The A-390 is a three speed synchromesh transmission. Lubricant capacity is 4 1 / 2 pints.
See Figures 1 and 2
- Remove the bolts that attach the cover to the case. Remove the cover and gasket.
- Remove the long spring that retains the detent plug in the case. Remove the detent plug with a small magnet.
- Remove the bolt and retainer securing the speedometer pinion adapter to the transmission case. Carefully work the adapter and pinion out of the extension housing.
- Remove the bolts that attach the extension housing to the transmission case. Slide the extension housing off the output shaft.
- Remove the bolts that attach the input shaft bearing retainer to the case. Slide the retainer off the shaft. Using a suitable tool, pry the seal out of the retainer. Be careful not to nick or scratch the bore in which the seal is pressed or the surface on which the seal is bottomed.
- Remove the lubricant fill plug from the right side of the case. Working through the fill plug opening, drive the roll pin out of the countershaft with a 1 / 4 " punch.
- Working with the countershaft bearing arbor and a soft faced hammer, tap the countershaft toward the front of the case with the arbor tool to remove the expansion plug from the countershaft bore at the front of the case. The countershaft is a loose fit in the case and will slide easily.
- Insert the arbor tool through the front of the case and push the countershaft out of the rear of the case so the roll pin hole in the countershaft does not travel through the roller bearings. The countershaft gear will drop to the bottom of the case. Remove the countershaft from the rear of the case.
- Place both shift levers in neutral (center) position.
- Remove the input shaft assembly and stop ring from the front of the case.
- Remove the set screw that secures the first/reverse shift fork to the shift rail. Slide the first/reverse shift rail out through the rear of the case.
- Move the second/third shift fork rearward for access to the set screw. Remove the set screw from the fork. Using a suitable tool, rotate the shift rail one quarter ( 1 / 4 ) turn.
- Lift the interlock plug from the case with a magnet.
- Tap on the inner end of the second/third shift rail to remove the expansion plug from the front of the case. Remove the shift rail through the front of the case.
- Remove the second/third shift rail detent plug and spring from the detent bore with a magnet.
- Tap the output shaft assembly rearward until the output shaft bearing clears the case. Remove both shift forks. Remove the snapring that retains the output shaft bearing to the output shaft.
- Assemble the output shaft bearing removal tool over the output shaft and bearing. Remove the output shaft bearing.
- Remove the output shaft assembly through top of the case.
- Using a suitable drift, drive the reverse idler gear shaft toward the rear, and out of the transmission case.
- Lift the reverse idler gear and thrust washer out of the case.
- Remove the countershaft gear, arbor assembly, and thrust washers from the bottom of the case.
- Remove the countershaft roll pin from the bottom of the case.
- Remove the snapring that retains the second/third synchronizer clutch gear and sleeve assembly on the output shaft. Slide the second/third synchronizer assembly off the end of the output shaft.
Do not separate the second-third synchronizer clutch gear, sleeve, struts, or spring unless inspection reveals that a replacement is necessary.
- Slide the second gear and stop ring off the output shaft.
- Remove the snapring and thrust washer retaining the first gear. Slide the first gear and stop ring off the output shaft.
- Remove the snapring that retains the first/reverse synchronizer hub on the output shaft. The first/reverse synchronizer hub is a press fit on the output shaft. To avoid damage to the synchronizer, remove the synchronizer hub using an arbor press. Do not attempt to remove or install the hub by hammering or prying.
Shift Levers and Seals
- Remove the operating levers from their respective shafts. Remove any burrs from the shafts to avoid damage to the case.
- Push the shift levers out of the transmission case. Remove and discard the O-ring seal from each shaft.
- Lubricate the new seals with transmission oil and install them on the shafts.
- Install the shift levers in the case.
- Install the operating levers and tighten the retaining nuts to 18 ft. lbs.
Input Shaft Bearing and Rollers
- Remove the snapring securing the bearing on the input shaft. Carefully press the input shaft out of the bearing with an arbor press.
- Remove the fifteen bearing rollers from the cavity in the end of the input shaft.
- Install the 15 bearing rollers in the cavity of the input shaft. Coat the rollers with a thin film of grease to retain them during installation.
- Slide the input shaft bearing over the input shaft, snapring groove away from the gear end. Seat the bearing assembly on the input shaft with an arbor press.
- Secure the bearing with the snapring. Be sure the snapring is properly seated. If a large snapring around the bearing was removed, be sure to install it at this time.
If either synchronizer is to be disassembled, mark all parts so that they will be reassembled in the same position. Do not mix parts from the two synchronizers.
- Push the synchronizer hub off each synchronizer sleeve.
- Separate the struts and springs from the hubs.
- Install the spring on the front side of the first/reverse synchronizer hub, making sure that all three strut slots are fully covered. Hang the three struts on the spring and in the slots with the wide end of the strut inside the hub.
- With the alignment marks on the hub and sleeve aligned, push the sleeve down on the hub until the struts are in the neutral detent. Place the stop ring on top of the synchronizer assembly.
- With the alignment marks on the second/third synchronizer sleeve and hub aligned, slide the sleeve on the hub. Drop in the three struts in the strut slots. Install the spring with the hump in the center, into the hollow of the strut. Turn the assembly over and install the other spring so that the hump in the center of the spring is inserted in the same strut. Place the stop ring on each end of the synchronizer assembly.
