TKO 600 transmission shifting problem

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This is my
experience with the
Tremec third gear
shift problems you
can find mentioned all
over the Internet.
This is one
installation, and
may not apply to
every transmission.
While a clutch
problem could stop a
transmission from
shifting, that
certainly was not
problem in my car. Read this carefully
to see why I was
sure I did not have
a clutch or operator

My experience
conclusively shows
a current
production TKO-600,
purchased new in
2009, still had a
problem with the
shift rail design
and/or production.
This was
a fresh inventory transmission
purchased in July of
2009, and this means
the problem has not
been 100% cured. Hopefully
the information here will save weeks of work
and hundreds or
thousands of dollars
hunting for the fix.
I was so frustrated
I was nearly ready
to give up weekend
racing or install an
transmission, all because of the
TKO transmission
shifting problem.

Why did I change
transmissions, and
why choose the TKO?

My original goal
was a stock
appearing but very
fast street car. I
chose the Mustang LX
platform because it
was fairly light,
reasonably safe, and
proven parts were readily
available. I also
raced several
Mustang Fox Body
cars in the 80’s and
early 90’s. I always
found them very
reliable, and easy
to make fast. (My
1983 GT Mustang
small block was my
fastest, running
bottom 9’s and high
8’s in the 1/4 mile
off the motor, and
mid-8’s and faster
with nitrous.)

Tremec tko 600 shifing problem

While searching
to find my perfect
Cobra kit-car, I
stumbled upon and purchased
this clean
’89 LX in early
2009.  I
couldn’t pass it up.

My Mustang LX
coupe ran OK with
GT40 parts,
mid-to-low 13’s in
the 1/4 mile with
standard tires and
wheels. Further
engine modifications included TFS
twisted wedge heads,
TFS intake, Vortech
supercharger, 2003
Lightning MAF and
injectors, and
Motorsport “F”
camshaft. These
modifications  increased
engine power into
the 600 horsepower
region. The car ran
over 122 MPH in the
1/4 mile on Nitto
radials with a
100,000 mile 302.
(My eventual plan,
when the engine
fails, is to use a
9:1 compression 363
cubic inch “302”
Dart block built to
handle big boost.
That project is
underway right now.)

Naturally, even
with the tired old
small block, I
ran into the
expected T-5
After 30 or 40
successful runs, I hit third
under full power and
third gear failed. I needed to upgrade
my 5-speed World
Class with a
stronger or more
transmission, but
I did not want to lose
street drivability in the
process. I checked
other transmissions
but discarded them
because of life or

The best
transmission swap choices
appeared to be the T-45
6-speed, or a Tremec TKO-600 5-speed.
I knew extra gear ranges
would not be any
advantage for my
typical vehicle use. My
car has
plenty of power and
is geared correctly
for the 1/4 mile,
extra over- or
under-drive gearing
was not necessary.
Other advantages of
Tremec TKO 600
include it being lighter in weight
and smaller as well
as easier and
less expensive to swap.  Other
than the
transmission itself I would
only need a clutch
disk, bell housing,
transmission cross-member, driveshaft
yoke, and shifter.
This would give me a
600 lb/ft rated
transmission, which
in theory would be
over 600 hp at 6000

I used the
following Summit
Racing parts:

assembly (chosen for
good 2.87 first gear
and 0.64 overdrive

FMS-M-5059A Cross

FMS-M-4841-A Yoke

clutch disc

QTI-RM-6065 Bell
housing (chosen for
best clearance)

HUU-5380197 Hurst
5.5 inch shifter
stick (chosen for
appearance and shortest length
shifter, but now
going obsolete)

The forward
transmission gear
ratios I picked were:

Gear Ratio Percent drop in
4.10 rear end
overall gear
Shifting engine
Driveshaft RPM
at shift
After shift
engine RPM
first 2.87   11.77:1 6250 2178 x
second 1.89 34% 7.75:1 6250 3307 4116
third 1.28 32% 5.25:1 6250 4883 4233
fourth 1.00 22% 4.10:1 6250 6250 4883
fifth 0.64 36% 2.62:1 X X 4000

ratios keep the
engine in the “sweet
area” between 4100
and 6250 RPM, almost
perfect. The 2.87
first, as opposed to
being up in the
lower 3’s for first
gear like the T-5, would mean I’d
have much more time after
launch to grab 2nd.
Wheel spin would not
be so violent during
the 1-2 shift.


