| [GMCnet] BRAKES [message #86966] |
Wed, 02 June 2010 12:31  |
Charles Aulgur
Messages: 78
Registered: March 2006
Karma: 0
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Member |
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i'm confused. it is my understanding that going up to the wide shoes
does nothing to improve the rear brake effort so how can reducing the
shoe width lessen the brake effort?
--
Fred V
'77 Royale RB 455
P'cola, Fl
Fred, I'll admit it does sound a little confusion. I have no way of
telling what or how GM ended up installing 2" wide shoes in the OEM 2
3/4" wide drums. The area of brake shoes or disc pads that are in
contact does not even enter the equation for calculating braking
capability. It is based on the force that is being applied to the
brake lining or pad times the coefficient of friction of the brake
lining/pad material against the drum/disc material. Thus, changing
the brake shoe to a larger size, as myself and a lot of other GMCers
did after lessening to some expert telling us at rallies how it
provides more braking capability,
and applying the same forces (same size brake cylinder/caliper)on the
brake shoe/pad material reduces the force per square inch
accordingly and you end up with the same braking capability. It is
almost impossible to calculate the braking capability on drum brakes
because of their "self energizing" effect. However, it does make
your brake shoes/pad material last longer.
I would assume when GM realized they had to reduce the braking
capability to keep from sliding the mid axle and loosing vehicle
control, they probably reduced also reduced the wheel cylinder
diameter when they reduced the show width.
Chuck
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| Re: [GMCnet] BRAKES [message #87996 is a reply to message #86979] |
Thu, 10 June 2010 21:04  |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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The area of the brake shoe or in case of a disk does enter into the equation via the co-efficient of friction in the simple equation. As the friction members heat up, the co-efficient of friction can change--it is not a constant. If you don't take that into account you can rationalize that a pad the size of a pinpoint will be as effective as a pad on a Freightliner. Given all that, the drums on the rear of a GMC probably don't overheat under normal conditions.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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