Finally, someone who has actually read the Shop Manual!
Jesus' original question, as I understood it, is using the tool for a
"Major" brake adjustment, vs a "Minor" brake adjustment. Each brake shoe
has 2 ends. The ideal adjustment brings BOTH ends close to the drum
surface for TOTAL contact of the entire shoe. When drums are re-surfaced
and shoes relined, all the dimensions change. The ideal condition is the
curve of the shoes (arch) is the same as the drum, and both ends of the
shoes are the same distance from the drum.
The shoe arch is accomplished by grinding the new lining to match the
new curve of the drum. If the arch is too small, the shoe will only
contact the drum in the center. If the arch is too large, the shoe will
only contact at the ends, leaving a gap in the middle.
"Major" adjustment is accomplished by turning the excentric fixed anchor
bolt at the end of the shoe to bring the heel (trailing edge) of the
shoe close to the drum. This is what the tool is used for. If the heel
is too far out, the drum will not go on. If it is too far in, the heel
will not press against the drum when the brakes are applied.
"Minor" adjustment uses the cam in the middle of the shoe to adjust the
toe (leading edge) out so there is little travel needed by the wheel
cylinder to engage the shoes. This periodic adjustment compensates for
normal wear of the shoes. This gives the brake pedel a short travel and
hard feel.
When the entire backing plate assembly is assembled new, the "Major"
adjustment is critical to set the anchor pins. When the shoes are simply
replaced, this is less important. Hopefully, the new shoes have the same
dimensions as the old. When the drum is re-surfaced, it's surface moves
farther from the shoe. Often, replacement shoes are made slightly
thicker to compensate for turned drums or allow for arching the shoes.
If a "Major" adjustment is not done when the shoes are replaced and
drums turned, it will be either high or low. If too high, the drum will
not fit over the shoes. If too low, the trailing edge will not contact
the drum and braking will be reduced. The maximum braking and wear will
be when the entire shoe contacts the drum evenly from the beginning. If
the trailing edge does not contact initially, braking is reduced. A
slightly softer brake pedal feel may also occur if the shoe flexes to
fit the drum. But braking will improve over time as the leading edge
area wears down and the shoes fit the drum better.
Dave Homstad
56 Dodge D500
On Thu, May 3, 2012 at 1:41 AM, Rich Barber wrote:
It's always interesting to read messages from guys just running into
the
challenges of '55 MoPar brakes. The special tool referred to is the
no
longer available and very rare MT-19-L and its use is shown on pages
61-64
in the '55 Chrysler Service Manual (See John Holst's most excellent
website
for all sorts of parts and service manuals:
http://www.jholst.net/55-service-manual/brakes.pdf ) It is a tool
that
will fit on front and rear drums and front and rear spindles/axle
ends. It
is used to measure the inside radius of each brake drum and then
provide a
reference dimension for setting the OD of the shoes on that corner of
the
car to the drum radius less 0.006" for clearance. A clever mechanic
could
probably rig a similar tool and I've thought it might be neat to
reproduce
the tool. IF the new shoes are already arc ground to match each
individual
drum or IF you get lucky and the new shoes are the approximate correct
OD,
it would assure the drum would fit over the shoes and the shoes would
be
reasonably close as installed and the pedal would be hard at least
half-way
down.
But, then it would still be prudent to spin each wheel and use the
adjustment to get even closer. You can hear the drums start to engage
the
drums as you wrench on the adjusters and a little more will slow the
spinning wheel. This is somewhat of an art, but one this fumble-thumb
teen-age grease monkey learned while servicing these cars in the
'50's.
Once I learned which-a-way to crank the adjusters, I could do a great
job
of getting a high, hard pedal in about half the time spent on a car
with
star adjusters. We'd send the cars out with just a touch of shoe
drag,
knowing that the high spots would soon wear down and create that
desired
0.006" clearance. I doubt if any of the professional mechanics in the
shops
ever used the tool much as more time would be spent in set up than
would be
saved by having the shoes set close on first try. Setting the shoes
out and
bringing them in just enough to let the drum slide on would produce
similar
results. If the shoes are not arc ground and will not let the drum
slide on
in the fully retracted position, it will be necessary to arc grind
them.
Chrysler spec's call for 0.200" thick linings.
Good luck in developing and preserving the art. You will only read
about
mechanic art here and in similar venues. Manufacturer's manuals must
have
everything set up with detailed measurements as company policy, I
guess.
Rich Barber
Brentwood, CA e-mail: c300@xxxxxxx
'55, '64 & '86 Chryslers; '93 & '99 Jeeps; '05 Durango; '95 Tioga RV;
2.5
car garage
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