C900 Transmission Rebuild
Introduction
Introduction
DO YOU WANT TO SEE THE INSIDE OF A SAAB 5-SPEED TRANSMISSION...
I created this section because I was putting together a winter rat that needed a tranny.
Mostly I just wanted to take the tranny apart to understand how it functioned!
I am not a SAAB certified expert, so don't use this guide as the bible of tranny repair. I'm sure there are things I left out or completely missed.
I just went into the basement and decided to tackle the job. I did have advice from my mechanic on some things and I'll pass those on!
There are also some steps that require special tools that I did not have. If you can find a local Saab mechanic for advice, maybe they can help out with the special tools.
If you have a different year tranny and you want to know what's compatible and what's not, check out my 5-spd info page!
Tranny Info Page
If you are missing just the reverse gear, there is a good chance the townsend reverse gear fix could solve your problem.
Reverse Gear Fix
C900 Tranny Rebuild
Step 1
Step 1
I'm starting this section assuming you have already pulled the engine and tranny out of the car.
You can perform a tranny rebuild with the engine attached to the tranny, but it is much harder. I would recommend you pull them apart just to make life easier!
The first thing to do is to clean up the transmission case while all of the covers are still on.
The best way to do this is to use some engine cleaner spray and then scrub and power spray the housing.
The cleaner you make it now, the better off you are later!
Drain the tranny of all the oil and start removing the covers.
For the later year trannys, there is no drain plug so your only way to drain it is to remove the covers.
All of the bolt lengths are different for each cover so be sure to keep all of them together once you remove a cover.
I used separate coffee cans for each cover.
These covers are the sneak peak of what is to come!
The differential is where I like to start when tearing down a tranny.
In order to get the differential out of the housing, you have to remove the inner CV joint cups.
After pulling out both of these cups the differential will be free in the housing.
Be sure to keep the small spacers together with each cup and don't mix them up! These are very carefully measured and locate the differential correctly onto the pinion gear.
If you keep the spacers and use the same pinion/differential you will not need the special tool to
measure this. It will not change after the rebuild.
The next thing to do is to remove the differential. To do this you have to twist and pull it a certain way. I cannot explain it, but it is a little tricky.
The housing will look something like this when you're done.
C900 Tranny Rebuild
Step 2
Step 2
After taking a break and sucking down some beer, you're ready for the real fun!
You have to remove the transfer case in order to get to the main housing.
In order to remove the transfer case there are a couple things you need to do!
First you must remove the 2 chain gears that drive the transmission. These will need a big air gun to remove!
The best way to do this is to lock up the gears by engaging 5th gear and reverse at the same time.
To engage 5th just move the shift rod into 5th gear. To engage reverse you must take off the reverse linkage and move the reverse gear back engaging the gear.
After doing this you can remove the huge nuts and chain gears rather easily. I believe one of the chain gears has a circlip on it.
Once you remove the big gears, you have to remove the primary drive. This is held into the transfer case with 6 bolts.
5th gear is next. Before you can remove 5th gear you must remove the rod holder and pull/push the cluster gear rod and pull it out enough to clear 5th gear.
DO NOT PULL THE ROD ALL THE WAY OUT! Everything inside will come crashing down if you do!
Here you can see the rod on the lower right removed about halfway. The top rod is the reverse gear rod.
It's almost time for that second beer! After the cluster gear rod is out of the way, you can get 5th gear out.
First, you have to slide the spacer off of the pinion shaft and then 5th gear will
practically fall out!
Now we are ready to remove the transfer case.
Remove the bolts to the transfer case.
Be sure to get the one that is on the opposite side than all the others!
Next hammer out the circle spacers that hold the transfer case straight onto the housing.
This is what you should be looking at. Here you can see the big circle where the spacer goes.
It's time for that second beer!
C900 Tranny Rebuild
Step 3
Step 3
Now it's time for the real fun! Lots of parts to lose and forget about!
The first thing to do is to remove reverse gear completely.
You can remove the shaft on the other side and reverse will just fall out.
Now the easy part. Removing the guts of the transmission.
Have a table right next to you when you do this.
As you remove the parts of the transmission, lie them down in order of removal on the table.
This makes it a thousand times easier to put back together!
You will have to remove the big cluster gear first.
Then you can remove the primary gears and shift forks.
This is what the housing should look like after you remove everything.
Now you have a table of parts!
Since this should have only taken about 10 minutes, it's your choice to have a beer or not!
If you're wondering if you can really put it all back together again maybe a beer won't hurt!
C900 Tranny Rebuild
Step 4
Step 4
About the only thing left to remove is the pinion shaft and housing. This is quick work. 4 bolts and It will slide right out!