Countershaft Gear and Bearings
- Remove the countershaft bearing arbor, the roller bearings and the two bearing retainers from the countershaft gear.
- Coat the bore in each end of the countershaft gear with grease.
- Insert the countershaft arbor and install twenty five roller bearings and the retainer washer in each end of the countershaft gear.
- Position the countershaft gear and arbor assembly in the transmission case. Align the gear bore and the thrust washers with the bores in the case and install the countershaft.
- Using a feeler gauge, check the countershaft gear end-play. The end-play should be within 0.004-0.018". If the clearance is not within limits, replace the thrust washers.
- After establishing the correct end-play, install the arbor tool in the countershaft gear and lower the gear and tool out of the bottom of the transmission case.
- Coat the countershaft gear thrust surfaces in the case with a thin film of grease and position the two thrust washers in place. Place the countershaft gear and arbor assembly in the proper position in the bottom of the transmission case. The countershaft gear will remain in the bottom of the case until the output and input shafts are installed.
- Coat the reverse idler gear thrust surfaces in the case with a thin film of grease and position the two thrust washers in place. Install the reverse idler gear in the case and align the gear bore with the thrust washers in the case bore. Install the reverse idler shaft.
- Measure the reverse idler gear end-play with a feeler gauge. End-play should be 0.004-0.018". If the clearance is not within limits, replace the thrust washers. If the end-play is correct, leave the reverse idler gear in place.
- Lubricate the output shaft splines and the machined surfaces with transmission oil.
- Slide the first reverse synchronizer onto the output shaft with the fork groove toward the front. The first/reverse synchronizer hub is a press fit on the output shaft. To eliminate the possibility of damage to the hub, install the hub using an arbor press.
Do not attempt to install the hub by hammering or driving.
- Secure the hub on the output shaft with the snapring. Slide the first gear and stop ring onto the output shaft, aligning the slots in the stop ring with the struts. Install the thrust washer and snapring.
- Slide the second gear and stop ring on the output shaft.
- Install the second/third synchronizer assembly on the output shaft. Rotate the second gear to index the struts with the slots in the stop ring. Secure the synchronizer with a snapring.
- Position the output shaft assembly in the transmission case. Place the transmission in a vertical position with the front of the case flat on the work bench. Place a 1 1 / 4 " block of wood under the end of the output shaft. The block of wood will hold the output shaft assembly up during installation of the output shaft bearing.
- Install the large snapring on the output shaft bearing. Place the bearing on the output shaft with the large snapring up. Drive the bearing on the shaft until it is seated on the shaft. Secure the bearing on the output shaft with the snapring. Return the transmission to a horizontal position.
- Insert both shift forks in the case and in their proper sleeves. Push the output shaft assembly into position and tap it forward until the output shaft bearing is seated in the transmission case.
- Install the shortest detent spring followed by a detent plug into the case. Place the second/third synchronizer assembly in the second gear position.
- Align the second/third shift fork and install the second/third shift rail. The second/third shift rail is the shortest of the two shift rails. It will be necessary to depress the detent plug to enter the shift rail in the bore. Move the rail inward until the detent plug engages the forward notch (second gear position).
- Secure the fork to the rail with the set screw. Move the synchronizer to the neutral position.
- Install a new expansion plug in the transmission case.
- Install the interlock plug in the transmission case with a magnet. If the second/third shift rail is in the neutral position, the top of the interlock plug will be slightly lower than the surface of the first/reverse shift rail bore.
- Align the first/reverse fork and install the first/reverse shift rail. Move the rail inward until the center notch (neutral) is aligned with the detent bore. Secure the fork to the rail with the set screw.
- Using a suitable tool, install a new oil seal in the input shaft bearing retainer bore.
- Coat the bore of the input shaft gear with a thin film of grease.
A thick, heavy grease will plug the lubricant holes and prevent lubrication of the roller bearings.
- Install the fifteen roller bearings in the bore. Place the stop ring, slots aligned with the struts, into the second/third synchronizer. Tap the input shaft assembly into place in the case while holding the output shaft to prevent the roller bearings from dropping.
- Roll the transmission over so that it rests on both the top edge and the shift levers. The countershaft gear will drop into place. Using a screwdriver, align the countershaft gear and thrust washers with the bore in the transmission case.
- Working from the rear of the case, slide the countershaft into position being careful to keep the countershaft in contact with the arbor to avoid dropping parts out of position. Be sure that the roll pin hole in the countershaft aligns with the roll pin hole in the case.
- Install the roll pin. Install a new expansion plug in the countershaft bore at the front of the case. Install the plug flush or below the face of the case to prevent interference with the clutch housing.
- Slide the extension housing, with a new gasket, over the output shaft and against the case. Coat the attaching bolt threads with a sealing compound. Install and tighten the attaching bolts to 50 ft. lbs.
- Install the input shaft bearing retainer and a new gasket. Make sure that the oil return slot is at the bottom. Coat the threads with a sealing compound, install the attaching bolts and tighten to 30 ft. lbs.
- Install the remaining detent plug into the case followed by the detent spring.
- Install the filler plug and the back-up light switch. Pour lubricant over the entire gear train while rotating the input shaft and the output shaft.
- Place the cover and a new gasket on the transmission. Coat the attaching screw threads with a sealing compound. Install and tighten the attaching screws to 22 ft. lbs.