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C900 Performance, Mods & Tuning Covers Tuning & Performance modifications for the Classic 900 (C900)

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  #1  
Old 12th April 2007
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Default Simple gearbox upgrade?

I just saw the post on the LSD's with a link to saabrally.com, and one of the products stated there is a steel read diff cover for the 5-spd gearbox...would that $100 save our gearboxes from most of the gearbox problems we face, and uprate it for a bit more torque?

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  #2  
Old 12th April 2007
shaverjeff shaverjeff is offline
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I would help with the flex but its not a cure.
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  #3  
Old 13th April 2007
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Its a nice touch, you need stronger bolts too
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  #4  
Old 13th April 2007
El_Raul_Turbo_Freak El_Raul_Turbo_Freak is offline
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the gear teeth will colapse and there is no cure there, so who cares if the differential is bullet proof.
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Old 13th April 2007
Eric van Spelde Eric van Spelde is offline
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The gear teeth 'collapse' because the case flexes which in turn misalign the gears.
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  #6  
Old 13th April 2007
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Default

That's what I figured. The problem with the C900 gearbox is that the casing flexes too much and this is why the gears go, because they are grinding against each other at the wrong angles, so the differential being bullet proof would prevent this type of damage.

Gear teeth do not simply collapse due to stress.

Of course, there are other methods such as chillcasting that I've heard of...the point of which, as I understand, is to strengthen the casing itself from flexing. As I understand, this is the major upgrade done to the gearbox, and then there are swapping pinions and gears for an intermediate upgrade...

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Old 13th April 2007
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Chill-cast is what we get when using a 99turbo gearbox, some of them where chill-cast, it's not (as far as I understand) something you do to the box, it's done while beeing cast, i.e being chill-cast.
I most definetly want a chill-cast at some point, as I don't fancy running around replacing them all the time, once I'm up and running 200plus bhp in the t8.
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Old 13th April 2007
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It will probably help to an extent, but it might be worth finding another supplier or making your own...100 bucks seems steep. The factory covers are pretty rickety, though. At best it will probably reduce stress enough to have the pinion crack later rather than sooner, under big boost
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  #9  
Old 15th April 2007
Adrenaline406 Adrenaline406 is offline
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what about this coupled with the internals? might be as close of a fix as we can come.

edit: those internals are listed at 38,570 Kr. When i convert it it comes to $5,618 USD, 4,551 Euros, or 2,833 GBP... mighty steep there...

Last edited by Adrenaline406; 15th April 2007 at 04:27 AM.
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Old 15th April 2007
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I didn't think the casing could flex enough to cause this kind of problem, looking at my gearbox casing it has alot of ribs all around it, it seems like it would have to snap or crack before its flexed?

You could just take your gear casing to a metal foundry and have them dip the case into some more alloy a few layers of alloy will make it heavier but I am sure it would make it much stronger and resists this flexing you guys are worried about.

You could weld up some mega crossed ribs around the casing as well, thats really cheap and cost effective.
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  #11  
Old 15th April 2007
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I recently found a Saab spec on materials. From what I can tell, "normal" gearbox cases are made using sand castings, chillcast (kokill) are gravity die cast. To quote: "Aluminium castings made in permanent dies are, as a rule, stronger than sand castings". So both types are gravity fed as opposed to pressure fed (why didn't saab do that? Screw the cost!), but the chillcast as well as having additional strengthening ribs (possibly only possible with a permanent die?) but use a different mould method altogether.
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  #12  
Old 15th April 2007
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Richard, could you scan that spec (hi-res! ) and put it on the forums? We've ever seen literature from Saab to substantiate the chillcast gearbox thing.

Everything I have ever read about the gearboxes as been second-hand. Would be very useful to put some credibility on the subject.
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  #13  
Old 15th April 2007
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Don't need to - it's all on the web (easy when you've got something to search for!)

http://supplier.saab.com/std/docs/500012.pdf

Ooh, now this looks to be a very technically interesting site:

http://supplier.saab.com/std/ext/indexe.html

I should point out that it's an assumption on my part that these standards apply to the gearbox cases.
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Last edited by nutcase; 15th April 2007 at 07:09 AM.
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