Thanks to Matt Hoffman for contributing to this FAQ!
A few notes before we dive in: I have only the one 900 and this is the first time I've muddled through this without the factory tools. Fell free to contribute updates. I didn't have the Saab trans-axle repair manual on hand, and this description is provided almost as much to help you decide to have a pro do the job, as it is to help you get the job done. You may not want to handle this repair the way I did. There is actually another page on thesaabsite.com faqs with more information as well.
My 1991 900 5 speed started by shuddering, feeling as if one spark plug was cutting out above 50 mph. The gear shift knob would also shake while accelerating or holding speed uphill. That plus the fact that the shake did not change with the engine speed (downshifting) but rather vehicle speed, told me this was a driveline problem. I noted that the speedometer needle would also 'jump' at low speeds.
I checked the Saabsite here and found the note about inner driver failure, causing shuddering on acceleration. It was a few months before I could find a time to take the car out of service for repairs. By the time I thought I was ready, the car was not happy to be driven above 50 mph at all. Oddly, at lower speeds it was fine - even on hard acceleration below 30 mph.
In my case, I needed work on both shafts since the outer boots were nearly shot anyway. In fact, the right outer boot failed on the way to my friend's barn. I ordered the gaskets, outer bearings
and inner drivers hoping that was all I needed.
First, review the 'halfshaft removal procedure' in your favorite repair book for your Saab. If that seems daunting, then just read along but plan to have a pro do the fix. I noticed that another
person mentioned that the inner drivers 'just pop out' of the Saab transaxle.
I recommend buying all the parts in the Saabsite's inner driver kit. You will probably want to replace all those parts. If you are replacing a halfshaft with a rebuilt unit, (note: Saabsite
references instances of bad luck there) the only part you won't need is the inner tripod. You may or may not need the inner (large) bearing.
Make sure to get the right (ABS-Non-ABS) halfshaft-Inner Driver for your application.
With the inner boot off, and the halfshaft removed, check the inside surfaces of the inner driver.
In my case, there was a wear point on only one face of the six inside the driver. It was a clearly evident pocket about halfway along that face. So don't just do a quick check on one or two spots, check all six.
Once you have determined that it's time to replace the driver, remove the six bolts that hold the
side cover on the transaxle. If you are removing the left driver, first remove the bolt that holds the speedometer cable retainer. Note that this bolt is longer than the rest. Remove the cable and retainer.
Place a catch pan under the differential area. When the side cover is removed, the transaxle
lubricant (and the rest of the transmission oil for manual trans) will spill out. Using a clean pan will allow you to assess how much metal is present in the spilled oil. Remove the remaining bolts and slide the inner driver and side cover out of the transaxle as one assembly. There is a spring and bushing that rests inside a pocket in the end of the inner driver. Don't let that spring and bushing fall into the differential housing. Keep track of the shims that are present between the side cover and transaxle. Don't change their orientation or order when reassembling.
*Note that the left side shims don't have evenly spaced bolt holes.Removing the inner driver from the side cover:
Removing grease as necessary, place the assembly on a bench with the driver face down.Inspect the bearings and the inside of the cover for metal powder and shavings. You will also have a good view of the large bearing's race. The large bearing is a roller type.
There is a circlip that will need to be removed before the inner driver can be pulled from the small bearing. Once the inner driver is free, the small (ball type) bearing can be removed from the side cover, and the seal as well. Remove the outer o-ring and clean the assembly.
Replacing the large bearing:
Keep in mind that there are tools designed to do this job which make this job easier but Matt I did not have these tools so I did it this way. Maybe not the best but the job got done. In my case, the large bearing on the driver's side appeared OK, but the passenger side bearing had a lot of powdered metal in the transaxle, and noticable scoring on the race surface. I stuffed a rag in the differential, below the roller bearing. I destroyed the roller carrier by cutting it with diagonal cutters, then pulled out each roller by pliers and by hand, then pulled the carrier off the inner race.I carefully checked the number of carrier slots versus the number of rollers to make sure that no parts had fallen into the transaxle.Using a two leg gear puller, a 3/8" to 1/2" socket adapter, and a Craftsman 32 MM socket, I was able to put pulling pressure on the inner race. This is done by putting the 3/8 to 1/2 adapter inside the socket, so that when the socket is viewed from the side, the adapter is hidden. This makes a place to put the center shaft of your two leg gear puller, as you use the legs to grab the bearing race. Otherwise the gear puller won't have anything to push against in the center of the shaft. I had to use a Mapp gas torch to heat the race enough to free it from the driving shaft.
