Mating Transaxle to Engine...advice needed - 986 Forum - The Community for Porsche Boxster & Cayman Owners

hoyabob2003 · 09-11-2016, 02:52 PM

I searched and am looking for some sage advice before proceeding.

I have the transmission up on a jack , all the holes are lined up perfectly to the point where all the bolts can be inserted through the transmission case into the engine and yet the transaxle and engine cases are still 2" apart.

The question: Do I tighten the bolts to bring the engine and transaxle together or should I bring the transmission back out in a attempt to slide it in completely?

I've pulled the 2 apart several times only to wind up at the place again and again. I recall that it took a bit of force to separate the 2, and so the natural inclination is to tighten the bolts to bring the 2 together, but this inclination of mine has been wrong before.

Looking for sage advice here...

Meir · 09-11-2016, 05:04 PM

99% of the time, the problem lies in alignment between the transmission spline and the clutch friction plate. Make sure the friction plate is properly centered.
If you are using the plastic alignment tool, use also your vision to confirme it is centered. Put the transmission in gear, and turn the axle hubs a little bit at a time , while you are pushing in the transmission towards the engine.
Hope it helps.

Gelbster · 09-11-2016, 06:21 PM

We had a great discussion about this recently. The short version is - geometry.
Gently insert a 3/4" copper pipe abut 2 ft long through the clutch into the flywheel . Measure &/or adjust the angle of the tube relative to horizontal. Figure out a way to align the input shaft perfectly to the plane of the tube. Remove tube .Mate up. It is very easy to get the gearbox input shaft a few degrees misaligned left/right, up/down - because there is no leveling bubble on the engine and gearbox to guide you.
You need to fiddle with levels and bubbles to do this. I think it is worth the effort because just brutally tightening the bellhousing bolts could cause issues.
I am sure you have tried rotating the input shaft a few degrees back and forth while trying to coax the two parts together so logically it is an 'out of level' problem.
I think this is why some people remove the cross member and mate the engine and gearbox while they are both out of the car. Even then it is difficult.

hoyabob2003 · 09-11-2016, 07:07 PM

Thanks for the advice. That's a really good suggestion. I noticed that the ride height of the rear has risen substantially with the removal of the transaxle. Although the engine is very much midships, I am sure that the angle of entry for the transaxle must be different than the angle of removal, which had the transaxle relatively level relative to the ground...

thstone · 09-11-2016, 07:26 PM

Quote:

Originally Posted by hoyabob2003

The question: Do I tighten the bolts to bring the engine and transaxle together ...

No, never do this as you'll be sure to damage the housing. The trans should slide "home" without force. There is a reason why its not mating - you need to find the reason and remedy it.

Here is my experience: Transmission Re-Install Help

hoyabob2003 · 09-11-2016, 08:54 PM

Thank you. I actually read your thread - 3 times - before I posted this. I just wasn't clear how it all ended up - did you mate the housings before tightening down? Sounds like you did. This is the sage advice that I needed.

I will reposition, re-level, and take another go...and another...until I get the housings to mate completely prior to placing any bolts or tightening anything down.

I don't think I would enjoy having a 986 if it were my only car....I am thankful that I can take my sweet ass time on this one. I'll get it together when I get it together.

thstone · 09-13-2016, 03:37 PM

Quote:

Originally Posted by hoyabob2003

Thank you. I actually read your thread - 3 times - before I posted this. I just wasn't clear how it all ended up - did you mate the housings before tightening down?

Yes, when everything is aligned it will slide back together by hand with a little push - no significant force required.

If its not sliding back together, try rotating the big gear through the hole a bit to make sure that the drive shaft splines are aligned.

If that doesn't work, you'll have to do some sleuthing to figure out where its being held up at/from.

hoyabob2003 · 09-13-2016, 06:57 PM

Thanks so much for all the good advice. I re-aligned the clutch today - it might have been a little off - and will have another go at having the transaxle slide easily onto the flywheel tomorrow. I'm sure I'll get it now that I know how I should expect it to go.

Gilles · 09-13-2016, 08:53 PM

it also helps a great deal to use studs to align the transaxle to the engine, you can cut the hex head off two or three spare/old bolts (same as the ones holding the gearbox and engine together) and these will guide the transmission into the engine (you may have to rotate the engine a teeth or two), then replace the studs with the right bolts.

jcslocum · 09-12-2016, 03:45 AM

It takes a bit of finesse. The dif doesn't turn the input shaft unless you hold one hub and turn the other. Unless of course you have a limited slip. It will take same lifting and lowering to get it just right. It will also take some pushing and shoving back and forth, up and down, side to side.

Take your time and it will just slide together.

jb92563 · 09-13-2016, 11:38 AM

I just did this last week and it took a few tries, but in the end I looked at the transmission and engine flange to make sure the distance was equal all the way around and adjusted the angle of the transmission till it was.

Then it just slides in with little effort.

Using the plastic alignment tool to tighten down the clutch is crucial to the whole process.

I think I spent an hour fiddling with it to finally get it home, including lowering and repositioning the transmission on the jack to make it balance nicely on the jack so there was little effort to tilt it forward or back.

