Finally going to fix this rear axle...

[a12]

So here's some pics, please excuse the mess it's an old barn I was doin this in:

[a12]

O.k. so pics below are meant to illustrate the basic idea for measuring camber and "average" toe.

Here's the procedure and results:
Make sure you level the axle before doing this, it will give you more accurate measurements. By extending bars outwards as I did, you are basically using a method known as "similar triangles". If the bars are straight, by magnifying the difference between measurements by extending the surfaces, the measurements become more accurate. tan^-1 (inverse tangent) is used to find each angle, but for small angles, inverse sine could also be used. Make sure you have 2 levels, a pair of calipers, and a tape measure handy.
So, in pic 1 you can see I measured across the hub mounting faces using the tape measure, extended two straight bars outwards a known length (16" in my case), made sure they were level with each other,and measured again.
In pic 2, I clamped the bar to each hub mount face, leveled it out vertically and held a 24" level against it, firm against the top surface of the hub mount. I then very carefully pulled the base of the level out until the bubble became perfectly centered in the viewing window, and measured the gap with the calipers at the bottom where the level was pulled away.
Here are the calculations:
***Note: make sure your calculator is in degree and not radian mode.***
"Average" Toe:
X=[(measurement across back)-(measurement across front)]/2
Y=distance between front and back measurement.

tan^-1(X/Y)=degrees toe

Camber:
X=distance level needed to be pulled out to center bubble.
Y=Length of level

tan^-1(X/Y)=degrees negative camber
(very unlikely you would have positive camber on one of these axles, if you did, when you pulled the level away, the bubble would get further from being centered.

My measurements for toe were X=1/8" & Y=16", so my average toe came out to be .2235 degrees per side.

For camber, my X=.5-.51" per side and Y=24", so my camber came out to ~1.22 degrees per side.
I think these measurements are pretty good, Justinjameshayes (who I bought the axle from) informed me the tire wear was good on the car this axle came off of (straight wear right across the tread) and this really confirms that. I would have liked to have checked toe per side and not just the average, but I had to get the axle to the weld shop to get braced up so I didn't have time.
Abbott Racing specifies 1 degree negative camber and 20 minutes of toe in for optimum handling and roadholding.
Saab factory specs are -2.1 to -1.1 degrees negative camber and 1mm toe out to 3mm toe in for a 16” tire and wheel package (didn’t do the math on this one).
Well, 1.2 degrees negative camber is pretty close to 1 degree negative camber and any small changes can be made with shims available form genuinesaab.
When talking degrees, 1 minute is equal to 1/60 of a degree, so 20 minutes is actually equal to 20/60=1/3 of a degree, or .333 degrees. I measured about .2235 degrees average, so this is also pretty close. I would say this is a pretty straight axle and it will be interesting to see how close my measurements were when I get a four wheel alignment done in the near future. I will keep you guys posted and put some pics up when I get the axle back form the weld shop.
Hope this helps people out in the future.

[justinjameshayes]

Hey man. Let me just say, amazing what you've got so far. After we talked at MiccyDee's I went home and tried to sketch what you were saying. I'm thankful for this post, as I didn't get very far.

Also, I'm sorry the axle wasn't 100%. The tread on the tires are dead even at 7/32, in and outside, from the car that axle was taken from.

At any rate, thanks for the pics and the awesome explanations. I'm pulling my donor axle tomorrow... and bringing it right to the shop to get a brace welded. I'll take pics and post em. Keep the progress coming!

[a12]

Originally Posted by justinjameshayes

Hey man. Let me just say, amazing what you've got so far. After we talked at MiccyDee's I went home and tried to sketch what you were saying. I'm thankful for this post, as I didn't get very far.

Also, I'm sorry the axle wasn't 100%. The tread on the tires are dead even at 7/32, in and outside, from the car that axle was taken from.

At any rate, thanks for the pics and the awesome explanations. I'm pulling my donor axle tomorrow... and bringing it right to the shop to get a brace welded. I'll take pics and post em. Keep the progress coming!

Nice-glad for the extra info on the tire tread that gives me some piece of mind that it will be straight.
Hope your axle comes out nice, make sure you check it before you brace it up.

[a12]

So I took the axle to a weld shop and it sat there for a week and a half. The guy never started it, said he had "bigger jobs to do" every time I called.
So me and my buddy from Uconn (both ME students there) went with his pickup truck and got it, brought it to an undisclosed shop and Tig welded it ourselves. He's on the Uconn Formula car performance team and is a pretty good tig welder.
It came out really nice, it's reinforced with the chromemoly at 3 different surfaces on each side of the axle.
It was then painted with Duplicolor Black brake caliper paint which almost dries to a powdercoat-like finish.
I hope to get it on this Friday (Good Friday) and take it to the Uconn car show next weekend (April 10th).

I will post up some pics soon.

[hstanton]

Nice to someone doing more than strap-ons, oops I meant bolt-ons, and calling it 'custom'.
Love the ingenuity - keep it up!


p.s. Pics or it didn't happen

[Sleepy7666]

I'm interested how this turns out. Best of luck to you a12!

[a12]

Here's a bunch of pics of what I did to brace it:

[Marks9-3]

Originally Posted by a12

Here's a bunch of pics of what I did to brace it:

Looks good. Interested in how it drives!

[a12]

And more....

[a12]

Originally Posted by Marks9-3

Looks good. Interested in how it drives!

Drives much better!
It is driving straighter even though my steering wheel is crooked now-I must have been correcting for this that much and didn't even know it. My old axle had 6 degrees negative camber on the drivers side before I shimmed it with 1 thick and 2 thin shims (which is actually more than you are supposed to put), and even then I think it was at like 3 or 3.5 degrees on that side, AND the toe was way out too. The front of that rear driver's side tire was actually sticking out when it's supposed to be slightly pointed inward.
I have to get an alignment but I can say for sure it already feels better and is driving straighter.

I put one thin shim on each side of this axle, just for good measure. We will see how it is when i get an alignment.

[a12]

You can see in the pics there are 3 different points of reinforcement on each side:

1. Webbing between twist axle and axle arm that hubs are bolted to. (3/16" thick 4130 chromemoly plate).
2. 1" O.D. 4130 chromemoly tubing (.095" wall thickness) from front of hub mount to axle arm.
3. Triangulated pieces added to rear portion of hub mount upright (also 3/16" thick chromemoly).
These were all tig welded as well.
I figured I did not need to triangulate the front of the hub mount upright as Yankton had done since the tubing was already there for reinforcement to arm portion.
Also, we finish welding the seams where they welded those arms onto the twist beam. They had not welded it all the way at the factory so we completed it.