Transmission Installation
 

04 S 6 speed

This has been the toughest task yet with the whole engine rebuild, what a PITA! 3 days 4 tries (2 - 3 hrs each try) and finally last night on the 4th try it slid in.
Each try I couldn't get the transmission closer than 1.25 inches, engine flange to transmission flange. The distance was even, 1.25", all the way around the flange but wouldn't slide in, so I descided to take the pressure plate and clutch plate off and re-align with the centering tool.
Since I had the clutch assembly off I tried installing the transmission onto the flywheel and pilot bearing. After a small bit of adjustment the 2 flanges came together nice and tight so I now knew that it would fit. I marked the transmission jack and took measurements, again, around the transmission so I could duplicate a successful insertion when I attached the clutch assembly again.
This method of fitting without the clutch assembly was definitley a help but for the final assembly I still had to tweak the jack (about 1/8") and turn the crank to align the splines and it finally slid in!
I'm glad thats behind me.

With the engine already in the car is there any easier method?

I had the same issue, first time it went in like butter in 2 minutes or less. Second time spent 2 to 3 hours wrestling it, had to walk away. Next morning after good night's sleep it went right in, they can be persnickety about it.

The engine was in the car.

The common problem with reinstalling the gearbox is making sure it is properly aligned with the engine. While hard to see on the ground, the front of the gearbox bell housing has to be parallel to the rear of the engine on both axis, if it is just slightly off it is going to give you a hard time.

I measured continuously the 2 flanges, thinking I was parallel all the way around but obviously now it has to be exact. I even lightly installed 4 of the transmission bolts to use as guides but that didn't really make a difference.
What about the splines of the shafts, are they self aligning or must the installer turn the engine crank hoping he'll turn the spline to the correct alignment?

Coreseller, it was because of your earlier posting with this transmission experience I limited myself to the 2-3 hr period, then walk away. I didn't want to allow my steam to rise to high and ultimately ruin something. Thanks for the heads up on this job.
Damn I'm glad its behind me!

They are not self aligning.

Glad to hear it. JFP is right about exact alignment, it's just tough to tell how exact it is while you're on your back sweating and cussing. :cheers:

I used a prybar through the gap between engine and trans to adjust the flywheel position by pushing on the teeth. I think you might be able to attach a wheel and axle and turn the wheel a little to adjust the angular position of the input splines until it slides on.

Does having the transmission in neutral matter? I'd assume so.

The old trick in the Miata world is to put the driveshaft in the tranny output, put the tranny in gear, and turn the output shaft to make the input shaft rotate.

This is more difficult in the Boxster because of the internal diff. If you spin just one output flange, the other one counter-rotates without spinning the tranny. A long bolt in one output flange to contact with the case prevents this from happening, so you have one hand to spin the other flange and a free hand to push on the transaxle.