Installation went
smoothly. The old
T-5 transmission and
bell housing were
removed, the new
clutch disk and

QuickTime bell
installed. The
QuickTime I
purchased was
dimensioned, run out
was measured to be
well within Tremec
spec with no special
locating pins or
adjustments. I
particularly like
the QuickTime
because of the extra
room around it
compared to other
more “cylindrical”
SFI approved scatter
shields. The
transmission bolted
in without a
problem, the
stock speedometer
drive gear fit
The Motorsport
transmission cross
member was slid all
the way back to
allow transmission
mount alignment and
the mounting tubes
at each end were welded in place.

The clutch was
set to be sure it
engaged about an
inch below the top
and fully disengaged
well before reaching
the floor. We did
have to adjust the
clutch pivot in the
bell housing by
about an inch or so
to get proper clutch
disengagement. A
diaphragm clutch can
“stick to the floor”
at high RPM if it
opens too far, and
of course if a
clutch  does
not open (release)
far enough the
transmission will
not shift or

At this point I
made an executive
decision I later had
to undo. Since the TKO
transmission nearly
touched the floor in
the transmission
tunnel, I initially
did not shim the
transmission mount.

Note: The transmission-mount surface on the
TKO-600 is vertically 0.8
inches closer to the
output shaft
centerline than an
original T-5
transmission. This
means the
transmission mount
requires a 0.8 inch
shim (increases
height of mount) to maintain
original output
shaft height and
driveshaft angles.
Without shimming the transmission’s tail shaft will point downwards
considerably below the stock
T5 transmission. In a
Mustang Fox body, it is a
probably a good
idea to slightly
raise the
transmission tunnel
near the block-off
plates for the
forward alternate shifter
locations in the
TKO. The edges of
the TKO600 block off
plates actually
strengthening ribs
in my car’s
transmission tunnel
when the
transmission is
shimmed to stock
driveshaft exit


driveshaft height
change is shown by
comparing dimension
“E” in the two
drawings below:

TKO Tremec transmission shifting and  vibration problems

Tremec TKO shifting problem T-5 height

First Drive

One thing that
jumped out at me was
an almost total lack
of gear whine in any
forward gear. The TKO 600 was
very quiet compared
to the old T5
transmission. It was
also a pleasure to
have a reasonable
1st gear ratio
instead of the T-5’s
nearly useless 3.35
first gear ratio.

The first problem
noticed was a bad
vibration at about
60 MPH (I have a
4.10 gear). My car
never had that
vibration with the
T-5. This turned out
to be a slightly out-of-balance driveshaft
that became
noticeable with the
new u-joint
angles. To correct
angles it is
necessary to restore
stock exit height.
rear mount should be raised about 0.8
inches with a spacer.
Unfortunately this put the
transmission into the
transmission tunnel
roof, so
we used a
slightly shorter 0.5 inch
spacer as a
compromise. By
readjusting the
pinion angles and
fiddling with the
transmission mount spacer we were
able to get a sum of
zero degrees (the
rear angle was the
compliment of the
front angle) with
reasonable u-joint

Once the
driveshaft was
replaced with a
properly balanced
steel shaft, the
u-joint angles could
be adjusted all over
the place without
noticeable vibration.
The slightly
out-of-balance drive shaft,
not noticeable with
stock angles,
made the system
much more critical
for u-joint angles.

