Triple watts link?

[feeble]

In a solid rear axle car, does anyone know of any examples of a suspension that incorporates a watts link on either side of the axle on or near the axle housing ends, replacing the lower links (in a 3 link suspension for example). The “propeller” for the watts links at the ends of the axle housing would have to pivot on the axle tube.


A traditional watts link could be used to locate the axle laterally and an upper 3rd link to control the axle housing “roll” front to back (My terminology is not right, most of this is pretty new to me.)


It seems to me that as view from the side, the axle motion would be up and down rather than scribing an arc as would be done with a single lower link on each side.




Would there be any handling benefit to such a suspension compared to a traditional 3 link? Does this exist somewhere already? Could maybe be used in conjuction with a De Dion tube?

Thanks!

[Derek69SS]

Wissota Modifieds use something like that... probably other series of dirt-track cars as well.

http://www.youtube.com/watch?v=GFZWNuq8C7A

They do a watts style on one side, and 2 forward links on the other, and both sets of brackets rotate on the housing. Goofy stuff, and I don't fully understand it, but they make it work...

[andrewb70]

Wissota Modifieds use something like that... probably other series of dirt-track cars as well.

http://www.youtube.com/watch?v=GFZWNuq8C7A

They do a watts style on one side, and 2 forward links on the other, and both sets of brackets rotate on the housing. Goofy stuff, and I don't fully understand it, but they make it work...

Holy pinion angle change Batman!

Andrew

[exwestracer]

Very common on dirt track cars of all types. It's commonly referred to as a "Z" link setup. And YES, you do need birdcages to make it work. Just ask any mini-truck guy sitting on the side of the road with his driveshaft in his hands....



Here's an example of a bearing birdcage.

These fit right over 3" axle tubes, but you must run a floater hub (no flange on the end of the tube). They also make 2pc birdcages that will clamp together over a tube with a flange.

[exwestracer]

http://www.youtube.com/watch?v=i57Dn...eature=related

Here's another video showing a birdcage (but not a Z link) in action. WARNING: These images may be disturbing to some viewers who like BIG sway bars...

[feeble]

Thanks for the info. Having a name helps much to research it. Here's naive question. Is there a reason that the z-link style suspension is not used more on street / track PT cars? Too expensive? Too complex? Not reliable?

[andrewb70]

....Just ask any mini-truck guy sitting on the side of the road with his driveshaft in his hands....

....

Ray,

Can you please elaborate on the above statement? I mean, I understand the words, but I am looking for a reason why a driveshaft would fail.

The dirt track videos definitely show the extreme pinion angle changes that occur under acceleration and braking.

Andrew

[exwestracer]

Ray,

Can you please elaborate on the above statement? I mean, I understand the words, but I am looking for a reason why a driveshaft would fail.

The dirt track videos definitely show the extreme pinion angle changes that occur under acceleration and braking.
Andrew

A lot of trucks are bagged using a Z-link system and NO birdcages. I have personally seen trucks that had 45deg of pinion motion through the range of bag travel.

[andrewb70]

A lot of trucks are bagged using a Z-link system and NO birdcages. I have personally seen trucks that had 45deg of pinion motion through the range of bag travel.

I am just trying to get my brain wrapped around this whole concept, so please bear with me. It sounds like with the z-link there are extreme pinion angle changes throughout the suspension travel. By using the birdcages the axle is allowed to freely rotate inside the housing and thus the pinion angle can remain constant thru the suspension range of motion. I also see a third link in the center of the rear housing that uses a spring loaded link. I assume that is there to control pinion angle movement, but why is it spring loaded?

Andrew

[Nessumsar]

What is the advantage of this type of setup? Are they using the axle "wrap" as a sort of traction control?

[Norm Peterson]

I am just trying to get my brain wrapped around this whole concept, so please bear with me. It sounds like with the z-link there are extreme pinion angle changes throughout the suspension travel. By using the birdcages the axle is allowed to freely rotate inside the housing and thus the pinion angle can remain constant thru the suspension range of motion. I also see a third link in the center of the rear housing that uses a spring loaded link. I assume that is there to control pinion angle movement, but why is it spring loaded?

Andrew

As soon as you install birdcages on your Z-bars so that the axle will quit being a huge rear sta-bar, you lose control of pinion angle change/axle rotation as seen in side view and you'll need to add another link (or links*) to put that control back.

Spring loading it softens the 'hit' from suddenly applying lots of torque from a large responsive engine with little or nothing in the way of a flywheel to bleed off any torque.


* you might even find an "upper link mechanism" that splits the duties of resisting acceleration and braking torques to separate components, and in this case spring loading can ease the transition from accel to decel and vice versa. The decoupled torque arm that is/was available for F-bodies did something more or less along these lines.


On edit, I seem to recall that one of the Chrysler Corp Trans-Am teams back in the day experimented with some sort of Z-bar arrangement but eventually reverted back to the leaves.


Norm

[Derek69SS]

The ones I've seen have the Z-link in the right side, and both links pointing forward and upward on the left. This gives them huge amounts of rear-steer when the body rolls, which I assume is what they're trying to achieve by setting it up that way.



If I ever get around to building something crazy just for the sake of trying out some of my goofy theories, I'd like to set up a car with birdcages both sets of upper frame brackets... set it for lots of rear-steer for autocross, and flip the upper link to keep the axle straight for road course and drag racing, and do 2 separate adjustable sliding upper links for accell and braking forces.

[exwestracer]

Norm is right on the money. Many dirt cars run a torque arm (just like 3rd gen Camaros) that has vertical springs to independently control acceleration and braking axle torque. These are usually referred to as fifth and sixth coil systems.

Since dirt tracks have much lower traction potential than dry asphalt, it's necessary to allow a LOT of pinion wrap to keep the tires reasonably hooked up. I has been proven time and again that there's no need for this much pinion monkey motion on the street, although the basic idea may be useful to a lesser extent.