Why is an adj. phb needed when lowering a car?? I was thinking of lowering my car but just bought an aftermarket non. adj. phb about 2K miles ago, didn't really want to buy another one.

TIA

 

PHB connects the diff on the driver's side to the frame on the passenger side and is at a pretty steep angle. So the relative distance between those 2 points is somewhat less than the length of the PHB.

When you lower the ride height of the car, you lower the body. This movement of the passenger side (frame) pick up point for the PHB shortens the PHB's angle and the relative distance between the 2 pick up points increases.

So, a shorter bar is necessary.

And, because every manufactirer of spring has a different opinion on what the "perfect" ride height is, a single, shorter bar is not practical.

 

Imagine a pendulum on a grandfather clock. Notice how when the pendulum swings from side to side how the bob at the end rises up and drops down (i.e. it swings in an arc)? Turn it on its side and this is essentially the same motion, albeit exaggerated, that your PHR will follow as the rear axle moves up and down through its range of suspension travel. Knowing this, it stands to reason that when you lower the car it has the same effect as compressing the rear suspension - and that is to move the PHR in an arc, which, in turn, will pull your axle in one direction (in this case it pulls it toward the passenger side since the PHR is mounted to the body on that side and sits level at stock suspension height). HTH

 

The rearend of fourth-gen F-bodies is located side-to-side by the panhard bar. The way it's mounted to the rearend on one side and the frame on the other causes it to move like a swing arm. As the rear moves up and down, the mount point on the axle moves in an arc relative to the body of the car, which pulls the rear axle to the left and right. In most cases, when you lower the car the bar is too short to compensate, and the rear axle is now shifted towards the passenger side. This is complicated by the fact that in most f-bodies, the rear isn't centered to begin with (call it "production tolerances") which worsens when the car is lowered. It isn't a big deal on a car that has stock-size wheels and tires (including the SS/WS6 275/40R17), but if you install wider rear tires you need to buy an adjustable panhard rod to re-center the rear. This prevents one tire from rubbing the inner fenderwell while the other sticks out past the quarterpanel. If you go with 315/35R17 tires, an adjustable phb is a must. Cars that run autocross or road courses will also benefit, as centering the rear helps the car track straight and true (helps prevent "dog-tracking"). One good thing about lowering, though, is that at a lowered ride height the panhard bar sits almost perfectly horizontal, which, along with the stiffer spring rate and reduced suspension travel that comes with installing lowering springs, minimizes the shifting of the rearend. Bottom line, though: If the rear tires don't rub and the position of the rear tires relative to the car body looks o.k., then you don't need to swap it. If you do get rubbing, or the rear is too off-set to your liking (one tire sticks out farther than the other), then you should get an adjustable one and center the rear.

 

I believe they answered ou question. And cleared up some things for me. Thanks.

 

Sweet!! Man that answered the question I asked and a few I hadn't even thought of asking yet!! :thumbup:

 

could incorrect adjustment on the PHB cause the car to lean to one side. In my case, it's lower on the passenger side.

 

Incorrect adjustment of the APHR could cause the axle to be offcenter, but it won't impact the ride height. Its VERY common for our F-bodies to "lean" one way or the other in the rear. I've had three different sets of rear springs and two rear axles in mine and the driver's side has always been ~3/8" higher than the passenger side in the rear. Fronts are dead on in my case.

 

I'm on fourth-gen f-body number four, and all of them leaned to the passenger side at the rear. It's just a quirk of the f-chassis that shows up over time, possibly due to the unibody deforming slightly in response to driveline torque. Most shops I know of just trim the driver's side spring to compensate. The best way to fix it is with a ride height adjustment kit. Leaving it the way it is won't have any negative effects, though.

 

where can i buy some shims because it drives me frickin crazy!!

 

My rear was 3/8" off center after lowering 1". An adjustable PHB fixed it

 

www.ground-control.com

They have a rear height adjustment kit. They also carry adjusters for the front.