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Since the
very beginning, transmission issues have plagued the GTX. The
first trans was built by a local performance shop with less than
stellar results. (see Tranny
Trouble for additional details) After having the trans
freshened up, the car ran thousands of trouble free miles but large
aluminum shavings found in the pan at every service was making me paranoid.
The decision was made to find a usable 727 core and learn to build
an automatic transmission myself. Here's what the core looked like
after a session with the pressure washer, numbers indicate that it
started life in a '67 C Body.
The innards
of the core were downright nasty. It smelled horribly burnt. Even
though everything was coated with an oily sludge, many of the steel
parts had become badly rusted. Everything was scrubbed clean and a
lengthy list of necessary replacement parts was made. Once the parts were
clean, I reassembled and disassembled the trans numerous times to
become familiarized with all the sub-assemblies. One thing I
learned right away was the importance of having a good snap ring
pliers!
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To supplement the factory service
manual I picked up a copy of the Torqueflite A-727 Transmission
Handbook from Amazon.com. It details performance modifications and
has good pictures to aid in parts identification and assembly. After
studying the 727 Handbook, the Moparts.com
Tech Archives and Tom
Hand's guide to the Torqueflite automatic transmission on Allpar.com
I felt informed enough to discuss parts selection with transmission
parts vendors. With recommendations from Turbo Action, A&A Trans
and "T'Flite Patty" a list of parts
was generated and the process ordering
parts began. Though some of the items selected defy conventional
wisdom, the trans performs flawlessly and should prove to be a
reliable combination for a big block powered street cruiser. Time
will tell... |
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Most
of the following parts were chosen for improved performance and
reliability, others were chosen because the original parts in the
core transmission were in such bad shape. I didn't want to tear back
into the trans because I was too cheap to replace any questionable
parts.
Trans
Build Parts List
TCS steel-sleeved
aluminum front drum
Borg Warner tan clutch frictions
Raybestos steel plates
Basic bushings, gaskets, sealing
rings, lip seals, exterior seals, etc...
Reaction shaft support – 1971+
(required with TCS drum)
Rear clutch piston retainer – 1971+
Borg-Warner flex KD band
Rigid low/reverse band
4.2 KD lever (Max Wedge & Race Hemi)
Output shaft ball bearing
& snap rings
Bolt-in sprag
w/rollers & springs
12 front clutch release springs (new Chrysler)
Front clutch spring retainer
2 pressure plates (new Chrysler)
HEMI governor kit (inner, outer, spring, snap rings)
Thrust washers
Sun gear and reaction shaft
support bushings (not included in basic kit)
Turbo Action "Pro Street" forward pattern manual/automatic
valve body
A&A deep steel pan with drain plug and billet aluminum filter
extension
B&M Heavy duty SFI rated flex plate
9.5" "tight" torque converter - custom built by
Dynamic
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The biggest
single expense of this build was the TCS steel banded aluminum drum.
The primary reason for using this type of drum was for an added
measure of safety, the stock cast drum can violently explode as a
result of driveline failure. Additional benefits are the billet
aluminum drum is more than 2 lbs. lighter than stock, it holds an
extra clutch and includes a billet piston. The TCS drum uses the
late style wide bushing so a '71 + wide bushing reaction shaft
support must also be used. The support from the trans core was badly
rust pitted so it needed replacing anyway. |
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A
45º bevel had to be machined on the rear clutch drum to eliminate
contact with the front clutch drum. TCS included simple instructions
with the drum so I brought the rear drum to a local machine shop to
have it done. $20 later it was good to go. |
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Case
prep was fairly basic, after being thoroughly deburred, all threaded
holes were retapped and cleaned. I brought the case and tail housing
to a local transmission shop to be cleaned in their hot, high
pressure parts washing cabinet. A 12 pack of MGD was all the
proprietor wanted as payment, to show my appreciation, I brought him
a case. Once the case was back on the bench, a bolt in sprag was
installed to reduce the chance (however unlikely) of the outer race
spinning in the case. Before installing the sprag a 1/8”
hole was drilled from the trans cooler return channel to aid sprag
lubrication. |
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Once the
case was ready to receive the internal parts, it was time to
assemble all of the subassemblies and check clearances. The clutch
clearances were right where they needed to be according to the
A-727 Transmission
Handbook. The only special tool needed for the subassembly
was a compressor for the front drum piston return springs. I
fabricated this compressor using miscellaneous stuff that was laying
around the shop, putting the spring retainer snap ring on without it
would be nearly impossible. My brother in law made some drivers for
the tail shaft and front pump bushings since they were larger than
anything in my bushing driver set. Thanks Ron... |
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The
clutch assemblies had to come apart again so the frictions materials
could be soaked in ATF. Instructions recommended soaking them for a
minimum of 15 minutes so I poured a couple quarts in a disposable
cake pan and began soaking. The clutches soaked for over an hour
while I cleaned up the workbench and garage. I saved the pan full of
ATF because the bands will need soaking before they're installed.
After soaking the clutches the front and rear clutches
were assembled for the final time. |
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The
sunshell, thrust washers and planetary gears were assembled on the
output shaft and the clearance was carefully measured, at .017"
the clearance was right where it needed to be. The planetary
geartrain was disassembled and everything was slathered with
assembly lube (Vaseline) and reassembled for what should be the
final time. |
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Like
everything else, clearances in the pump also have to be checked.
Here I'm checking the outer rotor to case clearance. Specs call for
.004" to .008", this was right in the middle with
.006". Clearance between the tips of the inner gear and outer
gear also has to be checked as well as rotor side clearance. Once
again everything measured within spec, this almost seems too easy...
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Endplay
is another critical clearance that has to be verified. The observed
reading was .021 which is a little more than the .012 -.015
recommended in the Torqueflite Handbook but tighter than the
.037-.084 spec provided in the FSM so I left it alone. With all of
the important clearances confirmed I pulled the front pump,
installed the o-ring seal and reinstalled it using new front pump
bolts and sealing washers that were purchased from the local Dodge
dealer.
All that's left was to install the
band struts, adjusters and perform an air check of the hydraulic circuits
before finishing with the valvebody and pan. I Didn't put the deep
pan on because I use a floor jack under the trans pan to lift the
transmission into position and didn't want to risk damaging the new
pan. |
Before installing the new trans I bolted the new heavy duty B&M
flexplate onto the crankshaft, it appears to be a much
sturdier piece than the Mopar Performance flexplate it was
replacing. The 9.5" Dynamic converter was partially filled with
ATF and wrestled into the input shaft. The fit was very tight so it
took some effort to get it to seat properly. With the trans
installation nearly completed I tried to install the driveshaft but
to my dismay it would only slide onto the tailshaft about an inch.
After much head scratching it was determined that the tailshaft of
the core transmission was somehow damaged. Out came the trans again,
thank goodness I had figured out that the trans could be swapped
without removing the headers! Once again the trans was disassembled
and the output shaft from the old transmission was carefully cleaned
and reinstalled. This time everything went together without a hitch.
The trans was filled with Type F ATF and the motor was fired up. The
fluid level was brought up to the add range until everything reached
operating temperature, then I topped it off to the full mark and
carefully checked for leaks. Everything looked good so I took a
little test drive, the converter seemed slightly tighter than the
10" unit it replaced but the trans performed flawlessly. Good
thing too, Mopars in the Park was only a week away and I still had
to get the car cleaned up after a long Winters storage. |
| Update:
After a brief break in period I used and abused the trans throughout
the summer, it hasn't missed a beat in nearly 2,000 miles. |
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