MANUAL TRANS DIAG./EXCHANGE PROCEDURE (REPLACEMENT). GMC Truck GMC C Pickup

TRANSMISSION APPLICATIONS: MANUAL TRANSMISSION

TRANSMISSION MODELS:

SUBJECT: DIAGNOSTIC AND EXCHANGE PROCEDURE (SERV. INFO)

VEHICLE APPLICATIONS: 91-92 C2, C3, K2, K3, P3 TRUCKS W/MANUAL TRANS. RPO MT8

THIS BULLETIN COVERS:

Preliminary diagnosis and exchange procedure for the NV4500 manual transmission.

In order to provide needed product feedback, and until further notice ANY NV4500 manual transmission requiring warranty repair will be exchanged for a replacement unit.

IMPORTANT: Customer pay units requiring repair should be serviced using complete assemblies available through CANSPO.

SERVICE INFORMATION:

* Transmission Identification Information:

- The identification tag is located on the driver's side PTO cover and the serial number is located on a bar code label on top of the shift cover, refer to Figure 1.

* This transmission incorporates the following unique operating features which should not be mistaken for a transmission problem.

- Low and 1st gear overspeed downshift inhibitors. This feature prevents overspeed damage to drivetrain components by mechanically blocking high RPM 2-1 or 1-Low downshifts. Attempted downshifts into 1st when 2nd gear engine speeds are above 3000-3200 RPM or into Low when 1st gear engine speeds are above 3600-3800 RPM will be prevented.

- Overdrive to reverse inhibitor. This feature prevents shifting the transmission directly from overdrive into reverse. If an overdrive to reverse shift is desired it will be necessary to first move the shift lever to the "2-3" position of neutral and then into reverse.

Preliminary Diagnosis Procedure;

- Ensure correct oil level. Transmission capacity is 3.78L (4 qts).

IMPORTANT: This transmission requires a special synthetic lubricant P/N 12345871. Do NOT substitute any other lubricant as internal transmission damage may occur. - Ensure clutch operation is normal, refer to Figure 2 - Ensure that all engine and transmission mounts are tight.

* On-Vehicle Warranty Service Procedures (Transmission Removal Not Required): - Resealing of the PTO cover. - Replacement of the extension housing oil seal. - Replacement of the speed sensor. - Replacement of the back-up lamp switch assembly.

* Service Manual Reference: - Refer to section 7B of the 1991 C/K Service Manual.

SERVICE ACTION:

* While this exchange program is in effect, Technical Assistance should be contacted ANYTIME a problem is encountered with a NV4500.

* Exchange transmissions must NOT be disassembled and exchange units must be returned with the stub lever intact.

EXCHANGE PROCEDURE:

1. Reference Figure 3 and have information available before calling. It is necessary to record this information as the form will be returned with the transmission. (Blank forms will be shipped with exchange unit). Record the the unit serial number from the bar code label located on top of the shift cover.

2. Call GMC Technical Assistance (TAC) with all the information necessary for a case. If an exchange is determined necessary, a transmission will be shipped. Replacement transmission will be shipped filled with fluid.

3. When the exchange unit is received, the replaced unit is to be returned within 10 days to avoid a chargeback. The T.A.C. number must be written on the transmission case in black marker before its return. If the case is excessively greasy, write the T.A.C. case number on a tag and attach it to the case with wire. A return shipping label will be sent with the exchange unit.

4. The replaced unit MUST be returned complete as removed from vehicle without any disassembly of the unit. Dealerships returning units even partially disassembled will be subject to billing for materials furnished.

5. The exchange unit will have a plastic bag attached to it. This bag will contain: * Reporting form (Figure 3) * Instruction sheet (Figure 4) * Return shipping label * Return shipping carrier information

PREPARATION FOR SHIPPING:

1. Drain all oil from unit.

2. Remove all plastic shipping plugs and covers from the replacement unit and install them on the replaced unit.

3. Place the report form and a copy of the repair order in the enclosed plastic bag and attach the bag to the complaint unit.

4. Write the T.A.C. case number on the Case of the complaint unit.

5. Repack the replaced unit into the original shipping container.

6. Place the shipping label on the original shipping container.

SERVICE PARTS INFORMATION:

Part Number Description

12345871 Fluid, Manual Transmission (1 gallon)

DIAGNOSIS OF THE CLUTCH ======================== PROBLEM ------- Fails To Release (Pedal Pressed To Floor - Shift Lever Does Not Move Freely in And out of Reverse Gear Without Gear Clash

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Improper pedal travel. 1. Check for floor mat under pedal or misassembled bump stop. 2. Bent clutch pedal. 2. Replace pedal. 3. Faulty driven disc 3. Replace disc. 4. Fork and bearing not 4. Install properly and very lightly assembled properly. lubricate fingers at release bearing with wheel bearing grease. 5. Clutch disc hub binding on 5. Replace or repair. input shaft splines. 6. Clutch disc warped or bent. 6. Replace disc. 7. Clutch-to-flywheel bolts loose. 7. Torque bolts to spec. 8. Air in hydraulic system. 8. Bleed air from system. --------------------------------------------------------------------------- PROBLEM ------- Slipping

