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What stock gear
ratios came on the base GM trannies?
Can I replace my
TH350 tranny with a TH400?
Can I replace my TH350 or TH400
tranny with a 700R4?
Can I replace my TH400 or 700R4 tranny
with a 4L60E or 4L80E?
What can I do about a sqeaky clutch
pedal?
How can I easily determine what rearend gear ratio I
have?
How can I determine if I have a "posi"
rearend?
How can I recalibrate my speedometer swapping for
shorter/taller gears?
How can I recalibrate my automatic
tranny shift points with a gear swap?
What stock gear ratios came on the base GM trannies?
These came in a package from Greg Curless at Curless
Racing:
TRANSMISSION 1ST 2ND 3RD 4TH 5TH
Borg-Warner T-5 (GM Applications) . 2.95 1.94 1.34 1.00 0.63
Borg-Warner T-5 (GM Close Ratio) .. 2.75 1.94 1.34 1.00 0.74
Borg-Warner T-10 2nd Design ....... 2.64 1.61 1.23 1.00 -
Borg-Warner T-10 2nd Design ....... 2.88 1.74 1.33 1.00 -
Borg-Warner T-10 2nd Design ....... 3.44 2.28 1.46 1.00 -
GM Muncie (M-21, M-22) ............ 2.20 1.64 1.28 1.00 -
GM Muncie (M-20) .................. 2.52 1.88 1.46 1.00 -
GM Powerglide ..................... 1.76 1.00 - - -
GM Turbo Hydra-Matic 350 .......... 2.52 1.52 1.00 - -
GM Turbo Hydra-Matic 400 .......... 2.48 1.48 1.00 - -
GM Turbo Hydra-Matic 200-R4 ....... 2.74 1.57 1.00 0.67 -
GM Turbo Hydra-Matic 700-R4 ....... 3.06 1.62 1.00 0.70 -
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Can I replace my
TH350 tranny with a TH400?
Yes. The
motor/tranny bolts should line up, but you
do have to shorten the driveshaft. You also have to deal with the dreaded
Throttle Valve Cable to control your shifts, instead of the vacuum modulator.
You have options regarding the different mounting pad location at the rear of
the tranny. If you can get a TH400 crossmember for your car, or there is a
TH400 mounting position for your current
crossmember, then you can get a
replacement tailshaft extension from GM that puts the mounting pad where you
want it. Otherwise, you can move the crossmember to line up with the 700R4's
pad and drill new frame holes to mount the
crossmember. This way may sound
easier, but some people have had problems with the height of the
tailshaft, and
had to fabricate or modify the crossmember. Also, the new holes in the frame
have to be double-drilled. That is, you have to bore large holes in the bottom
of the frame to get the bolts in, and smaller holes in the top, just like the
factory holes.
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Can I replace my
TH350 or TH400 tranny with a 700R4?
Yes.
Similar to the instructions above, but here are
the parts that will be needed (including part numbers). The following are
B&M parts: 700R4 Tranny 30-spline (117101), Hole Shot 2000RPM Lockup
Converter (70417), TV Bracket (90747), TV Cable (70242), and Converter Lockup
Control Dash Mounted (70244). Get a 700R4 tailhousing for the TH-400 bracket
from Chevy (part# 8673406). You may also need a shortened driveshaft if you
have a TH350. Finally, call Year-One for a TH-400 crossmember (part# 8606N for
67-69 models).
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Can I replace my
TH400 or 700R4 tranny with a 4L60E or 4L80E?
Yes, but be prepared to do a lot of work to get it to
fit and function. The converter for the 4L80E is a huge and heavy. And it's not
cheap. A rebuilt unit will probably cost $1000 to $2000. Of course the
driveshaft will have to match up and you will definitely need an aftermarket
computer controller. Accel, Turbo Action, and Premier Performance Transmissions
make them. They cost around $650 to $700 which includes the wiring harness. In
order to use it, you need a throttle position sensor of some kind on the motor.
Engine RPM is needed as well and it may be possible to pick it up from the
tach. You might also need to convert to an electronic speedometer. Your best
bet is to call Precision Turbo 708-418-5227. They've done a number of these
conversions, but mostly on fuel injected cars.
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What can I do about a
squeaky clutch pedal?
Lay on your back on the driver's side floor with a
flashlight and a can of teflon/silicone spray with a straw attachments affixed
on it. Find the pivot point of the clutch pedal. You'll know you found the
pivot point when your back is killing you because of the weird way you have to
be bent to get access to it. Soak it with the spray (but WATCH your eyes). Then
get up (if you can) and work the pedal a few times (make sure the parking brake
is set). Repeat the procedure one more time. This should silence any noise
coming from the pedal.
If this doesn't work, then the clutch actuator
(clutch slave cylinder) might need to be replaced. This mechanism is mounted on
the tranny and it pushes on the clutch fork.
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How can I easily
determine what rearend gear ratio I have?
Jack up the whole rear of the car. While turning the
tire on full rotation, count the number of times the drive shaft turns. A chalk
mark can be used as a reference point. If you have a posi rear, then the number
of turns of the driveshaft (per single wheel rotation) is your gearing (i.e.
3.50 turns would be a 3.50 rear, or a 3.55 more likely).
If you have an open
(non-posi) rear, then you must
multiply the number of driveshaft turns by 2 to get the gearing (i.e. 1.5 turns
would be a 3.0 rear [1.5 * 2 = 3.0], or a 3.08 more likely). The reason for
multiplying by 2 is that in an open differential, the
planetary gears cause the
driveshaft to rotate half as fast as in a posi if only one tire is being
rotated. Therefore, you must multiply the drive-shaft turns by 2 to get an
accurate ratio, otherwise you must rotate one tire then the other (and not
multiply). When one tire is not moving, the planetary
gears are "walking"
around the differential housing in the opposite direction causing the
drive-shaft to rotate slower than if the diff were "locked".
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How can I determine if
I have a "posi" rearend?
Turn one side of the rear end. If the other side
turns the same direction, it's a Posi. If the other side turns in the opposite
direction, it's not.
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How can I recalibrate
my speedometer swapping for shorter/taller gears?
Cyberdyne sells a box which can recalibrate it. You
can one from JEGS, Summit, or a local speed shops for around $65. On 1994 and
newer cars, the speedometer can be recalibrated through the ECM with
programmers like that from Hypertech. Tell them what gearing you have and they
will create a customized program to recalibrate your speedometer.
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How can I recalibrate
my automatic tranny shift points with a gear swap?
The only way to do it is to reprogram the ECM or
replace the computer chip. As for aftermarket chips/programs, most of them
which adjust the speedometer for gear changes, also modify tranny shift points
at redline for wide open throttle. However the problem with these chips is that
they don't modify the shift points under partial throttle. Since shorter gears
(which are numerically higher, like 3.73) rev higher, the stock computer
program/chip will still be shifting at its preset points. So the engine may hit
3000 or 4000 RPM before shifting (whereas before it would shift at 2000 RPM).
Some people believe there is a Federal law which prohibits modification to the
stock partial throttle shift points on automatic transmissions (most likely
related to emissions), but this is possibly only rumor. Try contacting your
chip/program company of choice and check with them about a custom set-up.
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