Re: TOY: Sequoia Rear Brakes - more

[Thom Singer <ntsqd@xxxxxxxxx>]

I'm not familiar with the calcs of servo-action drum brakes so I can't,
yet, calc the braking torque of them. The ideal rear system from I, and
others, have seen is a drum parking brake combined with discs. Witness
Wilwood's new street rod rear disc kits with drum parking brakes and
the Exploder set-up.
The used to be common drum parking brake mounted on the rear output
suffered mostly from oil leaks and open diffs. Those that used to come
on the rear of SM 420's were an external contracting shoe (band) up to
at least 1967 or 1968. Also, as Karl pointed out, an open diff isn't a
great thing when it's the drive shaft you're stopping and not the
wheels. Which brings up the ?? of what happens when you don't have a
rear driveshaft ?
That being said, I plan on ultimately having LA front calipers on the
rear and using the LSPV to dial out rear braking as needed.

--- Erik Bibelheimer <thebeebs@jps.net> wrote:
> Interesting calculations & info, Thom, but how is it different for
> drums
> vs. disks...?
> 
> Most of the goal of a disk brake swap is to be RID of the drums (or
> so I
> thought...?).
> 
> So how hard would it be to rig up a drum style t-case e-brake? :-D
> I know some TLC's had them but supposedly they were problematic? Or
> was
> that only if the t-case leaked?  If its not that bad of a design, how
> hard
> would it be to bolt one onto a mini? (I've never seen one).
> 
> I'd like to swap to rear disks, but I'd also like to have a strong
> mechanical e-brake of some sort so that is the main thing holding me
> up.
> I've heard of a few problems w/ the AP t-case brake and the price is
> more
> than I'd like to pay anyway...
> 
> - Erik Bibelheimer, Auburn, CA
> '86 44Runner, '97 T100
> http://home.off-road.com/~bibelheimer
> 
> ----------
> > From: Thom Singer <ntsqd@yahoo.com>
> > 
> > If MISF's experience is anything to judge by, hydro-mechanical
> calipers
> > should be avoided on 4x4's. Drums for parking brakes are the way to
> go.
> > The mechanical or hydro-mechanical caliper works fine until you
> park on
> > a steep hill. My mentor at work is fighting that battle right now.
> > (Wonder if the OEM's use San Francisco's streets as a guideline for
> > hill parking ?) I think the only reason AP's t/c mounted caliper &
> disc
> > works at all is because of the diff gears.
> > 
> > Some rough numbers:
> > Leverage ratio of a Mech. caliper - ~8:1 (typically varies from 6:1
> to
> > 12:1 depending on caliper & application)
> > Pad Coef. of Friction (Cf) - ~.5
> > Truck est. weight - 3500 lbs.
> > Rotor radius (to pad centroid) - ~5.25"
> > Slope - 20* (WAG)
> > Assumed: Tire to ground Cf - Infinite (not real, but simplifies
> things)
> > 
> > I come up with needing 6285 lbs*in of braking torque required to
> hold
> > the truck still on a 20* incline (3500*Sin 20=1197lbs;
> > 1197*5.25"=6284.6). The .5 pad Cf means that it needs 2398 lbs
> clamping
> > force (1197/.5)=2398). Which means there has to be 300 lbs tension
> in
> > the cable (2398/8=299.75). Average upper design limit for an Ebrake
> > handle pull is about 75 lbs, which means that lever hanging under
> the
> > truck has to have about a 4:1 ratio (299.75/75=3.996), not likely.
> OR
> > you could move the brake off the axle and take advantage of the
> diff
> > gearing.
> 
> 4x4Wire.com Toyota Section http://www.4x4wire.com/toyota/


=====
TS
Ventura, CA

"Teach you all I know and you're still stupid."
-- Howdy Lee

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