If I were doing
the install over, I
would hammer the
transmission tunnel
up slightly bear the
highest points and
just use a 0.7 inch
shim. This would
result in stock
drive shaft exit
height at the rear
of the transmission
without annoying
floorboard contact.

First Trip to
the Track

This is where
disaster struck.

First, I’m very
good at shifting
transmissions. I
grew up speed
shifting some very
transmissions. My
father owned mostly
six cylinder stick
shift cars. I
started driving by
rolling his cars
down the driveway
and going for
secret midnight rides when
I was 13. My first
“personal” car was a
Green $350 1956
Studebaker with a
275 hp 352 cu in
Packard engine and 3
on the tree with
overdrive. I later
had old used manual
transmission cars
like a 409 Chevy, a
390 Ford, and so on.
I could easily power
shift my 301 cu in
’56 Chevy despite
the high RPM
full race cam, and I set
the D/S national
record in a factory
4-speed Rambler. I
could always shift
transmissions where friends had
problems, and
virtually never
missed a shift. I
often was
sought out to drive
buddies cars in races,
including a
friend’s 427 Impala
SS during street
races and another
friend’s aluminum
head 69 Camaro. Both
cars were difficult
to keep straight,
let alone power

I was dumbfounded
when, during my
first pass with the
new TKO, I missed
3rd gear like a
driver weaned on a
power glide. Making
several more passes, I tried
various shifting
styles. Every time I tried
to hit 3rd with the
TKO-600 it was
like slamming the
shifter into a brick wall.
It just would not
go. I finally tried to
hold the clutch
longer than normal
at only 5000 RPM and
I pushed really
hard. The
transmission went
back into 1st! I
beat my car to death
trying to shift this
transmission into
3rd. In 40
years of racing, the
Tremec 2 to 3 shift
was the worse thing
I ever remember. It
was like trying to
speed shift my
tractors, or an old
three-speed stick!

The Problem

One thing of
note, I
could easily power
shift 1-2 or 3-4
and never miss. I
could shift at 6800
RPM from 1 into 2, or
from 3 into 4. Holding
the clutch on the
floor at 4000 RPM or
so, I
could pull the transmission
from 5th to reverse
grinding gears.
These are clear
indications the clutch was
fully disengaging.
The car also had
good clutch disk
clearance and very
good pedal feel, it
fully disengaged
around two inches
from the floor.

I searched
Internet for “2-3
shift problem TKO
600” and was amazed
at the number of
results describing similar problems.
probably never would
have bought the TKO
600 if I had
searched first.) I
wondered if this was
a big $3500 mistake.

Tremec stated they
were not aware of
2-3 shift
problems and
suggested I probably had a
clutch problem. They
provided the name of
a shop in Florida,
so I called that

The shop owner
was a helpful
person with years of
racing experience.
He suggested
changing my clutch
disc, saying he was
largely unsuccessful
using  dual
friction discs. He also
said I should change
the clutch adjuster,
the fire wall was
and other

told him I didn’t
see how the clutch
system could be bad because
I could easily speed-shift
1-2, 3-4, and even
4-5! I could also pull the
shift lever into reverse
without a grind,
even with a revved
engine. To me, this
is a very strong
indication clutch
disengagement is
adequate. I
said it seemed to be
lockout problem inside the
transmission. It did
not feel like the
transmission was
even getting into
the third gear gate.

countered by saying
the 2-3 shift would show
a bad clutch even
other gears would
shift because 3rd
gear has the largest
ratio drop. I knew
that was not
entirely accurate.
1-2 actually has the
largest RPM mismatch
during a shift.

also said 3-4 shifts 
“hardly needed
a synchronizer”
because fourth “was
a 1:1 ratio”. I knew
that was not true because
actually matches the
input shaft speed to
the selected gear
speed. If the input
shaft is spinning 6300
RPM, the
synchronizer has to
block the slider
out of the
desired gear ratio until the input
shaft system and
everything it drives matches
the RPM of the
transmission components tied to the output
shaft. Then the
slider falls through
the gate formed by
the synchronizer
teeth and locks the
shaft to the desired
gear. A transmission
needs a 4th gear
synchronizer just as
much as we need a
synchronizer in any
other “shift while
moving” gear.

