Aftermarket Tremec T-56 Installation

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This article covers the installation of an Aftermarket Tremec T-56
Transmission into my 1975 (Type C-3) Corvette. I bought
the transmission from
Forte\’s Parts. It differs
from the
transmission GM uses in its F-body sport cars. This
transmission is made to
use the original clutch, bell housing and
speedometer plug/cable, out of older
sports cars, including most C-3
Corvettes. This conversion is NOT a bolt-in
operation. You will need
to alter or fabricate several items on the car, in
order to install
this transmission.

My vehicle is a slightly altered 1975.
Originally this car was an L-48 with
a 4-speed. After a wreck in
1994, I replaced the small block with a big block
and the 5-speed
transmission with an automatic. To accept the automatic, I had
modify my existing cross-member. My cross-member was originally welded, so
I cut mine inside the frame, welded on end plates and now mount each
side with
four bolts. The specific way I modified mine is not
mandatory for this installation,
so you can modify yours anyway you
please, as long as it will accept this transmission
and can be
removed from the vehicle. Also, I eliminated the cable (on manual
transmission cars), which eliminated you from removing your ignition key
first putting the car in reverse. This cable was attached to
the shift arm of
the old transmission, but the new transmission has
an internal shifting rail,
so there is no place for attachment. I
can now remove my key, no matter what
gear, including neutral.

installation of this transmission
was done bolted to the motor and
installed as a unit. I did not put it in by
itself, with the engine
already installed. Therefore, I cannot say that you
will be able to
install it separately, although it does appear highly possible
to do
so. You would need to, at the least, remove the shifter from the
and drop the back of the engine down enough to allow
insertion of the input
shaft into the adapter plate and bell
housing. You may need to remove the fan
blade and/or distributor and
loosen the motor mounts.

Major Items Needed For This

� After market Tremec
T-56 Six Speed Transmission
(Approx. $2K)
� Custom-built
transmission cross-member. (Approx. $200.00)
� Turbo 350
transmission output shaft yoke for Corvette (Approx. $170.00)

Driveshaft shortened and balanced (Approx. $50)
� Console cover
plate modification
� New shifter arm or modify your old one.


1. Prep
your vehicle to a point where you
can remove your
transmission. Disconnect the battery cables. Take all
appropriate steps to remove the entire console, as you will need to
get to the hole in the tunnel.
NOTE: You might be able to work with the
console in place, but it will be tight.

Reference the installed height and location of your current
driveshaft/yoke position, before you remove the strap bolts holding the
u-joint to the yoke. If you build a new cross-member, you will
want the
output shaft on the same plane as the original. Also,
measure the distance
from the front of the bell housing (where
it bolts to the motor) back
to the u-joint centerline. Write
this measurement down. It will help you
derive the correct
amount to cut the driveshaft later on.

2. Remove the old transmission
associated shifter/cables/connections. Remove the bell housing.

3. If you have an existing manual
car, you will need to have the cross-member
converted into a removable
unit. Some manual vehicles had
this, but most were welded. If this vehicle
was an automatic,
your cross-member is already removable.

I suggest you
have a new cross-member built.

You will be able to save the original one,
in case you decide to switch
transmissions in the future.
Building a new one will eliminate the exhaust
holes and
clearance problems.

Disconnect the battery cable from the
starter. Loosen battery
cable clamps in the tunnel. You will need to eliminate
clamp stud in the back of the tunnel. Click on the picture below and
read the caption.

Remove the tunnel insulator, to expose
the hole in the tunnel
for the shifter.

6. Although it\’s not mandatory,
fabricated a piece of aluminum to cover the big hole, then applied black
gasket maker and riveted it to the tunnel floor.

If you have to remove the shifter during
installation, you will need a tunnel
hole big enough to allow
installation of the shifter from the top. Therefore,
your cover
plate will need to be removable, using screws to secure it to the
tunnel floor. Your tunnel insulator will need to be altered to cover the
hole as well.

The first picture below shows the hole cut
in the center of the
tunnel. I cut the hole to the same diameter of the boot
on the
transmission, but you don\’t need to fit it this close. As referred to
in step #6, you will probably need a removable cover plate, so you
can cut and
adjust your hole size after the transmission is
installed. Install your tunnel
insulator and re-clamp your battery
cable. Because I made my own tunnel insulator,
I was able to shorten
the piece going back into the tunnel, near where the yoke
will be.
You will probably have to do this to yours as well. You can see the
back part of the insulator in second picture below. If you have a
converter heat deflector plate, you might have to cut
yours, like I did, to
get the proper yoke clearance.

Installation Part

mentioned before, I installed the transmission
and engine as a unit,
so I was able to increase the installation angle of the
whole unit,
more than you would be able to with the engine already in the car.
My radiator/support was not installed, distributor was out and motor was
seated into the mounts.

1. If your clutch is old, replace it and have
your flywheel resurfaced and balanced. Check your input shaft
bearing for wear
and replace if necessary. Re-install. Use disc
alignment tool to align the clutch
disc. The transmission uses a 26
spline clutch disc. I used a Centerforce disc,
pressure plate and
throw out bearing.

