Rear Double A-Arm Suspension ?
 

Anyone here using a double wishbone/A-Arm rear suspension? What are you using for uprights. I am considering building my own using Beetle bearing housings and 930 axles. I will fab my own control arms.

Here ya go. I don't think it was ever completed. Look under Pictures.

Dobergoose

I think getting the back clip off of one of these babies would be perfect.

Saker Motorsports

Jason

Thanks, I belive these are the bits and pieces I saw on the GermanLook main page under suspension. The uprights are similar to what I had in mind. I would make them using the Beetle bearing hubs that I can get aftermarket. Now your other alternative would be killer but I can only imagin what the cost might be. You're using a strut setup aren't you?

Yeah, I'm using MkII KW Variant III coilovers. I know the shocks will be great, but I'm worried about front end geometrys transition to a rear application.

I thought about using an upright from a fwd application. and fabing a new top to accept a ball joint or bushing like the Fiero/Lambo guys do. I would think in your application getting the length and location of the tierod correct is the big concern. Bumpsteer and all. I think I'm going to start fabing up a set of homemade hubs and see how it works out.

Yeah, I'm sure I'll probably have toe change issues. I'm prepared to change the inner tie rod pivot points up and down and forward and back, and also relocate the outer tie rod ends to the bottom of the spindles. I just don't know yet which way I need to go. The guys at Momemtum Tuning back east did a mid engine 1.8t conversion into a MkII golf, and they had toe issues, but I don't really know what ride height they were using and what angle the lower control arm sat at.

Jason

If it were double a-arm, mapping out the pivot points would be easy but I am unfamiliar with the Strut setup. I suppose you could mock something up easy enough and see what the results are through the suspension travel.

Anyway, I'm going to draw up my rear hub carriers in Auto Cad and post it as a jpg and let anyone who wants through darts at the design and see if I'm overlooking anything.

Hey -Oval,

I'm doing a 5-link IRS, somewhat similar to what you're planning. I happened to luck into a NOS set of Chassis Shop uprights after looking around quite a bit to see what was available. Unfortunately, C/S no longer makese these uprights - which are pretty neat because they'r fairly lightweight and take all standard air cooled bearings and stub axles.
The other alternative as I see it is either go with alloy formula car style uprights (these generally take water cooled VW bearings & axles), or the more reasonable approach cost wise is to adapt a set of standard FWD spindle assemblies - the ones that use bolt-on struts. Modify the upper mount to take an a-arm or link, fab up a custom lower arm to fit the ball joint and use the steering arm for a toe link.
Either way, it's a lot of custom work - but seeing your frame and oval project it doesn't seem out of line for what you're building.

Jeff

PS: Jason,

The correct location for the tie rod/toe link is on a line that extends from the tie rod connection point at the spindle - that is the exact center of the "ball joint" of the tie rod end - to the virtual swing arm vertex point. The VSA vertex is determined by using a front view (or maybe rear view in your case) of the as-built suspension geometry.

The short version is: remembering you're working from the actual pivot point centers (which may or may not be directly in-line with the suspension members!) - you draw a straight line from the lower spindle (main) ball joint through the lower chassis a-arm pivot point, extending out the other side of the car. Now draw another line that passes through the upper strut pivot point and is 90 degrees to the strut axis (or more accurately 90 degrees to the line that passes through the upper and lower strut pivot points, the exact centers of those joints). Where those lines cross is the VSA vertex and will determine your roll center among other things. Going back to the tie rod - it should fall on another line that crosses that (imaginary) vertex point, but coming from the tie rod joint "center" at the spindle. You have to plot everything out on paper to determine these imaginary points, but the tough thing is doing the measurements from the chassis itself - to figure out where these points actually are in space! I just spent the better part of this past weekend doing just that on my aftermarket Mustang II suspension parts, to be able to reverse-engineer the design and create the proper pick-up points on my tube chassis buggy.

Cheers,
Jeff

Thanks for the feedback. GS, do you have a picture of the Chassis Shop upright?

Thanks guys. I'm going to have to do it with the suspension travel method. Lasers are cheap these days, so I'm going to attach on on either wheel then have a white board behind to trace the travel path. The trouble is that this car has anti-lift(?) built into it. The rear inner lower control arm pivots make a V that points to the front of the car, when the V should point to the rear of the car. I'll just have to see how well I can make it work.

Jason

If i got it right this setup is used on the lotus elise/exige...(lucky enough to be able to see such a rolling chassis every day) the rear a arms have the V that Jason mentioned and viewed from the top the V goes well to the front of the car, but ALSO to the centerline (centreline). Actually the pivots are located at the front of the engine bay,similar to where the normal IRS trailing arms pivot points are on a beetle.

Chris

Yep, thats the trouble. My BMW is the same, there is a main pivot point almost in front of the rear tires. I might be able to do something like that later, we'll see. I believe that's the kind of wheel travel I need.

Jason