TRANSMISSION UPDATES SUMMARY 125 TRANSMISSION

This bulletin provides the necessary information to update any of these transmissions when internal repairs are required.

When making internal repairs on any 1980-1982 THM 125/125C transmission, the following latest design parts should be used where applicable.

Bulletin Part Number Part Reference

8631987 (1980-1981) Solid turbine shaft 80-T-6 8631968 (1982) seal rings

8637640 Band anchor plug (if 82-I-46 dislodged)

8643964 Third accumulator 82-T-102 check valve & spring

8637836 (1980-1981) Oil weir 82-I-44

112496 Pressure regulator 82-T-24 valve - solid pin

To help you provide this service, WDDGM will package the parts indicated as a single item under the following part numbers:

1980-1981 models 8643995 1982 models 8643996

In addition to the above items, the following should be checked:

Check and drill vent hole in the case cover if not present. 81-T-27

Check wear in differential carrier bore to determine need for right drive axle external bearing repair package. Pack- age part number is 8643931. The axle shaft sleeve seal originally available only in this kit is now available as a separate part under P/N 8643962. 81-T-78

If inspection of the transmission at the time of disassembly reveals any form of internal damage, the transmission cooler lines should be cleaned and flushed using the procedure provided in Section 7A of the 1982 Chevrolet Service Manual, page 7A-2.

Also only Loctite #515, P/N 1052756, should be used at the case cover to case gasket to prevent leaks in this area.

Before using Kent-Moore Tool J-288535 (Intermediate Band Apply Pin Gauge), it should be checked and recalibrated per instructions in Bulletin 82-I-114.

SOLID TURBINE SHAFT OIL SEAL RINGS

Solid oil seal rings are used to minimize converter oil drainback. Excessive converter oil drain-back can result in delayed engagement into drive or reverse. Therefore, only solid seal rings, which are included in the update kit, should be used when re ssembling the transmission.

Instructions for replacement of scarf cut or damaged solid oil seals is as follows:

1. If the turbine shaft was originally equipped with solid type oil seals, remove them by carefully cutting with a knife (Figure 1, Page 4). Scarf cut seals do not require cutting.

2. Place the seal installer (J-29569-1) over the turbine shaft and lubricate the installer with petrolatum (Figure 2, page 4).

3. Place the solid oil seal ring over the seal installer and carefully, but quickly slide the seal down to the seal ring groove. Remove the seal installer (Figure 2, Page 4).

4. Lubricate the inside of the sizing tool (J-29569-2) with petrolatum or equivalent. Push the sizing tool down over the seal and turn. Remove the sizing tool and inspect the seal to be sure that it is properly seated in the groove (Figure 3, Page 4).

5. To install the seal on the other end of the shaft, turn the shaft over and repeat the above procedure.

NEW DESIGN BAND ANCHOR PLUG

Beginning in mid-June, 1981, all THM 125 and 125C transmissions were assembled with a new design band anchor plug. The new design band anchor plug has a tab which holds the part in place (see Figure 1).

Service Information

1. Transmissions built with the past design band anchor plug required a staking operation to hold the part in place (see Figure 2). This staking operation is not required with the new design band anchor plug as it is held in place by the reverse oil pipe (see Figure 3).

2. To remove or replace the new design band anchor plug, the reverse oil pipe must be removed.

3. For service, use the new design band anchor plug, P/N 8637640, which is included in the update kit.

BURNT INTERMEDIATE BAND AND DIRECT CLUTCH FAILURE

To prevent the possibility of intermediate band failure, the new style dual land valve and conical spring, service part number 8643964, which is included in the update kit, should be installed in 1980-1982 THM 125 transmissions if not present, using the following instructions:

1. Remove the intermediate servo cover and gasket.

2. Remove the third accumulator check valve and spring.

3. Inspect the third accumulator valve bore for presence of the valve seat (Figure 1) Also, inspect for wear or damage to the seat.

4. Plug the feed and release holes in the bore using petrolatum (Figure 1).

5. Replace the third accumulator check valve with a dual land check valve. Center the valve so as to seat it properly.

6. Leak test the valve seat by pouring solvent into the accumulator check valve bore. Check for a leak on the inside of the case. (A small amount of seepage is acceptable.)

7. If the valve leaks, tap the valve with a brass rod and rubber mallet, to try to reseat the valve.

8. Releak test the valve seat.

9. If the valve continues to leak, it will be necessary to replace the case.

10. If the valve doesn't leak, remove the check valve and install the new conical valve spring onto the valve (small end first). Refer to Figure 1. Install the valve into the case bore (Figure 2).

11. Install the servo gasket and cover. (DO NOT USE OLD GASKET.)

OIL WEIR

The oil weir which first went into production in September, 1981, should be installed in all THM 125 and 125C transmissions if not present.

The oil weir is located in the rear case - oil pan area and will revise the lubrication flow around the differential assembly (see illustration).

The oil weir, P/N 8637836, is held in place by a retaining clip, P/N 8637837, and both parts are provided in update kit.

SOLID PRESSURE REGULATOR VALVE RETAINING PIN

If the pressure regulator valve retaining pin is worn or missing, or is not the new solid pin the new one, P/N 112496 provided in the update kit, should be installed using the following directions:

1. Position the control valve and oil pump assembly with the machined portion face down. Be certain the machined face is protected to prevent nicks, burrs, scratches, etc. Completely disassemble pressure regulator valve train as shown in Figure 2.

2. Use a 3/8 drift punch and hammer to stake (close) the pressure regulator valve retaining pin hole. See insert Figure 1. Stake the pin hole only enough to hold the new retaining pin in place after assembly.

3. Reassemble the pressure regulator and reverse boost valve training assembly (see Figure 2).

4. Retain the valve train with a new steel retaining pin, P/N 112496. The new pin must be inserted from and flush with the machined face of the control valve and oil pump assembly.

OIL OUT THE VENT DIAGNOSIS

The following instructions should be used to drill a vent hole in the case cover, if not present, to prevent the possibility of an "oil out the vent" condition.

1. Disassemble the transmission to the case cover.

2. Remove the case cover and inspect the areas adjacent to the manual valve for flatness to case and external porosity.

3. Wash case cover completely with solvent to remove all transmission oil and dry before proceeding with the following drilling operation.

4. Drill a 6.0mm (1/4") hole through the breather area of the cover as indicated in illustration. Late 1980 production has this passage and does not require drilling. Use a small drill or punch to start hole.

When drillinq operation is completed, deburr both sides of hole and brush out chips. Rinse cover completely with solvent.

5. Replace both spacer plate gaskets with new spacer plate gaskets, P/N 8637096.

6. Reassemble transmission.

INTERMEDIATE BAND APPLY PIN GAUGE CALIBRATION CHECK AND ADJUSTMENT PROCEDURE

The following calibration check and adjustment procedure should be made prior to using Kent-Moore Tool J-28535, Intermediate Band Apply Pin Gauge.

To check calibration:

1. Hold J-28535 gauge down tightly against J-28535-50 checking block. Rotate shoulder pin to assure it is seated on flat surface.

2. White line must be across center of sight hole.

To adjust calibration:

1. Calibration pin is secured with Loctite.

2. Turn pin with a small pipe wrench or vise-grip pliers. Applying heat to Loctite will ease turning effort.

3. Adjust pin to center white line in siqht hole.

4. Reseal pin with Loctite No. 290 or equivalent.

NOTICE: Once gauge is recalibrated, do not intermix shoulder pins with other gauge bodies. Stamp or mark shoulder body to denote they are matched.

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.