[DeTomaso] NPC - Brake Drum Wear Limits, does Porterfield R4S material eat drums, etc.

jderyke at aol.com jderyke at aol.com
Mon Dec 14 16:24:22 EST 2015 

Jeff, way back when drum brakes were the norm, one famous racer said he never turned his drums. The wear, scratches etc slightly increased the surface area and once new shoes were mated to rough drums, the system worked fine. 
As far as wear limits, its when the drum bell-mouths and braking efficiencydrops off. So it depends on lots of factors, not just a dimension.

 

 

 

-----Original Message-----
From: JEFFREY COBB <jeffcobb1 at me.com>
To: Guido deTomaso <guido_detomaso at prodigy.net>
Cc: De Tomaso List <detomaso at poca.com>
Sent: Mon, Dec 14, 2015 3:21 am
Subject: Re: [DeTomaso] NPC - Brake Drum Wear Limits, does Porterfield R4S material eat drums, etc.

Your guy is correct and the internet is wrong about safe usable size limits.
Minimum thickness or max diameter cast or stamped unto a brake rotor or drum indicates the safe min thickness or max diameter. Depending on your lathes bit size and feed rate, you can take off as little as .004 as a fresh up.

Jeff Cobb- I pad
W-225-343-7525
C-225-907-4514

On Dec 13, 2015, at 8:12 PM, Guido deTomaso <guido_detomaso at prodigy.net> wrote:

>    Have done a little driving with the Porterfield rear pads installed,
>   to match the fronts.  While the fronts made a huge difference, not
>   really feeling a big difference after changing the rears.  Ought to get
>   out in the rain though, make sure the fronts are locking up first.
>   Is there any downside to this R4S material, other than initial cost?
>   Short life?  Eats rotors or drums?  Otherwise seems too good to be
>   true.
>   I also installed the four shoes I had relined, drum brake non-Pantera
>   application, new drums too since the shoes cost so much, not really
>   seeing yet the huge improvement like I saw on the Pantera.
>   The old drums have a max diameter shown as 9.114 inches, mine are at
>   9.095 .  Thought I'd get them turned, swap them back on someday, but my
>   guy says 9.114 is the wear limit, not the machining limit, so he can't
>   take anything off.  Internet research seems to support both positions,
>   both you can and cannot machine/turn to the max diameter cast into the
>   drum.  Any thoughts/experience?
>   Also what's the minimum a brake lathe can take off typically?  If .010
>   on the diameter, that would put me at 9.105 with .009 leftover.
>   Same ideas would apply to rotors ... Pantera rotors too ... is the
>   minimum thickness a "machine to" number, or a "wear to" number?
>   Thanks,
>   GD
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-------------- next part --------------
   Jeff, way back when drum brakes were the norm, one famous racer said he
   never turned his drums. The wear, scratches etc slightly increased the
   surface area and once new shoes were mated to rough drums, the system
   worked fine.
   As far as wear limits, its when the drum bell-mouths and braking
   efficiencydrops off. So it depends on lots of factors, not just a
   dimension.

   -----Original Message-----
   From: JEFFREY COBB <jeffcobb1 at me.com>
   To: Guido deTomaso <guido_detomaso at prodigy.net>
   Cc: De Tomaso List <detomaso at poca.com>
   Sent: Mon, Dec 14, 2015 3:21 am
   Subject: Re: [DeTomaso] NPC - Brake Drum Wear Limits, does Porterfield
   R4S material eat drums, etc.
   Your guy is correct and the internet is wrong about safe usable size
   limits.
   Minimum thickness or max diameter cast or stamped unto a brake rotor or
   drum indicates the safe min thickness or max diameter. Depending on
   your lathes bit size and feed rate, you can take off as little as .004
   as a fresh up.
   Jeff Cobb- I pad
   W-225-343-7525
   C-225-907-4514
   On Dec 13, 2015, at 8:12 PM, Guido deTomaso
   <[1]guido_detomaso at prodigy.net> wrote:
   > Have done a little driving with the Porterfield rear pads installed,
   > to match the fronts. While the fronts made a huge difference, not
   > really feeling a big difference after changing the rears. Ought to
   get
   > out in the rain though, make sure the fronts are locking up first.
   > Is there any downside to this R4S material, other than initial cost?
   > Short life? Eats rotors or drums? Otherwise seems too good to be
   > true.
   > I also installed the four shoes I had relined, drum brake non-Pantera
   > application, new drums too since the shoes cost so much, not really
   > seeing yet the huge improvement like I saw on the Pantera.
   > The old drums have a max diameter shown as 9.114 inches, mine are at
   > 9.095 . Thought I'd get them turned, swap them back on someday, but
   my
   > guy says 9.114 is the wear limit, not the machining limit, so he
   can't
   > take anything off. Internet research seems to support both positions,
   > both you can and cannot machine/turn to the max diameter cast into
   the
   > drum. Any thoughts/experience?
   > Also what's the minimum a brake lathe can take off typically? If .010
   > on the diameter, that would put me at 9.105 with .009 leftover.
   > Same ideas would apply to rotors ... Pantera rotors too ... is the
   > minimum thickness a "machine to" number, or a "wear to" number?
   > Thanks,
   > GD
   > _______________________________________________
   >
   > Detomaso Forum Managed by POCA
   > Posted emails must not exceed 1.5 Megabytes
   > DeTomaso mailing list
   > [2]DeTomaso at poca.com
   > [3]http://poca.com/mailman/listinfo/detomaso_poca.com
   >
   > To manage your subscription (change email address, unsubscribe, etc.)
   use the links above.
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