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What are the stock
tranny gear ratios and torque capacities?
What's the
difference between the 4L60 and 4L60E tranny?
What is CAGS
(skip shift) and how does it work?
How do I disable
CAGS?
Why does my Service Engine Light come on now that
CAGS is disabled?
How do disable the Skip Shift light as
well?
Why is there no selectable 1st gear for my automatic
tranny?
Why does my automatic tranny have trouble going
into and out of reverse?
What's that screeching noise from
my automatic tranny on hard shifts?
What's that rattling
noise from my manual tranny upon acceleration?
What's that
vibration I feel around 1800-2000 RPM?
Why does my manual
shifter pop out of gear just after going into 2nd?
What's
the best way to install a Hurst shifter?
Why was the
rear end ratio on the 6-speeds changed from 1993 to 1994?
What GM rear gears are available for my car?
What's that clunking noise from the rear when
decelerating?
What's that whining/grinding noise from the
rear on slow turns?
Should I use synthetic
rear end gear
fluid and limited slip additive?
What does ASR stand
for?
What are the stock tranny gear
ratios and torque capacities?
The following were available by year:
Year Model/Optn 1st 2nd 3rd 4th 5th 6th Final
---- ------------ ---- ---- ---- ---- ---- ---- -----
1993 Manual/M28 3.36 2.07 1.35 1.00 0.80 0.62 2.73 (GU2)
1993 Manual/M29 2.97 2.07 1.43 1.00 0.80 0.62 3.23 (GU4)
1993 Auto/MX0 3.06 1.63 1.00 0.70 -- -- 2.73 (GU3)
1993 Auto/MX0 3.06 1.63 1.00 0.70 -- -- 3.23 (GU5)
1994 Manual/MN6 2.66 1.78 1.30 1.00 0.74 0.50 3.42 (GU6)
1994 Auto/MX0 3.06 1.63 1.00 0.70 -- -- 2.73 (GU3)
1994 Auto/MX0 3.06 1.63 1.00 0.70 -- -- 3.23 (GU5)
The '95s and later have the same ratios as the '94s.
Aside from the CAGS provision and different gearing/input shaft (on the post
93's), all of the 6-speed transmissions are basically the same.
Because of differences in the ratios, the torque
capacities are different for each model. The shorter the tranny gear (higher
numerically), the less torque it can handle. Note that these ratings from GM
can be are considered conservative as they are most likely measured at normal
load over 100,000 miles:
Year Model/Optn Torque Capacity
---- ---------- ---------------
1993 Manual/M28 360 lbs-ft
1993 Manual/M29 400 lbs-ft
1993 Auto/MX0 400 lbs-ft
1994 Manual/MN6 450 lbs-ft
1994 Auto/MX0 400 lbs-ft
Note that the '95s and later have ratings that are the
same as the '94s as nothing changed.
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What's the difference
between the 4L60 and 4L60E tranny?
The 1993 cars came with the 4L60 automatic tranny
while the 1994's and later got the electronic version (4L60'E'). The 4L60E got
an electronic valve body which can vary the shifts and feel dynamically to meet
the existing driving conditions. Acutally, if you drive a '93 and '94 (under
normal conditions), there is a noticeable difference in that the 93 shifts are
much more firm and abrupt. The 94 (and later) have a "variable" feel depending
on throttle position, which of course at wide open throttle, feels like the 93.
This electronic valving is also supposed to reduce the wear over the life of
the tranny. If you have a 93, you might want to try driving in 3rd (or "D" on
the Pontiacs). Once the revs get to high in 3rd, put it into 4th (or "OD")
manually. Due to the valving, the shifts should be much firmer at all times in
3rd than 4th.
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What's CAGS (skip
shift) and how does it work?
