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| [GMCnet] Brake Discs [message #108905] |
Sat, 18 December 2010 20:59  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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The on-going brake pad replacement discussion reminded me of something
I've been meaning to bring up:
These are the thickness specifications for our discs:
Original 1.200"
Minimum allowable after turning 1.185"
Absolute Minimum allowable 1.170" (cast into the disc)
Have any of you ever checked the thickness of your discs? As heavy as
they are, and having never heard a GMCer complain of warped discs, I'd
never given that spec. much thought until a couple of weeks ago.
Undisclosed until now, I decided to move the small calipers (post-79
GM) from the center of my GMC to the rear, replacing the calipers I
removed several years ago. On the center, I reinstalled the standard
GMC front calipers. As a part of that exercise, I inventoried the
pile of discs I've been thinking were all good spares.
Of the 9 spare discs I have, 4 are GMC-ready, 2 of them already
turned. The other 5 are apparently new Toronado/Eldorado discs which
have never been used; nor have they been drilled to fit GMC hubs. I
don't know the original source, nor application for those discs, but
they need only additional holes drilled in them to make them usable on
the GMC.
This is the surprise: Two (2) of the 9 discs, both used GMC, measure
1.185" or a little less. ALL of the others measure 1.170" or less!
Including the apparently new ones (which do not have minimum
thicknesses cast into them). And the 6 on the GMC are at 1.170" or
thereabouts.
I'm surprised. None of the used discs, including those on the coach,
show any sign of having been turned -- I'm surprised that the
machining was all done carefully enough to remove all ridges. Nor are
there wear ridges on any of them. How'd they all get down to
1.170"???
Jim K: I'm sure you have some new discs in stock; please mic a couple
and tell us what they measure.
Am I concerned? Not especially. As I said, I've never heard a GMCer
complain about a warped disc. These have all been through 70,000
miles or so with me, including two very aggressive brake pad testing
episodes, and are not warped. I will never neglect the brakes long
enough for the pads to wear beyond the travel of the caliper pistons
(the manual's caution). But I am surprised that I've found so many so
"thin" & my curiosity's aroused.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
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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] Brake Discs [message #108919 is a reply to message #108905] |
Sat, 18 December 2010 22:30  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Ken, the real danger in using discs thinner that 1.170" is not in having the
rotors warp, it is having the caliper piston travel out too far from home
position. If one of those pistons move out fall enough because of excessive
wear on the disk brake pads, there is a chance the "O" ring will extend past
the caliper bore and a subsequent catastrophic loss of brake fluid. I
personally have had my brake pedal go to the floor while exiting a downhill
freeway off ramp at about 70 mph. Nothing quite like that experience will
convince you that maximum rotor thickness is better than minimum. There are
machine shops that will turn rotors below minimum thickness without a second
thought. They don't drive 12,000 pound GMCs. When I work on brakes, I don't
care what the finish of the rotor looks like. I always measure them with a
brake micrometer. If they are thinner than 1.170", they get replaced. Just
What I do.
I think Jim Bounds & Jim K will tell you the same thing. I am not trying to
be contrary or argumenative, and I don't have a bone to pick with you. It is
a safety issue. The coach can look ugly, but it has to START/STOP/STEER,
before anything else.
Jim Hupy
Salem, Or
78 Royale 403
On Sat, Dec 18, 2010 at 6:59 PM, Ken Henderson <hend4800@bellsouth.net>wrote:
> The on-going brake pad replacement discussion reminded me of something
> I've been meaning to bring up:
>
> These are the thickness specifications for our discs:
>
> Original 1.200"
> Minimum allowable after turning 1.185"
> Absolute Minimum allowable 1.170" (cast into the disc)
>
> Have any of you ever checked the thickness of your discs? As heavy as
> they are, and having never heard a GMCer complain of warped discs, I'd
> never given that spec. much thought until a couple of weeks ago.
>
> Undisclosed until now, I decided to move the small calipers (post-79
> GM) from the center of my GMC to the rear, replacing the calipers I
> removed several years ago. On the center, I reinstalled the standard
> GMC front calipers. As a part of that exercise, I inventoried the
> pile of discs I've been thinking were all good spares.
>
> Of the 9 spare discs I have, 4 are GMC-ready, 2 of them already
> turned. The other 5 are apparently new Toronado/Eldorado discs which
> have never been used; nor have they been drilled to fit GMC hubs. I
> don't know the original source, nor application for those discs, but
> they need only additional holes drilled in them to make them usable on
> the GMC.
>
> This is the surprise: Two (2) of the 9 discs, both used GMC, measure
> 1.185" or a little less. ALL of the others measure 1.170" or less!
> Including the apparently new ones (which do not have minimum
> thicknesses cast into them). And the 6 on the GMC are at 1.170" or
> thereabouts.
