| OEM Front Caliper Confirmation [message #279889] |
Sun, 14 June 2015 15:55  |
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thainglo
Messages: 132
Registered: March 2015
Location: Iowa
Karma: 2
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Senior Member |
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Good afternoon! I'm about to start ordering parts to upgrade to 80mm calipers in front, but realized I had better confirm what system I already have on my coach. I pulled the right front wheel, casting number appears to be 5471975. It certainly looks original...
I searched thru all the GMC motorhome info archives I could find, couldnt see where the original calipers were identified.
If it is OEM, is there a use for these calipers if I later upgrade the rear to disc brakes?
Thanks for any help!
Matt Sladek
1976 Eleganza II
Coralville, IA
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| Re: OEM Front Caliper Confirmation [message #279891 is a reply to message #279889] |
Sun, 14 June 2015 16:37  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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The easiest way to check the calipers is to look at the brake line attaching to the caliper. If it screws in, it is original. If it attaches with a banjo bolt it is the 80 mm version.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] OEM Front Caliper Confirmation [message #279911 is a reply to message #279908] |
Sun, 14 June 2015 20:30 |
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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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G'day,
Please click on the link below and read the functions of the COMBINATION valve.
http://www.gmcmhphotos.com/photos/aa-miscellaneous-photos/p37696-combination-valve-cross-section.html
Please note the following description taken directly from Maintenance Manual X-7525
METERING VALVE FUNCTION (Spring and poppet on left side of Combination Valve)
The metering section of the combination valve operates to 'hold off' hydraulic flow (pressure) until about 130 psi has been built up
in the system before applying the front brakes. The pressure then blends to a full line pressure at approximately 400-600 psi line
pressure. There is no flow restriction when the brakes are released.
It does not proportion the pressure between the front and rear brakes. Changing the master cylinder will not affect the way it
works.
Regards,
Rob M.
The Pedantic Mechanic
-----Original Message-----
From: Steve Curlee
Matt:
I just went back to standard size calipers. The 80mm calipers will change the dynamics of your braking system from what I
experienced. The original design of the system seems to work best. By changing the to a larger size caliper, the proportional
valve is no longer working with the same proportions, and the master cylinder does not have enough fluid to manage the larger
calipers effectively. This is all just my opinion, but I did not have good results with the 80mm calipers. Others will disagree, I
expect.
Steve Curlee
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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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