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Improper operation. 1. Correct as required. 2. Oil soaked driven disc. 2. Install new disc and correct leak at source. 3. Worn facing or facing torn 3. Replace disc. from disc 4. Warped pressure plate or flywheel. 4. Replace pressure plate or flywheel. 5. Weak diaphragm spring. 5. Replace pressure plate. 6. Driven plate not seated in. 6. Make 30 to 40 normal starts. CAUTION: Do Not Overheat. 7. Driven plate overheated. 7. Allow to cool. --------------------------------------------------------------------------- PROBLEM -------- Grabbing (Chattering)

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Oil on facing. Burned or 1. Install new disc and correct leak glazed facings. AT engine or transmission. 2. Worn splines on input shaft. 2. Replace input shaft. 3. Warped pressure plate or 3. Replace pressure plate or flywheel. flywheel. 4. Burned or smeared resin on 4. Sand off if superficial. Replace flywheel or pressure plate. burned or heat checked parts. ---------------------------------------------------------------------------- PROBLEM -------- Rattling - Transmission Click

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Release fork loose. 1. install properly. 2. Oil in driven plate damper 2 Replace driven disc. 3. Driven disc damper spring failure. 3. Replace driven disc. 4. Low engine idle speed. 4. Adjust idle speed. 5. Broken return spring in slave 5. Replace hydraulic system. cylinder. ----------------------------------------------------------------------------- PROBLEM -------- Release Bearing Noise With Clutch Fully Engaged

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Improper operation. 1. Correct as required. 2. Release bearing binding. 2 Clean, relubricate, check for burrs, nicks, etc. 3. Fork shaft improperly installed. 3. Install properly. 4. Faulty bearing. 4. Replace bearing. ----------------------------------------------------------------------------- PROBLEM ------- Noisy

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Worn release bearing. 1. Replace bearing. 2 Fork improperly installed. 2. Install properly and lubricate fork fingers at bearing. ----------------------------------------------------------------------------- PROBLEM ------- Pedal Stays On Floor

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Bind in linkage or release 1. Lubricate and free-up linkage and bearing. release bearing. 2. Fork binds in housing. 2. Free-up fork and lubricate. ---------------------------------------------------------------------------- PROBLEM -------- Hard Pedal Effort

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Driven plate worn. 1. Replace driven plate. 2. Fork binds in housing. 2. Free-up fork and lubricate. 3. Worn pedal bushings. 3. Replace bushings. ----------------------------------------------------------------------------- PROBLEM --------- Pedal Travels To Floor. No Pressure Or Very Little Resistance.

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Master or slave cylinder faulty. 1. Check components and replace. 2. Hose/pipe burst or leaking. Then bleed system. 3. No fluid in reservoir. ----------------------------------------------------------------------------- PROBLEM --------- Pedal Travels To Floor. No Pressure Or Very Little Resistance. Fluid In Master Cylinder Dust Cover.

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Rear seal failure in 1. Service or replace unit. Then master cylinder. bleed system. ----------------------------------------------------------------------------- PROBLEM --------- Pedal Travels To Floor. No Pressure Or Very Little Resistance. Fluid Level In Reservoir Rises As Pedal is Depressed.

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Master cylinder center valve 1. Service or replace unit. Then seal faulty. bleed system. ----------------------------------------------------------------------------- PROBLEM ------- Fluid in Area Of Master Cylinder Dust Cover And On Pedal

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Slave cylinder plunger 1. Service or replace unit. Then seal faulty. bleed system. ----------------------------------------------------------------------------- PROBLEM --------- Pedal Feels "Spongy" When Depressed

POSSIBLE CAUSES CORRECTION --------------- --------------------------------- 1. Air in system. 1. Check fluid level. Bleed system. Check and replace parts if symptom reoccurs. ----------------------------------------------------------------------------- PROBLEM -------- Pedal Effort High With Long Pedal Travel

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Incorrect size master 1. Check and fit correct unit. Then cylinder fitted. bleed system. ----------------------------------------------------------------------------- PROBLEM -------- Unable To Select Gears. Pedal Effort And Travel Normal.

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Clutch mechanism faulty. 1. Check and repair clutch. 2. Gearbox faulty. 2 Check and repair gearbox. ----------------------------------------------------------------------------- PROBLEM ------- Clutch Slip

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Clutch plate worn. 1. Check and replace. 2. Master and/or slave cylinder 2. Clean and service or replace unit. seal worn or damaged. 3. Overfilled reservoir. 3. Remove excess fluid. ----------------------------------------------------------------------------- PROBLEM -------- Pedal Effort And Travel Normal. Difficulty In Selecting Gears.

POSSIBLE CAUSES CORRECTION --------------- ---------------------------------- 1. Clutch or gearbox mechanism 1. Check and replace faulty or worn faulty. components. 2. Wear in clevis linkages.

Object Number: 78969 Size: FS

Object Number: 85273 Size: FS

Object Number: 85272 Size: FS

Object Number: 96396 Size: FS

Object Number: 96395 Size: FS

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.