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
    • Very quick off the line
  • 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.

* 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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