CAGS stands for Computer Assisted Gear Selection and
is on 1994 and on cars with 6 speed transmissions. It's purpose is to improve
gas mileage and avoid the "gas-guzzler" new car tax. CAGS comes into play under
the following conditions:
-
you're in 1st gear (of course)
-
you're at 35% throttle or less
-
you're between 15 and 21 mph
-
engine coolant temperature is greater than 171 F
(77 C)
This will energize the skip-shift solenoid and force a
1st to 4th shift. What happens is you'll be moving happily along when suddenly
the "Skip Shift" light goes on in the dash. At this point you will be locked
out of 2nd and 3rd. You simply cannot shift into them. At this point several
options are available to you:
Interestingly, 1st gear is determined by the PCM
calculating from the speed sensor input and the RPM values. Disconnecting the
solenoid connector disables CAGS but an error code 84 WILL be set if the PCM
does not measure voltage at the solenoid connection to the computer for a
period of 26 secs. This code is stored but will NOT light the Service Engine
light. Apparently Chevy correctly anticipated the rush for owners to disable
this function. A resistor inserted in the connector will allow voltage to the
PCM input and prevent this code setting but who cares since the code is
reference only.
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How do I disable
CAGS?
There are several electrical connectors going into
the transmission. There are three 2-wire connections on the drivers side of the
tranny. Two of them are hooked up to large, brass colored protrusions which are
solenoids. The third connection is to a small black box on the tailshaft of the
tranny. This is the speed sensor (no speedometer cable on the LT1).
Disconnecting this will stop CAGS, but your speedo will also not work and the
check engine light will come on. Of the other 2 connections, one is up on the
tailshaft. This is the reverse lockout solenoid, although it's really a reverse
enable solenoid since when it is not powered on, you are locked out of reverse.
The final connection is the CAGS solenoid, the farthest forward of the three in
the center of the tranny. Unplug it, tape it, and forget it.
The Service Engine light won't come on if you have a
1994 or 1995 car (note, no CAGS on the '93s), but the PCM stores an error code
of 84 indicating the open circuit in the CAGS wiring. Since an open circuit
(which a disconnected solenoid would be) using 2 wires can only be detected by
no current flow, simply insert a resistance relatively close to the DC
resistance of the solenoid coil across those wires. That way the current
detector will still see the load, assuming the CAGS solenoid is still there and
operational. See below for instructions on this.
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Why does my Service
Engine Light come on now that CAGS is disabled?
You most likely have 1996 or later car. In 1996, GM
instituted the OBD-II standard on the F-Body computers. This makes modifying
the car much more difficult than in the past. Simple changes (such as disabling
CAGS) will cause the computer to sense a problem and light up the service
engine light. Luckily, you can fool the computer into thinking CAGS is still
connected.
The resistance of the CAGS solenoid is 15 ohms.
Assuming 13.5 V, that means about 12 W are dissipated. Go to Radio Shack or any
local electronics store and pick up a 15 ohms, 10 W resistor (about $0.50). 10
W should should be fine as it will be mounted to the tranny which will work as
a heat sink and the skip shift is only active a few seconds at a time, so there
won't be much time for any extensive heat build up. But in hotter environments,
you might want to use a resistor of 2200 ohms rated at only a 1/4 to 1/2 W.
Simply put the resistor in place of the CAGS solenoid
thereby closing the circuit and making the computer think CAGS is still
connected. You can also buy some heat shrink tubing to put around the resistor
to protect it. Then take a tie wrap and fasten the "eye" of the wire connector
to the tranny so everything is nice and tight. The connection be returned to
stock form in less than 5 minutes if needed and easily be duplicated again for
$1.
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How do disable the
Skip Shift light as well?
The following procedure requires a 10mm socket,
extension, ratchet, and awl (or similar tool with a pointed tip):
-
Disconnect the battery.
-
Remove the two bolts holding the PCM to the inner
fender well. (The PCM is the cigar box sized unit located near the passenger
side hood hinge.)
-
Pull the PCM from its lower retaining slot and
position the unit so that the connectors are accessible.
-
To disable CAGS, remove the 32-Way F Micro-Pack
connector marked "Blue" on the PCM. There is a red retaining clip that needs to
be removed first. (Once the connector is removed you will be able to see a blue
connector pin guide.)
-
Use the awl to open the gray connector back shell
(3 snap latches).
-
Use the awl again to remove the blue connector/pin
guide located on the front of the connector (2 snap latches).
