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How to Remove the Transmission &
Replace the Rear Main Seal
1990-1994 Lexus LS400

By Andy Vogel

Before doing anything read my disclaimer & safety info.



Please direct any questions and feedback regarding this tutorial to Andy, not LexLS.

The day after I bought my beloved '93 LS I put it on a car lift and discovered some engine oil as you can see on the picture. Diagnosis: leaking rear main seal. I was a bit naive and thought "a Lexus never breaks...," so I didn't put the car on a lift *before* buying it. I hope you don't make the same mistake! The rear main seal itself isn't very expensive, but changing it means removing the transmission. This costs about $1000-1500, so I decided to do it myself with the help of an experienced friend. It took me altogether about 20 (!) hours, so it's a big job. But afterwards you feel quite proude ;o)

1) Disconnect the negative battery terminal.

2) Remove the front exhaust pipe & catalytic converters. Also remove the steering damper,
torque = 20 ft-lb (26 Nm).

3) Remove the driveshaft.

4) Remove the transmission dip stick & Drain ATF. Just drain the fluid, you don't need to remove the pan.

5) Remove the shift control rod, as seen on the right side on this picture.

6) Remove the front attachment as seen here.

7) Remove the oil filler tubes. You should use a special open end wrench, a damaged nut in this case is no fun. The oil tubes leading forward are attached at two points, remove these attachments and it'll be easier.

8) Remove the 4 bolts and the exhaust pipe support bracket. Torque = 32 ft-lb (43 Nm). On the picture you can see the leaking oil.

9) Search for the Transmission oil filler tube, unscrew it and remove it. Remove the two additional heat shields on both sides.

10) Remove the TRAC cover. Disconnect the throttle cable.

11) Follow the throttle cable to the rear side of the engine. Release the several attachments, don't break the clamps.

12a) Unplug the five electrical connectors to the transmission (connector 1 shown). Connectors are designed to stay connected, don't swear too much while trying to disconnect them. Search for the 5 clamps retaining the cables to the transmission housing, open them carefully.

12b) Connector 2

12c) Connector 3, 4

12d) Connector 5

13) Remove the engine under cover.

14) Support the transmission. We did it as shown above. Looks funny, but it worked perfectly :o)

15) Unscrew the 4 rear transmission mounting plate bolts. Torque = 19 ft-lb (25 Nm).

16) Here it's getting a bit complicated, so I couldn't take pictures. Lower the transmission while checking the rear clearance of the engine to the engine bay. Don't lower it too far! Using 3 (!) long 1/2 inch extensions, you're able to reach and unscrew the upper bolts of the transmission. There are 10 of them. Now you can pull the transmission backwards, and it's off!

17) Next thing is to remove the six torque converter bolts. Torque = 25 ft-lb (33 Nm). Remove the two bolts of the converter cover. Mark the position of one bolt in relation to the converter. Then turn the crankshaft by turning the lowest pulley in the front of the engine to reach the next bolt.

18) Here you can see the backside of the engine and the flywheel. Unscrew the 8 bolts as indicated. Torque = 72 ft-lb (98 Nm); apply thread lock to a few threads of the bolts when reinstalling.

19) This is the rear main seal. Check how deep it's installed, the edges should be even to the seat. Carefully pry it out, don't damage the crankshaft or the engine! Lexls note: See that elusive EGR pipe up there (upper right)! Now would be a good time to check it and replace it if it's cracked.

20) Rear main seal removed. Lube the new one with fresh engine oil. Carefully tap it back into its seat. Be very careful, I almost damaged the seal because I didn't see that the lip of the seal was flipped outwards. Grrr.

21) Front side of the transmission. I thought it would make some sense changing the transmission front seal at the same time. Using a calipers and straight edge, measure the distance as shown, from the bolt plate of the torque converter to the front of the tranny housing (back edge of the straight edge shown). The distance should be 17.1mm. Be sure to reinstall the torque converter in the same position. Pull out the torque converter, pour out the old transmission fluid.

22) Pry out the seal, install a new one. Of course don't damage the transmission while prying. Tap the new seal back in, check for correct depth. Lubricate the seal lip with new transmission fluid. It's difficult to put the torque converter back in when the transmission is in horizontal position. We put the whole transmission frontside upwards and could slide the torque converter back in. Check for the correct distance as measured before removal.

23) I decided to change the transmission mount damper too. It didn't look bad, the rubber wasn't broken and I didn't have any bad vibration. And honestly, I don't feel any change after installation, but I heard that vibration because of bad transmission mount can occur after about 100k miles.

24) Install is reverse of removal. Refer to your official shop manual for more info.

Lexls.com Notes: Thanks for all the great pictures of all these complicated procedures! Obviously, you need to pretty much have a full shop with lifts and plenty of tools to do this yourself. And you definitely need to know what you're doing!



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Last revised: Sunday, 29-Oct-2023 15:46:32 EDT