The next thing to do is to remove the shaft from the housing. You'll need a big tool for the job!
Now you can replace that dreaded pinion bearing!
Removing the bearing is pretty easy. A press will push the bearings out of the housing. There are two bearings in the housing. One on each side.
After really cleaning the housing, you should look for stress cracks on the mounts of the housing. This is an very important step.
If the housing is cracked or even slightly cracked, you will have a premature failure when you start applying a lot of horsepower and torque to the transmission.
The last thing you need to do is remove the race for the roller bearing on the pinion shaft. There are a couple of ways this can be done.
The easy way is to use a bearing puller (bearing "knives") and the press. It should come off easily with this tool.
Another way is to use a diamond cutter on a hand grinder.
The main drawback is that you can cut too far into the shaft and throw the balance off.
Go about 2/3 of the way through and then take a chisel and hammer and break the spacer apart.
It's time to take a step back and take a look at what you have.
C900 Tranny Rebuild
Step 5
Step 5
Now that the everything is empty, you can go and really clean up the transfer case and housing.
I used a parts cleaner to do the big stuff and then a couple cans of brake cleaner to finish the job.
Cleaning the inside is the main objective.
After this, you need to look at what needs to be replaced and what is re-usable.
This is where you can break the bank. If you really want to do it right, you have to spend the dough!
These parts add up fast, but if you choose not to replace something, it is always in the back of your mind when you're driving it on the road!
The biggest challenge now is actually getting brand new parts. The suppliers are not producing parts anymore and it is getting harder to get new parts.
Here is a small list of things that should be looked at and replaced if necessary.
Pinion Bearings. This is the main failure point in most SAAB transmissions. Always replace these bearings.
When a pinion bearing fails, interesting damage occurs at the 4th and 5th assemblies.
Look carefully for any worn or deformed part and replace it.
Damage can occur to the guides; springs; the 5th hub gets battered and its lock ring retainer lip ground off;
4th gear gets battered on the 3rd side and machined on the bearing side.
Ring and Pinion. Examine the ring and pinion very carefully, looking for ridges and rifts at the bottoms of the teeth.
Also look for damage at the opposite end of the pinion shaft, looking for scarring or metal accretion on the shaft particularly under the 4th bearing sleeve.
If metal has accreted, it may be possible for a machinist to dress it to spec.
1st and 4th gear Synchros. In order to determine if a synchro needs to be replaced, you have to feel it.
With a brand new brass synchro, you can feel the sharp edges.
In older, used up synchros the edges will be worn and will not sync the gears properly.
If you think you may reuse a synchro ring, examine its ridges closely for embedded bits of steel and either pick these out or reject the synchro.
2nd and 3rd gear Molysynchros. Replace them if you see wear spots in the grey molybdenum coating.
Cluster Gear Rod. I don't have a picture yet, put this one is easy to tell if it needs to be replaced.
There will be wear marks on the rod from the bearings.
The wear marks are actually grooves on the rod. If you can see wear marks, you should replace this.
Cluster Gear Bearing. Always replace this. It's a small roller bearing that goes inside the cluster gear.
This is spinning just as much as the pinion bearing. It's cheap and a good insurance.
All Seals, All gaskets. For obvious reasons!
All Roller bearings. If one's got 100,000 miles on it, you may as well replace it!
Shift forks. To tell if a shift fork needs to be replaced, you need to look at 2 things.
Is it bent? It will be bent up by the shifter notch. This will make it pop out of gear.
Are there are wear marks on the fork? The forks go over the synchromesh sleeves and the
synchromesh sleeves are steel and the fork is brass. This causes a groove that forms in the fork.
You can feel the grooves with you finger. If the wear marks are excessive, you won't get the gear fully seated into the
synchromesh sleeves. Hence, popping out of gear.
Synchromesh Sleeves. The synchromesh sleeves only need to be replaced if the teeth are worn or gone and the inner smooth surfaces is scored.
You can tell this by looking at the sleeve. When you grind a gear, you are grinding on the gear and the
synchromesh sleeves' teeth.
If the teeth are not sharp and you don't replace them, you will get gear grinding with a new rebuilt tranny.
Also examine the inner smooth surfaces of the synchromesh sleeves to verify that the tiny bits of steel from grinding gears didn't score these surfaces.
It's worth the money to get these replaced. If you can find some good used ones, then use those.
Anyone that's rebuilt numerous gear boxes should have extra synchromesh sleeves around.
Gears. These are pretty much the same as the synchromesh sleeves. When you grind a gear, it's these gears and the
synchromesh sleeves that are grinding.