-
Find the white wire in location 15. The pins are
marked on the back of the connector where the wires go in to it.
-
Gently lift the pin retainer for slot 15 while
gently pulling the wire from the back of the connector. Once the wire end is
clear of the retaining latches, release the pin retainer. Continue to pull the
wire until it is free of the connector body. (There is a seal near the back of
the connector that will add a little resistance to the pulling.)
-
Tape off the wire end.
-
Reinstall the connector/pin guide. (It only goes on
one way.)
-
Snap the back shell in place.
-
Reinstall the connector on the PCM.
-
Reinstall the PCM by reversing the first two steps.
-
Reconnect the battery.
Even though the procedure looks complicated and
intimidating, it should only take about 15 minutes to complete. This will cause
error code 91 to be set and stored in the PCM in addition to code 84 set by
removing the solenoid.
It is interesting to note that on the pre-OBD-II cars
with CAGS (1994-1995), instead of disconnecting the CAGS solenoid from under
the car (as described in the section above), CAGS can also be disconnected in a
similar way to the shift light disconnection. In addition to removing the
connector in location 15 of the "Blue" connection on the PCM, also remove the
gray connector at location 13 of the "Black" connection on the PCM. This will
disable CAGS without having to disconnect anything under the car. However, on
the 1996 and later cars, the service engine light will remain lit upon
disconnecting connector 13. So the resistor method as described above is
recommended for those cars.
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Why is there no
selectable 1st gear for my automatic tranny?
On cars with automatic trannys and the 2.73 rear
(GU2) 1st gear can't be selected because in order to pass the Federal noise
pollution tests, GM had to lock out selectable 1st gear. It has to do with
downshifting into the lowest selectable gear at some speed as the car goes
through the sound traps. With the 3.23 rear end, the required speed is high
enough that the tranny won't allow a manual downshift all the way to 1st gear.
But with the 2.73 gears, the car will downshift all the way to 1st when
manually selected thereby increasing engine and exhaust noise. So GM had to
prevent 1st gear from being selected on the 2.73 cars in order to meet the
guidelines.
However, making 1st gear selectable on these cars is
relatively easy. Lift off shifter cover, locate plastic (nylon) stop at the
right side of the notched selector ramp, use a hacksaw or X-acto blade to
remove the offending (square) stop. Then you will have first gear.
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Why does my automatic
tranny have trouble going into and out of reverse?
While it's normal to take a second or two for the
4L60(E) to shift in and out of reverse, if you find the duration unacceptable
or a problem, then check with your dealer on this as there are Technical
Service Bulletins for the problem. TSB #4771120A is for 1993 and 1994
automatics where the car has a delay in shifting from park into reverse or
drive. Then TSB #677148 is for 1995 and 1996 automatics with delayed gear
engagement with reference to the adjustment or replacement of the clutch spacer
plate.
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What's that screeching
noise from my automatic tranny on hard shifts?
If you've ruled out that it's the rear tires chirping,
then it's most likely belt slippage. This is common on the Corvette LT1s and
even some of the later L98 motors. On hard shifts (auto and manual trannys),
the shift in the speed of the pulleys will throw the belt and hence the screech
of it slipping. It's pretty harmless, although it can be annoying.
You can check with your dealer as there is a Technical
Service Bulletin (#476109) which calls for replacement of the belt tensioner
with an improved one (part #10238703). Some people have also replaced the A/C
pulley, (part #2724717) and the belt (part #12550149).
Others believe the power steering pump pulley to be
the culprit. The do-it- yourself solution is to raise the vehicle and support
it with jackstands (or ramps). Either look to make sure you have an underhood
sticker that shows the routing of the belt or make yourself a picture. Then get
under the car and use the appropriate socket and "tighten" the center bolt on
the belt tensioner pulley. As you "tighten", the bolt shouldn't move, but the
tensioner will swing out, allowing you to pull the belt off with your other
hand. Then take an old toothbrush and soak the head in alcohol. Then, for each
pulley, spin it with one hand and hold the toothbrush against the surface of
the pulley where the belt normally touches. Repeat this until you are pulling
back a relatively clean toothbrush on each pulley. Since you can't turn the
main crank pulley, just run the toothbrush around it until the pulley is clean.
