Trailing arm alignment

[Bad Bob]

Thanks David. That gives ma a good idea of where to start.

[jhoefer]

One other thing to keep in mind, a height-adjustable trailing arm pivot does not just change camber. It also alters the rear roll center height. This will alter the car's understeer/oversteer balance. How much depends on the amount of adjustment and whether you'll notice depends on how hard you push the car.

For comparison, if you look at a BMW E30 DTM rear trailing arm setup, it has a vertical adjustment on the chassis' pivot point for independent roll center changes just as in the previous examples in this thread. By moving one of the trailing arm's pivots up or down, you are changing the angle of its rotational axis and this changes the roll center height. But then there's a second vertical adjustment just behind the pivot on the trailing arm itself to allow for camber changes independent of the roll center. For this one, the actual points the trailing arm is pivoting on don't change. This adjustment only changes the angle of the axle in relation to the pivot axis so only camber changes. Further, by using a rod end as the trailing arm's pivot, this setup also gives independent toe adjustment. http://www.locostusa.com/forums/viewtop ... 4f#p165868

On a Porsche, you can use the camber adjustment between the spring plate and trailing arm to help decouple the roll center changes of an adjustable inner pivot box from the camber settings. On a VW, it takes some modifications to get that much camber adjustment.

And if you're that deep into it, you can also change the camber and toe gain curves by moving the inner trailing arm pivots forwards or backwards.

[Bad Bob]

So, I've finally got around to making an inboard pivot points. The 3/4" hiem joints are probably overkill, but the price was right. There is a 1/2" of adjustment up or down from the center with spacers on the bolt. [img]

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[dd-ardvark]

Hey Bad Bob

Kudos for thinking out of the box on that pivot point..., very nice idea. I love it when someone figures out something you've also been toying with, without you exhausting your time.
This does makes adjusting the chamber very simple and you have a bit of toe adjustably too.

This is cheap enough, I can't see more than about a $150-200 in parts, welding and time.

I can see the key piece here is setting the Trailing Arm up though..., so please elaborate.

David / dd-ardvark

[Bad Bob]

David, the only part I purchased were the rod ends and the bolts - about $60. The other parts were from the scrap pile. The tabs/gussets are 1/8" sheet and the threaded boss on the trailing arm is 1" round bar drilled and tapped 3/4-16. Install the spring plate where it would normally ride ( I set mine about 3/8" above the stop). Then bolt the trailing arm to the spring plate in a neutral position. I tried to get everything in the middle of its range of adjustment before welding. Next, I used a laser level to shoot a line down the center of the pan and marked it on the wall. The laser was placed on the outboard surface of the wheel bearing housing to make another mark on the wall and pulled the trailing arm inward until both the laser lines are parallel to get the toe neutral. I cut about 2" off the trailing arm where the rubber bushings are. The 1" boss will fit inside the arm pretty well and just needs a few tacks to hold it in place. After it was tacked, I used the O/A torch and a hammer to form it around the boss before welding. If you can't see it from the pics above, there are 1/2"spacers above and below the rod end to allow vertical adjustment on the bolt. I hope this makes sense. See JHoefer's BMW link above for more ideas.