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Discussion Starter #1 (Edited)
This is for an M2Y4 & M2U4 transmission for a Honda Prelude.

Your specs could vary so check your manual (Chapter 13)

Quite a few inspections were left out to keep it shorter; the manual will have details/images of everything.

This is not intended to be a replacement for a manual.

You are responsible for any damages you do to yourself, others, or your vehicle.

Tape the splines of the input shaft to protect it and place the transmission down on some blocks so the input shaft does not touch the floor. Mine was level with the case so I did not tape my splines.

Using an 18mm wrench remove the backup light switch

Remove speedo sensor. Replace O-Rings.

Use a 3/8 drive socket wrench to remove the sealing bolt (we will get back to this in a minute)

Remove all the transmission housing bolts with a 12mm socket 14mm for the two bolts up top

Remove these two bolts, spring, and the metal ball

Remove bolt holding reverse

Remove housing for shift assembly, remove interlock bolt, and unbend the lock tab on the 10mm bolt

Slide arm shifter out and put to the side

There are three tabs you will use to separate the housing. You are only trying to break the seal, not remove the case yet. Once the seal is broken and the case can move up and down a little go to the next step.

Go back to the sealing bolt location and separate the snap ring while you put lift the case a little so that the ring moves out of the groove.

Now you can easily separate the housing watch that sneaky snap ring so it doesn’t go back in it’s place.


With feeler gauges check the reverse shift piece pin clearance (.0xx-.0xx in) service limit (.0xx)

Using a 10mm socket remove the reverse shift fork.

You can now slide the pin and reverse gear out. I had to shift one of the synchro rings up to pull out the shaft.

Using both hands remove the input and counter shafts from the housing. It will probably require some jiggling to get them free.

You will have a washer and spring washer on the main shaft. These should be discarded and replace with new parts.

Remove the thrust shims for the main shaft. There is a metal oil guide plate under the shim for the main shaft, remove and clean it, replace if bent or dented. Also remove the oil guide and clean with brake cleaner.

Now use the bearing puller and slide hammer to remove the countershaft bearing.

And the input shaft bearing. After which you can remove the countershaft oil guide plate and clean it, replace if needed. Remove the input shaft and axle shaft seals and discard them.

You can now clean your transmission housing with brake cleaner. Clean the magnet. Paint case if you want.

After you've cleaned everything you can start the reassembly by replacing the side axle seal.

Push the input shaft oil seal back in. (make sure to put in the correct direction)

Tap the input shaft bearing in, make sure you use a drift that only contacts the outer race.
Tap the counter shaft bearing back in.

You can also put the oil guide plate back in the other half of the housing along with the snap ring and oil plate.

Shaft Break Down

Use a bearing puller to remove the main shaft bearing. Or you can press the entire assembly off like I did.

Press off all gears as an assembly and try not to drop the parts.

It helps to lay out all the gears the way it came off

Clean everything out with brake cleaner. Be sure to check the oil holes in the shaft for obstructions.

Inspect synchro rings and inside parts of the synchro sleeve for abnormal wear.

Reassemble gears in order. Make sure you line up the notch of the synchro to the hub. Also note the direction the "U" in the hub is facing. The main shafts bearing should have the words facing up and taper side facing the gears and stop.

Press the hub on to the shaft

There is a partially cut tooth in the synchro sleeve that must line up to that "U" in the synchro hub. Once that's on slide the other synchro then the next gear on.

Don't forget to put the 5th gear synchro sleeve back and that black ring with a lip before pressing on the main shaft bearing.

On the other shaft remove the lock nut and spring washer, they need to be replaced.

Use a gear puller to pull the countershaft bearing off or press it all off as an assembly

You should replace these friction dampers while you're here. (fathergoat’s image)

Put everything back together as you took it off.

After which replace the spring washer and nut, tighten to 80lb-ft and stake it.

Take both assembled shafts and place back into transmission as once piece with the arms. It will be a little hard but must be done this way.

Put the reverse shaft in then the idler gear.

The reverse fork is next. 11lb-ft

Line up the black ring with the case, install case, snap the ring and install a couple of bolts tightened to specs.

Install shift arm and selector

Check that all gears shift easily.

Remove case again and go to next step


Smear Hondabond all around where the housing halves will contact including where bolts insert.

Expand the snap ring when you put the two halves together.

Put the brackets back on but don't tighten the bolts.

Torque to 35lb-ft in this order. Some require less than 35lbs-ft. Check Manual

Honda Bond the sealing bolt and torque to 18lb-ft.

Install the passengers side axle oil seal if not already done. I added a little Honda bond on the outside of the seal before installing.

Reverse sensor.

Install shift arm, bend/stake the tab on to the 10mm bolt, smear Honda Bond and install cover. Tighten the four bolts to specs.

That's about it. Don't forget to REP and Post up pictures!
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