed NJ state inspection so at least the government thinks they are safe.
>>
>> Dan
>> Allentown NJ
>
> Dan,
>
> When the GMC coaches hit the street, one of the things that they were heralded for were the remarkable brakes. At the time, not even all the passcars
> were disk front and radial tires did not yet have that great market penetration. If you drive any six ton vehicle it will not stop like your little
> passcar.
>
> As good as they can be, they are nothing like what a passcar can do today. For a while, I drove a 1987 Ford Turbo-coupe with 4 wheel anti lock disks.
> A tail light got cracked in a parking lot. When I called the local scrappers to look for a replacement, I was laughed at. Finally I asked one what
> was so funny. He told me that with those brakes, they were getting rear-ended regularly. When he got one (which was rare - he allowed) he could sell
> it that day for twice what he would expect for the standard model.
>
> Back to the subject at hand. You have an additional problem - NJMVC. You have to have a parking brake to pass. To that end, and even if you were to
> move to NY (for an additional consideration - you pass inspection) I will suggest that you consider
> what they call reaction arms here. In the motorcycle world, they were called floating brakes for years. We fit a set on our coach some years back,
> and the change was immediate and remarkable. AND, we no longer worry about flat spotting the rear tires. My wife (she drives most) still tries to
> provide the required space to make a safe stop, but when the stupid little toy car jumps into that space, it no longer requires panic and evasive
> maneuvers too keep from flattening the idiot. Ours is a very light coach - by TZE standards, but still a full panic can lock a rear tire and often as
> not it has been and intermediate when I had the chance to figure out which locked.
>
> It is a brake upgrade that I routinely recommend. If you install the kit and later want to go to disk rear (when you leave NJ), JimK can supply the
> parts to do that - too.
>
> Matt
> --
> Matt & Mary Colie - Members GMCMI, GMCES
> '73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
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Unsubscribe or Change List Options:
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| Re: [GMCnet] Residual pressure valves [message #270889 is a reply to message #270875] |
Sat, 31 January 2015 16:55 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Dolph,
Neat piece of kit!
I assume you have plumbed it into the rear brake line to actuate the rear brakes?
Kerry came up with this clever idea: http://www.gmcmhphotos.com/photos/g6433-kiss-parking-brake.html
It does essentially the same thing but uses the master cylinder.
When I bought Double Trouble it had six wheel disk brakes, Caddies on the back and no parking brake. I had to register it in NJ to
my cousin (long story). Ken Frey wound up taking the rear disks off and installing drums with a parking brake because I believed
that NJ requires a mechanically actuated parking brake on vehicles of the GMC era. Having said that I wonder if they would accept
your setup as a mechanically actuated parking brake?
Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: Dolph Santorine
Matt:
I currently have one of these mounted, and it seems to do just fine.
Last summer, I drove a young man's S-10 that was heavily modified at the vehicle dynamics area at PittRace.
Big brakes (lots of pistons), and made them good and hot - with one of these:
http://sddimage.com/originals/sdd/speeddaddyebay//HANDB-T1-BL.jpg
In the motorhome, it gives me an "emergency" brake, as well as a parking brake (well, parking, as long as it takes me to motivate my
fat ass and put the chocks in place).
I know some people will take issue with it. That's fine.
It's safe, and it works for me.
Dolph
DE N8JPC
Wheeling, West Virginia
1977 GMC 26' Palm Beach
TZE167V100820
1976 GMC 26' Donor Coach
TZE166V101610
> On Jan 31, 2015, at 2:35 PM, Matt Colie wrote:
>
> Daniel DeLuca wrote on Fri, 30 January 2015 13:36
>> I really think people who are "new" to these coaches don't know what to expect when it comes to braking a 35 year old 12,000
pound 6 wheeled
>> vehicle. I certainly don't. When I redid the brakes this summer, I replaced the master cylinder, the fronts got the 80mm
"upgrade" rears got new
>> shoes, lines and cylinders but otherwise stock. Frankly, I was less then impressed when all was said and done. Adjusting the
rear brakes helped
>> immensely, and now that they have begun to 'seat' I would call braking 'adequate.' Having never driven another coach, I have no
real way of
>> knowing. I could have the best brakes in the world or the worst. I passed NJ state inspection so at least the government thinks
they are safe.
>>
>> Dan
>> Allentown NJ
>
> Dan,
>
> When the GMC coaches hit the street, one of the things that they were heralded for were the remarkable brakes. At the time, not
even all the passcars
> were disk front and radial tires did not yet have that great market penetration. If you drive any six ton vehicle it will not
stop like your little
> passcar.
>
> As good as they can be, they are nothing like what a passcar can do today. For a while, I drove a 1987 Ford Turbo-coupe with 4
wheel anti lock disks.
> A tail light got cracked in a parking lot. When I called the local scrappers to look for a replacement, I was laughed at.
