Home » Public Forums » GMCnet » [GMCnet] line lock
| [GMCnet] line lock [message #121871] |
Thu, 14 April 2011 22:42  |
paul h cashman
Messages: 176
Registered: May 2005
Karma: 0
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Senior Member |
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Hi All
I really wanted to attend the Paterson Rally ,I could just taste those
Crawfish,but it just wasn't meant to be.
My Motorhome has been dead in the Water since the new Disc brakes locked up,
I have found the cause.
When you apply Brakes with the OEM M/S the excess Fluid is returned to the
Resivour.
When you apply brakes to the P30 M/S with Drum Brakes ,the check Valves keep
all the Fluid from going to the Resivour and creating residual
pressure.which is good.
When you apply Brakes to the P30 M/S with Disc Brakes so little Fluid is
used you do not have any residual pressure.
When you apply pressure to a P30 with Disc Brakes and want to apply the
line Block ,you pump the pedal to get maximum pressure to the back brakes
,the resivour has to add more fluid ,because the Piston is demanding more
fluid and the new fluid is locked behind the check Valves,when you release
the line block there is a rush of fluid ,the pressure builds up and cant be
released because of the extra fluid and check valves .
Now you have a hard pedal ,and pressure on your Brake Calipers ,and your
Motorhome has locked up Brakes. like mine.
I now use the Old OEM M/C that I have shortened the Piston Rod length by .25
inch to give it more Volume and it works great ,better than the P30
the OEM has a 1.25 Bore just like the P30
If you have Disc Brakes and a P30 M/S and a line Block this problem will
occur.
Paul Cashman
Riverdale Ga
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Paul H Cashman
Riverdale Ga
1978 Transmode
1975 Corvette
1978 Beetle Convertible
1989 Harley Davidson Sportster
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| Re: [GMCnet] line lock [message #121874 is a reply to message #121871] |
Thu, 14 April 2011 23:30  |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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what line lock are you using?
gene
On Thu, Apr 14, 2011 at 8:42 PM, Paul Cashman <paulcashman@bellsouth.net>wrote:
> Hi All
> I really wanted to attend the Paterson Rally ,I could just taste those
> Crawfish,but it just wasn't meant to be.
> My Motorhome has been dead in the Water since the new Disc brakes locked
> up,
> I have found the cause.
> When you apply Brakes with the OEM M/S the excess Fluid is returned to the
> Resivour.
> When you apply brakes to the P30 M/S with Drum Brakes ,the check Valves
> keep
> all the Fluid from going to the Resivour and creating residual
> pressure.which is good.
> When you apply Brakes to the P30 M/S with Disc Brakes so little Fluid is
> used you do not have any residual pressure.
> When you apply pressure to a P30 with Disc Brakes and want to apply the
> line Block ,you pump the pedal to get maximum pressure to the back brakes
> ,the resivour has to add more fluid ,because the Piston is demanding more
> fluid and the new fluid is locked behind the check Valves,when you release
> the line block there is a rush of fluid ,the pressure builds up and cant be
> released because of the extra fluid and check valves .
> Now you have a hard pedal ,and pressure on your Brake Calipers ,and your
> Motorhome has locked up Brakes. like mine.
> I now use the Old OEM M/C that I have shortened the Piston Rod length by
> .25
> inch to give it more Volume and it works great ,better than the P30
> the OEM has a 1.25 Bore just like the P30
> If you have Disc Brakes and a P30 M/S and a line Block this problem will
> occur.
> Paul Cashman
> Riverdale Ga
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: [GMCnet] line lock [message #121878 is a reply to message #121877] |
Fri, 15 April 2011 03:05 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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No matter which MC is used, some freeplay should exist between the end of
the pushrod and maximum returned position of the pedal mechanism. If
clearance is not allowed, bypass ports will not be uncovered and there will
be residual pressure in the brake lines. Some MCs have check valves in
addition to bypass ports as I believe some of the P-30 MCs do. Line locks
will not release if there is any residual pressure as that is what they are
designed to do. What we end up with is a mixture of brake pieces, each good
in their own right, but not engineered to work with each other. When we mix
pieces from different systems, it becomes our individual responsibility to
verify that issues like Paul describes are addressed. Be safe out there
people. Be analytical in anything that you do with brakes that is not OEM,
and make sure the new parts are not only new but also good. Offshore
manufacturers never see 12,500 pound Motorhomes that their MCs go into.
Check, Check & Double Check. If you have a combination that has problems,
sound off on the net so the rest of us don't have to learn the lessons the
hard way. Paul has a keen mind and understands all this and still got bit by
it. I have as well.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Thu, Apr 14, 2011 at 10:49 PM, Mike Miller <m000035@gmail.com> wrote:
>
>
> paul h cashman wrote on Thu, 14 April 2011 20:42
> > ... I now use the Old OEM M/C that I have shortened the Piston Rod length
> by .25
> > inch to give it more Volume and it works great ,better than the P30. ...
