Hey guys, remember that the A-518 is basically the same tranny as the 727,
and the A-500 is basically the same as the 904. Main differences, other
than the electronic OD unit added to the tailshaft, is that the newer
trannies are set up to shift softer (for today's yuppie drivers). The soft
shifting can be eliminated with a good shift kit, and a reputable shop
should be able to get back all of the 727's strength in the A-518. Just
don't race it (or tow) with the OD on, and you essentially have a 727.
The A-518 (and later electronically-controlled variants) got a bad rap
because the ones behind diesels were giving up the ghost early. The
tremendous off-idle torque of the diesels is really rough on the torque
converters of these auto trannies (as it would be on a 727). The other
problem stemmed from the soft shifts which decreased clutch-holding strength
somewhat - enough to cause problems for the people who used snowplows or
other equipment with lots of back&forth shifting. Another problem is people
towing heavy loads in OD, or towing in hills/mountains with OD on - the OD
unit gets overworked and heats up the tranny.
High Performance MoPar did a write-up on this a few years ago - this is a
copy of the article (sans pictures):
Article from High Performance MOPAR, Vol. 10, No. 4, July 1996.
REVERSE DISCRIMINATION (Robert Gross, author)
Warning: The Surgeon General has determined that soft shifts may be
hazardous to your Ram's transmission.
If you own a 1500-, 2500- or 3500-series Dodge Ram truck or van with an
A-518 automatic overdrive transmission and use it as a work truck, then you
should consider this tranny trick.
Back when trucks were trucks, they were rough-riding, tough-looking,
bare-bones work horses. Now that the new Ram has become popular among the
trendy yuppie community, its operating characteristics have been modified to
reflect the wants of the expanding market. It is now more sporty and
luxurious, made for Mom to tote the kids to school, as well as being Dad's
weekend work vehicle.
One of the more user-friendly features of the modern Dodge truck is a
soft-shifting automatic transmission. If your Ram is so equipped and you use
it for more than just light-duty activity, then you need to know the lowdown
on the Low-Reverse shift band modification. If you use your truck in severe
situations, such as plowing snow, when Reverse is used constantly, this
modification is imperative.
When you put your 518 automatic in Reverse, the front clutch is applied
first, then the Low-Reverse band is applied to the spinning clutch. This
calibration allows very soft, comfortable shifts due to slow time lapses
between the engagement of the front clutch and the Low-Reverse band.
Unfortunately, this comfort is fatal to the L-R band, which can wear rapidly
from the increased friction and heat caused by contact with the spinning
clutch.
In older trucks with the 727 Torque-Flite transmission, from which the 518
is derived, when Reverse was engaged, the L-R band was applied at the same
time as the front clutch, resulting in a harder yet damage-free shift.
Pat Barrett, owner of Level 10 Performance Transmissions in Hamburg, NJ, has
the fix for the A-518, which includes applying the old-school philosophy of
simultaneous clutch and band application (thereby sparing the life of the
band) and increasing main line and servo pressure.
"These modifications, which can be performed with the transmission in the
truck, should be made as a preventative measure before Reverse is lost,"
says Barrett. "However, if the trans is being overhauled, it will serve as
insurance against failure in the future." Here's how it's done.
(Pic 1) Once the transmission is relieved of its fluid, pan, screen and
pick-up, remove the valve body to gain access to the L-R servo unit.
(Pic 2) Remove the L-R servo assembly (piston; L-R servo spring; retainer;
C-clip) from the trans casing. When the transmission is put into Reverse,
fluid pressure builds below the L-R servo piston. Tension from the L-R servo
spring, located above the piston, reacts against the fluid pressure until
the force of the fluid overcomes the spring tension, thus actuating the
piston. A cushion spring on the piston plug located inside the L-R servo
spring then applies counter pressure to the piston, slowing its actuation by
serving as a buffer and allowing softer shifts to occur.
(Pic 3) The stock spring will be replaced with a stiffer spring that will
allow more fluid pressure to accumulate under the servo piston before the
servo is actuated, thus reducing the duration of the shift.
(Pic 4) Spacers that measure .120 inch are installed on the piston plug
beneath the cushion spring to fully compress it, rendering the spring
inoperative and eliminating all buffing action. Now when Reverse is
selected, it engages without hesitation.
(Pic 5) This servo modification will cause Reverse to be applied in a much
quicker fashion with a more dramatic shift. After the new spring and spacer
are installed, the L-R band is adjusted to 72 lbs./inch, then backed off two
turns.
(Pic 6) Now that the stiffer servo spring will allow more pressure to build
up under the servo piston, fluid has to get there faster. The orifice in the
separator plate that feeds fluid to the servo reservoir needs to be enlarged
to 3/16 inch to increase flow. Note: The original size of orifice varies
depending on the model and year of your truck.
(Pic 7) In addition to drilling the separator plate, two check balls in the
valve body are removed to further increase fluid pressure. Removing ball A
gets fluid to the servo quicker. This mod speeds the engagement process of
Reverse. Eliminating ball B allows fluid to reach the rear clutch faster,
which provides stiffer shifts for the forward gears.
(Pic 8) Now that Reverse will be applied quicker, the valve body must be
recalibrated to supply the proper increased volume of fluid to the rear
clutch and L-R servo. Main line pressure is increased 20 percent over stock
by turning the 3/16-inch Allen wrench adjustment screw counterclockwise to
obtain a 9/32-inch measurement. Use a caliper or a drill bit.
(Pic 9) The throttle valve setting, which measures throttle opening as
determined by engine load, is increased 30 percent over stock. Turn the
adjustment screw clockwise to 3/16 inch as shown, using a 3/16-inch Allen
wrench. Now that you've done the Reverse-apply modification and firmed up
the shift for the forward gears, you can reinstall the valve body, pickup,
screen and pan, fill the trans with fluid, and get that truck back to work.
SOURCE: Level 10 Performance Transmissions, 188 Rt. 94, Hamburg, NJ 07419,
201-827-1000, Fax: 201-827-7846 (performance transmissions and
shift-improving kits)
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