Finally I asked one what
> was so funny. He told me that with those brakes, they were getting rear-ended regularly. When he got one (which was rare - he
allowed) he could sell
> it that day for twice what he would expect for the standard model.
>
> Back to the subject at hand. You have an additional problem - NJMVC. You have to have a parking brake to pass. To that end, and
even if you were to
> move to NY (for an additional consideration - you pass inspection) I will suggest that you consider
> what they call reaction arms here. In the motorcycle world, they were called floating brakes for years. We fit a set on our
coach some years back,
> and the change was immediate and remarkable. AND, we no longer worry about flat spotting the rear tires. My wife (she drives
most) still tries to
> provide the required space to make a safe stop, but when the stupid little toy car jumps into that space, it no longer requires
panic and evasive
> maneuvers too keep from flattening the idiot. Ours is a very light coach - by TZE standards, but still a full panic can lock a
rear tire and often as
> not it has been and intermediate when I had the chance to figure out which locked.
>
> It is a brake upgrade that I routinely recommend. If you install the kit and later want to go to disk rear (when you leave NJ),
JimK can supply the
> parts to do that - too.
>
> Matt
> --
> Matt & Mary Colie - Members GMCMI, GMCES
> '73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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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] Residual pressure valves [message #270910 is a reply to message #270889] |
Sat, 31 January 2015 22:05 |
Dolph Santorine
Messages: 1236
Registered: April 2011
Location: Wheeling, WV
Karma: -41
|
Senior Member |
|
|
Rob:
Having lived in NJ, I remember the inspections. I used to run my hot rod on Propane to get it through the emissions test, and their running brake test of that era was something else.
That was before I learned that by involving President Jackson in the discussion, nearly anything would pass.
It’s not the third most corrupt state for nuthin!
Dolph
> On Jan 31, 2015, at 5:55 PM, Robert Mueller wrote:
>
> Dolph,
>
> Neat piece of kit!
>
> I assume you have plumbed it into the rear brake line to actuate the rear brakes?
>
> Kerry came up with this clever idea: http://www.gmcmhphotos.com/photos/g6433-kiss-parking-brake.html
>
> It does essentially the same thing but uses the master cylinder.
>
> When I bought Double Trouble it had six wheel disk brakes, Caddies on the back and no parking brake. I had to register it in NJ to
> my cousin (long story). Ken Frey wound up taking the rear disks off and installing drums with a parking brake because I believed
> that NJ requires a mechanically actuated parking brake on vehicles of the GMC era. Having said that I wonder if they would accept
> your setup as a mechanically actuated parking brake?
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> Sydney, Australia
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
>
>
> -----Original Message-----
> From: Dolph Santorine
>
> Matt:
>
> I currently have one of these mounted, and it seems to do just fine.
>
> Last summer, I drove a young man's S-10 that was heavily modified at the vehicle dynamics area at PittRace.
>
> Big brakes (lots of pistons), and made them good and hot - with one of these:
>
> http://sddimage.com/originals/sdd/speeddaddyebay//HANDB-T1-BL.jpg
>
>
> In the motorhome, it gives me an "emergency" brake, as well as a parking brake (well, parking, as long as it takes me to motivate my
> fat ass and put the chocks in place).
>
> I know some people will take issue with it. That's fine.
>
> It's safe, and it works for me.
>
> Dolph
>
> DE N8JPC
>
> Wheeling, West Virginia
>
> 1977 GMC 26' Palm Beach
> TZE167V100820
>
> 1976 GMC 26' Donor Coach
> TZE166V101610
>
>
>
>> On Jan 31, 2015, at 2:35 PM, Matt Colie wrote:
>>
>> Daniel DeLuca wrote on Fri, 30 January 2015 13:36
>>> I really think people who are "new" to these coaches don't know what to expect when it comes to braking a 35 year old 12,000
> pound 6 wheeled
>>> vehicle. I certainly don't. When I redid the brakes this summer, I replaced the master cylinder, the fronts got the 80mm
> "upgrade" rears got new
>>> shoes, lines and cylinders but otherwise stock. Frankly, I was less then impressed when all was said and done. Adjusting the
> rear brakes helped
>>> immensely, and now that they have begun to 'seat' I would call braking 'adequate.' Having never driven another coach, I have no
> real way of
>>> knowing. I could have the best brakes in the world or the worst. I passed NJ state inspection so at least the government thinks
> they are safe.
>>>
>>> Dan
>>> Allentown NJ
>>
>> Dan,
>>
>> When the GMC coaches hit the street, one of the things that they were heralded for were the remarkable brakes. At the time, not
> even all the passcars
>> were disk front and radial tires did not yet have that great market penetration. If you drive any six ton vehicle it will not
> stop like your little
>> passcar.