Note that you can accomplish this cleaning with the belt installed and the
engine running if you know what you are doing, but this can be EXTREMELY
DANGEROUS if you don't have practice and a steady hand because IT IS EXTREMELY
EASY TO GET THE TOOTHBRUSH CAUGHT BETWEEN THE BELT AND A PULLEY WHICH COULD
CAUSE SERIOUS INJURY. Try the first way to be on the safe side. After the
pulleys are clean and the factory belt is off, you can roughen up the PS pump
pulley by simply running sandpaper across the PS pump pulley from above. Watch
your hands though, because those hoses up there can be HOT. Just scrape the
sandpaper across the top of the pulley in a motion from the front to the back
of the car. The trick is, you want to roughen the pulley, putting scratches in
it in the opposite direction of the belt's travel. Scratch it just enough to
dull the surface all the way around. Use a paper towel damp with alcohol to
clean off the pulley all the way around where you sanded it to get the grit
off. Finally, install a new belt (preferably, Gates K060637, 21mm x 1635mm) and
make sure the routing is correct and the belt is centered on each pulley. Lower
your car, start it up, and make sure the belt is staying on. Then you can hit
the road and open it up, enjoying your quiet shifts (hopefully).
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What's that rattling
noise from my manual tranny upon acceleration?
This is a common problem among 6-speed cars. GM is
aware of the problem. The faint but distinct rattling noise can usually be
heard with the tranny in neutral and the clutch out. A few quick revs at about
1/8 throttle and it should get louder for a fraction of a second, then
disappear, and then return when the engine drops back to idle. You should also
be able to hear it when starting out in first from 0-10 mph.
Unfortunately, there's no Technical Service Bulletin
or recall to address this problem. But GM does know about it. In 1993 and 1994
cars, the GM Tech Assistant Group (TAN) called for the dealer to replace the
clutch with a revised one. Two different part numbers for the revised clutch
were found, (12551803 and 12551809), but no one is sure which is correct or if
they really exist. 1995 and later cars are supposed to have a revised clutch
(part #12551309), however, even people with these cars report to have same
rattling noise. As of now, there seems to be no fix for the problem. It's even
accepted to be normal by most dealers considering no one has reported any
abnormal wear or damage which might be related to the noise.
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What is that
vibration I feel around 1800-2000 RPM?
This problem is an unbalanced driveshaft. Most people
with the problem feel it at its worst between speeds of 90 and 120 MPH. Others
claim they can also feel it by slowly bringing the RPMs up to the 1800-2000
range with the car in park or neutral. But that isn't necessarily the same
problem. Some even start to feel it as low as 60 MPH. It usually starts with a
mild resonating vibration you can feel through the gas pedal. Then in at 80 -
90 MPH, the vibration intensified and feels as though it's coming from the
center of the car.
It seems cars are coming off the assembly line with
the unbalanced drive shafts. A Technical Service Bulletin (#674101) addresses
this calling for replacing the stock driveshaft with a 3rd generation
all-aluminum driveshaft (part #10085375) which came with the 1LE equipped cars.
Although there have also been instances prior to the TSB where it was replaced
with the standard 3rd gen steel driveshaft (part #26004464). Either seems to
work just fine (although the aluminum one is lighter in weight). Make sure you
let your dealer know what the TSB number is as it will be fixed under
warranty.
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Why does my manual
shifter pop out of gear just after going into 2nd?
Check with your dealer on this as there is a
Technical Service Bulletin (#477202) which is supposed to fix the problem. You
may also want to install a Hurst or B-and-M shifter.
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What's the best way
to install a Hurst shifter?
Open the arm rest and remove the 2 nuts in the
bottom. Remove the ashtray and disconnect the ashtray light. Remove the shift
knob (unscrew it) and remove plastic trim cover. Remove the nut inside the back
of the cassette/ CD holder below the radio. Remove nut inside the
ashtray well.
