J-Rho's '67 Camaro Z28 STX build Jason Rhoades builds a 1967 Camaro Z28 clone for SCCA STX autocross

6Feb/130

Watts up with the Camaro?

A long time ago there were some posts on the panhard rod I had built for the Camaro:

http://www.rhoadescamaro.com/build/?p=793

http://www.rhoadescamaro.com/build/?p=866

The reality is, if that had been the last project before the car's completion, I probably would have gone with it and been perfectly happy.

But lots of time has passed, and I've had more time to think about it, and some of the imperfections of the idea chipped away at me.

One thing bugging me, which isn't the panhard's fault, is it was tied to this axle with its welded-on components.  It hadn't occurred to me back then, but I've since realized, it might be nice to be able to swap out complete rear ends to change final drive ratio.  This could be for damage repair, or between venues like autocross and track.  By keeping the lateral locator bolt-on, it enables easier swapping between rear ends.

Another, totally my fault, is I probably had John build the panhard rod backwards.  The way it was built, mounting to the axle on the left and the chassis on the right, improves grip in left-hand turns, but worsens it in right-hand turns.  Totally the right thing to do for circle track, but not necessarily autocross - autocross tends to be fairly neutral in left/right turn distribution, but there are other things about a live-axle car that make it favor left-hand turns (to the detriment of right-handers) and this mounting approach amplifies this disparity.  Should have mounted it to chassis on left, axle on right.

The last thing, is I'd always had in the back of my mind, might like to change to a Watts later at some point.  The car will be headed into the exhaust shop soon, and I've decided it's better to have the rear in a more final state, for that part of the process.  Don't know if I'll be able to get the exhaust to exit the rear of the car, but if it can, want to have it do so now, with what is more likely the final rear lateral location solution.

So I bought a Watts.  Fortunately this was a pretty easy choice in the aftermarket, there appears to only be one standalone pure bolt-in Watts kit, made by Fays2.  Very reasonably priced.

fays2_watts

It's pretty straightforward - the red (only color offered) crossmember piece bolts to the rear frame rails.  A central propeller rides in one of the overlapping holes in the center of the unit, allowing ride height adjustability over a ~6" range, in 1/2" increments.

Total weight is a little higher than the panhard setup, though fortunately the weight isn't in a terrible spot (low and rearward) and the crossmember portion should theoretically add some stiffness to the chassis.  And of course, it should bring the innate benefits of a Watts over the panhard - elimination of axle lateral movement through suspension travel, and more consistent handling behavior in left and right turns.

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Since switching from the panhard is going to be a bunch of work - requiring removal of the rear end, cutting away all the nicely welded-on work John did (I'm sure he'll be laughing at me when he reads this!), and installing the Watts, might as well make a couple other little changes while it's apart for the umpteenth time.

One plan is to modify the front spring eye bushings - they are mostly as they arrived from Flex-a-Form, and in their provided design, they offer quite a bit of lateral stiffness to the spring, not allowing the end to move at all.  This comes at some cost, they also bind the end of the spring a little bit as it looks to rotate in normal suspension travel.  With a good lateral locator like a panhard or watts, you no longer need the leaf springs themselves to provide the lateral location.  Once could argue you could even go to spherical bearings in the spring eyes, but I won't be going that far.  Will just be trimming the bushings, so they still provide good longitudinal location of the spring eye, so they still transfer drive, brake, and wind-up forces quickly and securely to the chassis, but remove the lateral pieces.  This should reduce/eliminate bind in the front, and maybe save an ounce or so!

The other plan is to "adjust" the rear ride height lower.  Since the rules disallow changing to coilovers, have to manage ride height through leaf spring spacer blocks.

spacer_blocks

The car has 1" units on it now - on the left are 1.5", 2" on the right.  Will be going to the 1.5" to see how that looks/feels, that way can go up or down a little as needed.

With larger spacers, the axle gets "further away" from the spring, which makes it more difficult for the spring to control axle wrap-up forces under acceleration and braking.  I'm hoping the relatively modest grip from street tires, modest rear tire size, and a relatively stiff/thick rear leaf spring, will keep those motions under control.

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