Factory tools will make this step unneccessary but again I don't have these tools. Make sure you have gloves handy for the next step - preferably leather gloves, not light cotton. I made sure to move the Mapp gas torch around the bearing race to heat it evenly and was careful not to ignite any of the transmission oil that was still around / under the car.Once the race let go it made quite a loud 'pop' that was repeated as I retensioned the puller and reheated the bearing. It took a few minutes of tightening the puller, heating the bearing, hearing the 'pop' and then starting the process again. It only moved a little bit each time. Bear in mind that this will leave a very hot wearing race and tools that will be looking to fall. Wear gloves.Make sure the puller does not damage the inner seal surface, some puller's legs may scrape the walls of the transaxle. I had to use a grinder to make the legs a little thinner to reach the bearing race. This is one of the reasons I say 'you may not want to do it this way'. Grinding down the legs could make the two leg puller unsafe. I recommend that if you chooseto do that, then discard the puller afterward, as part of the cost of the repair.
Press the new bearing back onto the transaxle driven shaft, making sure to have the orientation correct. Replace the race in the side cover to complete the large bearing replacement. I used a hammer and a large socket, to just gently coax it onto the shaft, after oiling the inner part of the race and the shaft.
Installing the new driver in the side cover:
A press would be really handy for this step. I didn't have one and it was a pain.
Clean all parts that will be re-used. Remember that your differential (or entire transmission
for 5 speed) has no filter. Any grit, metal flake, etc. will only be removed if you get rid of it
The bearing and driver shaft are a tight fit. I placed the bearing in the side cover, then installed the seal. Be careful not to place the seal too deeply in the side cover, it should just be flush. I lubricated the driver shaft with oil and then pressed it into the new small bearing. Installing a new circlip is the best way to reassemble the unit. Make sure to find one of the proper size. Install the new o-ring in the slot provided. Oil it lightly. If the outer race for the large bearing is not in place, place it. Oil everything inside the side cover. I poured a little bit of oil right into and over the small bearing. The seal held this small amount of oil to pre-lubricate the bearing without trouble. There's no point in doing all this work to let that new bearing get spun without oil.
Make sure that the final assembly has all the needed parts:
inner (large) bearing race
spring and bushing in driver pocket
Failing to install any of these will require removal of the side cover. It's hard to do with all new parts. (I know that because I forgot the left side spring/bushing the first time)
Ensure that the shims have the same orientation as when removed and are clean. Place all the
bolts and carefully turn ones on opposite sides of the cover to help 'wiggle' the assembly into
place. Don't let it get cocked by turning / fully tightening only one bolt. Placing all the bolts loosely will ensure that all the holes in the shims are lined up right. On the left side, there is one hole that is offset for the speedometer drive. If the shims get rotated, the last long bolt won't go in. (Three guesses how I learned that.)
Left side only:
Once the housing is mostly seated, remove the long bolt and install the speedometer cable and
retainer. Install the long bolt. This sequence will prevent you from crushing the speedometer
drive gears when installing the left side cover. Those gears are plastic.
I tightened the bolts to 15 ft-lbs as a best guess. Remember to refill the differential (or
transaxle for manual trans) with oil before starting the engine. It might be a good idea to flush out this oil after a few hundred miles to help wash out any dislodged metal particles or dirt. I used a suction gun to pull out about 3 quarts and replace it with new oil a week after the repair.
I noticed that the 'gear whine' noise has decreased quite a bit, and suspect that the new bearings
are causing the differential gears to mesh better. I have not noticed any leaks after reassembly
in the 3000 miles so far.
Thanks to Marty Patrovsky for contributing to this FAQ!
The two legged gear puller looked like a lot of work so after I removed the inner driver cup and housing I removed the circlip and then rested the housing on a wooden bench-top and used a soft rubber hammer (BFRH) to drive the cup and shaft out of the bearing inner race. On re-assembly when the parts get her I'll freeze the cup and shaft and hopefully slip it into place without a press.