Furthermore, it
is often possible to
overpower the
blocking caused by
synchronizers by
pulling or pushing
very fast and hard,
and I could not do

Someplace in all
that conversation he
also said he did
some “internal mods”
to shifting
components in the transmission,
and that made me
suspect those
“internal mods”
might be the real
fix for my

I’m not a big fan
of changing a half
dozen things hoping
something fixes a
problem for three

  1. We would not
    know what actually
    fixed the problem, so we
    would not learn the
    true source of a
  2. We could
    actually add new
  3. Throwing
    random parts at a problem wastes
    time and money

In the
industry, we call
this “shot-gunning a
system”. I
don’t shotgun
anything, let alone
things that are full
of new expensive

Liberty’s Gears

It was evident
Tremec was not going
to be helpful and I
did not want to
start changing
clutch parts when
there was no hint
they were bad (they
were all new) or
they would not work.

My second call
was to Paul at

Liberty’s Gears

in Taylor, Michigan.
I found Paul to be
a professional and experienced
excellent knowledge
of transmissions and
mechanical systems.
Paul did not act
surprised to hear
about a TKO 600 2-3
shifting problem.
Paul said he
worked on hundreds
of TKO 600 transmissions
that would not shift
from 2nd to 3rd
gear, and said my
description of it
being like “hitting
a wall’ was typical
of a common shift
rail system problem.
His mechanical
descriptions made
perfect logical
sense to me. He also
claimed a nearly
100% success rate in
curing the 2-3 shift

decided to let
Liberty’s Gear take
a shot at the
repair on my brand
new transmission. I removed
the top cover
assembly and rear
housing. I sent
Paul everything
related to moving
the sliders in the
transmission. I did
not send gears or

In less than week
Paul shipped my
parts back.

reassembling the
transmission (took
about one hour) and
reinstalling the
transmission (took
about three hours) I
pulled my car out
onto a local test
track. I wound the
engine up
in 2nd gear to about
6000, and pushed
forward with a
normal “palm shift”
I use on more
spring loaded
shifters. Using
a very fast
clutch in-and-out,
the TKO 600
transmission went
into 3rd gear
flawlessly! This was the very
first try with the
Liberty’s modified
parts, and it
was a flawless shift. This
was the first time I
could get the
TKO transmission into
3rd under full
power! I made about
three more tries
using various
shifting techniques,
including a “point
and push” into 3rd.
Every shift was
flawless. Finally I
ran a wide open
throttle run from
first, shifting at
6300. 1-2, 2-3, and
3-4 were all
flawless very fast
shifts. Since then I
have driven the car
several times, and
never missed a

I was totally
blown away by the
difference in shift
feel. While it was
not like a Hurst
Competition Plus or
even a standard T-5
with its single rail
internal shift
system, it actually
felt like a pretty
good shifting
system. The brick
wall “won’t go in
third with a sledge
hammer” feel was

Do Over

If I ever do this
again, I will never
install another
TKO-600 without
sending it to
Liberty’s Gears
first. They
delivered everything
they promised. For a
few hundred dollars
they turned this
unshiftable 2-3
transmission into
something that
worked. Had I
listened to Tremec,
I would have spent
several hundred
dollars or more
wasting time and
parts chasing
and correcting

These days
manufacturers seem
to play a little
game of “if some
of these don’t produce
we must not have a
problem in any of
them”. The proof,
however, is in the
pudding. Without
changing the clutch,
clutch adjuster,
clutch adjustment,
or anything else….. the
transmission now
shifts 2-3 just fine. All it
took was a few
hundred dollars at
Liberty’s Gears to
make the worse
transmission I have
ever shifted into
something that is
quite acceptable for
racing or daily
driving, and the
problem was clearly
all in the shift
rail system.