Synchronizer
reassembly
Pre-94, all gears (I think)
94 and on: 3-4 synchro only (1-2 is a different type - see further down)
5th gear synchro is dead simple on the 94 (and, I assume, earlier models)
Note that there are some longer teeth/deeper valley combinations that need to be aligned - see the text below. (The Saab manual calls them "high heels" and "deep valleys").
In general, these synchronizers consist of a free-running gear
(on needle bearings) with a beveled surface on the back side; a beveled brass synchro ring that
fits onto the gear bevel; a slotted hub that is fixed (splined) to the shaft; another
brass ring
and free-running gear set on the other side of the hub, again with the beveled back side of
the gear facing the hub; a slotted sliding synchro sleeve that slides on the hub; and three
each small springs, plungers and rollers. Synchro
parts pic
The three spring-loaded plungers act on the three rollers, which are
housed in three slots in the synchro hub. These
(acting on the inner shape of the sliding sleeve) give a “detent” action,
much the same as an electrical switch is spring-loaded to on, off and neutral
positions. Synchro spring-load parts
pic
Unfortunately, you can put these things together wrong,
such that they appear to be working, but in fact will not work.
There are three sets of two teeth each on the synchro sleeve that are
different from the rest (longer, not squared off on the ends).
Pic
To install correctly:
First, the shaft should be standing on end, with the 3-4
gear end upward. You could clamp it
very lightly in a vise, or any number of things (I put mine in a file cabinet
drawer). This is essential for the
step where spring-loaded components are installed.
Install the needle bearing for third gear, then install the
gear. Next, install the brass ring
with the teeth next to the gear teeth and the beveled surfaces mating.
Pic
Now for the critical part, the sleeve.
The sleeve is identical from end to end, which is to say that front and
back are the same, so you don’t have to worry about which way it’s flipped.
Look carefully to locate a pair of the longer teeth. They’re longer and more rounded than the others, as seen in
the pic above.
Looking with the sleeve tilted at an angle helps.
When you find them, align the sleeve with those teeth centered midway between
any two notches in the hub, then drop the sleeve onto the hub.
If you miss by one tooth one way or the other, the sleeve will only go
about 1/8 of an inch; when alignment is correct, it will drop all the way onto
the hub and engage the gear. Pic
If you want to see how it can be done wrong, you can rotate the sleeve 60 degrees until the teeth align with the notches in the hub. Note that the sleeve will now drop onto the hub, and will APPEAR to engage the teeth (just the ends of the teeth), but it won’t actually engage the teeth solidly, which you'll see if you try to hold the sleeve in one hand and the gear in the other and give it a twist. Diabolical, eh? One guy posted on TSN that he had had to remove his trans and take it to a pro after he mis-assembled the synchro – this is what he had done. He said, "Next time I'll mark them before disassembly." Trouble is, they'll probably be to oily to mark, and besides, you probably wouldn't know what to mark even if you could mark it. There's only one way to deal with these synchros, and that is to understand the nuances, and how they assemble. It's easy as pie once you know. If you don't understand just from reading and looking at the pictures, I'm sure you will once you have the pieces in your hands and these pictures and text to guide you. OK, so now that you know how NOT to do it, rotate the sleeve 60 degrees to again align the teeth so that the odd ones are mid-way between the hub notches, so the sleeve will drop onto the hub and fully engage the gear teeth.
Actually, that was a dry run – there’s one more thing we need to do. Remove the sleeve and set it aside, maintaining the alignment so it can be easily installed in a minute. Install the plungers into the springs, then install those three spring/plunger assemblies into the three holes in the hub, with the plunger heads facing out. NOW you can install the sleeve, again making sure that it slides fully onto the hub and engages the teeth on third gear.
Now for the three rollers - this step isn’t anywhere near as hard as it might appear. The shaft should be standing on end, with the 3-4 gear end upward. The ideal working conditions would be a barren room, so that if any of the springs or plungers fly out, you could find them, although it probably won’t happen. Lift the sleeve far enough to install one of the rollers from underneath, then gently set the sleeve back down to retain it. Retain that one with one finger of one hand while you again lift the sleeve and install a second roller. Set the sleeve back down to retain them. Now retain those rollers with two fingers of one hand while you lift the sleeve again and install the third roller with the other hand. GENTLY and SLOWLY push down on the sleeve, JUST UNTIL THE CENTER CHANNEL SNAPS OVER THE ROLLERS. Don’t retract or over-extend the sleeve now or the rollers will pop out. Now, wasn’t that a whole lot simpler and easier than you thought it was gonna be?
Now install the needle bearing for fourth gear. Install the brass synchro ring onto fourth gear, mating the beveled surfaces, then install that assembly onto the shaft, aligning the bosses on the ring with the notches in the hub.
Now you can double check that the synchro sleeve slides smoothly from its center detent, to third and fourth, fully engaging each gear and snapping into each position. Be sure to keep fourth gear pressed onto the shaft while you do this or the rollers will pop out.
Handle the assembled shaft carefully until you can get the bearing pressed on to retain everything. Until the bearing is pressed on, fourth gear is free to move forward, which would dislocate all the spring-loaded components. Saab makes a special tool for keeping the synchro'd gear sets together.
94 and on: 1-2 synchro
The 1 - 2 synchros on the 94 and later 5-speeds are really beefed up. Each of the single brass synchro rings is replaced by a sandwich of two brass rings around a stainless steel ring. Their assembly is interlocking, and should be straight forward to figure out. These ring sets go onto the beveled gears the same as the single rings.
Another difference is that instead of using spring-loaded rollers, this one uses three small metal pieces that Saab actually calls "beans". They're about 5/8" long, 1/8" thick and 1/4" wide. They fit into notches in the synchro hub and are retained by two circular wire springs.
The hub has three wide slots (for the ring bosses) and three narrow slots (for the "beans").
First, assemble the three rings to each gear, aligning all the notches. Set them aside.
Note the three sets of three notched teeth each in the sleeve. Align one of each of these with the narrow slots in the hub, then assemble the sleeve onto the outside of the hub. Now, slide the hub down so you can install the three beans into their narrow slots - the raised ridge in the center of each bean fits into the notch in the tooth of the sleeve. Center the sleeve on the hub. Now install the wire spring "clockwise" - hook the up-turned end of the wire clip onto one of the beans (it will fit against the raised ridge in the bean), then insert the clip so that its end points to the right (clockwise). Note which bean you hooked into, because the other clip must hook into that same bean. Carefully flip the unit over, hook the bent end of the clip into the same bean, then install it clockwise, again when looking at it from above. Now assemble the gears to the hub, aligning the ring bosses with the hub notches. NOTE: The shift fork groove in the sleeve must face first (largest) gear. Now you should be able to hold the sandwich together and cycle the sleeve from gear to gear, making sure that you get positive detent action in neutral and in each gear, and positive engagement of each gear.