Gelbster · 09-13-2016, 12:21 PM

If you are mating the engine and transmission using a jack, I suggest using a screw-type jack. A hydraulic jack may sink imperceptibly and complicate the alignment process. I have a cheapo HF trans jack that works very well for this. item#61232
The suggestion to carefully measure the gap between the two components at the bellhousing is simple and better than the bubble level method some fool suggested earlier. "Measure-the-Gap" method ensures 360 degree alignment - not just vertical.
Important to note that this O.P. and others have had alignment/mating difficulties with the two components on the floor. Can you imagine doing this with the engine already in the car ? On jack stands ! Up at a crazy angle. What is the technique to get easy mating then?

flaps10 · 09-13-2016, 01:11 PM

I have one of those HF transmission jacks (FYI no way in hell would I load that thing to listed capacity. The lead screw struggles with the 99 pound boxster transaxle as it is.). I made a wooden cradle that picks up the fins in the bottom of the transmission to keep it from moving around.

One thing I found is that the pilot bearing in the flywheel is easily damaged by misalignment - more so than any other car I've done. Once damaged it makes slipping that pilot shaft into place that much harder.

The first time this beat me down I just stopped for the night. The next day it wiggled right in. With the HF trans jack and my wooden cradle it's a straight forward job.

Gelbster · 09-13-2016, 02:27 PM

Sorry ,I was not clear. One HF jack under the trans. The engine is on a hoist with a leveler.

Gelbster · 09-13-2016, 02:51 PM

Hi Flaps,
Thanks for yery useful comment:
"One thing I found is that the pilot bearing in the flywheel is easily damaged by misalignment - more so than any other car I've done. Once damaged it makes slipping that pilot shaft into place that much harder."
But how did you determine you had damaged it before your completed the installation ? Well, I hope you found out before and not after?

flaps10 · 09-13-2016, 03:06 PM

I recently pulled my transmission because I still had clutch drag after having bleeding the system several times, changing clutch master and slave cylinders, 987 style clutch lever and all the bits and pressure plate.

This time I replaced the flywheel and disc even though both checked okay. Right as rain.

I observed the damaged pilot bearing on the old flywheel and just thought I'd pass along what I saw.

I have been supporting the engine with a large floor jack, which allows me to raise and lower the engine a bit to assure alignment with the transmission going back in.

Gelbster · 09-13-2016, 03:24 PM

Excellent and timely info for those tempted to force the engine and trans together by brute force.
Interesting to note the M96 uses a (needle roller?) bearing for the pilot not a bronze bushing. I suspect the bushing is a bit more tolerant of temporary misalignment during mating.

alexpinson5 · 03-14-2024, 07:13 AM

Sorry to bump an old thread but I was wrestling with my transmission last night and just wanted to add what worked for me should someone else's Google-fu lead them here like it did me.

Threading the two studs into the engine as mentioned here probably would have helped a lot. So does a buddy to have eyes on the front of the transmission while you shift it around in the back. Out of sheer stubbornness and/or not finding this thread until it was too late, I did neither.

I was able to get the transmission pretty close by eye but I was fighting the alignment of the transmission up and down (think a truck with a broken frame, the bed and cab are sagging in the middle). I had a jack on the engine and a transmission jack at the back of the trans that let me adjust this, but it was really difficult to eyeball and of course if it's not perfect it doesn't push in. What I did was take a random socket whose diameter was close to the gap between the engine and transmissions' mating surface. Using some of the longer mounting bolts I could get them started into the threads making sure things were pretty well aligned. The threads can NOT bind, you don't want these supporting the weight of the transmission yet or you can foul up the threads. Once in place I could jack things up and down and get a feel for the threads to tell if they were aligned with both the engine and trans. Once close here I took that socket (in my case, the round end of a 3/8" drive 6mm hex bit for the pressure plate bolts) and used it as a spacer all the way around. I inserted it in four spots (12, 3, 6, and 9 o'clock) and tightened screws and adjusted the jacks until the gap was even all around. Once it was even I knew things were aligned and I could start tightening bolts.

You have to be pretty careful doing this, the screws should be almost loose enough to tighten by hand the entire time so they aren't supporting the weight of the transmission. If the splines aren't aligned you could also damage them if you keep tightening and the trans isn't going. I took it VERY slowly to take the trans the last half inch or so to the mating surface on the engine, but once I started using the socket as a spacer to check alignment all around it was much easier.

Edit: to clarify, this isn't using the bolts to actually pull the transmission into alignment - I was using the 'feel' of the threads turning by hand to tell which side needed to move and then sliding things together by hand. The key for me getting the last half inch or so was using the spacer to check my alignment and things were easy from there.

Gilles · 03-14-2024, 10:48 AM

I had use the tip from JFP and it works very well, just get two long bolts with their heads cut off and you should be able to align the tranny properly, you may have to rotate the input shaft a bit to align the input shaft with the clutch splines

alexpinson5 · 03-14-2024, 11:40 AM

Quote:

Originally Posted by Gilles

I had use the tip from JFP and it works very well, just get two long bolts with their heads cut off and you should be able to align the tranny properly, you may have to rotate the input shaft a bit to align the input shaft with the clutch splines

Yeah, so this is more or less what I did but I was using the standard mounting bolts. Wish I'd read up on JFP's route because you have to get it pretty close to aligned before those bolts will have enough thread to go in, I probably would have saved myself a lot of hassle using some longer ones and removing them after. Using that socket as a spacer just helped get the side to side and top to bottom alignment just right for the last little push and then I felt it slide into place.