Steering, Suspension, & Brakes

tips, technology, tools and techniques related to non-driveline mechanical components

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roverman
Art Gertz
Winchester, CA.
(2854 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Backwards Brake Rotors ?
Posted by: roverman
Date: June 13, 2016 12:15PM

Seems many TV wonder build car programs, (Chip Foose/etc), and the installation stickers, left/right, (Full Stop brand brakes), have the vented, cross drilled and slotted rotors on "backwards" ? This seems to be in conflict as to what I was taught in college. The vented rotor should work similar to a centrifugal fan. Air or water is drawn in near the center and pumped outward with centrifugal force. Seems to me the angular slots on rotors should have a squegee effect , to shear water outward, with aid of centrifugal force. Comments ? roverman.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5240 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Backwards Brake Rotors ?
Posted by: BlownMGB-V8
Date: June 13, 2016 04:06PM

This is generally true but if you look at squirrel cage blowers (and some water pump impellers oddly enough) you will sometimes see the reverse practice. Why, I don't know. Noise maybe?

Jim


avbates
Tony Bates
San Jose California
(25 posts)

Registered:
03/22/2008 12:16PM

Main British Car:
74 MGB roadster 4.2 litre Rover

Re: Backwards Brake Rotors ?
Posted by: avbates
Date: June 14, 2016 10:53PM

When I have install slotted rotors I have always installed them so they "draw" the air in towards the middle


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5240 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Backwards Brake Rotors ?
Posted by: BlownMGB-V8
Date: June 15, 2016 08:11AM

I'm not sure that makes sense Tony. Centrifugal force will always push any spinning element to the outside so you are attempting to fight centrifugal force. Brake ducting always goes to the center of the rotor and flow is from the center out. Pump flow is always from the center out, fan flow is also always from the center out.

Granted the rotors aren't turning that fast, but even a few hundred rpm is enough to move some air.

I suspect that the centrifugal force is greater than can be overcome by the angle of the vanes (I've seen vaccum cleaner blowers with the vanes facing the "wrong" way.) but it would seem to me like the vanes should be angled to assist rather than retard the air movement.

Jim


roverman
Art Gertz
Winchester, CA.
(2854 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Backwards Brake Rotors ?
Posted by: roverman
Date: June 15, 2016 12:16PM

Jim and clan, In contrast to sound theory, my Huffaker GT 1 TR8, has the front rotors installed "backwards". The rotor diameter is relatively small, and there wasn't enough room , to get adequate air flow into the center of the rotor. To counter this , Huffaker put a large supply box around the outside of the rotor, with the curved vanes attemting to scoop air from it. Who am I to argue with Huffaker ? Onward, roverman.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5240 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Backwards Brake Rotors ?
Posted by: BlownMGB-V8
Date: June 15, 2016 10:49PM

Do a test. Chuck the rotor up in a lathe and spin it both ways. See which way the wind blows. I think that will tell you what you want to know.

Jim


302GT
Larry Shimp

(169 posts)

Registered:
11/17/2007 01:13PM

Main British Car:
1968 MGB GT Ford 302 crate engine

Re: Backwards Brake Rotors ?
Posted by: 302GT
Date: July 03, 2016 06:50PM

I have slotted rotors on my car and the arrows that were stamped on the rotors make the slots draw air into the center. I originally installed the rotors the other way around but after some use the arrows showed up very clearly so I reversed the rotors to avoid potentially embarrassing questions.



MGBV8
Carl Floyd
Kingsport, TN
(3143 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Backwards Brake Rotors ?
Posted by: MGBV8
Date: July 04, 2016 11:11AM

IMO, it is not critical which way the slots are. The most important issue for left/right is if using directional/curved/angled vanes. They should be oriented so that they seem to "lean" toward the back of the car.


88v8
Ivor Duarte
Gloucestershire UK
(472 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
TR6 74 2.5 injection six

Re: Backwards Brake Rotors ?
Posted by: 88v8
Date: July 23, 2016 04:40AM

Just to air my ignorance now discussion has ended, I thought the slots or dots or drillings were there primarily to break the gas cushion?

Ivor


Orange Alpine
Bill Blue

(42 posts)

Registered:
12/20/2010 07:36AM

Main British Car:
1967 Sunbeam Alpine 2.5 Ford Duratec

Re: Backwards Brake Rotors ?
Posted by: Orange Alpine
Date: July 26, 2016 01:58PM

The shape and orientation of vanes is done to fine tune air movement. IIRC, a "backward" vane will develop higher pressure, but lower volume, that a "forward" vane.

Bill


KadettB
David Stephens
SLC, UT
(10 posts)

Registered:
07/14/2017 03:41PM

Main British Car:
Absolutely original custom freak TBD, probably '98 Vortec 7400

Re: Backwards Brake Rotors ?
Posted by: KadettB
Date: July 14, 2017 04:12PM

They're supposed to sling the air out.


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