Re: TOY: Sequoia Rear Brakes - more

[Thom Singer <ntsqd@xxxxxxxxx>]

Couple things I forgot to mention.
In all fairness to hydro-mech. caliper's, since there are two of them,
each only needs to generate half of the braking torque.
Rotor Diameter. The rotors used on t/c's are neccessarily smaller in
diameter. That means more clamping force is required to generate the
same braking torque.
Factor of Safety. There is no FS included below, so to get the std FS =
2, 600 lbs tension would have to be easily developed in the cable for a
single caliper application.
Cable Efficiency. Cables have an 80-90% transmital efficiency, so at
the handle end that 600 lbs needs to be 660 lbs or that 300 lbs needs
to be 330 lbs.
Caliper Leverage Style. All I'm familiar with are simple lever type
mech. calipers. Most hydro-mech's use a lead screw that the lever turns
which could have a higher leverage ratio.
20* is beyond reasonable to need a car's p-brake to work on. It is
about where we really need a p-brake to work in a 4x4.

--- Thom Singer <ntsqd@yahoo.com> wrote:
> 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.
> 
> 
> --- Ed Wong <ewong_kaizen@yahoo.com> wrote:
> > Mea culpa on the confusion.
> > I started saying Tundra - but those use DRUM brakes.
> > I then chagned "Tundra" to "Sequioa" and musta fergot
> > a few.
> > 
> > One problem so far -
> > 
> > AFAIK the Sequioa rear axle is a semi floater,
> > just like the mini truck.
> > 
> > So - if all I wanted was disk brakes - maybe Id bolt
> > everything on with a backing plate and bracket.
> > 
> > But the other issue is that the parking brake cable
> > enters from the FRONT of the backing plate (like FORDS
> > do) So one would have to fab a whole new parking brake
> > setup...
> > 
> > Karl mentions the FZJ80's with full floaters and rear
> > disks. These also used a "mini" drim brake.
> > 
> > Anyone know how the cable enters the backing plate?
> > 
> > Its still looking like the Supra conversion from FROF
> > is still the way to go.
> > 
> > Id still be concerned about how well this holds the
> > truck.
> > The All-Pro setup has the advantage of diff
> > multiplication.
> > 
> > BTW - I was looking at Hummers (they had em up on a
> > "display" with a mirror under them) and they use
> > inboard brakes.. Cool - until the shaft snaps.
> > 
> > Ewong
> > 
> > 
> > 
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> 
> 
> =====
> TS
> Ventura, CA
> 
> "Teach you all I know and you're still stupid."
> -- Howdy Lee
> 
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=====
TS
Ventura, CA

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

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