Is there a link between diameter of sway bar and stock mounts tearing out?

[chrisp]

For those of you who have had failed sway bar mounts did you have large diameter bars on there? Something along the lines of a Weltmeister 22mm or a Smart Racing set up?

Do any of you have history with a narrower bar like a Weltmeister 18mm or 20mm and not have the mounts tear out?

[banjomike]

Mine were factory bars and my mounts tore out. I think that bigger bars will tear them out sooner. Agressive driving certainly accelerates the process. I tore out one at an autoX and tore out the next a year later at an autoX.

[no substitute]

22mm tore my rear mounts, not uncommon. Factory mounts were fine with stock bars. Someone makes a modified reinforced mount for the big bars. Someone here will remember who.

[911pcars]

It seems to be a combination of vehicle weight, sway bar OD, effective arm length and how agressively you drive.

A large OD sway bar places the most stress on the chassis (all other things being equal). An adjustable arm can reduce the effect of the sway bar if the drop link is furthest away from the bar. Conversely, shortening the arm length to the drop link increases the load on the chassis.

If you have a Carrera or heavier 911, I'd suggest reinforcing the sway bar mounts. In the front, add an additional layer of sheet metal around the body mount. In the rear, add reinforcement to the factory mounts. The archives contain several threads on these mods.

Hope this helps,
Sherwood
http://members.rennlist.org/911pcars

[real550A]

My right side rear mount on the '88 tore with the stock sway bar during "spirited" driving.

[aigel]

I think if you have stock swaybars, you are pretty safe. My stock mounts are still good. I drive a 81 SC with stock swaybars and mounts, 22/27 torsion bars, bilstein hd/sport. I drive the heck out of it for two years now, in AX and the big track on Kumho Victoracers. So far I have stayed away of upgraded sway bars because I wasn't ready to poke a hole through the front of the car. Also, good swaybars are a grand or more for the couple. I still need to learn how to drive too, that's slowing me down most!

George

[Dan J]

Chris,
This problem first appeared in large numbers with the G50 Carrera's So I think 20mm and up needs reinforcement. Call me I have a nice, cheap reinforcement kit for you
Dan J

[Jeff Alton]

Big bars put more force on the mount, plain and simple. I have big torsion bars along with big swaybars and I still broke a mount. I did not tear it off though, mine cracked right where the rear bolt goes into it.

Jeff

[imcarthur]

Both of my stock brackets with stock torsion bars & sways were toast. 62K. I suspect the truck transport Florida to Toronto via Houston had something to do with it. A PPI in Florida did not reveal it (although it could have been missed) and they were shot when I took the car for its safety check to plate it.

So a lot of bouncing was the culprit . . .

Ian

[edward993]

I would think that reducing the weight of the car would help too since the sway bars are dealing with less weight transfer. I've got carrera bars on an 82 that's on a diet; wonder if I should be concerned?

Edward

[Jeff Alton]

Be concerned, my car is a bit of a lightweight.

[pcar fanatic]

If torsion bars are standard and you choose to use larger swaybars, then the swaybars start to assist the torsion bars in certain instances (apart from its antiroll function). Under these conditions, the likelyhood of tearing a mounting bracket is increased.

[89911]

A quick answer is yes. There are many factors that will add to the likelyhood of your mounts breaking: Soft torsion bars, heavier car, track tires, track driving, etc. I've had both end break. The fronts I used a reinforcing plate of 1/8 steel. The rears were supported with brackets of the torsion bars. The biggest reasons I see are stock, soft torsion bars and heavier sway bars. The sway bars are taking over and aiding the softer torsion bars at the sway bar mounts, something the stock ones weren't designed for.

[edward993]

Hmmm, makes sense. So with heavier torsions (in my case 22/28) and "standard" carrera sways on my SC that's maybe at or just below the 2500lb mark, is reinforcing something that i should do as a pre-emptive measure for a track car? No R-compounds yet, but maybe next season.

Edward

[Wil Ferch]

The cross-over point seems to be 1985 vs 1986.

1986 uses a slightly bigger rear torsion bar ...25 vs 24.1 mm( speaking "stock" here)...and a proportionately yet bigger rear anti roll bar than before. It seems we see these being a problem with the 86+ cars...mostly.

Correct as posted here by others....the anti roll bar is sharing too much of the load as you increase stuff, like going to bigger rear anti roll bars first.....make sure torsions are upgraded first ( or proportionately) before you start making anti roll bar changes....this shifts the load where it belongs...to the torsions first.


Wil

[gerry100]

Both of my sway bar mounts failed on my '86. One at about 85K, the before I purchased.

Looking at the failure, it looks like work hardening/metal fatigue from the slight flexing of the mount during operation. ( similiar to bending a coat hanger back and forth until it breaks).

The replacements have an extra brace which prevents the flexing and should eliminate the fatigue failure.

[Wil Ferch]

The reinforced butterfly style replacements for the 86+ cars are only a band aid ...the problem will re-occur unless (either) stiffer rear torsion bars are used or a really hefty. substantial home brew anti roll bar mount is made ...

You need to shift the torsion load to the torsion bars, and not have the big burden on the anti-roll bars...

Wil

[Miguel Antonett]

Yes, larger sway bars accelerate the fatigue on the mount metal - no problem there, it is a known fact. Originals do fail also. Re-install (weld) the tab back.

[89911]

"A really hefty, substantial home brew anti roll bar mount is made."

Like this. Four year of heavy track use with 255 17 rear R compound tires, no problem.

[chrisp]

Thanks everyone.