The center console should be free of the driveshaft hump. There is a light and
switch assembly for the arm rest storage. From underneath the console, push up
on the switch. Pull it gently through the top. Remove the black retaining clip
from the top of the switch. Be careful not to break the tabs on it. Now you can
push the light back through the bottom of the arm rest. Fully raise the parking
brake. Lift rear of console up and slide the parking brake through the rubber
slit. Tilt the console onto the passenger seat. Be careful not to stretch any
wires. This should expose the shifter completely.
Remove the shift lever (2 hex nuts on the side).
Remove the large rubber boot. This has approximately six small nuts. Remove the
four 13mm nuts on the metal housing. Be careful not to strip these. Lift off
the old unit (a rectangle metal plate). Put the Hurst unit in its place. Make
sure to line up the round bearing with the mate gasket. Put a bead of silicone
sealant around the edge of the metal plate. Replace the four nuts with the new
ones supplied. Finally re-assemble everything.
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Why was the
rear end ratio on the 6-speeds changed from 1993 to 1994?
The only reason GM went to the 3.42 rear differential
for all the 1994 and later 6-speed models (versus 3.23 in 1993) was to
accommodate CAGS. A lower rear gear ratio would bog the engine down too much for
a 1st to 4th shift. Note the tranny gears between
1st and 4th were also made
much closer mostly due to a taller 1st gear for CAGS. If you combine both the
tranny and rear gear ratios, the '93 6-speeds equipped with a 3.23 actually
have a higher overall ratio from 1st to 3rd.
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What GM rear gears
are available for my car?
The following will fit the 4th generation f-bodies.
However, if you're upgraded from a stock 2.73 rear to above a 3.23 or above,
you'll need to upgrade your 2 series carrier to a 3 series carrier. If have a
3.23 or 3.42 stock rear, you can upgrade as up to a 4.10 with the 3 series
carrier.
Ratio Part number
-------- -----------
2.56 : 1 26019802
2.73 : 1 26043705
2.93 : 1 26016282
3.08 : 1 14089176
3.23 : 1 26046642
3.42 : 1 26029418
3.73 : 1 14091497
4.10 : 1 26016309
The ratio's and part numbers refer to GM's ring and pinion gears.
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What's that clunking
noise from the rear when decelerating?
This noise is most common on cars with an automatic
transmission. It usually occurs at downshift points where the rear gears
disengage. Some people claim that changing the rear differential fluid and
adding the rear diff additive (aka "limited slip oil") fixes this. But in most
cases it's a problem with the PCM downshift program. A Technical Service
Bulletin (#477124) addresses this in the 1993 - 1994 LT1 powered cars. The TSB
describes a "3rd to 2nd downshift clunk" and calls for the computer program to
be updated on all 1993 cars and all 1994 Pontiacs with a VIN sequence lower
than 239227 and Chevies lower than 194422. All later cars should have the
updated program.
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What's that
whining/grinding noise from the rear on slow turns?
The new 4th gens require
rear end service (differential
oil change) early in life - usually around 7,500 miles (although some have done
it even earlier). When you replace the differential oil, make sure you add GM
limited slip additive. (Note, the additive should not be necessary if you use
synthetic diff oil.) This should alleviate most of the noises coming from
rear end. Otherwise, it's probably standard rear gear noise. GM hasn't changed
the F-body rear end since 1982 and they all make some form of noise.
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Should I use
synthetic rear end gear fluid and limited slip additive?
As for the rear differential fluid itself, using a
good 75W-90 synthetic is the best way to go. As for using the limited slip
additive, that all depends on your application. If you primarily use the car
for street and strip driving, then use the additive as it will help prolong the
life of the rear end and ensure quiet operation of the gears. If you autocross
or do any type road racing on a regular basis, then not using the synthetic is
will provide better performance in the tight turns, but theoretically, the life
of the rear end will be shortened. How much shorter all depends on the type and
amount of driving you do.
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What does ASR stand
for?
It's short for "Acceleration Slip Regulator" - more
commonly referred to as "Traction Control".
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