Re: TOY: Sequoia Rear Brakes - more

[Thom Singer <ntsqd@xxxxxxxxx>]

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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