Some of you may recall that I recently bought a 2014 Honda CRV, replacing
the CRV we bought new in '99. That car received my "$30 Toad Brake" back
in '07 (or before):
http://www.gmcmhphotos.com/photos/g3291-2430-toad-brake.html
,
That brake served us VERY well, with no maintenance, for all the years
since. Hopefully, George Zhookoff will enjoy it as much, since he's now
its owner.
Then, a few years back, I designed a "$5 Toad Brake" for proportional
braking:
http://www.gmcmhphotos.com/photos/g5153-245-toad-brake.html
I never bothered to complete and install that conceptual design, so now
that I need a new toad brake, I've done a new design and fabrication. It's
been a slow process because of the right thumb surgery I had on Pearl
Harbor day -- I'm still almost one-handed. But, it's now completed and
installed. I guess, as I age, I'm becoming less frugal, because this has
turned out to be the "$200 Toad Brake":
http://www.gmcmhphotos.com/photos/g7150-24200-toad-brake.html
Before you try that URL, be advised that there are no photos yet, only a
wiring diagram. I'll try to get photos made and posted in the next few
days. In the meantime, here's a primer:
A dash switch controls a Viair 98C compressor to charge a 1/2 cf reservoir,
which is equipped with a pressure switch to control the compressor, a
safety valve, a bleed valve, a pressure gauge, a quick-disconnect for
external air usage, and, most importantly, an output pressure regulator.
That regulator is used to control the pedal force applied in the CRV when
the tow-er's brake lights come ON (or the momentary test switch on the CRV
dash is pressed). The compressor and reservoir are mounted on a custom
mount cantilevered off of two engine mounting bolts.
The regulator feeds a cutoff valve, required because the 5/2 control valve
which follows it tends to bleed air continuously. That control valve
either retract or extends a 1.4 sq. in. pneumatic piston whose cylinder is
mounted laterally and horizontally just above and behind the radiator.
A Bowden cable attaches the pneumatic piston shaft to the brake pedal to
pull it toward the floorboard when the shaft retracts.
That basic assembly is capable of applying about 140 lbf of force (1.4 sq.in.
X 100 psi) to the brake pedal, which is probably enough to provide
sufficient toad braking without vacuum boost. But, depending on that brute
force method would require that the CRV's brake booster ALWAYS be bled
before towing, else the first few stops would be DRAMATIC. And, I didn't
really trust the tiny Bowden cable I'm using to withstand that force long
term.
So, now the dash switch for the compressor also controls a vacuum boost
pump thru a vacuum switch and associated load relay. Turns out, there a
vacant "box" about 6' x 1' x 6" beneath the passenger side of the CRV; the
pump's mounted there. WIth boosted brakes, the pneumatic system needs to
exert only a slight tug to provide adequate braking.
This is still a pure "bang-bang" system; i.e., the brakes are either
applied or not. It would be relatively simple to add a sensor and variable
pressure control for proportional braking. But I'll probably never bother
since this is an improvement on the $30 Toad Brake which served me so well.
All that's explained by the wiring diagram.
Photos to follow.
Ken H.
the CRV we bought new in '99. That car received my "$30 Toad Brake" back
in '07 (or before):
http://www.gmcmhphotos.com/photos/g3291-2430-toad-brake.html
,
That brake served us VERY well, with no maintenance, for all the years
since. Hopefully, George Zhookoff will enjoy it as much, since he's now
its owner.
Then, a few years back, I designed a "$5 Toad Brake" for proportional
braking:
http://www.gmcmhphotos.com/photos/g5153-245-toad-brake.html
I never bothered to complete and install that conceptual design, so now
that I need a new toad brake, I've done a new design and fabrication. It's
been a slow process because of the right thumb surgery I had on Pearl
Harbor day -- I'm still almost one-handed. But, it's now completed and
installed. I guess, as I age, I'm becoming less frugal, because this has
turned out to be the "$200 Toad Brake":
http://www.gmcmhphotos.com/photos/g7150-24200-toad-brake.html
Before you try that URL, be advised that there are no photos yet, only a
wiring diagram. I'll try to get photos made and posted in the next few
days. In the meantime, here's a primer:
A dash switch controls a Viair 98C compressor to charge a 1/2 cf reservoir,
which is equipped with a pressure switch to control the compressor, a
safety valve, a bleed valve, a pressure gauge, a quick-disconnect for
external air usage, and, most importantly, an output pressure regulator.
That regulator is used to control the pedal force applied in the CRV when
the tow-er's brake lights come ON (or the momentary test switch on the CRV
dash is pressed). The compressor and reservoir are mounted on a custom
mount cantilevered off of two engine mounting bolts.
The regulator feeds a cutoff valve, required because the 5/2 control valve
which follows it tends to bleed air continuously. That control valve
either retract or extends a 1.4 sq. in. pneumatic piston whose cylinder is
mounted laterally and horizontally just above and behind the radiator.
A Bowden cable attaches the pneumatic piston shaft to the brake pedal to
pull it toward the floorboard when the shaft retracts.
That basic assembly is capable of applying about 140 lbf of force (1.4 sq.in.
X 100 psi) to the brake pedal, which is probably enough to provide
sufficient toad braking without vacuum boost. But, depending on that brute
force method would require that the CRV's brake booster ALWAYS be bled
before towing, else the first few stops would be DRAMATIC. And, I didn't
really trust the tiny Bowden cable I'm using to withstand that force long
term.
So, now the dash switch for the compressor also controls a vacuum boost
pump thru a vacuum switch and associated load relay. Turns out, there a
vacant "box" about 6' x 1' x 6" beneath the passenger side of the CRV; the
pump's mounted there. WIth boosted brakes, the pneumatic system needs to
exert only a slight tug to provide adequate braking.
This is still a pure "bang-bang" system; i.e., the brakes are either
applied or not. It would be relatively simple to add a sensor and variable
pressure control for proportional braking. But I'll probably never bother
since this is an improvement on the $30 Toad Brake which served me so well.
All that's explained by the wiring diagram.
Photos to follow.
Ken H.
