It really all depends on the serial number. It is pretty rare to have an N/A trans that is geared lower than a turbo trans, so I find that pretty odd. Hop on over to 900aero.com and look at the transmission serial numbers.

 

1991 900, i16(2.1), T16 cat GM45714
GM55706 9:35
3.89 13.89 7.98 5.29 3.82 3.04 15.27
1991 900 T16 GM55806 9:35
3.89 12.92 7.42 4.92 3.55 2.83 14.21

 

transmission is the same, gears are the same 91-93. What is different is the front primary chain cover, and primary chain ratio. That guy that says 900s tranny is better is BS. They are both the same. 91+ actually is weaker than 89-90. Saab used more inferior metals in 91+ models, I've seen more bad 89+ trannys than the older ones.
91+ tranny has thin forks, this was done to make the shifting smoother, but this design is worse for performance.
Best tranny would be 89-90 but it is minor improvement, they all go bad. If you use too high of a ratio for example primary chains from 900S, then gears will see more torque and more stress, and this is not good.

 

The 91-93 units have a faulty syncro design, which like Raul mentions leads to smoother shifting, however the units tend to explode and make the spring have a get together between the gear clusters. This will cause an instant and complete gear cluster failure, even if you are not being hard on the car during the failure. The gears and pinion housing design is fine on all the 89-93 transmissions, however the better syncro design in the 89-90 units make them the best one to run.

Also, Na / or turbo transmissions are the same, either one will work fine. Basically all 89-93 900-T and 900-S transmissions should have the #7 primary drives, so those are the same too, but they can be changed quite easily as well.

 

So 89-90 had a different sincros from the 88?

 

humm.. howcome my 91+ 900s tranny lasted 5 years of hight power and beating, while 3 88 trannies 2 off which were rebuilt by erikson did not last more 9 month and 15 month. The original one lasted 105k, but like i said the one that got most of the beating is the 91 900s tranny and it is the one that lasted the longest. and yes the 91 900s tranny felt smoother. It also added 5+ miles to the speedo in third @ about 5k rpm when compared to the 88 turbo tranny.

 

now who's got a tranny for me.

 

what about those scanwest tranns. any one tried them.

 

Got ya? Thanks

 

i blew up a 1993 trans, but that was at 260k miles,,,, beware that a lucky few transmissions in the later years didnt get drain plugs,, i had one of these,, no good.

i now have an 88 rebuilt trans in my car,, it def shifts notchyer thane before,, but the price and timing was right

 

not just a few, all 91+ trannys came without drain plugs.

Paul

 

Most of the pre -88 trannyes go bad because of lack of proper oil and oil level. Once the tranmission is FULL of oil it barely comes up to the countershaft bearing and this is so critical in those older transmissions because they used small bearing riding on that 14mm shaft. This is the most common wear, that shaft gets eaten away and counter gears move away and geer teeth colapse. Most saab enthusiasts check their oil level but other people don't. In my opinion you should slightly overfill your tranny just to be on the safe side.

Best tranny setup in my opinion is: 1990T trans with 91+ rear cover with filter.

 

While we're on the subject, anybody remember how much trans oil you need for a c900 trans?

I read in the bentley 3 quarts, but went to fill it up and it was past the "FULL" mark on the dipstick at 2.5 quarts. Anybody?

 

You fill it up until it reads "FULL." It only took 2.5 quarts because there was residual fluid in the trans case/primary case.

 

I've been reading up on it and if don't drain the area under the chains up front, you can have up to a quart of trapped fluid. At the same time total overhaul means this area is dry on first use unless you prelube the area before you put the forward side cover on.

 

There are other tricks one can do to make a pre '88 tranny shift less notchy and that is when rebuilding use only the 1-4 syncros for the 2-3 syncros, replace the washer/bushing with new on the cluster shaft next to the pinion housing, make sure the distance from top of case to pinion nut is exactly what is spec'd or 0.01mm less than spec and finally all shafts should not have any burrs or wearing of the hardening. Also the oil is critical for the geographical area in which one lives. Me being in Alaska and the extreme temp swings of 140°F per year (-50 in winter to +90 in summer) make for several tranny oil changes in a year. I use two, maybe three types of oil: -50 to 0, 0 to +50 and +50 and above.

I was lucky enough to find a '78 chillcast tranny housing and pinion bearing housing, with which I put a combo of '81, '84 and '88 parts to make one tranny. I did spring for all new bearings, got Luke's (SAABRally) steel diff cover and rare chillcast side cover for reverse gear. I decided to not use a tranny cooler because of the low ambient temps I drive in.

pierre