custom built leafs with watts link? First gen F-body

[JLM]

I've been trying to figure out exactly how I want the rear-end setup on my 69 Firebird. The car is about a month out from the paint shop and as soon as I get it back I'll start building the suspension.

I'm going to have a set of custom built leafs made for my setup to work with the high spring rates in the front.

My question is concerned with a watts link or PHB. I've been searching high and low on this and other forums and just haven't been able to find the info I'm looking for in regards to first gen F-bodies.

Firstly, would you run a watts link or PHB in the rear of a first gen f-body with a set of proper leaf springs?

If so, are there are kits on the market for the specific purpouse? I can say that if there are not I will not fabricate one...I just don't have the time or resources.

Any help would be greatly appreciated.

[Ackattack]

You don't need a watts link or PHB with leafs. A watts link or PHB locates the rearend laterally. The leafs take care of this function. That's one of the "advantages" of leaf springs. Fairly simple setup. I would think that if you were to add a watts or PHB to a normally mounted leaf spring set up you would introduce a lot of bind, and it wouldn't work so well (especially the PHB as it goes through it's arc)

[Mean 69]

I have seen a lot of debate over this for the past several years, and the conclusion I have to draw from all that I have seen is that your car will probably run faster using one, than it will without using one. Virtually ALL of the early Trans Am cars, and a darned good amount of the early B Production cars I have seen that use leafs either use a Panhard, or Watt's to futher locate the axle assembly. The A-sedan Camaro in my shop right now has a Watt's/leaf setup. There must be a reason for it!

The biggest debate comes in the form of defining the roll center. The leaf springs have one, and there would be a second one defined by the PHB/Watt's. If the two aren't matched (and this is nearly impossible in bump/droop), there will be some form of associated bind between the two. One of those things that you look at and scratch your head, until you see a car on track with one that performs really well (or in the case of the vintage races down here two weeks ago "dozens" of them working well).

If it is just a street driven car, I wouldn't bother, but I would go with a set of the available delrin type bushings. If the car is going to spend a good amount of time on the road course, I'd recommend looking into it a bit further. Though not offered as a product, it would be pretty easy to adapt the Watt's we are using on our three link kit for leaf's. There is a commercially available PHB, and Watt's for early Mustangs (Maier Racing, and Fays II, respectively).

Mark

[MrQuick]

The ones i've seen used with leafs mount on the topside of the axle and is primarily used for lateral location. My guess is that it would also not effect the already low roll center created by the leafs. Any thoughts on this Mark?

[Mean 69]

I've actually seen about as many different setups as you can imagine. High, low, middle, you name it. I don't think there was a terribly scientific approach to locating these back in the day, and my guess is that alot of it was done as a copy from other teams. Same goes for the traction devices, such as the over-rider bars, under riders, etc. The hot ticket for leafs these days "seems" to be an upper link (just like the top link on a three link) to keep the pumpkin from rotating under acceleration, and more importantly, under really hard braking. The right spring rate, bushings that don't bind rotationally, and whatever form of lateral location you like.

I honestly don't think the bind associated with the PHB/Watts in conjunction with leafs is terribly worse than the inherent mechanical bind associated with ALL four link trailing arm setups, truck arms, etc. It is extremely likely that we will put the 65 Fastback into "B Production Legal" configuration later next year and run it with the vintage clubs, and if so, we will without question be using a third link and Watt's. "I" would personally run one on the street too.

Mark

[4MuscleMachines]

When you are running a watts, would it help to also have a rear sway bar?

[Mean 69]

When you are running a watts, would it help to also have a rear sway bar?

For this context, that is a really good question. With a typical coil-over type setup running a Watt's, the lower the roll center height (which is where the bellcrank position is), the more you'll need a roll bar, in GENERAL. It depends on other things, but all else being equal, this is the case. With the leaf setup, it is not so clear, because as we pointed out previously, the roll center height is kind of ill defined, or rather, "over defined," so it isn't clear what the effect would be. My gut tells me that if your rear spring rate is high enough to not need a torsion bar to begin with, that you very most likely won't need one when you install a Watt's/PHB.

M

[Damn True]

To throw a monkey into the wrenchworks what if you include a variable such as GW's new Cat-V spring bushings. Seems like that would add a bit of lateral wigglieness (technical term there folks) that might be well served by a PHB or Watts.

[4MuscleMachines]

Thats a good question from me too, seems like the PHB might defeat the purpose of the GW CAT5 shackles/bushings since they have more lateral deflection?

[yody]

always wondered about the cat5 bushings also, I have never seen anybody run those? also it seems like they would promote a lot of body roll, i take it a big rear swaybar is necessary?

[Mean 69]

You know, those spherical bearings that Global and other use don't seem to offer ANY benefit in roll that I can see, nor that the research I have done (extensive) would indicate. I like the fact that they are rotationally free, because bushings in leaf's need to rotate easily to make the setup work at all, but there is NO basis from what I have seen, from good ole engineering principles, that would suggest that there is ANY benefit for improving performance in a roll situation. I'm sorry, but a leaf spring needs to bend torsionally in order to allow an axle to roll, and it is not a bad thing because they are not torsionally rigid. Any, and all, rotational requirements needed for a leaf setup to roll, are without question handled by the leafs themselves. Again, perhaps not ideal, but completely functional, and no worse that the effects necessary for a four link, or truck arm to roll: all are over-constrained. Period.

Mark

Edit: By the way, the spherical bushings don't allow "lateral" motion, they allow "angular" motion, but only at the front eye, the other end is not liberal angularly, and it wouldn't matter if it were, in roll something needs to bend in order for the system to work. Again, they work, and can be made to work pretty darned well, but there are physical constraints that cannot be overcome with such a system.