2. Clean
the bell housing, check for cracks,
clean and paint if desired. You
will receive an adapter plate and mounting bolts
with the
transmission. The plate is �\” thick steel with multiple
drilled in it. Bolt it to your bell housing. Note that the input shaft
housing is bolted to the adapter plate, rather than the transmission

I filled any
hole not being used, with red RTV, then covered with aluminum
The tape and RTV will keep water and dust from going into the cavity
the plate and transmission. I don\’t know if this step is
really needed, but
I did it anyway. The rest of the plate was
outlined with tape to maintain the
same clearance for mating it to
the transmission.

Two of the beveled bolts (supplied) and two of
my old transmission bolts were
used to mate the transmission and
plate. My adapter plate was for multiple applications.
Paint was

then the
entire unit bolted to the motor.

might need to loosely bolt the bell
housing to the motor. (One bolt)
Lift the transmission up into the tunnel, then
loosen the bell
housing up, so that it and the transmission can be moved around
slid forward together, allowing the input shaft a little play to help it
pass through the clutch disc. Make sure you have the throw-out
bearing over
the input shaft housing and the release fork installed,
before you loosely bolt
the bell housing in place. If you have
stabbed a transmission before, then you
know what to expect in order
for the shaft to pass through the clutch disc and
into the input
shaft bearing.

3. Have your driveshaft shortened.
original driveshaft was 29 �\” centerline of u-joint to

I cut it 5
�\”, leaving it 24 �\” from C/L of u-joints.
You MUST do your own
measuring. Do not use my exact measurements.

4. Bolt the transmission to the adapter
housing (bolts are 15MM metric). Slide the yoke on the
output shaft. Push the
yoke in all the way, and then back it out
where you have some play. I backed
mine out about �\”. Check with
the person doing your driveshaft,
as to how much this play should be
for a Corvette. Take a measurement from the
front of the bell
housing (where it bolts to the block) to the centerline of
u-joint. (The center is the middle of the u-joint, when properly resting
in the yoke.)

Subtract the previous measurement you took in
Removal Step #1, from the new
measurement, with the T-56, and you
will have the proper amount to shorten the
driveshaft. Have the
driveshaft shortened, balanced, then install it.

5. Once you have the transmission bolted to
bell housing and motor, jack it up into position. Remember to
get the transmission
back on the same plane you had identified
earlier in Removal Step #1. You are
now ready to build the
cross-member. I used �\” steel plate and 1
�\” tubing. Mine is
built high enough to allow the exhaust pipes
to pass under it. Cars
with catalytic converters might have to alter the design
or re-pipe
the exhaust, if a design like mine is used. Notice in picture below
how much I offset the transmission mount holes in order to get the
output shaft/yoke centered in the tunnel. I now have
�\” on both

might need to loosen your motor mount
bolts (all of them), or expand
the mount tabs a bit to allow the motor/transmission
to move freely
toward the center. The drive shaft pre-load angle will increase
slightly, between the yoke and driveshaft. Build and install the

Bolt up driveshaft.

6. Relocate the parking break pulley. The
below shows where I relocated mine. A small bracket was
built that bolts to
the transmission tail shaft housing. The pulley
bolts to this bracket. I was
left with about �\” clearance between
the cable and the yoke. Also,
my cable rests against the output
shaft housing. You can position your pulley
outward a little more
and prevent it from resting on the tail shaft. As I said
this was my cross-member design. You might come up with a lot better
design for your cross-member and eliminate the clearance issues

7. Install the speedometer gear housing/insert
from your old manual transmission. I had to fabricate a new hold
down for the
housing, as I did not have my old one. The hold down
bolthole has metric threads.
The speedometer cable will now be
located on the driver\’s side.

8. Install about 4 quarts of the specified
transmission fluid.

9. If you have back up lights, there is a plug
on the passenger\’s side, but you will need to obtain the proper
connector and
extend the wires to reach.

10. Put the console back together and measure
your console cover plate for cutting. I merely increased the open
area, by cutting
out a piece under the shift pattern insert, which
is more in the center of the
console cover plate. I fabricated two
aluminum pieces with mounting lips and
riveted them to the bottom
lip of the console, where the original boot used
to attach. Then, I
covered the fabricated pieces with thin, brushed aluminum.
I reused
my old shifter boot. It might be easier to cut a new hole in an automatic
console cover plate, as it has more surface on both sides of the new
hole to
work with and fill. It would eliminate fabricating the two
aluminum pieces.
Allow yourself to be creative with this step.

11. Install a shifter. I had
an old Hurst shifter
arm. I cut 2\” off the bottom, bent it toward
the driver\’s side about 10-15
degrees, drilled two new holes and
bolted it on.

12. Adjust your
clutch and check that everything
is tight and in

13. I would suggest you
test the drive train
on the jack stands, before you put it on the

14. Lower the car,
start it, put it in gear and
have fun. Break in is 500

15. Good

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