4th Generation (1993 - Present)


4.3 Transmission and Drivetrain

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Q: What are the stock transmission gear ratios and torque capacities?

A: 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 (GU2)
   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 (GU2)
   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 transmission 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.

*According to the GM Powertrain divison, the maximum torque the 4L60E transmission can handle is 350 lbs-ft of torque.


Q: What's the difference between the 4L60 and 4L60E transmission?

A: The 1993 cars came with the 4L60 automatic transmission 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. Actually, 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 transmission. 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.


Q: What's CAGS (skip shift) and how does it work?

A: 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:

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.


Q: How do I disable CAGS?

A: There are several electrical connectors going into the transmission. There are three 2-wire connections on the drivers side of the transmission. 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 transmission. 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 transmission. 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.


Q: Why does my Service Engine Light come on now that CAGS is disabled?

A: 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 transmission 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 transmission 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.


Q: How do disable the Skip Shift light as well?

A: The following procedure requires a 10mm socket, extension, ratchet, and awl (or similar tool with a pointed tip):

  1. Disconnect the battery.
  2. Remove the two bolts holding the PCM to the inner fenderwell. (The PCM is the cigar box sized unit located near the passenger side hood hinge.)
  3. Pull the PCM from its lower retaining slot and position the unit so that the connectors are accessible.
  4. 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.)
  5. Use the awl to open the gray connector back shell (3 snap latches).
  6. Use the awl again to remove the blue connector/pin guide located on the front of the connector (2 snap latches).
  7. Find the white wire in location 15. The pins are marked on the back of the connector where the wires go in to it.
  8. 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.)
  9. Tape off the wire end.
  10. Reinstall the connector/pin guide. (It only goes on one way.)
  11. Snap the back shell in place.
  12. Reinstall the connector on the PCM.
  13. Reinstall the PCM by reversing the first two steps.
  14. 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.


Q: I shifted too late, and just hit the rev limiter on my car with my manual transmission, did I damage anything?

A: The rev limiter is set at 6200 RPM from the factory on the F-body LS1s. The rev limiter is there to prevent the engine from damaging itself at too high of RPMs. Although most people will tell you to not try to hit the rev limiter, all it does is slow you down, so you should practice shifting right before 6200 RPM.


Q: When driving in 3rd gear, I accidentally downshifted into 2rd gear (or some other combination) and I redlined my engine, did I damage anything?

A: Although there is a rev limiter that is in place to prevent the engine from going too high in that gear, if you downshift into too low of a gear, the rev limiter can't stop that, and depending on what speed you were going, and how quickly you caught your mistake, yes you could have damaged something. If this happens, then you should turn off your radio and pay careful attention to the engine sound for the next few days. Make sure there's no strange ticking or clanking coming from the engine, and make sure there's no noticeable performance loss. If everything seems okay a couple days after, chances are you're lucky and the engine didn't hurt itself. However, in some cases, you could have bent your pushrods or done other damage to the engine.


Q: Why does my car seem to hit a rev limiter around 5800 RPM in first gear and closer to 6200 RPM in all other gears?

A: The factory tachometer in these cars is slower than the engine is, so when accelerating in first gear at wide open throttle, your tachometer cannot keep up with the engine RPMs, and is actually a couple hundred RPMs behind when you first hit the rev limiter. Because it takes longer for the engine to get that high in other gears, this shouldn't happen. Since this isn't really a problem, there's nothing you can do about it other than practice. With some practice, you will learn to listen to your engine and know when you're about to hit the limiter in first gear.


Q: I have a 6-speed and an aftermarket shifter, and sometimes when I put my car into reverse, the trans pops out of Reverse into Neutral, what is the problem?

A: A lot of times when adding an aftermarket shifter, part of the rubber boot is putting tension on the shifter. Take apart the console, and put the car in reverse and make sure there's nothing rubbing against the shifter. It might be that you just need to refit the new shifter in place, or you may even need to go as far as trimming some of the plastic or rubber so that the shifter goes into reverse unrestricted. This is less common with the stock shifter, but its still possible, if this is the case, let the dealer make the adjustments.


Q: Why is there no selectable 1st gear for my automatic transmission?

A: On cars with automatic transmissions 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 transmission 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.


Q: Why does my automatic transmission have trouble going into and out of reverse?

A: 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.


Q: What's that screeching noise from my automatic transmission on hard shifts?

A: 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 transmissions), 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).


Q: I have a 98 or 99 LS1 F-body with an automatic transmission, and each time I put my car into gear from park and each time I accelerate from a stop, there is a ping or tinking noise that sounds from underneath my car. Where is this coming from and how do I fix it?

A: This is a problem with the automatics that have an aluminum driveshaft. The aluminum driveshaft comes standard on the cars with the 3.23 (GU5) rear end. Although there is no TSB to fix this, if you have the dealer replace the driveshaft with a new one, the sound will go away. However most people who had this repair done report that it comes back. As of this time, there doesn't appear to be a permanent fix other than replacing the driveshaft with a carbon fiber one.


Q: What's that rattling noise from my manual transmission upon acceleration?

A: 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 transmission 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.


Q: What is that vibration I feel around 1800-2000 RPM?

A: 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.


Q: Why does my manual shifter pop out of gear just after going into 2nd?

A: 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.


Q: What's the best way to install a Hurst shifter?

A: 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.