>
>
> Something about this statement seems wrong. 8o
>
> Shouldn't there always be a small amount of slack between the rod and the
> m/c piston? (With the petal not pushed.) I know I read something about this
> before. The slack is to ensure the piston fully retracts... allowing the
> fluid to return.
>
> Someone know for sure?
>
> Was your rod and M/C stock to start with?
> --
> Mike Miller -- Hillsboro, OR -- on the Black list
> '73 26' exPainted D. -- `78 23' Birchaven Rear Bath -- `77 23' Birchaven
> Side Bath
> http://m000035.blogspot.com
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| Re: [GMCnet] line lock [message #121897 is a reply to message #121871] |
Fri, 15 April 2011 10:49 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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Paul
In your email you mention that you shortened the push rod "to give it more Volume". Actually shortening the push rod would give it LESS volume.
I think your problem was that the push rod was too long and not letting the piston return properly.
Here is something that I posted back in Dec. 2006:
>
> Correct pushrod length is essential to reliable braking. If the push rod is too long it causes the master cylinder compensating ports to be blocked off, eventually resulting in brake drag. If the rod is too short, it will give excessive pedal travel and not use the full stroke of the master cylinder which limits the volume of fluid going to the wheels.
>
> Here is how you can check it:
>
> 1. Remove the master cylinder cap.
> 2. Have an assistant depress the brake pedal (SLOWLY AND SLIGHTLY). Watch for fluid movement in the master cylinder when the pedal is depressed 3/8" to 1/2". This will indicate correct push rod length. On dual piston master cylinders, fluid movement may occur in the front reservoir only.
> 3. If the pedal travels more than 1/2" before fluid movement is noticed, the push rod is too short. If nothing happens no matter how far the pedal is depressed, the rod is too long.
> 4. To adjust the rod length, turn the adjustment (if you are using an adjustable rod), or replace the rod if its to short,. It its too long, either use shims between the booster and the master cylinder or grind the rod to make it shorter.
> 5. Install the master cylinder and recheck the rod length.
Another way to check the rod length:
>>>> check the length with some modeling clay on the
>>>> master cylinder end. I adjusted the rod length when I had about .
>>>> 015 clearance and then made a steel rod to that length. I uses a
>>>> drill bit of the same diameter as my original pushrod and ground
>>>> the end that goes into the master cylinder to a rounded shape and
>>>> left the end that goes against the master cylinder flat.
Some people has said to give 1/16" clearance (.0625") but I have found that .015" works fine and it gives a little more volume and more brake pedal height.
Emery Stora
On Apr 14, 2011, at 9:42 PM, Paul Cashman wrote:
> Hi All
> I really wanted to attend the Paterson Rally ,I could just taste those
> Crawfish,but it just wasn't meant to be.
> My Motorhome has been dead in the Water since the new Disc brakes locked up,
> I have found the cause.
> When you apply Brakes with the OEM M/S the excess Fluid is returned to the
> Resivour.
> When you apply brakes to the P30 M/S with Drum Brakes ,the check Valves keep
> all the Fluid from going to the Resivour and creating residual
> pressure.which is good.
> When you apply Brakes to the P30 M/S with Disc Brakes so little Fluid is
> used you do not have any residual pressure.
> When you apply pressure to a P30 with Disc Brakes and want to apply the
> line Block ,you pump the pedal to get maximum pressure to the back brakes
> ,the resivour has to add more fluid ,because the Piston is demanding more
> fluid and the new fluid is locked behind the check Valves,when you release
> the line block there is a rush of fluid ,the pressure builds up and cant be
> released because of the extra fluid and check valves .
> Now you have a hard pedal ,and pressure on your Brake Calipers ,and your
> Motorhome has locked up Brakes. like mine.
> I now use the Old OEM M/C that I have shortened the Piston Rod length by .25
> inch to give it more Volume and it works great ,better than the P30
> the OEM has a 1.25 Bore just like the P30
> If you have Disc Brakes and a P30 M/S and a line Block this problem will
> occur.
> Paul Cashman
> Riverdale Ga
>
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| Re: [GMCnet] line lock [message #121916 is a reply to message #121903] |
Fri, 15 April 2011 14:46 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Bruce, it kinda varies with the specific coach and booster/MC/rod
combination. Each component assembly needs to assembled and then the push
rod length can be checked. A minimum clearance as Emery described is
critical. .015" should be considered minimum, with .250" in my opinion being
too much. Just what I do.
Jim Hupy
Salem, Or
78 GMC Royale 403
On Fri, Apr 15, 2011 at 10:07 AM, Bruce Hislop <bruce@perthcomm.com> wrote:
>
>
> Emery,
> Thanks for posting that info about the M/C rod length. I remember this has
> been discussed before.
>
> I was getting a tad worried since i just got my disk brake kit from JimK,
> but have not installed it.
>
> I know Jim will have the proper rod included in his kit.
>
> --
> Bruce Hislop,
> S. Ontario Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI and ESC.
> Hubler front end and rear disk brakes are finally HERE!:)
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> _______________________________________________
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