>
> I'm surprised. None of the used discs, including those on the coach,
> show any sign of having been turned -- I'm surprised that the
> machining was all done carefully enough to remove all ridges. Nor are
> there wear ridges on any of them. How'd they all get down to
> 1.170"???
>
> Jim K: I'm sure you have some new discs in stock; please mic a couple
> and tell us what they measure.
>
> Am I concerned? Not especially. As I said, I've never heard a GMCer
> complain about a warped disc. These have all been through 70,000
> miles or so with me, including two very aggressive brake pad testing
> episodes, and are not warped. I will never neglect the brakes long
> enough for the pads to wear beyond the travel of the caliper pistons
> (the manual's caution). But I am surprised that I've found so many so
> "thin" & my curiosity's aroused.
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI+ & EBL
> www.gmcwipersetc.com
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Brake Discs [message #108983 is a reply to message #108919] |
Sun, 19 December 2010 12:35 |
Donny Smith
Messages: 7
Registered: October 2010
Location: Houston,Tx
Karma: 0
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Junior Member |
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>First time my front bearings was serviced had to replace one rotor was cracked..<
>Donny Smith<
> Date: Sat, 18 Dec 2010 20:30:26 -0800
> From: jamesh1296@gmail.com
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] Brake Discs
>
> Ken, the real danger in using discs thinner that 1.170" is not in having the
> rotors warp, it is having the caliper piston travel out too far from home
> position. If one of those pistons move out fall enough because of excessive
> wear on the disk brake pads, there is a chance the "O" ring will extend past
> the caliper bore and a subsequent catastrophic loss of brake fluid. I
> personally have had my brake pedal go to the floor while exiting a downhill
> freeway off ramp at about 70 mph. Nothing quite like that experience will
> convince you that maximum rotor thickness is better than minimum. There are
> machine shops that will turn rotors below minimum thickness without a second
> thought. They don't drive 12,000 pound GMCs. When I work on brakes, I don't
> care what the finish of the rotor looks like. I always measure them with a
> brake micrometer. If they are thinner than 1.170", they get replaced. Just
> What I do.
> I think Jim Bounds & Jim K will tell you the same thing. I am not trying to
> be contrary or argumenative, and I don't have a bone to pick with you. It is
> a safety issue. The coach can look ugly, but it has to START/STOP/STEER,
> before anything else.
> Jim Hupy
> Salem, Or
> 78 Royale 403
>
> On Sat, Dec 18, 2010 at 6:59 PM, Ken Henderson <hend4800@bellsouth.net>wrote:
>
> > The on-going brake pad replacement discussion reminded me of something
> > I've been meaning to bring up:
> >
> > These are the thickness specifications for our discs:
> >
> > Original 1.200"
> > Minimum allowable after turning 1.185"
> > Absolute Minimum allowable 1.170" (cast into the disc)
> >
> > Have any of you ever checked the thickness of your discs? As heavy as
> > they are, and having never heard a GMCer complain of warped discs, I'd
> > never given that spec. much thought until a couple of weeks ago.
> >
> > Undisclosed until now, I decided to move the small calipers (post-79
> > GM) from the center of my GMC to the rear, replacing the calipers I
> > removed several years ago. On the center, I reinstalled the standard
> > GMC front calipers. As a part of that exercise, I inventoried the
> > pile of discs I've been thinking were all good spares.
> >
> > Of the 9 spare discs I have, 4 are GMC-ready, 2 of them already
> > turned. The other 5 are apparently new Toronado/Eldorado discs which
> > have never been used; nor have they been drilled to fit GMC hubs. I
> > don't know the original source, nor application for those discs, but
> > they need only additional holes drilled in them to make them usable on
> > the GMC.
> >
> > This is the surprise: Two (2) of the 9 discs, both used GMC, measure
> > 1.185" or a little less. ALL of the others measure 1.170" or less!
> > Including the apparently new ones (which do not have minimum
> > thicknesses cast into them). And the 6 on the GMC are at 1.170" or
> > thereabouts.
> >
> > I'm surprised. None of the used discs, including those on the coach,
> > show any sign of having been turned -- I'm surprised that the
> > machining was all done carefully enough to remove all ridges. Nor are
> > there wear ridges on any of them. How'd they all get down to
> > 1.170"???
> >
> > Jim K: I'm sure you have some new discs in stock; please mic a couple
> > and tell us what they measure.
> >
> > Am I concerned? Not especially. As I said, I've never heard a GMCer
> > complain about a warped disc. These have all been through 70,000
> > miles or so with me, including two very aggressive brake pad testing
> > episodes, and are not warped. I will never neglect the brakes long
> > enough for the pads to wear beyond the travel of the caliper pistons
> > (the manual's caution). But I am surprised that I've found so many so
> > "thin" & my curiosity's aroused.
> >
> > Ken H.
