Diagonal Control Bars for swing axle suspension

[choc-ice]

Does anyone have experience of this tuning mod from the 60s?


Back when all this was just fields, and swing axles were something to be worried about, Superior made their Control Bars. You can see how they fit from here:


I'm considering making a set up but I can't quite get my head around whether they'll work or not, and as an Engineer I feel this is quite important before I get much further

I know that Renault used diagonal bars with their swing axles on the Renault 8 (I had one, it handled very well!) and Alpine A110. But they didn't have the VW steel trailing arm, they just used coil springs.

The demon modification back in the late 60s was to fit these in conjunction with a camber compensator, and EMPI did this to one of their race cars.

When I look at the system, the only thing I can see it doing is trying to bind up the system and pull the trailing arm into funny shapes.

Does anyone know if it'll help? Or what it will do? It doesn't seem to fit into any suspension type that I've seen so I can't see if it'll help the roll centre or camber change.

Converting to semi trailing arm suspension isn't an option for me by the way!

Any thoughts would be appreciated

[kdf]

I've never seen such a device before, but I can give you an educated guessimate.

Seems like this is a z-bar (camber compensator) like device, except it doesn't connect the rear wheels to each other. When the rear wheels are vertical (zero camber) the spring rate is zero. When there is bump or droop the spring rate will increase, thus the device will try to combat camber change from 0 camber. It also assumes that 0 camber is the hot setup, and isn't sensitive to camber change.

If it bends the trailing arms, it will be ineffective, because the forces to combat camber change will be "lost". Also the connection to the torsion bar housing is a bit questionable.

I can't see any benefits that this device would give, because with a swing axle you will probably have limited the droop travel, so it would have the same effect as increasing the rear spring rate.


I'm in the process of planning a swing axle bug for track use. I already have the car, but other projects use all my time.

In the rear I've planned to use a push rod operated monoshock suspension, limiting only camber change and bump, and a small roll bar to give some roll resistance at the rear. I've also planned to limit droop so that the camber can't go positive.
The car will be extremely light, below 1300lbs, because I think that the swing axle geometry will only benefit from a lighter weight. The CG height will also be kept as low as possible.

[sideshow]

I can't figure that out either.
When pushed swing axle car makes odd movements, maybe back in the day this was to reduce what was assumed was shaking of the tires. It looks to me like a device to stiffen the swing arm.

Now the big question is did this ever work?

[Marc]

I've only seen one set of these before (also not installed), about 25 years ago. We too pondered what good they could do. The only thing I could come up with is that they'd take side-thrust loads which would normally be handled by the axle-tube bells pushing against the sideplates and fed to the chassis via the trans mounts - I suppose that would reduce binding of the suspension and wear & tear on the mounts. You'd have to fit them to a car to see if they would also limit travel in either direction, but if that's their goal it seems to me there are simpler ways to get there.

[helowrench]

looks almost identical to the front suspension mod that ties in the lower frame with the outer ends of the front beam. (used to eliminate flexing)


rob

[choc-ice]

Some interesting replies, thank you! Here's a close-up of the installation picture on the box


As I said, on EMPI's racer, it was used in conjunction with a camber compensator, this car still exists and handles very well, but there's no chance of the owner taking these control arms off and giving a "before and after" comparison.

I think I agree with kdf, it's going to stiffen the rear suspension in bump and droop as well as roll, but wouldn't a set of T3 Squareback torsion bars do a more controlled job? I like the sound of your monoshock idea, I think Mercedes did something similar in the 60s with the Fintail!

Sideshow & Marc - you could be right about stiffening the trailing arm up, but are side loads on the axles really that bad? Grippy tires and sliding around tend to destroy wheel bearings, but I've never heard of a gearbox get damaged. I think it was marketed as a handling improvement rather than something to make the car last longer anyway.

I suppose the other question in my mind is whether it's worth getting the rear stiff to control camber, or is it better to keep it soft for more grip?

I really need a better understanding of these control bars before trying to make a set so I can decide on the pivots - if I just duplicate the originals surely the pivot bolts will wear through in no time?

Thanks for your thoughts so far guys!

[Bruce2]

Go with your engineering gut feel. They don't do a damn thing. I bet they came out after 68 when IRS appeared and there were still millions of swing axle cars on the roads.

[sideshow]

I think I figured it out;

This is one of the earliest attempts at a big type-R vinyl sticker. You see vanity goes back to before generation-Y. How impressive is a faux semi trailing arm rear suspension upgrade!

And the more I look at it, it must have to do with reducing the amount of left/right flex of the swing plate.

[choc-ice]

I think I figured it out;

This is one of the earliest attempts at a big type-R vinyl sticker. You see vanity goes back to before generation-Y. How impressive is a faux semi trailing arm rear suspension upgrade!

And the more I look at it, it must have to do with reducing the amount of left/right flex of the swing plate.

If it was that, wouldn't there be a better way of taking the sideloads than just that tab welded onto the torsion tube bracket?

In one sense, I'm glad that everyone is as baffled as me!

[sideshow]

No weld. Looking at the picture I would think that the torsion bar side of the bar has a pivot, fixed at the backing plate.

Like a semi trailing arm.

[Ozzie]

By looking at them, I would expect them to interfere with the left-right drive action of the diff.