| why is my brake pedal play amount erratic? [message #143425] |
Wed, 14 September 2011 21:19  |
armandminnie
Messages: 864
Registered: May 2009
Location: Marana, AZ
Karma: 2
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I have about 3000 miles on a disc brake conversion that I did just before I left on this trip. My brake pedal normally has what seems to be about an inch or inch and a half of pedal play when I step on it but occasionally it has virtually no pedal play. When this happens the brakes still work fine with no other symptoms. I have been concerned but since they work fine not overly concerned. Any ideas what is going on?
Armand Minnie
Marana, AZ
'76 Eleganza II TZE166V103202
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[Updated on: Wed, 14 September 2011 22:36] Report message to a moderator |
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| Re: [GMCnet] brake pedal play amount erratic [message #143553 is a reply to message #143453] |
Fri, 16 September 2011 09:35  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Armand, your MC pushrod is too long. If you have the adjustable one, shorten
it a turn. Be certain when no pressure is on the pedal that the MC piston is
against the retaining ring. This condition keeps the "bleed back" orfices in
the resevoirs closed and that is what causes the hard pedal.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Wed, Sep 14, 2011 at 9:15 PM, Tom Eckert <gmcrv1@gmail.com> wrote:
> Possible air in the lines?
>
> Tom Eckert N2VWN
> 73 Glacier
> Oakland, TN
>
> On Wed, Sep 14, 2011 at 9:19 PM, Armand Minnie <armand@minniebiz.com>
> wrote:
>
> >
> >
> > I have about 3000 miles on a disc brake conversion that I did just before
> I
> > left on this trip. My brake pedal normally has what seems to be about an
> > inch or inch and a half of pedal play when I step on it but occasionally
> it
> > has virtually no pedal play. When this happens the brakes still work
> fine
> > with no other symptoms. I have been concerned but since they work fine
> not
> > overly concerned. Any ideas what is going on?
> > --
> > Armand Minnie
> > Marana, AZ
> > '76 Eleganza II
> > TZE166V103202
> > http://www.minniebiz.com/gmcmotorhome
> > use the forum - it's easy
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
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| Re: [GMCnet] brake pedal play amount erratic [message #143560 is a reply to message #143554] |
Fri, 16 September 2011 10:15 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Armand, What I believe to be the case is the temperature of the brake fluid.
This causes the volume of fluid not exposed to atmospheric pressure (
calipers, lines & MC, but not the resevoirs,) to expand with heat. This,
combined with no head space at the pushrod, boxcars back to the pedal. That
is the reason for the requirement of some end play in the pushrod. I have
experienced similar problems to yours, and the fix was to shorten the
pushrod. With the number of different pushrods, MCs, boosters etc., it is a
miracle that more problems similar to this one do not occur.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Fri, Sep 16, 2011 at 7:49 AM, Armand Minnie <armand@minniebiz.com> wrote:
>
>
> Jim, I have been driving with this master cylinder for over 3000 miles and
> this only happens once in a while. Wouldn't it happen constantly if the
> push rod were too long?
> --
> Armand Minnie
> Marana, AZ
> '76 Eleganza II
> TZE166V103202
> http://www.minniebiz.com/gmcmotorhome
> use the forum - it's easy
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] brake pedal play amount erratic [message #143578 is a reply to message #143570] |
Fri, 16 September 2011 12:26 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Jim also has those push rods cheap. Buy one of them and modify it as necessary while keeping the original. Also when modifying the push rod, stick some modeling clay or silly putty on the end. (Emery's idea). Replace the MC and tighten it down. Then remove it again and see how much is was squished down. That will give the the amount of end clearance you have on the rod.
You could do the same thing with a test wooden dowel rod. Then after you find the correct length cut yours to match the wooden dowel.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] brake pedal play amount erratic [message #143579 is a reply to message #143570] |
Fri, 16 September 2011 12:26 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Depends on the thread pitch. If that is a 3/8" dia pushrod, and has standard
threads, there are 18 to the inch. 9 turns would be 1/2", 4.5 turns would be
1/4", 2.25 turns would be 1/8", 1 turn plus a frog hair would be 1/16". I
would try 1/8" first.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Fri, Sep 16, 2011 at 9:13 AM, Armand Minnie <armand@minniebiz.com> wrote:
>
>
> Jim, when I get to a place where I can shorten the fixed-length push rod I
> will give it a try. I assume that taking about 1/16 off would be equivalent
> to a turn on an adjustable?
> --
> Armand Minnie
> Marana, AZ
> '76 Eleganza II
> TZE166V103202
> http://www.minniebiz.com/gmcmotorhome
> use the forum - it's easy
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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