Servicing - A/t GMC Vandura I

SERVICE INTERVALS

Check transmission fluid level in Truck and Van models at each engine oil change. Change transmission fluid and filter at 100,000 mile intervals on vehicles in normal use. On all models, if vehicle is used in severe service conditions (commercial use, trailer pulling, constant stop and go city traffic), change fluid and filter every 15,000 miles. Adjust intermediate (front) band of THM 250C transmission every 60,000 miles, or as required.

CHECKING FLUID LEVEL

Bring engine and transmission to normal operating temperature. With vehicle parked on a level surface and engine at idle, move selector lever through all positions, ending in "P". Remove dipstick, wipe clean and check fluid level. Fluid level should be between "ADD 1 PINT" ("ADD") and "FULL" marks on dipstick.

If vehicle has been operated for an extended period of time at high speed, in city traffic, or pulling a trailer, and accurate fluid level cannot be immediately determined. Transmission must cool for about 30 minutes after vehicle is parked, before fluid level is checked.

RECOMMENDED FLUID

Use only Dexron or Dexron-II automatic transmission fluid (or equivalent).

FLUID CAPACITY

Note. Quantities listed below are approximate, and correct fluid level should be determined by mark on dipstick, rather than by amount added. DO NOT overfill.

TRANSMISSION REFILL CAPACITIES

DRAINING & REFILLING

1. Loosen transmission oil pan bolts. Pry pan loose carefully with screwdriver, allowing fluid to drain. Remove oil pan, gasket and filter or filter screen.
2. Thoroughly clean pan and screen with solvent and dry with compressed air. Paper type filters should be replaced. Use new pan gasket and install pan. Add proper amount of fluid to transmission through filler tube and start engine with selector in "PARK" position with parking brake set. Check fluid and add as required. See CHECKING FLUID LEVEL.

Scheme 89

Scheme 90

1. Remove cruise control rod (if equipped). Disconnect detent cable terminal from throttle assembly. Loosen lock nut on pump rod and shorten several turns. Rotate lever assembly to full throttle position and hold.
2. Lengthen pump rod until injection pump lever contacts full throttle stop. Release lever and tighten pump rod lock nut.
3. Remove pump rod from lever assembly. Reconnect detent cable terminal to throttle assembly. Depress and hold metal tab on cable upper end. Move slider through fitting in direction away from lever assembly until slider stops against fitting.
4. Release tab and rotate lever assembly to full throttle stop. Release lever. Reconnect pump rod. If equipped with cruise control, reconnect rod and adjust servo rod to minimum slack, then install clip in first free hole closest to bellcrank, but within servo ball. (Scheme 89): Self-Adjusting Detent Cable Press tab to move slider in correct direction. (Scheme 90): Throttle Valve (TV) Cable Adjustment 200C and 700-R4 transmissions only.

Gasoline Models

1. Depress metal lock tab on adjuster and hold. Move slider back through fitting away from carburetor lever until slider stops at fitting.
2. Release lock tab, and on all models, open carburetor lever to full throttle stop to automatically adjust slider to correct setting.

THM 400 Only

With engine off, push detent switch plunger as far forward as possible. This presets switch for adjustment. Depress accelerator pedal to wide open position. Switch will self adjust. Operation of detent switch circuit can be checked by connecting a test lamp across switch terminals.

VACUUM REGULATOR VALVE

Vacuum is regulated at idle and during heavy loads by a vacuum regulator valve. Valve is mounted to diesel fuel pump and can be identified by 2 vacuum ports extending from valve chamber.

Diagnosis & Testing

1. Loosely assemble throttle position switch to fuel injection pump with throttle lever in closed position. Attach a continuity meter across terminals (light duty vehicles IGN Pink and EGR Yellow).
2. Insert proper "switch-closed" gauge block between gauge boss on injection pump and wide open stop screw on throttle shaft. Rotate and hold throttle lever against gauge block.
3. Rotate throttle switch clockwise (facing throttle switch) until continuity pivot occurs (high meter reading) across terminals. Hold switch body at this position and tighten mounting bolts to 4-5 ft. lbs. (5-7 N.m.). NOTE: Switch point must be set only while rotating switch body in clockwise direction.
4. Release throttle lever and allow it to return to idle position. Remove "switch-closed" gauge block and insert "switch-open"gauge block. There should be no continuity across terminals.
5. In no continuity exists, switch is set properly. However, if there is continuity, then switch mist be reset by returning to step 1) and repeating entire procedure.

"C", "K" & "G" Model Trucks & Vans

1. Make sure shift tube and lever assembly are free in steering column. Disconnect shift lever rod from swivel at lower column lever. Move transmission lever clockwise to stop, then counterclockwise 2 detents. This is neutral position. Place selector lever in neutral. Locate position using mechanical stops, NOT indicator pointer.
2. Slide swivel and clamp onto shift lever rod. Install grommets, washers and nut (as needed) but do not tighten nut. Hold lower column lever against neutral stop on park side. Tighten swivel nut to 20 ft. lbs. (27 N.m.).

"S" Model Trucks

1. Make sure shift tube and lever are free in steering column. To adjust linkage, remove screw and spring washer from swivel. Turn transmission lever clockwise to stop, then counterclockwise 2 detents. This is neutral position.
2. Place selector lever in neutral. Locate proper position using mechanical stops, NOT indicator pointer. Hold swivel against shift lever, install spring washer and screw and tighten finger tight. Avoid applying force in either direction (along shift rod or lever) while tightening screw to 20 ft. lbs. (27 N.m.).

Trucks & Vans with Column Mounted Switch

1. Place gearshift selector lever in neutral position and loosen switch attaching screws. Rotate switch on column until a .095" (2.5 mm) gauge pin can be inserted into switch gauge hole to a depth of .4" (10 mm).
2. Tighten switch attaching screws and remove gauge pin. Check for engine starting in neutral and park only.

Trucks & Vans with Transmission Mounted Switch

1. Raise and support vehicle and loosen switch mounting bolts. Align hole in switch lever with hole in switch assembly. Insert a .095" (2.5 mm) gauge pin through switch holes to hold switch in neutral position.
2. With selector lever on transmission in neutral detent position tighten switch mounting bolts and remove gauge pin. Lower vehicle and check operation of switch.