85 900 turbo stripping

[Geoff]

hey, is that the Killer Colt in the background?

[Luke]

Ok, just not a massive difference that would be noticeable if you look at one without the other right there to compare.

Ok I measured the axle last night:

99: 1.95" OD
900: 2.15" OD

So thats not as much as I thought. But by my calculations it should result in an increase in stiffness of 35%

[Crazyswede]

have you tried to straighten any of your bent rear axles?

[Luke]

I haven't tried bending any back. I have heard of people purposely bending them to get a bit more rear camber but with a solid rear axle there is no camber change anyway and with todays tires I don't think its really neccesary.

[airsweden]

I remember reading something a few years ago about Abbott tuning the NG 900 for track. They said that one of the biggest handling improvements came when they sorted out the rear. They built some sort of jig after that to make make the adjustment consistant.
JT

[Jordan]

I thought putting in negative camber was to account for camber changes caused by body roll. The front suspension isn't supposed to change camber either through its normal travel, which I thought was the point of double a-arm suspension. But if the whole body rotates (enough to rotate suspension also) due to body roll, there is a camber change...no?

[Geoff]

In an equal length 4-bar linkage all parts will remain in their alignment as the linkage travels through it's motion. The dual a-arm suspension is a 4-bar linkage, however I seem to remember that it isn't equal length. I'm ashamed to say I've never measured....

[GRMPer]

Ideally, on a production car, you'd want a small amount of negative camber gain through the suspension's travel, to counteract the body roll. Say what you want about sport compacts...Civics/Integras are pretty good about this

[Jordan]

I'm ashamed to say I've never measured....

Right Geoff....right. :lol:

[Hans]

The 99/900 front is unequal length, non-parallel.

I haven't done it, but you can bend the rear axle with either brute force (a local alignment shop uses chains and jacks) or by heating the top center of the axle.

Pyrometer data from autoxing my 89T show that the rear wheels are not flat during cornering (the data also show that they aren't doing much more than going along for the ride). Just watching a beam axle FWD cornering on three wheels (a.k.a. "the pissing dog") confirms it.

I couldn't tell you the extent to which bending the rear axle would help on gravel, but I do know that folks racing Saabs on tarmac do it; long-time 99/900 racer and dealership owner Brad Schaffner, whom some of you may know from Saabnet, once told me that they spend much more time setting up the rear on their circle track cars than the front**. Paul Eklund, who now plays in dirt but who once autocrossed a 900T, recommended that the rear axle be bent as well. And guys racing FWD IT cars change their camber, too -- but they're lucky (some of them, anyway): unlike Saab, you can shim the axle to change camber. (See http://itforum.improvedtouring.com/forums/ if yer bored.)

**Brad's got two adjustable trusses atop the rear axle that attach at the center of the axle and span up to the highest point on the spindles. The trusses can be tensioned to bend the axle up (more neg camber) or relax it (less). This can be done on a regular 900, but you need to do it in a way that doesn't interfere with the panhard bar. It's easily done on Brad's car because the panhard bar has been moved off the top of the axle. (His car generates enough cornering force to bend stock panhard bars!) If you go to Saabnet's performance board, search "brad", find one of his posts, click on his name, you can see his gallery of his notchback racer -- it's a pretty cool car.

And if you've got some time, also check out the portable engine dyno they attach directly to the car!

[Jordan]

Very interesting...

[Crazyswede]

Last night I pulled the computer and tail lights out of the shell. I then went and worked on the old rally car and stig for a little while. I had to pull the clutch out of stig since I had my spline tool in the pressure plate. That clutch came out nice and easy as did the one in the rally car. Once I had the clutch out of the rally car I noticed that the pilot shaft bearing that should have been in the flywheel...wasnt in the flywheel. I dont know if it fell out somehow when I pulled the clutch, or if it wasnt in there to begin with. I am leaning towards it not being in there to begin with do to the mode of failure in the drive chain housing. When I pulled the input shaft out of the clutch, the top chain sprocket fell down and was totaly loose. Generaly this sprocket requires a snap ring to come off for removal. I am starting to think that maybe I missed putting the bearing in and the input shaft was floating around putting excess force on the upper chain sprocket. Sure this would have vibrated a lot and made a lot of noise.....but the car has a very loud exhaust and hockey pucks for motor mounts so there is already lots of noise and vibration. The extra force on the sprocket probably caused it to fail, or pop its snap ring resulting in drive chain failure. It looks like the front cover survived ok. Tonight I hope to jack up the front of the engine and pull the front cover off and take some pictures.

[Geoff]

that would explain the two drive chain failures you've had with different trannies in that car.

[Crazyswede]

The first drive chain failure was in a different transmission and the chain sprocket did not fail like this one. The first one failed because the jb weld that was covering the hole on the bottom popped off and the chains went dry. I am quite certain that there was a bearing in the flywheel then. Its possible that there was a bearing in this one too and it fell out when I pulled the clutch....I have to look on the skidplate tonight to see if its down there.

[99Super]

Both my 78 99 and my 86 SPG have bent rear axles. I took them to a local alignment shop and had them put a 2-3 degree bend in the center. The one on my 99 torned out perfect and really helps the way the car handles, especially in heavy cornering. Actually makes you feel like the back end is sharing some of the work.
The results on my SPG were more mixed. I think they got the bend a bit off and there is an extra degree or two of toe which can make the back end feel twitchy, especially if there is a bit of sand in the corner. OTOH, it corners like crazy!

john