Previously on eEuroparts‘ SAAB Manual Transmission Rebuild, we went to Europe, found the holy grail of C900 transmissions, managed to source the entire batch of 20 something reproduction performance gearboxes, and we’ve prepared our host car for the transplant. This time around, we’re getting the drivetrain ready to accept the new gears!
Before We Begin
The rebuild procedure information you’re about to read about in this, and the next part of our guide, applies to most SAAB 4 or 5-speed manual transmissions. In fact, you can apply most of the things we’re about to talk about to any manual gearbox. While gearbox designs can be wildly different, the core principles remain the same. With that said, find out what makes SAAB’s transaxle design so interesting.
The Unicorn Design Explained
SAAB hasn’t been around for a while, yet most of us car enthusiasts remember it quite well. From its aerospace-inspired design to its brutal turbocharged motors, SAAB as a brand continues to exist and is often mentioned in the automotive halls of fame. How did a regular car brand that no longer exists, leave such a massive impact on so many? The answer is simple — SAAB was different.
To understand this, all you need to do is look at the transmission on the C900, whose guts we’re about to reconfigure. It reveals a long list of unexpected decisions that have forced engineers to come up with rather ingenious solutions.
This SAAB features an inline engine orientation, yet it’s a front-wheel-drive car. Thus, the transmission had to be made to fit the new requirements. What they’ve come up with is nothing short of incredible SAAB engineers more or less reimagined the drivetrain by placing the clutch between the radiator and the front of the engine. If you thought that’s odd, you haven’t seen anything yet!
Since the C900 featured a longitudinal engine layout, SAAB designers couldn’t mount the transmission behind the engine, as you would on any front-engined, rear-wheel-drive car. Instead, they mounted the gearbox underneath the engine.
What else is underneath the engine? The oil pan. Instead of stacking these two parts of the drivetrain, SAAB engineers simply combined them. As a result, the gearbox on the C900 is also its oil sump.
But wait, how do you deliver power from the engine to the transmission if the gearbox is sitting UNDER the engine in an inline layout? Easy, you use sprockets and chains. Many sprockets and chains.
In fact, SAAB used three chains to drive a set of self-lubricating sprockets that connected the clutch to the input shaft of the transaxle transmission down below.
Needless to say, SAAB was pretty much the only brand crazy enough to go through with a design such as this one. The layout on a C900 is as unique as they come, especially in this day and age when ten different brands share the same platform, engines, and gearboxes.
SAAB Transaxle Gearbox
SAAB’s transaxle setup consists of 3 major parts — the primary sprocket system we’ve just described, the gear set that lies behind the input shaft, and the differential system that also incorporates the axles. The fact that the transmission also houses the diff and the axles is the reason why it’s called transaxle instead of just transmission.
Since we’re familiar with how the primary drive system works, let’s skip that part and move on to the next piece of the puzzle – the gear set. As mentioned in this guide’s first part, we went for an upgraded gearbox with 4-speeds and performance gears. When we come back with the third part of this guide, we’ll dedicate much more time to the gears themselves and other parts that came in handy with this build.
That being said, understanding the anatomy of the primary sprocket drive, you kinda get the idea why a certain number of these cars have had an issue with the factory gear set. Everything up to this point, starting with the engine, the clutch, and sprocket/chain system parts, has proven to be pretty beefy.
The factory gears? Not so much. Luckily, we have the remanufactured performance gearbox as well as a few hand-picked gears that we’ve selected to nail the optimal gear ratio for our purposes.
Limited Slip Differential
The third, last piece of the puzzle is the LSD. It’s one of the most essential parts of a drivetrain if you plan on pushing the car hard. Our C900 initially didn’t have an LSD, just like most other C900s. We sourced the Automatic Torque Biasing differential — a form of LSD design that was made popular by Quaife Engineering in the UK.
We’ve had to modify the LSD to fit our C900 since it was initially meant to be used in a 9000. On top of that, this LSD was designed with the original 5-speed in mind, meaning that we had to get our hands dirty and make a few mods, so our parts could fit.
When we say parts, we mean the 4-speed sprocket and few other parts unique to the 4-speed gearbox design. More on that in part 3 of this journey.
Getting the Prep Work Done
Alright, now that we’ve familiarized ourselves with the SAAB transaxle design and how it works, let’s get our host car ready for the transplant. The key to any automotive work is to clean everything you plan on reusing. Better yet, clean everything you touch.
This applies to transmission rebuild jobs, engine transplants, oil changes, and anything else. In our case, we’ve decided to keep the transmission case and a few other parts. Usually, when you do a transmission rebuild, you’ll swap out all the bearings, gaskets, and synchros. Since we’re getting all that with the latest gear set, we didn’t have to bother.
To clean the transmission case, we put it through a few cycles where we’ve used a commercial degreaser and a pressure washer. At this point, our car was ready to accept the new transmission parts, but more on that in the upcoming installment of this guide.
If you’re rebuilding a used SAAB 900 transmission and you’re searching for information on how to get it done correctly, stay tuned. The next part of this story is in the works!