School me on sway bars for beam axles: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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June 28, 2010 3:21 a.m. EvanR New Reader

I'm no stranger to sway bars. I've added or upgraded the bars on most everything I've owned.

But I am new to the beam axle. At least that's what I think it's called. On my '05 xB, the axle looks a lot like the letter "H", with the top of the H having the pivot points on the unibody, and the bottom of the H attaching the springs and shocks.

Since this is a rigid piece, the only point I see to the sway bar is to make it more rigid. Okay fine; I see how that would reduce body roll.

What I don't get is why bother to make it out of spring steel? Wouldn't (solidly) bolting a piece of square tube or similar to the axle accomplish the same thing?

Thanks, Evan
June 28, 2010 5:16 a.m. ddavidv SuperDork

Well, you need it to twist like a torsion bar (sort of what it is, akshully). If it were rigid it would make for some rather unwanted handling characteristics.

I've had sway bars that bolted to the beam with the end links going to the body to reduce sway. I've heard of people welding in steel tubing or similar to the beam but there's no real tunability in that method. There are lots of cars running around with that type of suspension (I think early fwd VWs used this) so copying something should not be difficult.
June 28, 2010 8:22 a.m. emodspitfire New Reader

If you make the "Add-on" stiffener out of mild steel tubing it will (probably) bend the first time you stress it. After it does that several times it will break...

Check out Fred Puhn's book on homebuilt sway bars.

BTW: If you measure all the attachment areas on your car and make a sketch, you can probably find an existing bar at he local U-pickit junkyard.

Rog
June 28, 2010 9:28 a.m. erohslc Reader

Mounting the body of the sway bar on the chassis rather than on the beam should reduce unsprung weight .... if that matters here.
June 28, 2010 9:54 a.m. bequietanddrive New Reader

On my xA, I've got the Hotchkis 24mm rear sway bar. It does bolt directly onto the torsion beam in the back, so I don't think it's a "true" rear sway bar. However, it definitely does it's job. Understeer is essentially nil.

Right now dealers are trying to dump their old scion accessories, so you can pick up something like this TRD bar for really cheap: TRD Rear Sway Bar
June 28, 2010 10:03 a.m. Gimp Dork

bequietanddrive wrote:

On my xA, I've got the Hotchkis 24mm rear sway bar. It does bolt directly onto the torsion beam in the back, so I don't think it's a "true" rear sway bar. However, it definitely does it's job. Understeer is essentially nil.

Right now dealers are trying to dump their old scion accessories, so you can pick up something like this TRD bar for really cheap: TRD Rear Sway Bar

Same for my fiance's Fit. The bar bolts to the lower spring perches, and never connects to the body. Did a nice job of balancing the car.
June 28, 2010 10:05 a.m. YaNi Reader

Check out my Cavalier rear sway bar build

The swaybar was 7/8" or ~22mm and it turned out to be more effective than the aftermarket solid 22mm swaybars. It worked great but I ended up taking it off because it was creating all kinds of squeaks in the GM cardboard unibody.
June 28, 2010 11:27 a.m. turboswede SuperDork

On our Dodge Shadow Chump Car, I built an adjustable bar out of 3/16" thick steel plate and mounted it to the bottom of the torsion bar between the rear wheels.

Using HD muffler clamps to hold the bar in place with the torsion bar, I can adjust sitffness by adding more clamps or sliding the ones there inboard or out. Worked well for the 24 hours we flogged the poor car.

Also have one on my street/AutoX car made out of thinner material.

The steel plate on our car is about 36" long by 2-2 1/2" wide. Can't remember that well, I just measured the stock torsion bar and got a piece close to the same width and length and a few muffler clamps the right size.

The whole point of a rear bar for a FWD car is to trade rear grip so that the fronts are not overloaded when you turn in for a corner. The car basically pivots on turn-in and you point the nose at the exit of the corner and punch it. Heavy use of left-foot braking is almost a requirement, especially with a turbocharged car like ours, otherwise no power on exit (or to pull out of a slide)
June 28, 2010 11:40 a.m. Vigo HalfDork

Ive just welded regular steel plates to box in the bottom of the beam axles on my k-cars numerous times. It definitely works. The hardest part is getting it welded well enough so that all the welds dont eventually crack after all the flexing it does. Never had a problem with the plate itself cracking.
June 28, 2010 2:20 p.m. EvanR New Reader

Ok, now I get it. You guys are the best!