DISTRESSED SECOND CLUTCH 440-T4/4T60 DIAGNOSIS

SUBJECT NO SECOND GEAR, SLIPS IN SECOND GEAR, SLIPS OR SHUDDERS DURING 1-2 SHIFT - 4T60 TRANSAXLE

MODELS AFFECTED: 1985-1990 DE VILLES AND FLEETWOODS 1986-1990 ELDORADOS AND SEVILLES

Some 1985-1990 DeVilles and Fleetwoods and 1986-1990 Eldorados and Sevilles equipped a Hydra-Matic 4T60 transaxle may exhibit one of the following conditions:

1. Slips or shudders during 1-2 shift.

2. Slips in second gear.

3. No second gear.

This may be caused by a worn or damaged second clutch. When diagnosing a transaxle for one of the above conditions, the following item should be checked first:

1. Test drive the vehicle to verify the condition.

2. Verify proper fluid level.

3. Verify proper transmission line pressure according to the chassis service manual procedure. Check minimum pressure by applying 18" of vacuum to the vacuum modulator (use a hand vacuum pump).Check maximum line pressure with no vacuum applied to the vacuum modulator (vacuum line disconnected. Check both minimum and maximum at 1250 rpm in each range. If there is no boost in pressure with zero vacuum, check for an inoperative vacuum modulator or modulator valve. ruptured aneroid bellows in a vacuum modulator will result in no boost in pressure with zero vacuum applied.

NOTE: Do not measure maximum pressure by pulling out on the TV cable. 1987 and later models will give you a boosted pressure at full TV which is not the same as the maximum pressure reading with zero vacuum. Using the TV cable can give you a false maximum pressure reading and will not reveal an inoperative vacuum modulator.

3a. Check vacuum modulator. Tools required: J-36619 for 1985-1986 models and J-35258 for 1987-1990 models. Refer to Figure 1.

- Install a known good modulator of the same type on one side of the comparison gage.

- Install the modulator to be tested on the other side of the gage.

- If the gage line remains blue, the test modulator is not acceptable.

- If the gage line is white, the modulator is acceptable.

4. Use a vacuum gage on the vacuum line at the vacuum modulator end to verify full engine vacuum is available at the vacuum modulator. The vacuum should register immediately as the engine is started and should respond quickly to engine load changes. When you flash the throttle from idle, the vacuum gage should drop instantly and recover as soon as the engine returns to idle. If response is slow, repair by using a .031" (.76mm) drill bit to check and/or clean out the TBI modulator fitting. To prevent recurrence check the metal vacuum tube connecting the fitting to the modulator for debris by removing the short vacuum hoses at both tube ends and blowing through the tube with air.

Knowing the results of the previously listed checks will help determine the causes of a damaged second clutch once you get inside the transaxle. The second clutch applies and caffies torque in second, third, and fourth gear. Therefore, if fluid level or pressure is low or if the pressure doe's not boost when the engine is loaded, the second clutch will be one of the first components to slip and eventually wear or burn.

Once inside the transaxle, there are several items to look for when diagnosing a damaged second clutch:

1. Mispositioned second clutch snap ring.

2. Split, cut, or rolled second clutch piston seals or damaged piston. Ensure later design seal is used. Refer to Service bulletin T-88-99.

3. Second clutch housing leaking through cracks in the housing or welds.

4. Fluid leaks through second clutch housing check ball or its retainer.

5. Check for deformed or damaged piston return springs in the apply ring and return spring assembly. If these springs are weak, they can allow the second clutch plates to drag while the second clutch is released in first and reverse. This may result in premature wear of the second clutch plate.

NOTE: The piston return springs are easy to overlook but may be a cause of repeat failure of the second clutch.

5. 1985-1986: Check driven sprocket support cast iron seals for wear or damage. Check for rooves worn into the inside diameter of the second clutch drum. If so, replace the second clutch drum and install a revised driven sprocket support with the later style support using vespel ring seals. Refer to Service bulletin T-88-7.

1987-1990: Check driven sprocket support vespel ring seals for wear or damage. Check for damaged or mispositioned four lobe support seals under the vespel rings.

6. Check the second clutch ap ly passage between the driven sprocket support and bushing. Look for the bushing out of position or worn. If either condition is found, the driven sprocket support should be replaced. Blow air through the passage to check for restrictions or foreign material. If full apply pressure cannot get through to the clutch, it will slip and wear.

7. Check for a leak at the sealing surface where the driven sprocket support contacts the channel plate.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.