I've got 5 each first gens, 2 each 1988 sedans, 1988 coupe, 1987 coupe, 1990 coupe and my son has a 1990 coupe. That being said if memory serves me correctly the 1990 has subtle modifications to the automatic that the previous years do not have. It has to do with shift characteristics which I notice when stopped and immediately moving the shift lever between drive and 2nd gear before the transmission computer does so automatically after about 3 to 5 seconds; automatically shifting into 2nd when stopped lessens the foot pressure needed on the brake pedal. Prior to 1990 immediately shifting to 2nd when stopped causes a shift shock/bump in the drive train whereas the 1990 is subtle.

I'll hazard a guess that if you put a 1989 automatic into the 1990 you may well have to also put the 1989 transmission computer into it to make it behave properly.

 

Thanks for the insight on this matter. While the ‘89 is nearby (50 miles away) I am definitely leaning towards the road trip to Georgia from Texas now to get the closest 1990 transmission available….

 

Additionally, what do you perceive as faulty in your transmission? Of the 6 first gen Legends I've had experience with the automatics have been "bullet proof" (my son's 1990 coupe has 275+K miles). The only problem I've had has been with the "shift solenoids" of one of them due to previous owners not changing the fluid every 30K miles. The solenoids become impacted with normal steel wear metal due to them being electromagnets which move the pintle valves directing hydraulic fluid to shift the clutch packs. It evidences through delayed or prolonged shift lockup or failure to shift to the next gear.

My 1988 coupe would delay shift between 2nd & 3rd. I removed both pairs of external solenoids of which only one would "click" when energized with 12 volts. I used WD-40 with its red straw which exactly fit into the solenoid oil passages along with the butt end of a 3/16" drill bit to gently push on the pintle to loosen the wear metal which flowed out as a black residue. After I flushed the wear metal out each solenoid would "click" when energized. After re-installation the transmission worked perfectly. This MAY be your problem, and flushing the solenoids is much easier than to R&R the transmission. You will need to source 2 each figure 8 "O" rings which seal the solenoids to the transmission.

 

See that’s exactly what I needed to hear, I have taken my Coupe to a Honda Specialist and also a Transmission Chain Shop and they both said I will need a “FULL REBUILD” at $2,600. I have heard other people speak on these solenoids before but now I have a much better understanding of them and how they work. I wish I would have pulled them off of the ‘88 Coupe I had junked, I know they’re going to be a pain to find if I need to replace them. Time to break out the Chilton’s Books and study up on these parts.

Thanks Again…

 

The solenoids pairs are located on the drivers side of the transmission; as I remember you'll need to remove the air filter to gain access. They are beside each other with two bolts (memory says 10mm) holding each one. Be careful with the electrical connectors as age makes them brittle.

For a bit more information, the transmission computer controls the solenoids with one pair controlling the torque converter lockup for 2nd, 3rd & 4th gears (i.e. direct drive) while the other pair control the shifting clutches for all 4 gears. Under light throttle in Drive, if you pay close attention, you'll feel 1st shift to 2nd, then converter lockup in 2nd, then shift to 3rd, followed by lockup, then to 4th, followed by lockup; in effect you'll feel 7 each shift "shocks".

Another transmission idiosyncrasy which goes unnoticed is about 3-4 seconds after a full stop the computer shifts the transmission from 1st gear to 2nd gear so that you don't have to hold the brake pedal with as much force as you would if left in 1st gear. Upon lifting off the brake pedal, if you are aware, within a fraction of a second you'll feel a subtle shift shock/bump as the transmission computer shift from 2nd back to 1st for better acceleration.