The teeth get worn down, just as much as the synchromesh sleeves. Most likely, if your
synchromesh sleeves are worn, so are the gears.
Also look for "galling" on the faces of the gear teeth, particularly 1st and 3rd. These wear from impact, sort of like pot holes.
Look for chipped teeth. A chip here and there may be acceptable if cost is an issue and you can't find a better used gear.
If you rebuild your tranny with both of these worn down, you will be grinding gears and it may be popping out of gear.
To see if the gear is worn down, you have to push the synchro down and look at that part of the gear.
The other half of the gear is always against the cluster gear and does not get worn down.
A brand new gear would have sharp corners at the end of the gear where the synchro is.
Sometimes you can find these gears used with pretty good edges. That's up to you do decide!
Reverse Gear. Reverse gear can become pretty battered as well as the reverse idler gear.
Some reverse gear sins can be overcome by virtue of the reverse gear selector modification.
In this picture the teeth are completely gone and we had to replace it with a used one.
The transfer case chains. I usually don't replace the chains, but I did have one instance where I broke all 3 chains.
This was a messy day. The chains broke through the transfer case and almost through the hood of the car.
Replace the chain sprockets if the teeth appear worn. Wear here makes a noisy transmission whenever the clutch is engaged.
Start calling people for prices on new parts and don't be afraid to spend money. If it's done right, a good rebuild can last you another 100,000 miles!
Can you see where mechanics can cut corners? This is why we have many bad tranny rebuilds around.
Why bother just replacing the pinion bearing, when all of this other stuff needs to be replaced also?
C900 Tranny Rebuild
Step 6
Step 6
At this point you have bought all of the parts necessary for the rebuild. Now you can put it back together and drive off in the sunset!
I've been waiting to get some more pictures to detail the re-assembly, but I've been slacking on my 2nd tranny rebuid!
Some of the things you need to measure is the pinion preload. This is done when you attach the pinion shaft back onto the housing.
Another thing you need to measure is the pinion backspacing. Saab made a special "T" looking tool that made this fairly easy.
After that, everything pretty much just goes back together. If you screw up or miss something, the parts will not fit back together again!
C900 Transmission Info Page
Over the years SAAB has changed the 5-spd transmission very little.
The key thing to understand is that any year 5-spd will bolt up to any C900 engine.
However, there are some small differences between them that you should be aware of.
The most common mistake is thinking that the internals of one tranny can be transplanted
into the case of another tranny. SAAB did change the internals a couple of times, so pay attention
to which two trannies you are swapping parts between.
Serial Number Designations
type(G=manual)1st digit
version(engine combination)2nd digit
number of forward gears-3rd digit
primary gear ratio(see below)-4th digit
variant(stage of development)5th digit
1984 Onward:
GM=manual tranny-1st digits
GA= auto tranny-1st digits
transmission version-2nd digit
number of forward gears-3rd digit
primary gear ratio(see table below)-4th digit
variant(stage of development)5th digit
4th Digit: Gear Ratios for Manual Trannies:
| Primary Gear Ratio | Input Gear # of teeth |
Output Gear # of teeth |
Final Drive Ratio |
| 4 | 31 | 30 | .97 |
| 5 | 30 | 27 | .90 |
| 6 | 31 | 26 | .84 |
| 7 | 32 | 25 | .78 |
| 8 | 33 | 24 | .72 |
| Gear Set #8 was only available for the Autobahn and is very difficult to find today. This set works great for modified engines as all the gears will be longer. | |||
Tranny Serial Number According to Year and Model
| YEAR | Non-Turbo | Turbo |
| 1979 | G34402 | G34602 |
| 1980 | G34402 G45702 |
G45702 |
| 1981 | G23404 G45704 |
G44604 G45704 |
| 1982 | G34406 G45606 |
G45606 |
| 1983 | G45606 | G45606 G45706 |
| 1984 | G34506 | G45606 G45706 |
| 1985 | GM34506 | GM34506 GM45706 GM45X08 |
| 1986 | GM45706 | GM45706 |
| 1987 | GM45X10 | GM55X02 |
| 1988 | GM45X10 | GM55X02 |
| 1989 | GM45X12 | GM55X04 |
| 1990 | GM45X12 | GM55X04 |
| 1991 | GM45X14 | GM55X06 |
| 1992 | GM45X14 | GM55X06 |
| 1993 | GM45X14 | GM55X06 |
Changes made during the years:
1986 - Inner Drivers Changed. May be related to the change in internal centering.
1986 - Change to internal centering.
Mid-1989 - Drain plug removed on turbo boxes.
1990 - Drain plug removed on non-turbo boxes.
