AOS from bottom with clutch/IMS/RMS install

I'm just starting a clutch/IMS/RMS job on my 99 996, and keep reading that the AOS is "while you're in there" job. Can the AOS be replaced solely from the bottom of the car? Is it truly easier/faster than later from the top? Not relishing the idea of removing intake manifolds AND doing all the transmission work. I had replaced just the AOS bellows a few years back (had thrown a CEL) but now with 100k miles, it's probably time to do the whole thing. Thanks

no tips, huh? i've searched but haven't found many threads/pics on doing the AOS from the bottom. i've got the transmission out now, and yeah, there is some room now to get to the AOS. still is going to be hard with all those clamps!

You may find it easier if you drop the transmission end of the engine a bit.

Yes, I believe that the AOS can be replaced solely from the bottom of the car if you remove the transmission. Either way, it is a pain to replace without dropping the engine or the transmission. I would recommend doing it now that you have the trans out. I have replaced the AOS on my 996 Mk 2 without dropping the engine/trans and that is even more tricky. I am not doing that again.... Robert

It almost appears that dropping the engine/trans might be a good idea. Then you could detail the engine bay, check all the other stuff that's hard to see/get at, etc. It's probably what I'll do next time, but I'm OCD like that...

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I'm OCD too, I love a clean engine bay even though no one can see it, lol.

This is where we see the KK disciples coming out of the woodwork.

I'm no clean freak, just want my 996 back on the road! I'm trying to avoid dropping the engine, it will require getting the car even higher, finding ATV jacks, etc. Although I'm aware that the net time might still be faster than doing it only via the transmission drop. I'm a little scared that I won't be able to get one of the clips/clamps from the bottom, and then I'm stuck!

Bob - having done my AOS replacement (99 996 3.4L) back in January due to a cracked casing I can tell you that you have to work from both the bottom and top of the engine. It was very difficult to do and a royal PITA. I think I have wounds on my arms and aches in my fingers to this day from that job. In my opinion you are correct about your concerns regarding the hoses and clips/clamps that attach to the AOS. I could not undo one until I had the entire AOS out and pulled to the back of the engine bay, almost out of the car. Actually, I don't think having the transmission out would have made much of a difference, however, lowering the engine as much as possible did make a big difference. I had to remove the rear bumper and heat shields in order to lower the engine to the limit, and even then it was a contortionist act. The situation may be thus: with the transmission out, how low can you drop the engine without actually removing it? If you can lower it as much as possible (almost dropped out completely) that will make things a bit easier while removing the left side manifold to get to the AOS. But to gain significant engine drop you will have to undo the AC compressor, water hoses and 02 sensor cables, as well as the cross member the engine will hit while dropping (that cross member limited my engine drop to about 6-8 inches only). Maybe you already have that out since you have the transmission out. Anyway, I think you will still have to work from both the top and bottom of the engine. Good luck!

Hi guys, sorry for the late reply but wanted to follow up. The AOS can indeed be replaced from the only the bottom with the transmission out, and I didn't need to lower the engine on the mounts. One trick is not to bother unclamping the coolant hoses on the old AOS--just crack them off as the plastic will be brittle. Pull the hose ends from the top and remove the old clamps/broken nipples, and then push the hoses back ready for the new AOS. The bottom clamp on the bellows is not included with the new AOS. The one I purchased from the dealer was a cool "grenade" clamp: already pre-compressed with a plastic finger pull. Just slide it on the bellows and then the engine fitting and pull the pin! No mucking with pliers or a spring hose-clamp tool!

Bro, if you do this your gonna make me and Alpy so proud!

I replaced my AOS when I did my clutch a year or two ago. Was not *that* big of a deal that I recall. One of the bolts was blind I think, but I don't remember the hoses being all that difficult.

You don't really have to drop the engine all that much. Drop it enough to rest on the crossmember and you have enough room (just barely) to replace the AOS. It is a job that will frustrate you because of the limited space to work within but it can be done just by disconnecting the engine from the motor mounts and resting it on the crossmember (with a jack still underneat it).

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Were you able to do the whole job from the bottom? Looking to do this on my 996.2 while I have the transmission out for a clutch/RMS/IMS.

Yes you can do it all from the bottom IF the gearbox is removed.

I�m not sure how different the 996.1 and 996.2 are for this job but I replaced my �99�s with the UAOS while the car was on my lift. There were some things that I still had to do from the top, but I didn�t remove the intake plenum and fair amount of the work was done from below. YMMV Search the UAOS Tips and Tricks thread for lots of good info there.

On my 996.2 (2003) I did the UAOS install when doing the IMS Solution. Engine in, transmission out. Not that hard of an install. If you have not replaced the AOS crossover pipe from the passenger side head - you might want to do that at the same time. Mine failed about a year later - just due to age likely. Skip has a redesigned crossover pipe for it (after I had already replaced though). I believe you can also go with a later 997 crossover pipe that doesn't go across under the intake plenum - that one goes outside the intake plenum to the flywheel side of the engine and crosses over there. Here is the link that mentions the hose going behind the intake: https://rennlist.com/forums/996-foru...l#post18467820 Here is the full thread about Skip's crossover hose https://rennlist.com/forums/996-foru...ther-hose.html -Tom

The trans being out makes the 996.1 much easier because you can see the bolts easily. The 996.2 is still a bit of a pain because the bolts go in from the top whereas the 996.1 go into the side from the bottom.

So far I�ve got my IMS taken care of, I spent most of that time fighting the rear bolt of the AC compressor- what a nightmare. I had to teach in from the flywheel side with a box wrench to loosen the back alternator bolt. Next on my list is the AOS, I�ve managed to loosen the 10mm bolt on the flywheel side, but I�m baffled on how to get to the second bold without removing the intake. I managed to disconnect the vent hoses, but am shrugging to get my hose clap tool onto the 3 spring clips. Not sure if I need a box wrench to loosen the other AOS bolt, �� drive with a wobble/universal joint? Having an equally hard time attacking it from either the left, right, or above.