C900 5 Speed Gearbox Rebuild - Nutcase Style

[nutcase]

Oh I doubt putting locking f on the nuts would do any harm, not entirely convinced it would help - as long as it's properly staked they aren't going anywhere

Interesting thought on the pinion bearing housing screws though. Do you know if it happened to make removing the screws a mission when it came to another rebuild?

[Jim Mesthene]

Originally Posted by nutcase

Do you know if it happened to make removing the screws a mission when it came to another rebuild?

It was no trouble at all. It's threadlocker, not epoxy.

[nutcase]

Great, thanks

[Jim Mesthene]

Originally Posted by nutcase

.... as long as it's properly staked they aren't going anywhere ....

We found that wasn't so.

[peva]

Originally Posted by nutcase

as long as it's properly staked they aren't going anywhere

Originally Posted by Jim Mesthene

We found that wasn't so.

I agree with you Jim. Staked fasteners can come loose. It's tough conditions in a gearbox.

[nutcase]

Ok thanks folks

[crwchf01]

Hey, have you thought about trimming this down to the essential step and photos and maybe making it a reference? BTW, I am increasing my accessible tools and have the block and pinion removal fitting on the way. Looking forward to not having to plan on a 2hr round trip when they are stuck

[nutcase]

Might be able to copy out a lot of it, would take a long time so not something to be done just yet

[AJs900Turbo]

Originally Posted by nutcase

Small amount of progress, got the bearing swapped to the correct SCH2212 and have fitted that along with the now single shielded bearing to the primary casing



I also re-tried pressing the pinion front pinion bearing home and succeeded. The press safety valve hissed a couple of times, but the bearings are now down to no play. Next step there is to tighten to the correct pre-load.

I've put the diff in temporarily and fitted the speedo side bearing housing. I need to find my tirque trench now so I can measure the pre-load shim requirements for the diff.

What is the torque spec for the bolts holding the cover over the left bearing?

[nutcase]

6.3-10 lb/ft and you need loctite 242 on them.

[crwchf01]

Dang Nutcase, where did you find the tirque wrench?? I need one to adjust my Johnson Rod on my Harley

[nutcase]

EBay of course!

[S900t8v]

Nutcase, I've just come across a strange thing

I have a Gm45712 from a 89 N/A, it's P/N says it should have larger rear pinion bearing, ages ago I thought I checked the pinion bearing housing and it had the same p/n as a chillcast housing.

Is this possible with a gm45x12? I thought x10 and earlier were the only ones with chillcast pinion housings?

[ejenner]

There is a lot of cross-compatibility across the boxes. On one occassion I even had the case milled-out very slightly where the pinion housing sits so the earlier case would accept the pinion housing with the un-equal bearings. Can't quite remember the exact details but at the time it seemed like it was a necessary modification.

For my personal rebuilds I tend to aim to get the chillcast bearing housing from the 88-era boxes as the forum rumour factory suggests they're stronger.

[spg1]

Originally Posted by ejenner

There is a lot of cross-compatibility across the boxes. On one occassion I even had the case milled-out very slightly where the pinion housing sits so the earlier case would accept the pinion housing with the un-equal bearings. Can't quite remember the exact details but at the time it seemed like it was a necessary modification.

For my personal rebuilds I tend to aim to get the chillcast bearing housing from the 88-era boxes as the forum rumour factory suggests they're stronger.

Are you saying that the 88 transmissions are stronger than the 89's, or is this the case just for the pinions and not the gears?

[ejenner]

Originally Posted by spg1

Are you saying that the 88 transmissions are stronger than the 89's, or is this the case just for the pinions and not the gears?

People dig the 99t 4-speed chillcast gearbox case. I compared the weights between two empty casings. A 4-speed chillcast case v.s. 5-speed case from 1988-ish era. The earlier 4-speed case was 3kg heavier. Quite a difference considering the dimensions of the case are so similar.

In those 4-speed chillcast cases you have a choice of a few different kinds of pinion bearing housing. Externally more or less the same size. Internally more or less the same size. Bearings, more or less the same size. Just made from a different material. Of the different options the pinion housing from the 1988-ish box is supposed to be chillcast and stronger than other bearing housings. Having said all of this, I've not seen a broken bearing housing yet. So I wonder how important it is to have the strongest bearing housing.