>>
>> As good as they can be, they are nothing like what a passcar can do today. For a while, I drove a 1987 Ford Turbo-coupe with 4
> wheel anti lock disks.
>> A tail light got cracked in a parking lot. When I called the local scrappers to look for a replacement, I was laughed at.
> Finally I asked one what
>> was so funny. He told me that with those brakes, they were getting rear-ended regularly. When he got one (which was rare - he
> allowed) he could sell
>> it that day for twice what he would expect for the standard model.
>>
>> Back to the subject at hand. You have an additional problem - NJMVC. You have to have a parking brake to pass. To that end, and
> even if you were to
>> move to NY (for an additional consideration - you pass inspection) I will suggest that you consider
>> what they call reaction arms here. In the motorcycle world, they were called floating brakes for years. We fit a set on our
> coach some years back,
>> and the change was immediate and remarkable. AND, we no longer worry about flat spotting the rear tires. My wife (she drives
> most) still tries to
>> provide the required space to make a safe stop, but when the stupid little toy car jumps into that space, it no longer requires
> panic and evasive
>> maneuvers too keep from flattening the idiot. Ours is a very light coach - by TZE standards, but still a full panic can lock a
> rear tire and often as
>> not it has been and intermediate when I had the chance to figure out which locked.
>>
>> It is a brake upgrade that I routinely recommend. If you install the kit and later want to go to disk rear (when you leave NJ),
> JimK can supply the
>> parts to do that - too.
>>
>> Matt
>> --
>> Matt & Mary Colie - Members GMCMI, GMCES
>> '73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
>> SE Michigan - Twixt A2 and Detroit
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| Re: [GMCnet] Residual pressure valves [message #270918 is a reply to message #270910] |
Sat, 31 January 2015 23:11 |
|
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
|
Senior Member |
|
|
Dolph,
DAMN! Had I known involving a President would have helped I would have done so, however, since my GMC needed inspection in 2008 it
was long time since the '70s and I'd probably have to get Ben Franklin involved.
Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: Dolph Santorine
Rob:
Having lived in NJ, I remember the inspections. I used to run my hot rod on Propane to get it through the emissions test, and their
running brake test of that era was something else.
That was before I learned that by involving President Jackson in the discussion, nearly anything would pass.
It's not the third most corrupt state for nuthin!
Dolph
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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] Residual pressure valves [message #271138 is a reply to message #270814] |
Tue, 03 February 2015 20:01 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
|
Senior Member |
|
|
glwgmc wrote on Fri, 30 January 2015 08:54I noted with interest a recent post about installing residual pressure valves to cure the low brake pedal issue when changing over to six wheel disk brakes. I was not familiar with these so started digging. Here is what one site has to say:
"Residual Pressure Valves are used in a both front and rear brake system as follows:
• 2 PSI Valves - These valves are used in a disc brake system only and are required when the master cylinder is at, or below, the height of the calipers. It's purpose is to act as an anti-siphon valve preventing the brake fluid from siphoning back into the master cylinder when the brake pedal is released. Even if the master cylinder is even or slightly above the calipers, put one in anyway. If you don't and you park on a hill, fluid will siphon! These valves are cheap insurance - put them in!
• NOTE: You will know if you need one of these valves if you had to pump the pedal twice to get a good pedal. See illustration for more.
• 10 PSI Valves - These valves are used in a drum brake system to prevent air from being ingested into the hydraulic system when you release the brake pedal. Typical wheel cylinder seals only seal when there is pressure behind them. Rapid release of the brake pedal creates a vacuum in the system which causes the seals to relax and air is ingested into the wheel cylinders. Maintaining 10 PSI in the system at all times prevents this. Some disc/drum master cylinders have 10 PSI residual pressure valves installed internally, some don't. If you're not sure, call us and we can tell you how to check. Also, some new style wheel cylinders have cup expanders which negate the need for the residual pressure valve. Either way, if you are not sure whether you have one or not, put one in. They are not cumulative and it won't hurt anything if you have two. Don't worry about brake drag, it takes roughly 75 PSI to overcome the return springs."
I could not find info on why they would be necessary when our master cylinder is way higher than the calipers front and rear. Can anyone shed more info on the benefits or lack there of from the use of these valves in the six wheel disk brake set up? If they would be helpful for our six wheel disk system, how many and where should these be installed?
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
Visitors always welcome!
glwork@mac.com
http://jerrywork.com
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I just ran a series of tests on drum brakes both in the lab and on the road. Drum assemblies like ours require up to 70 psi to start to move the shoes off the pins. A slight amount of residual pressure up to 10 psi is not going to hurt and I can see why some people may like them on our coaches, You do have to be carefull in that you want the shows to retract enough to allow the adjusters to work. When it comes to disks, there is no reason for residual pressure since the piston seals are designed to retract the pistons just a hair when pressure is released. I wouldn't interfere with that.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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