Home » Public Forums » GMCnet » Primary and Secondary brake shoes (Which goes forward)
| Primary and Secondary brake shoes [message #320636] |
Tue, 18 July 2017 07:27  |
77Royale
Messages: 461
Registered: June 2014
Location: Mid Michigan
Karma: 6
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Senior Member |
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Morning to all.
I reviewed my MM and parts book. As we know there is a primary and secondary brake shoe. One has more friction material than the other. I forget at the moment which one is called the Primary.
The first drawing with the exploded view in the MM appears to show the shoe with more material on the left side when looking at it (presumably toward the front of the coach) with the other shoe, with less material toward the rear of the coach. Is that the correct placement for the shoes?
Ive see a few other photos and it appears the reverse. The parts book, while a drawing not a photo appears to show the shoe with more material toward the front of the coach as well.
Just wondering before I put it all back together. I have to believe it makes a difference otherwise all the shoes would be identical.
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
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| Re: [GMCnet] Primary and Secondary brake shoes [message #320638 is a reply to message #320636] |
Tue, 18 July 2017 08:02  |
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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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Wayne,
The line drawings in all the GMC Manuals (X-7525, X-7625, X-7725 & Parts Book 78Z) are the same. They show the passenger side with
the small shoe facing forward. They should have put an arrow on those drawings to clarify the shoe position.
Better yet they should have labeled the drawing "Brake Assembly Rear, Passenger Side" and included a second drawing showing the
driver side.
I'll bet there are LOTS of driver sides out there incorrectly assembled!
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Wayne Rogewski
Sent: Tuesday, July 18, 2017 10:27 PM
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Primary and Secondary brake shoes
Morning to all.
I reviewed my MM and parts book. As we know there is a primary and secondary brake shoe. One has more friction material than the
other. I forget at
the moment which one is called the Primary.
The first drawing with the exploded view in the MM appears to show the shoe with more material on the left side when looking at it
(presumably toward the front of the coach) with the other shoe, with less material toward the rear of the coach. Is that the
correct placement for the shoes?
Ive see a few other photos and it appears the reverse. The parts book, while a drawing not a photo appears to show the shoe with
more material toward the front of the coach as well.
Just wondering before I put it all back together. I have to believe it makes a difference otherwise all the shoes would be
identical.
--
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
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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] Primary and Secondary brake shoes [message #320639 is a reply to message #320638] |
Tue, 18 July 2017 08:18 |
77Royale
Messages: 461
Registered: June 2014
Location: Mid Michigan
Karma: 6
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Senior Member |
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Thank You both,
So for the good of the order. The SMALL(er) shoe goes FORWARD on all 4 of the rear drum brakes.
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
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| Re: [GMCnet] Primary and Secondary brake shoes [message #320641 is a reply to message #320636] |
Tue, 18 July 2017 08:35 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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> Servo and self-energizing action is produced by the hooking the heel of the primary shoe to the toe of the secondary shoe. When the wheel cylinder forces the top ends of the shoes out against the drum, the forward shoe will tend to stick to the revolving brake drum and be carried around with it. As the primary shoe attempts to revolve, it will jam the secondary shoe against the single anchor pin. This stops both shoes and produces a binding effect that actually helps the brakes shoes apply themselves. This servo and self-energizing action reduces the amount of pedal pressure necessary.
>
> The primary shoe on self-energizing brakes generally has a smaller amount of lining. The primary lining is usually also of a different composition. The secondary shoe does more of the braking, and less is needed on the primary shoe."
>
> The secondary shoe always faces the rear of the vehicle
>
> If the shoes are accidentally reversed, there will be adverse wear, more pedal pressure required and poor braking.
>
> So, if any of you are doing your own brake work, remember "Big pad to Back”.
The last issue of the GMC Motorhomes International magazine had an excellent article on this. (I wrote it!).
Emery Stora
77 Kingsley
Frederick, CO
> On Jul 18, 2017, at 6:27 AM, Wayne Rogewski wrote:
>
> Morning to all.
>
> I reviewed my MM and parts book. As we know there is a primary and secondary brake shoe. One has more friction material than the other. I forget at
> the moment which one is called the Primary.
>
> The first drawing with the exploded view in the MM appears to show the shoe with more material on the left side when looking at it (presumably toward
> the front of the coach) with the other shoe, with less material toward the rear of the coach. Is that the correct placement for the shoes?
>
> Ive see a few other photos and it appears the reverse. The parts book, while a drawing not a photo appears to show the shoe with more material
> toward the front of the coach as well.
>
> Just wondering before I put it all back together. I have to believe it makes a difference otherwise all the shoes would be identical.
> --
> 77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
> Mid Michigan
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: [GMCnet] Primary and Secondary brake shoes [message #320643 is a reply to message #320642] |
Tue, 18 July 2017 09:00 |
77Royale
Messages: 461
Registered: June 2014
Location: Mid Michigan
Karma: 6
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Senior Member |
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I answer to pretty much anything:)
Most of the time "hey you" stops me in my tracks.
I think the email view of the forum puts Karma under everyones usernames.
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
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| Re: [GMCnet] Primary and Secondary brake shoes [message #320647 is a reply to message #320642] |
Tue, 18 July 2017 10:22 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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The reason for that design is the fact that the shoes wedge up and that is
what really puts the force on the drum.
When we were testing and recording the rear Drum /Drum Reaction Arm Kit,
the wheels were skidding on the inteermediate wheels several times. I was
upset at my guys for not adjusting the shoes properly and brought it back
and I inspected them and readjusted them.
So when we re tested them , same results.
Called Tom Pryor and explained the phenomena.
He did not have an answer then , but requested time to figure that out.
Bottom line was that the Disc brakes can be charted as to when it will
grab, while the drum shoes cannot be charted as there is no way of knowing
when it will grab.
On Tue, Jul 18, 2017 at 6:54 AM, Larry wrote:
> 77Royale wrote on Tue, 18 July 2017 08:18
>> Thank You both,
>>
>> So for the good of the order. The SMALL(er) shoe goes FORWARD on all 4
> of the rear drum brakes.
>
>
> Oh...so your name is Wayne? ...not Karma?
> --
> Larry
> 78 Royale w/500 Caddy
> Menomonie, WI.
>
> _______________________________________________
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--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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