Servicing - A/t GMC Pickup R3500

Transmission

Check transmission fluid level at each engine oil change. Change transmission fluid and filter at 100,000 mile intervals on vehicles in normal use. 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.

Transfer Case

Check transfer case lubricant at every oil change or every 12 months. Under severe conditions check more frequently.

CHECKING FLUID LEVEL

Note. One pint of fluid will raise level from "ADD 1 PT." ("ADD") mark to "FULL" mark on dipstick in a hot transmission. DO NOT overfill.

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, an accurate fluid level cannot be immediately determined. Transmission must cool for about 30 minutes after vehicle is parked, before fluid level is checked.

Remove fill plug. Check oil level. If level is not up to fill plug opening, add lubricant until it is.

RECOMMENDED FLUID

Both transmissions and transfer cases use DEXRON-II ATF.

The transmission refill capacities given below are approximate. Correct fluid level should always be determined by marks on dipstick, rather than by amount of fluid added. DO NOT overfill transmission.

TRANSMISSION REFILL CAPACITIES

TRANSFER CASE REFILL CAPACITIES

Loosen transmission oil pan bolts. Pry pan loose with a large screwdriver and allow fluid to drain. Remove oil pan, gasket and filter or filter screen. Replace paper element filter (if used). Clean filter screen and pan with solvent and blow dry with compressed air. Install oil pan with new gasket. Add fluid to proper mark on dipstick.

Remove drain plug from transfer case. Remove fill plug for easier draining. With fluid fully drained, reinstall drain plug. Fill transfer case to fill plug opening with Dexron II.

Scheme 61

1. Remove cruise control rod (if equipped). Disconnect detent cable terminal from throttle assembly. Loosen lock nut on pump rod and back off several turns. Rotate throttle lever assembly (at valve body) to full open position and hold.
2. Lengthen pump rod until injection pump lever contacts full throttle stop. Release throttle 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 adjusting tab on cable adjuster. Move slider through fitting, away from throttle lever, until slider stops against fitting. Release tab.
4. Rotate lever assembly to full throttle position and release. Reconnect pump rod. If equipped with cruise control, reconnect rod and adjust servo throttle rod to minimum slack with engine off. Install clip in free hole nearest to bellcrank and within servo bail.

Gasoline Engines

Depress metal lock tab on adjuster and hold. Move slider back through fitting away from throttle body lever until slider stops at fitting. Release lock tab and open throttle body lever to full throttle stop. This automatically adjusts 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.

With Electrical Control

1. Loosely assemble throttle position switch to fuel injection pump with throttle lever in closed position. Attach an ohmmeter across terminals IGN (Pink wire) and EGR (Yellow wire).
2. Insert "switch-closed" .624" (15.8 mm) Gauge Bar for Emission Label Code YJH or .646" (16.4 mm) Gauge Bar (J-33043) for all other models, between gauge boss on 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 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 bar and insert "switch-open" .646" (16.4 mm) Gauge Bar (J-33043) for Emission Label Code (YJH) or .668" (16.9 mm) Gauge Bar for all other models. If no continuity exists, switch is set properly. If continuity exists, switch must be reset or replaced.

With Vacuum Regulator Valve (VRV)

1. Loosen VRV-to-injection pump bolts enough to allow for regulator valve rotation. Attach vacuum pump to bottom vacuum port of valve (vacuum gauge to top port).
2. Insert .646" (16.4 mm) Gauge Bar (J-33043) between gauge boss on injection pump and wide open stop screw on throttle lever. Rotate throttle shaft against bar.
3. Apply 18-21 in. Hg vacuum to VRV. Slowly rotate VRV body clockwise (facing valve) until vacuum gauge reads 7-9 in. Hg. Hold valve body in this position and tighten mounting screws. NOTE: Valve MUST be set while rotating in a clockwise direction.
4. Check adjustment by allowing throttle shaft to return to idle position, then rotate shaft back against gauge bar. If vacuum gauge reading is not 7-9 in. Hg, re-adjust valve.

Astro, Safari, "S" & "T" Models

1. Ensure 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 "N". 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).

All Other Models

1. Ensure 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 "N". 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).

With Column Mounted Switch

1. Place gearshift selector lever in "N" 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 "N" and "P" only.

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 "N" position.
2. With selector lever on transmission in "N" detent position, tighten switch mounting bolts and remove gauge pin. Lower vehicle and check operation of switch.

S10, S15, S/T Blazer & S/T Jimmy 4WD Transfer Case Vacuum Diagram. Scheme 62