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C900 Tranny Rebuild
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.

Clean Case

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.

Pinion Housing

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.

Synchros  New 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.

syncromesh sleeves

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!

Old Gear

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.

Bad Reverse Gear

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?

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