I'd be willing to bet the 4-speed chillcast case is in fact stronger than the later cases given what I know regarding the different weights. Not so sure when it comes to guessing on different bearing housings. Bigger is probably better so the later gearboxes 1989-on had a bigger rear bearing(?) which must be better than a smaller one.

[S900t8v]

My understanding is

in <88 housings - chillcast housing is ideal (front rear pinion bearing same size as rear) (if you go later then larger rear pinion bearing is apparently better)
91+ gearsets are ideal compared to all others as they're slightly wider/more durable (although MMOE mentions that this probably doesn't matter if you shot peen and cryo treat earlier gearsets)
89-90 shift forks synchro sleeves and muffs are ideal (you have to change all synchroniser gear inc springs and possibly retainers with shift forks)

I personally shy away from 91+ for shift forks synchros etc as the shift forks were narrower, synchro rings were of different design (harder) and apparently wore considerably worse giving poor shift characteristics earlier (despite saabs intention to make them last longer) than 89-90 and earlier, as did the reverse gear and idler - many 91+ boxes have toasted reverse idlers from what people report (the 4 <88's I have all have immaculate idlers. (damage apparently because reverse gear is narrower than 89-90 and <88)

The larger rear pinion bearing is meant to be better as it normally wears out first because under load the ring and pinion are pushing away from each other, although the tranny I'm disassembling atm has a worn out front pinion bearing. Totally shot - not sure why... I have a welded 4th gear so can't finish disassembling without my press, found bits of bearing race though that suggests the front pinion race disintegrated (too much backlash on deceleration transmitting the load to the front bearing? all guesses from me at this stage)

If I'm not mistaken technically you could use <88 pinion and ring gear with 92 layshaft and gearsets with 89/90 shift forks synchro rings, muffs and sleeves to get the 'apparent' best of all worlds

This is all compiled from what others on the forum say.

Personally, I'm probably going to use 89/90 gearsets and shift forks with either chillcast <88 housing or maybe 89 housing (with large rear bearing) because crush sleeves are still available whereas pre 88 aren't. For strength I'm probably gonna try cryo treating the gears and case, the case is alloy and unless it's been over tempered it should respond well to cryo... but then again my knowledge of cryos is rudimentary. That plus a steel diff cover...

You must match gearsets and cluster gear, they cannot be mixed, just like ring and pinion. If I understand correctly you can technically put any gears on either early or late style pinion shaft (the diameter change is around the pinion housing). AFAIK you cannot use a different pinion housing than what the pinion shaft originally accommodated - obviously if the diameter around the housing is different.


All thoughts from me. Could be wrong with lots of these ideas.

[nutcase]

Originally Posted by S900t8v

Nutcase, I've just come across a strange thing

I have a Gm45712 from a 89 N/A, it's P/N says it should have larger rear pinion bearing, ages ago I thought I checked the pinion bearing housing and it had the same p/n as a chillcast housing.

Is this possible with a gm45x12? I thought x10 and earlier were the only ones with chillcast pinion housings?

The EPC does indeed say it should have the later bearing housing. Unless someone had swapped it over previously I don't think it would come from the factory to a different spec.

[nutcase]

Originally Posted by ejenner

For my personal rebuilds I tend to aim to get the chillcast bearing housing from the 88-era boxes as the forum rumour factory suggests they're stronger.

As I understand it, the 89- pinion bearing housing is as strong as the -88 8720732 Chilcast housing. Prior to that there was a sandcast unit (8720239 I think) and prior to that a die cast unit that is failure prone (possibly 8704215). Of those three the chillcast is the desired part. Not sure exactly when it was introduced, but the sandcast one came in some time in 1982 so not long after that as it wasn't used for a while. When older boxes came in for refurb the die cast housing was replaced as a matter of course (if Saab's instructions were followed!).

The larger rear bearing on the 1989- pinions give a longetivity improvement. Some have suggested however that some of the other bearings in the box get the chance to wear more in the mean time causing more damage than if the bearings are changed when the older style pinion bearings start to whine. Not sure on that one though

You must match gearsets and cluster gear, they cannot be mixed

Not sure where you got that info from? You can mix and match like for like between boxes.

[spg1]

This would make sense since with my 89 I can still drive it forward with no problems, but forget going in reverse. Too bad they didn't use two large bearings instead of one. One thing I thought as well, a foundry should be able to pour a cast steel casing and since we already have good castings to take a mold from, it should be possible. Im surprised no one has done this.