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  1. #1
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    14 Aug 2010
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    RPM-dependent gearbox whine

    Well, since I know all the be-all, end-all people have spoken on the other forums, it is time to go this one alone. I put in a set of #8 primary chains and sprockets, taking care to not lose the chain's place on the sprocket (voodoo and probably not important) and also not lose the chain's location front to back (probably actually matters). I did the whole thing according to the fabulous primary drive swap guide posted here. I torqued (75 ft-lbs) and loctited/staked the new nut, I put the tensioner in right-side-up, and I put everything back the way it was supposed to go. Being able to do 70mph at 2500rpm is wonderful, yes, but now my gearbox emits an rpm-dependent whine that it did not emit before

    The sources on Saabcentral did not say much of anything. Adrian (TooMany2cvs) thought I should look for things the chain is hitting, which was a step in the right direction. A post on Saabnet, though, revealed a bit of a surprise: the bearing in the top sprocket can go bad!

    Here, then, is my chronicle of diagnosis and treatment of the stupid rpm-dependent whine.

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  2. #2
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    First step was to acquire a new bearing. WHOA, from eeuro and The Saabsite, these are VERY expensive! I spent a few hours googling and came up with these part numbers:

    SAAB # 8710865
    Timken #s U298 and U261L (cup and cone respectively) OR U298-90011 (unit part number)
    SKF # 331579B
    Asking a NAPA auto parts store in the USA for a BR9 (or searching on the Napa site for it) will also get you this bearing, probably an SKF 331579B, and at a rate much cheaper than what eEuroparts or the Saabsite charges. RockAuto also uses the SKF BR9 part number but I haven't actually seen one of those. It comes with a compression sleeve for use in a rear axle, but this is a separate part and means nothing to us (would make a good paperweight). They also go in rear axles of certain American cars (jeep ZJ with 44 or 35 rear axle to name one), as well as in some John Deere implement.

    From Napa is more like it! $30! Done and done. Now to get a new nut...eeuroparts, here I come.

    I'm starting to think I should found a c900 gearbox parts company, given how much some of this stuff costs and how cheaply I can get it with a bit of digging.

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  3. #3
    Hear my Saab a comin' nuclear944's Avatar
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    19 Dec 2010
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    Bulgaria - Eastern Europe
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    Saab(s)
    Past: 1989 SPG & 1989 900 N/A Sedan
    Thumbs Up:   0
    To clarify things, this setup lets you cruise the country without the noisy engine and bad MPG's. It also increases top speed to...how much exactly?

    Did you get the bearing(s) replaced and is th whine still there?

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  4. #4
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    Top speed in an N/A is rather hypothetical. However, the old-style (pre-1989) ring-and-pinion also gives you a high gear ratio. I originally had this with type 6 primaries, but now I have combined this with type 8 primaries (which never happened from the factory), creating a box that gives me 2500 rpm in 5th at 70mph. 2500 in 4th is around 55. 2500 in 3rd is around 40. 2500 in 2nd is around 30. And it's not just about cruising. It makes the existing ratios more useful for American traffic and speed limits, such as we see today. For example, as I said, 75 and 55 are both at 2500, giving me ample revs to decelerate behind slow traffic or climb a hill without downshifting. Fourth becomes the gear of choice for country two-lane, and fifth is strictly a highway and downhill-efficiency gear.

    IF you want a good, high-ratio gearbox and don't want to spend money, I advise getting the old ring and pinion (I believe your cars have the new one sadly) and a set of type 7 primaries (easy to find). You'll then have a box with as high a ratio as anything SAAB ever produced from the factory. The post-'89 with type-8s will have about the same ratio as the pre-'89 with type 7s.

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  5. #5
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    And if you want to check your gearbox for what ring-and-pinion it has, look at its part number (on top of the primary case) and reference it to the definitive tranny info page.

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  6. #6
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    I pulled everything apart, which was quite a chore. First I had to grind away the peenings on the lower nut. I did so with a Dremel tool, looking through the A/C condenser. The radiator was up out of the way, like so:
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    And I could see through the A/C condenser like a keyhole, just enough to get the circlip out and dremel properly placed:
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    My compressor wouldn't put out enough pressure to allow the impact gun to pull the lower bolt off:
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    So I made a special tool to hold the upper sprocket steady (box in neutral) while I reefed on the nut with a breaker bar:
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    When I got the primary drive off, I was greeted with this ghastly sight:
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    The upper bearing had been spinning on the shaft. Egad!!
    The bearing looked like this on the inside:
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    Looks as though it was shot from the get-go (even overheated due to lack of lube once, by the look of that blue streak on the inner race).

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    Last edited by euromobile900; 20 December 2010 at 16:44.
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  7. #7
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    Upon disassembling the bearing (removed from upper primary sprocket using a drift), I found this on the outer race:
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    False Brinelling (straight line shaped marks) and some fretting.

    Rollers show some small wear marks:
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    Inner race shows massive fretting:
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    Coincidentally, this is only present on the same side as the "overheat mark":
    Name:  IMG_4396.jpg
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    Nasty stuff, eh?

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  8. #8
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    Here's how I fixed it

    The bearing had been very loose on the aluminum shaft, because of the wear of it spinning against the aluminum. Upon the suggestion of my indie mech, who lives next door, I put about 100 little dimples in the top of the shaft with a punch. The edges of these craters are raised, giving me a press-fit again.
    Name:  IMG_4377.jpg
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    I put Permatex Bearing Mount for Worn Parts on to cement the bearing well in place. Loctite would've worked too. So far, it's held up for about 50 miles and 5 cold starts. We'll see how it does in the future, I guess I am worried, and I slip the little round cover off of the primary case every time I stop the engine to see whether it's doing OK and hasn't spun.

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  9. #9
    Hear my Saab a comin' nuclear944's Avatar
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    Past: 1989 SPG & 1989 900 N/A Sedan
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    Bloody Nora!

    And I thought I was under adverse conditions during my timing chain replacement....

    Interesting compressor..looks like a vintage?

    Good job- I think it will hold up.

    My sedan had the "VT" marking as well. The PO's sister made 20 trips a year to vermont from Colorado....hence the mileage!

    I am also noticing the faded emblem...It's such a nuisance and both of my C900 have the same sickness.

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  10. #10
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    Saab(s)
    '90 900 LPT with a flat-nose conversion
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    The conditions weren't that bad inside the shed I was working in, but the trek out to the shed was arduous. I had a 500w halogen lamp that I'd shine at whatever I was working on, to warm my hands up. This way, the feet always froze first, even with big boots on.

    I just drove about 150 miles to Boston, and the bearing hasn't spun, though the gearbox "sings" at 70mph. Wonder if it's the pinion... (totally unrelated, cannot be affected by addition of type 8 primaries except that I'm going fast more quietly so I can hear it)

    The compressor is from some time after they invented electricity. Beyond that, I don't know. It's a Craftsman. I should break it and see if I can get it replaced with a new one under the lifetime warranty. It's really a carpenter's compressor, not fit for automotive use (not enough air for painting nor impact tools, but fine for the occasional nailer).

    I went to Middlebury College, and drove twice a year from Minnesota to Vermont, and once from Washington state to Vermont, but not near as often as your car! My god.

    Emblems are cheap, but I don't feel like buying one. Someday I'll find one at a junkyard and pry it off but until then I can live with it. If you want to renew yours for cheap, just buy an emblem sticker on ebay! I'm sure a quick search will turn one up.

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    Last edited by euromobile900; 22 December 2010 at 16:51.
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