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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Old 03-10-2010, 03:34 PM   #1
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Finally going to fix this rear axle...

O.k., so my rear axle has been way out of whack for a while and I'm finally going to fix it. I had like 6 degrees negative camber on the driver's side rear and I keep going through tires like crazy. I tried the shims genuinesaab sells but they don't provide enough adjustment to fix the problem. I could only get it down to like 3.5 degrees and still have crazy tire wear.

I bought a good used rear axle and am going to brace it up. I already ordered some 4130 Chrome moly steel plate and tubing, which is basically the standard for reinforcements in both the aerospace and automotive fields due to it's strength, weldability and modest weight.

I will post pics up on here and explain what is being done to reinforce it and why.

If anyone can also post up what they have done or any suggestions please feel free to do so.

I am going to do more like what Abbott Racing has done and not take the Yankton approach.

I feel the Abbott approach maintains more of the suspension movement and will not affect handling in a detrimental way.

Abbott method: http://www.abbottracing.net/product.php?id_product=223

Yankton method: http://www.kyankton.net/saabng900/suspension.htm

More to come soon...
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Old 03-10-2010, 03:52 PM   #2
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you building a jig?
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Old 03-10-2010, 04:24 PM   #3
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Ahhh, just what I need to do. Sorry I couldn't have helped you with that axle I have, but I really need to do this too. 3 months/5k miles on a set of PZeros is not cool...

I'll be watching this thread.
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Old 03-10-2010, 04:59 PM   #4
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Yeah no problem on the axle Seth, this one looks to be in good shape and the guy I bought it from (Justinjameshayes) assured me the car it came from had no rear alignment issues.
I don't have a jig, but I do have a magnetic base and dial indicator. I may rig something up to check it out.
I plan on having it welded slowly to keep any chance of warpage to a minimum.
If it's done slowly there should be no issues.
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Old 03-10-2010, 05:11 PM   #5
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I really can't see much from that picture on the abbott site. Do you have it enlarged someplace handy?

My plan in my head up to this point was to do something similar to the picture of KY's car. But you're right that this could definitely affect handling. Seems that putting braces there would be like putting a pretty stiff ARB in place. And, I'm not thinking that the axle warping in that place is what is causing the issue.
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Old 03-10-2010, 05:50 PM   #6
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Originally Posted by stromer View Post
I really can't see much from that picture on the abbott site. Do you have it enlarged someplace handy?

My plan in my head up to this point was to do something similar to the picture of KY's car. But you're right that this could definitely affect handling. Seems that putting braces there would be like putting a pretty stiff ARB in place. And, I'm not thinking that the axle warping in that place is what is causing the issue.
No you're right I feel the same way, it's the arms that come off of that main twist beam that are getting bent, not the twist beam itself.
I don't have an enlarged pic, I tried but it didn't come out too great-too pixelated.
Eliminating that flex of the twist beam (torque beam) will cause extra understeer, and coupled with the stiffer rear sway bar will give the vehicle a great tendency to have the ass end break loose. The flexing of that beam allows both wheels to stay planted longer. If you just stiffen the whole thing, one wheel will lift sooner and you will loose traction-less warning before breaking loose.
That's the way I see it anyways.
I think the reason it has a tendency to bend also is the positioning of the spring and wheel hub attachment location. If you picture hitting a pothole or big bump, the spring will act to push down on the inside of that arm and twist the axle clockwise (when viewed from the back), if you look at the wheel, the torque when that hits the bump will also want to turn the arm clockwise: so you have to forces working together when you hit a big bump trying to twist the axle in the same direction. Does that make sense.
What I'm basically saying is if they had located the spring perches on the centerline of those arms they would not be trying to twist the arms everytime you hit a bump.
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Old 03-10-2010, 07:39 PM   #7
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What you're saying about the spring perfect makes perfect sense. I wonder if there is a way to strengthen just this part of the axle. Something like "boxing" it, or at least making a splint.

My other thought is what "causes" them do bend like this. Obviously its wear, but are the stiffer sway bars, stiffer springs, or stiffer dampers making it worse? I'm curious to consider if just swapping in a 100k axle from a stock 9-3 would be a fix, or better at all.
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Old 03-11-2010, 07:51 AM   #8
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What you're saying about the spring perfect makes perfect sense. I wonder if there is a way to strengthen just this part of the axle. Something like "boxing" it, or at least making a splint.

My other thought is what "causes" them do bend like this. Obviously its wear, but are the stiffer sway bars, stiffer springs, or stiffer dampers making it worse? I'm curious to consider if just swapping in a 100k axle from a stock 9-3 would be a fix, or better at all.
Yeah I think swapping another one in is useless, especially on a performance car, it will just bend again. The stiffer sway bar would actually help prevent bending, but stiffer springs would help aid bending. Just look at the way each one of these is trying to twist the axle when force is applied.

