| [GMCnet] Brake Discs [message #108905] |
Sat, 18 December 2010 20:59  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma:
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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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