Cherokee 180 soft brake - causes?

Our A&P hates bleeding Cherokee brakes, but it's more of a repetitive
pain than a really difficult procedure. He just climbs under the wing,
holds the line (or brake assembly?), and has me pump the brakes until
nothing but fluid comes out. It can take several pumps, and uses a bit
of brake fluid, but it works well. (I've not seen what he's doing under
there, since I'm inside the plane, but he's catching the fluid in a
container of some sort.)

They can't be bled from the bottom up?

They can, but this is my A&P's method of preventing the OP's problem of
eternally soft brakes. It apparently ensures that no air is left hiding
anywhere in the system.

All I know is that it works. My brakes aren't mushy.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:
Our A&P hates bleeding Cherokee brakes, but it's more of a repetitive
pain than a really difficult procedure. He just climbs under the wing,
holds the line (or brake assembly?), and has me pump the brakes until
nothing but fluid comes out. It can take several pumps, and uses a bit
of brake fluid, but it works well. (I've not seen what he's doing under
there, since I'm inside the plane, but he's catching the fluid in a
container of some sort.)

They can't be bled from the bottom up?


They can, but this is my A&P's method of preventing the OP's problem of
eternally soft brakes. It apparently ensures that no air is left hiding
anywhere in the system.

I know, that's why you do it from the bottom up, no pumping the brakes
required. My mechaninic rebuilt my left main strut this week and since
that requires disassembly of the brake system on that side I helped him
today bleed the brakes. Reason #6458 why Beech has the reputation they
do for quality and good engineering and design. The reservoir is on the
firewall, no having to wiggle over the front seats to wait for the fluid
to come squirting out onto your carpet.

Newps wrote:
: I know, that's why you do it from the bottom up, no pumping the brakes
: required. My mechaninic rebuilt my left main strut this week and since
: that requires disassembly of the brake system on that side I helped him
: today bleed the brakes. Reason #6458 why Beech has the reputation they
: do for quality and good engineering and design. The reservoir is on the
: firewall, no having to wiggle over the front seats to wait for the fluid
: to come squirting out onto your carpet.

Not to argue since all I know is heresay at this point, but my mechanic had
problems bleeding a guy's cherokee *even though* they were bleeding bottom-up.
Top-down, bottom-up, it didn't seem to matter.... they couldn't get all the air out.
Ended up having to replace some weird seal/gasket/valve thingy (don't know the
specifics). Apparently it's a common thing to have to replace... maybe why all the
FUD about bleeding Cherokee brakes. Perhaps it's only a PITA if this other thing is
broken. Sounds like Jay doesn't have any trouble.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

On Sun, 26 Feb 2006 14:55:26 +0000 (UTC),
wrote:

snip

Not to argue since all I know is heresay at this point, but my mechanic had
problems bleeding a guy's cherokee *even though* they were bleeding bottom-up.
Top-down, bottom-up, it didn't seem to matter.... they couldn't get all the air out.
Ended up having to replace some weird seal/gasket/valve thingy (don't know the
specifics). Apparently it's a common thing to have to replace... maybe why all the
FUD about bleeding Cherokee brakes. Perhaps it's only a PITA if this other thing is
broken. Sounds like Jay doesn't have any trouble.

really depends where the air is trapped in the system. the primary
problem with the Cherokee's is the fluid inlet to the toe cylinders is
on the bottom of the near-vertically mounted cylinder (and goes "up"
to the handbrake and reservoir). the outlet is on the top, and goes
"down" to the calipers.

pressure bleeding from the reservoir or from the caliper is
problematic due to this routing. a little air here or there can
usually be worked out, but if there is a lot of air trapped, the
quickest solution is to remove the toe cylinders (mechanically, not
hydraulically) and invert them. a pressure pot from the bottom will
then clear the lines fairly rapidly.

the nastiest one I ever worked was on a Cheyenne that wouldn't leak
fluid out static or under applied brake pressure, but would leak air
in when the cabin was pressurized. if I hadn't had seen it, I never
would have believed it.

TC