All this twisting is causing the negative camber increases.

I need to put up a pic, but what I'm going to brace is kinda like what abbott did on the outside, but also brace a little bit on the inside portin of the arm, and further triangulate those uprights where the wheels attach. That will give additional rigidity but still allow the axle to flex in that center piece as it should.
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Old 03-11-2010, 08:16 AM   #9
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This is what I am thinking of doing:
(Thanks cruzer51 I used your pic hope that's o.k.)
All braces would be triangulated with 4130 steel plate and tubing.
Attached Images
File Type: jpg rear axle possible bracing.jpg (39.4 KB, 85 views)
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Old 03-11-2010, 05:16 PM   #10
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Good news. My rear axle must be f'd. inside tread is steel belt and outer is mint. thought it was just me.


BTW, I'm looking for an axle. what fits a 2000 Viggen ???
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Old 03-11-2010, 06:59 PM   #11
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Good news. My rear axle must be f'd. inside tread is steel belt and outer is mint. thought it was just me.


BTW, I'm looking for an axle. what fits a 2000 Viggen ???
I think they are all the same, ng900-og9-3, 1994-2001. Check to make sure but I think that is right.
Yeah mine are down to steel belt also, it will be great once fixed.
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Old 03-12-2010, 01:15 PM   #12
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Sooo I took some measurements today. Kind of a crude method, but I wanted to check the axle to make sure it was straight. I came up with about 1.2 degrees negative camber each side and approximately 0 degress toe. The method I used is not super precise, but gave me some piece of mind and now I know the axle is really close, i can shim it the rest of the way. I will know the exact numbers once I get it on and bring it in for an alignment.
I took some pics and will post them up with how I checked the camber and toe.
It's amazing what can be done with a couple of levels, a tape measure and dial calipers.
Axle is currently at the weld shop waiting to get braced up.
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Old 03-12-2010, 03:09 PM   #13
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Quote:
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I think they are all the same, ng900-og9-3, 1994-2001. Check to make sure but I think that is right.
Yeah mine are down to steel belt also, it will be great once fixed.
Up to 2002 also.
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Old 03-12-2010, 03:10 PM   #14
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Originally Posted by a12 View Post
This is what I am thinking of doing:
(Thanks cruzer51 I used your pic hope that's o.k.)
All braces would be triangulated with 4130 steel plate and tubing.
I like your strategy. It was kind of what I was thinking in my head, but the picture makes it a lot clearer.
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Old 03-12-2010, 03:17 PM   #15
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I like your strategy. It was kind of what I was thinking in my head, but the picture makes it a lot clearer.
Yeah I think maintaining as much of that twist feature is key. Strengthen the arm parts and allow the center section to flex as it was designed.

Once I get it back from the weld shop, I'm probably gonna have my friend grit blast it, I will then paint it with Duplicolor caliper paint. I used this paint on my strut housings and it actually holds up really well, dries hard and shiny, it almost has the look and feel of a powder coat.

Have you tried just shimming your for now Seth? How far out is your camber?
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Old 03-12-2010, 03:19 PM   #16
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Up to 2002 also.
+2003 vert...
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Old 03-12-2010, 03:38 PM   #17
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yeah, the yankton rear axle would be incredibly unsafe, IMO. the rear axle is designed to flex. the ARB limits that flexing. between the bracing he did, and the HUGE mp performance anti roll bar, that car would be as tail happy as a drift car, until the rear axle snapped in half.
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Old 03-12-2010, 06:01 PM   #18
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yeah, the yankton rear axle would be incredibly unsafe, IMO. the rear axle is designed to flex. the ARB limits that flexing. between the bracing he did, and the HUGE mp performance anti roll bar, that car would be as tail happy as a drift car, until the rear axle snapped in half.

lol

Yeah that's the last thing I want is the rear end comin around on me on a twisty highway at 80 mph.

It's funny, iirc people on Saabnet were asking Kevin Yankton to post up reviews on the rear axle after the car was complete, I never heard anything. I know he sold it, I'd like to find out how the rear of that car handled.
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Old 03-12-2010, 11:45 PM   #19
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lol

Yeah that's the last thing I want is the rear end comin around on me on a twisty highway at 80 mph.

It's funny, iirc people on Saabnet were asking Kevin Yankton to post up reviews on the rear axle after the car was complete, I never heard anything. I know he sold it, I'd like to find out how the rear of that car handled.
I sure on ice it would have handled well.
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Old 03-13-2010, 06:18 AM   #20
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Have you tried just shimming your for now Seth? How far out is your camber?
Its beyond shimming... But I might just shim the new axle when I put that on and see how it does. I would rather fix it for good though with some bracing. AND, I would rather brace it while its more or less true, than source another one later on.
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