34xxx: Old Style CV Drivers
456xx: Old Style CV Drivers
GM45xxx: Solid Motor Mount
GM55xxx: Hydraulic Motor Mount
GM45x06: I don't know for sure, but I believe the very early boxes have incompatible synchro rings from other GM45x06 boxes.
GM45x08 is a 1 year box for the 85 900 turbo. It has an extra bearing on the input shaft. It is basically the same as the GM45x06.
GM45x10 and GM55x02 have internal centering, but parts are compatible with GM45x06 and 08.
GM45x12 and GM55x04 has internal centering large pinion bearing. NA cars 89-90 early boxes have drain plugs. Internal parts are not compatible with x10 or lower versions.
GM45x14 internal centering large pinion bearing and revised shift forks. Internal parts are not compatible with x10 or lower versions.
x12 and x14 internal parts cannot be transplanted into x10 or earlier cases.
If you have more interest in the SAAB manual gearbox, the manual is still available from the dealer for around $20.
There is really no substitute for the book. The front of the book explains all the part numbers and what application they had.
Even if you never plan to rebuild a box, the book is neat to look at.
Here is a link that goes into great detail on how to do an automatic to 5-spd swap:
- Learn how to swap your crappy auto 3-spd for a 5-spd transmission.
Many thanks to those who contributed this information!!!
If there is some wrong information or I've missed something, please e-mail me with the updates!
E-Mail Jeff
Townsend Reverse Gear Fix
Is your shifter popping out of reverse?
Do you want to fix it without pulling the tranny or buying gears?
Because the Saab transmission does not synchronize reverse gear, they decided to limit the amount of surface area available for the gear to work with.
This helps prevent people from breaking the gear when they slam the car into reverse before they are fully stopped.
Unfortunately, when the gear wears down from grinding, it starts to pop out of gear.
Luckily you are able to change the reverse mechanism in the tranny so it will fully engage reverse gear!
Flipping around the reverse gear arm allows full travel and engagement of reverse.
Remove the side cover where the dipstick goes in the tranny. Watch out and don't lose the spring and
détente ball behind this cover, they shouldn't fly out but know they are there.
You should see reverse idler gear right in front of you. It is attached to an arm with a swiveling flat screwdriver
type ear to engage the gear. Note the end of this arm at its end away from the idler. The notch cut in it to engage reverse shift fork is
offset, not centered. Note which way it is offset. We're going to flip it so the offset is to the other side.
Remove the 10 mm bolt securing the arm to the shaft, remove the e clip holding the swivel to the arm. There is
a washer spot-welded to the arm where the swivel came off. Carefully remove this washer in order to place it on the other side of the arm.
I use a hammer and chisel with the arm in the vise. You could use a hacksaw if you want. Switch everything to the opposite side of the
arm than it was originally so that the offset notch in the top is offset the opposite way than it was.
There is a spacer/pivot point that rides in the center of the arm. With the other pieces off the arm, temporarily tighten it in place on the tranny and check for play
by pulling in and out on the arm. If you need to adjust for this play, you need to slowly file away the surface of the spacer where it
extends from the arm until you can bolt it up and still have free pivot action, but little play (better too loose
than too tight so don't go too far with the filing).
When this feels right, make sure the end for the gear turns smoothly in the washer you removed, don't worry about fastening the washer down,
it won't go anywhere, its there to strengthen and space the assembly, just file it smooth from the old
weld marks(do the same for the arm marks) and secure it with the clip.
Reinstall with LocTite on the bolt torqued to 50 INCH/lbs.(snug with a regular wrench will do with the LocTite).
If you notice how far reverse is engaged before the mod you see that 50% gear mesh between 1st and the idler is about all you get from the factory.
A great all purpose sealer for the car line is LocTite's 518 Anaerobic Gasket Eliminator. Its space age stuff that really seals and is factory recommended for
a lot of engine and transmission repairs. Parts stores here carry it. No danger of it clogging an oil pickup or passage like excessive
silicone sealers that break off and drop down, it only sets in the absence of oxygen (between parts).
After the repair, you might want to check the motor mounts, especially the front one.
To get the best shifting, check the shifter's white plastic ball and bushing on the shaft in the housing.
Lubing here with wheel bearing grease smoothes things up.
Look at the shifter adjustment and on early gearboxes (-86.5) the external centering mechanism and its spring.
/ saab / Fix_My_Saab_Backup / Saab_900 / Transmission_Rebuild
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- clean_case.jpg
- differential1.jpg
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- oldsynchro1.jpg
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- pinionhousing1.jpg
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- synchros.jpg
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- tranny_reversefix.jpg
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