BURNED 2-4 BAND/3-4 CLUTCH SHIFT SLIPPING THM 700-R4

MODELS: LIGHT DUTY WITH THM 700-R4 TRANSMISSION

The following diagnosis procedure is for a burned 2-4 band and/or a burned 3-4 clutch. The probable customer comment for these conditions would be (1) slipping 1-2 shift or no 1-2 shift and/or (2) slipping 2-3 shift or no 2-3 shift. This procedure is a general guide, and you will need to refer to your service manual for additional information if questions arise.

SERVICE PROCEDURE

1. Verify the condition as follows:

a) Check and correct the oil level.

b) Check the T.V. cable for sticking or binding. Adjust the T.V. cable.

c) Road test the vehicle at normal operating temperature and check oil pressure.

2. For conditions of high or low oil pressure, refer to the service manual for proper diagnosis.

3. As a diagnosis aid, you can check the oil pressure differential between line pressure and the 2nd, 3rd, or 4th clutch. If the pressure differential between line and any of these clutch circuits is more than 10 psi (assuuming your oil pressure gages are accurate), there is a possible oil leak in that clutch oil circuit.

I. DIAGNOSIS PROCEDURE FOR A SLIPPING 1-2 OR NO 1-2 SHIFT

Step 1. After verifying the condition, remove and disassemble the 2-4 servo cover and piston assembly. Check the following.

a) Proper servo pin length

b) Damaged or worn seals; Replace if necessary.

c) Porosity, nicks, burrs, sharp edges, or ring groove damage in the pistons, cover, servo pin or servo bore.

d) Blocked servo exhaust hole. See Figure No. 1.

e) Blocked or missing orifice cup plug in the case servo bore.

Step 2. Reassemble and install the 2-4 servo piston and cover.

Step 3. Remove and inspect the governor assembly and cover.

a) Governor assembly - damaged gear teeth, scored sleeve, stuck or sticking valve, missing springs, and sticking or damaged weights.

b) Case governor bore - scoring, damage, or governor support pin off location, loose, or missing.

Step 4. Install the governor assembly and cover.

Step 5. Road test the vehicle. If the vehide operates satisfactorily stop here, if not, continue.

Step 6. Remove the oil pan and oil filter.

a) Remove the 1-2 accumulator cover and pin assembly, 1-2 accumulator spring, and the 1-2 accumulator piston. Inspect for porosity, nicks, damaged ring grooves, cut seals or broken spring.

b) Remove the solenoid and "O" ring assembly.

c) Remove the T.V. lever and bracket assembly. Inspect both the T.V. cable and the T.V. lever and bracket assembly for sticking or binding.

d) Remove the valve body assembly and check the following valves for freeness: T.V. limit valve, accumulator valve, line bias valve, throttle valve, 3-4 relay valve, 1-2 shift valve, 1-2 T.V. valve, modulated T.V. up valve, modulated T.V. down valve. Disassemble and clean the valve body assembly or replace as necessary.

e) Remove the oil passage cover plate, the spacer plate and gaskets, and the checkballs.

f) Inspect both the case and the valve body faces for nicks, damage, or out of flat faces.

g) Be certain the band anchor plug is installed.

h) Check the oil filter for small cracks, plugged screen, flash plugging filter neck, or cut "O" ring.

i) Check for plugged governor filters.

j) Reassemble the transmission. Be certain all checkballs are properly installed and bolt torque are correct.

Step 7. Road test the vehicle. If the condition is corrected, stop here. if not, continue.

Step 8. Following the service manual procedure, remove the transmission from the vehicle, disassemble, and inspect. Pay careful attention to the following items:

a) Inspect the oil pump assembly for stuck or sticking pressure regulator valve; loose, mislocated, or missing stator shaft sleeve and scored or damaged bearing journals.

b) Inspect the reverse input housing for scored or damaged bushings. Also, check the clutch housing outer diameter for scoring, damage or dishing. See Figure No. 2

c) Inspect the turbine shaft seal rings for cuts, nicks, or damage. Make sure the rings are free in the ring grooves.

d) Check the lip seals on the forward, overrun, and 3-4 clutch pistons for cuts or damage.

e) Check the forward clutch "O" ring seal on the input housing hub for cuts, nicks or damage.

f) Check the forward, overrun, and 3-4 clutch piston for porosity or damage.

g) Inspect the forward, overrun, and 3-4 clutch checkballs for sticking or leaking conditions.

h) Inspect the reaction sun gear shell and reaction sun gear for damaged tangs, stripped splines, broken hub, or scored bushings.

i) Inspect the reaction carrier for damaged pinion teeth.

j) Inspect the 2-4 band assembly for wear or damage.

Step 9. Reassemble the transmission. Replace any worn or damaged parts as necessary. Recheck the 2-4 servo pin length and be certain clutch pack and transmission end plays are correct.

Step 10. Install the transmission into the vehicle amd road test.

II. For a coondition of slipping 2-3 or no. 2-3 shift or a combination of that and the condition diagnosed in section I, follow the diagnosis procedure in section I except as follows:

1. During step 6, also check the following:

a) Check the valve body assembly to be certain the following valves are free: 3-2 control valve, 3-4 relay valve, 2-3 shift valve, 2-3 T.V. valve.

b) Check the 3-4 accumulator piston and case bore for porosity, nicks, burrs, damaged ring grooves, or cut seal.

2. During step 8, also check the following:

a) Be certain the three sealing balls are in the turbine shaft and they are not loose.

b) If after checking all other possibilities you find no apparent cause for the condition you are diagnosing, replace both the input housing and shaft assembly and the 3rd accumulator re tainer and ball assembly (part number 8634400).

IMPORTANT: After installing the 3rd accumulator retainer and ball assembly, leak check it as follows:

Install the 2-4 servo piston assembly and cover.

Pour solvent into the 3rd accumulator bore at the case oil passages. See Figure No. 3. Watch inside the case for leakage.

3. Reassemble the transmission. Replace any worn or damaged parts as necessary. Recheck the 2-4 servo pin length and be certain the clutch pack and transmission end plays are correct.

4. Install the transmission into the vehicle and road test.

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.