Manual
Transmission changes
THANKS TO Stephen and Zeke and David Prantl for this information.
Don't take it as gospel, though, as some discrepancies have been noted
Major points:
- The inner end of the axel has a three-roller
"fist" (tripod joint) that goes into the driver cup on the transmission.
These tripod joints/driver cups come in two sizes. The axel end tripod joint size must match the driver cup size. See the
"Inner Driver" column of the chart
- A major design change took place in '94:
- Synchronizer added to reverse gear
- First/second gear synchronizer totally redesigned
- Three-ring sandwich for each gear instead of a single synchro ring
- Larger diameter input shaft
- 94 and later transmissions will NOT mate to '93 and
earlier engines
- Different mounting bolt pattern
- Larger diameter input shaft and clutch splines
- 94 and later transmissions are the best design
- Much smoother, more positive action
- Much tougher synchros on 1 - 2 gears
- Note, however, that Eriksson says that the 3rd gear
snap ring on the input shaft is a failure item on these
transmissions. Saab did a mod to include a thrust washer, but
no one knows when. Eriksson can do the mod for around $50
labor plus $50 parts
- Michael Smith reports that this snap ring
failed in his 97 Aero at 74000 miles
- My 94 Aero had this failure at 97000 miles
- Symptoms are loud noises in reverse and/or a
"clunk" of varying intensity in neutral - when it gets
bad enough, it should scare you sufficiently to admit that yes,
you really do have a serious problem and it's time to fix
it. The symptoms are caused by the gear cluster moving
axially (back or forward), causing the meshed gears to bind and
then violently release, and it is perceived as a binding-up of
machinery. The hell of it was that it only happened very
occasionally at first and, fortunately, only in reverse and
neutral. The most reasonable fix is a rebuilt transmission
from Erikssen.
Apparently this is not a widespread problem, as it is not
reported as a common failure item.
- Final drive ratios
- Higher numerical ratio is a lower effective gear
ratio
- Higher number/lower ratio = quicker, more revs per
mile
- Lower number/higher ratio = less quick, better gas mileage, quieter highway
cruise
- Non-turbo transmissions have a very low final drive
ratio
- Necessary for non-turbo acceleration
- 86 - 92 turbo transmissions have a pretty low final
drive ratio
- 93 and later turbo transmissions have a higher final
drive ratio
- Very "long-legged" on the highway.
Less blitz, but better mileage, quieter highway cruising
- 88 - 93 trans have a dip stick to check fluid level
- (although the fluid is so clear that it makes the
usefulness debatable)
- 94 and later have no dip stick; they have fill, level-check
and drain plugs
Interpreting the Type number (next to transmission serial number)
- Earlier models ('85 - '87, from Saab service manual 333674)
- ID number format: GMT5x0y
- GM appears to stand for "gearbox, manual"
- T stands for transverse-mounted
- 5 is for 5 forward gears
- x is the final drive ratio
- y is the variant number
- Later models ('94 -, from Saab service manual 355875)
- ID number format: FMT5x yz SN
- F stands for "front wheel drive"
- M stands for "manual"
- 5 is for 5 forward gears
- x is the final drive ratio
- y is the engine/car adaptation
- z is the variant number
- SN is the 6 digit serial number
- The first digit is a letter designating the production line
- FM51 001 Final drive ratio: 3.13:1
- FM54 001 Final drive ratio: 2.85:1
- FM57 101 Final drive ratio: 2.54:1
The following chart is based in part on hear-say, particularly the years
and numbers that are in yellow. Model year '93, indicated by peach colored
text, is a crossover year that I think has the '94 style transmission, although
I think some '93 models may have the earlier transmissions. Final drive
ratios are stated as the overall ratio, not the 5th gear ratio; the final drive
ratio is lower because 5th gear is an overdrive gear.
Model
Year |
Trans
Model # |
Final
Drive
Ratio |
Spider
Bearings |
Inner
Driver |
Fill hole location |
Dip stick
w/Fill hole |
Level plug
and
Fill plug? |
Drain
plug? |
Reverse
Syncro? |
Improved
Syncros? |
86 - 87,
Turbo |
GMT5301 GMT5204 |
2.88:1
2.83:1 |
Bushings |
Small |
Rear |
No |
No |
No |
No |
|
87, Non-turbo |
GMT5202 GMT5203 |
3.04:1
2.99:1 |
Bushings |
Small |
Front |
Yes |
No |
No |
No |
|
88 - 90,
Turbo |
GM57401 GM57301
GM57402 |
2.88:1 |
Bushings |
Small |
Front |
Yes |
No |
No |
No |
|
88 - 90
Non-turbo |
? |
? |
Bushings |
Small |
Front |
Yes |
No |
No |
No |
|
91 - 92,
Turbo |
GM57403 |
3.04:1 |
Bushings |
Large |
Front |
Yes |
No |
No |
No |
|
90 - 92 Non-turbo |
? |
? |
Bushings |
Small |
Front |
Yes |
No |
No |
No |
|
93 CST, CSET,
Aero |
GM57101 |
3.61:1 |
Needle
Bearings* |
Large |
Front |
Yes |
No |
No |
No |
|
Design
changes in '94 make the transmission to-engine mating incompatible with
pre-94 models |
'94 CST, CSET, Aero |
FM57101 |
2.54:1 |
Needle Bearings |
Large |
Front |
No |
Yes |
Yes |
Yes |
Yes |
94 Non-turbo |
FM51001 |
3.04:1 |
Bushings |
Small |
Front |
No |
Yes |
Yes |
Yes |
Yes |
'95 - 98 CSET, Aero |
FM571xx |
2.54:1 |
Bushings |
Large |
Front |
No |
Yes |
Yes |
Yes |
Yes |
'95 - 97 CS LPT |
FM510xx |
3.04 : 1 |
Bushings |
Small |
Front |
No |
Yes |
Yes |
Yes |
Yes |
* The Saab repair manual says "In certain
gearboxes the differential is fitted with needle bearings instead of wear
discs." (Wear discs are cupped discs that fit on the back side of the
spider gears). My 94 Aero does have needle bearings (incorporated
into the discs).
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