The Quintessential Classic Saab 900 Engine Swap Part 5: Mating the Transmission to the Engine

Unlike the head, mating the transmission to the engine is not a complicated task.  Take your time and follow the instructions, because although this is a bolt up job, mating up your major engine segments doesn’t take much to screw up if you’re not paying attention. If done wrong, it could mean repeating a long, arduous, and expensive work process or, even worse – a damaged engine or transmission. That said, it’s not rocket science. Here are 5 tips to build your confidence:

1. First and foremost, make sure the mating surfaces are CLEAN! I use a gasket scraper or a brand new razor blade to cut out all of the old gasket before scrubbing the surface with brake cleaner and a lint-free rag. Remember, even one big speck of dirt can contribute to a bad seal and an eventual leak under pressure. Once it’s clean, don’t hesitate to clean it again if any doubt arises or time passes. It can never be too clean.

A clean surface is a leak free surface

2.  Understand the installation process. On the classic Saab 900, the transmission gasket has a gap where it should be filled with silicone to create a thorough seal. I would not have known about this if not for owning and memorizing the transmission installation section of my shop manual. And don’t cut corners – I’ve found that shortcuts often present unnecessary risks and end up taking longer than the normal procedure anyway.

C900 Transmission GasketTransmission gasket RTV

3.  Unless it is specifically not recommended, create a bead of silicone sealant on both sides of the gasket, especially around the oil passages, before installing the gasket. I ordered a full tube of oil-resistant black RTV silicone that could be applied with a caulking gun – my mechanic lauded this decision because he said it was the most controllable setup that he had ever seen. Much better than squeezing by hand. Make sure that it’s oil resistant silicone.

SAAB anerobic sealant

Make sure a smooth and consistent bead makes it all the way around

4.  Clean and prepare your mounting bolts. I cleaned all of the threads on a wire wheel to prevent binding when they were torqued. If yours requires high torque settings, this can mean the difference between the bolt fully threading, stripping, or snapping inside. Once clean, lay them out in the correct order. Mine had four slightly different sizes that I may not have noticed if not for a diagram in the shop manual. Some bolts will need to be coated in anaerobic sealant to prevent leaks through the threads, and the other should be coated with thread locker to prevent them from loosening.

SAAB 900 engine block

5.  Once it’s all clean and ready, be sure that you mate it evenly. As you might imagine, the gasket is meant to compress. If one side compresses before the other, the compression will not be even and could lead to leaks later on. Call a friend in to help you lower the block down – even call in a third person to keep it lined up as you bring it down.

All in all, transmission replacement can seem daunting, and horror stories pop up abound, but like I said, it’s not rocket science. Just make sure you do the simple things right and you’ll be back on the road in no time!

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