> > Americus, GA
> > '76 X-Birchaven w/Cad500/Howell EFI+ & EBL
> > www.gmcwipersetc.com
> > _______________________________________________
> > GMCnet mailing list
> > List Information and Subscription Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Brake Discs [message #108993 is a reply to message #108983] |
Sun, 19 December 2010 13:23 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
|
Senior Member |
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|
I hope that person that did the job knew about the bearing and knuckle
assy. to put it back properly and torque the big nut to 200 ft lbs.
We see so much of the people that do not understand these and destroy
it for the owners.
On Sun, Dec 19, 2010 at 10:35 AM, Donny Smith <donnystruck@hotmail.com> wrote:
>
>>First time my front bearings was serviced had to replace one rotor was cracked..<
>>Donny Smith<
>
>> Date: Sat, 18 Dec 2010 20:30:26 -0800
>> From: jamesh1296@gmail.com
>> To: gmclist@temp.gmcnet.org
>> Subject: Re: [GMCnet] Brake Discs
>>
>> Ken, the real danger in using discs thinner that 1.170" is not in having the
>> rotors warp, it is having the caliper piston travel out too far from home
>> position. If one of those pistons move out fall enough because of excessive
>> wear on the disk brake pads, there is a chance the "O" ring will extend past
>> the caliper bore and a subsequent catastrophic loss of brake fluid. I
>> personally have had my brake pedal go to the floor while exiting a downhill
>> freeway off ramp at about 70 mph. Nothing quite like that experience will
>> convince you that maximum rotor thickness is better than minimum. There are
>> machine shops that will turn rotors below minimum thickness without a second
>> thought. They don't drive 12,000 pound GMCs. When I work on brakes, I don't
>> care what the finish of the rotor looks like. I always measure them with a
>> brake micrometer. If they are thinner than 1.170", they get replaced. Just
>> What I do.
>> I think Jim Bounds & Jim K will tell you the same thing. I am not trying to
>> be contrary or argumenative, and I don't have a bone to pick with you. It is
>> a safety issue. The coach can look ugly, but it has to START/STOP/STEER,
>> before anything else.
>> Jim Hupy
>> Salem, Or
>> 78 Royale 403
>>
>> On Sat, Dec 18, 2010 at 6:59 PM, Ken Henderson <hend4800@bellsouth.net>wrote:
>>
>> > The on-going brake pad replacement discussion reminded me of something
>> > I've been meaning to bring up:
>> >
>> > These are the thickness specifications for our discs:
>> >
>> > Original 1.200"
>> > Minimum allowable after turning 1.185"
>> > Absolute Minimum allowable 1.170" (cast into the disc)
>> >
>> > Have any of you ever checked the thickness of your discs? As heavy as
>> > they are, and having never heard a GMCer complain of warped discs, I'd
>> > never given that spec. much thought until a couple of weeks ago.
>> >
>> > Undisclosed until now, I decided to move the small calipers (post-79
>> > GM) from the center of my GMC to the rear, replacing the calipers I
>> > removed several years ago. On the center, I reinstalled the standard
>> > GMC front calipers. As a part of that exercise, I inventoried the
>> > pile of discs I've been thinking were all good spares.
>> >
>> > Of the 9 spare discs I have, 4 are GMC-ready, 2 of them already
>> > turned. The other 5 are apparently new Toronado/Eldorado discs which
>> > have never been used; nor have they been drilled to fit GMC hubs. I
>> > don't know the original source, nor application for those discs, but
>> > they need only additional holes drilled in them to make them usable on
>> > the GMC.
>> >
>> > This is the surprise: Two (2) of the 9 discs, both used GMC, measure
>> > 1.185" or a little less. ALL of the others measure 1.170" or less!
>> > Including the apparently new ones (which do not have minimum
>> > thicknesses cast into them). And the 6 on the GMC are at 1.170" or
>> > thereabouts.
>> >
>> > I'm surprised. None of the used discs, including those on the coach,
>> > show any sign of having been turned -- I'm surprised that the
>> > machining was all done carefully enough to remove all ridges. Nor are
>> > there wear ridges on any of them. How'd they all get down to
>> > 1.170"???
>> >
>> > Jim K: I'm sure you have some new discs in stock; please mic a couple
>> > and tell us what they measure.
>> >
>> > Am I concerned? Not especially. As I said, I've never heard a GMCer
>> > complain about a warped disc. These have all been through 70,000
>> > miles or so with me, including two very aggressive brake pad testing
>> > episodes, and are not warped. I will never neglect the brakes long
>> > enough for the pads to wear beyond the travel of the caliper pistons
>> > (the manual's caution). But I am surprised that I've found so many so
>> > "thin" & my curiosity's aroused.
>> >
>> > Ken H.
>> > Americus, GA
>> > '76 X-Birchaven w/Cad500/Howell EFI+ & EBL
>> > www.gmcwipersetc.com
>> > _______________________________________________
>> > GMCnet mailing list
>> > List Information and Subscription Options:
>> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>> >
>> _______________________________________________
>> GMCnet mailing list
>> List Information and Subscription Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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