Sway bar question, need some help!
 

Hello everyone,
Just purchased a set of sway bars for an early car. I was told the front bar was a 19mm (through body) and the rear an 18mm. When I opened the box the rear appeared much larger in diameter than the front. The front is stamped 15 on the end, the rear is stamped 18. So just out of curriousity I placed my calipers on the bars and the front measures 19mm but the rear 23mm. The rear is stamped 911 701 07 and appears to be a 18mm based off what I can find from the part number, but the front I am guessing is a 15 based on what is stamped. The person I purchased them from thinks the front is a 19 based on the caliper measurement. Any help would be great. Thanks

If they're Porsche bars, I don't believe they made a 19. They made a fairly rare 18 that came in the first year 930's

The stampings are usually correct on a factory bar. Maybe they've been powdercoated.

Edit: where did you put the caliper? Don't measure the ends, measure the body.

I think you are talking about torsion bars, not swaybars.

Factory fronts are 18.8mm. Rears were 23.x in some years.

Through body torsion bars? :D

911-333-701-07 is an 18mm rear anti-roll bar for a 911SC.

Scott

Yes they are sway bars not torsion bars. The measurement I took was from the body of each bar not the ends. The front and rear are factory. The front is stamped on the end 15. There is one on eBay for sale as a 15mm with the same stamp. I have a feeling the diameter measurement has non relation to the actual size.

The diameter is the size. That is the measure of their spring rate. Are your calipers calibrated? Are you holding them perpendicular to the bar?

The only other thing I could think of would be if they are hollow, then they would have a larger diameter than their equivalent spring rate in a solid bar.

Yup, that is how the early cars were and how most of the later aftermarket bars work. There is a triangular boss on either side of the front inner fender behind the strut on all cars up to 1989 for this, just no hole for the bar. It runs through the body behind the fuel tank. There are lever arms that mount to the end of the bars and attach to drop links that connect to the lower control arms (read A-Arms).

The pictures in this tech article provide more details...

http://www.pelicanparts.com/techarticles/914_front_swaybar/914_front_swaybar.htm

Hey guys, I am not sure if I am being clear. Yes the front is a through body sway bay, factory bar, not hollow. I am fully aware of how they mount and what they look like. I am only trying to clarify if the stamp on the end of the bar has any relation to its size. The front bar has a 15 stamped on the end, but when you measure the "body" with a caliper, it is 19mm. I am just trying to confirm if the bar is a 19mm or a 15mm. My understanding is that they never made a "factory" front through body sway bar in a 19mm. The reason I think it is a 15mm is because the rear bar I have has a part number on it that decodes as a 18mm bar but when you measure the body of it, it measures 23mm, which leads me to believe the diameter has no relation to the bar size. I hope I am being clear now. Please note this is regarding factory sway bars not torsion bars or hollow sway bars. Thanks guys

If the bar ODs are 19 and 23mm respectively, that is what they are. As for the numbers stamped differently, how about "stamped incorrectly"?

Sherwood

ok, lets say the bars are stamped incorrectly, the rear has been confirmed 18mm carrera bar even though the measured diameter is 23mm. Next question would be, did porsche ever make a 19mm through body front sway bar?

unclebilly,

You missed the point. There are no such things as through the body torsion bars.....

Scott

I think you are confusing some folks with your terminology.

Concerning the front through the body sway bar... this is what Porsche offered:

Factory stamped 13mm. This measures 13mm diameter.
Factory stamped 15mm. This measures 15mm diameter.
Factory stamped 16mm. This measures 16mm diameter.
Factory stamped 18mm. This measures 18mm diameter.

The factory stampings on the bar ends identify the diameter of the bar.
Just because it looks like a factory bar does not necessarily mean it is a factory bar.

Other aftermarket companies have produced a solid through the body sway bar that is a 19mm. It measures 19mm diameter. I actually have one.

A picture of the stamping would help. The number font used is distinctive.

To be most clear and accurate, a sway bar (anti-sway bar) is technically a torsion bar (a bar in torsion - by design). For the purposes of Porsche-discussion, the term "torsion bar" is generally used to describe the type of spring in the suspension system.

S

Thanks for the response, that make a little more sense. I will post some pics tonight for clarification. Maybe the bar is an aftermarket and stamped 15 for what ever reason.
Do the rear bars measure the same, I know the rear bar I have is factory, it is stamped 911-333-701-07 and just above that is 18. When I decoded the rear bar, it comes back as a 1979 SC 18mm rear sway bar. When I put my calipers on the body it measures 23mm. This is why I am getting so confused! I will post some pics when I get home from work tonight so you guys know what I am talking about.

As Flieger stated "are your calipers calibrated?" Are you using electronic or mechanical non electronic? If so maybe try another set for A/B comparison. By your measurements it appears the readings are getting more inaccurate the larger diameter you measure, 4mm larger front and 5mm rear. Just a thought.

David

Let's get technical and very clear. No one calls an anti-roll bar a torsion bar because it is not one. Yes, the anti-roll bar is a torsion spring, but that does not make it a torsion bar.

Calling an anti-roll bar a torsion bar because both are torsion springs is like calling a Doberman a German Shepard Dog because both are dogs.

Scott

OP, if I may suggest, post a pics of your parts so some of us less enlightened can get over the terminology and actually try to assist your concerns.

A ruler next to the part would help immensely.

Maybe this will help:
http://img.photobucket.com/albums/v5...OA5OG/PAG4.jpg
http://img.photobucket.com/albums/v5...OA5OG/PAG3.jpg
http://img.photobucket.com/albums/v5...OA5OG/PAG2.jpg
http://img.photobucket.com/albums/v5...OA5OG/PAG1.jpg
http://img.photobucket.com/albums/v5...OA5OG/PAG5.jpg
So OP, which is it?

http://img.photobucket.com/albums/v5...026-WA0002.jpg

You guys are killing me. I am going to squash the "torsion bar" argument now. I am not talking about torsion bars, I am talking about sway bars or anti-roll bars, not torsion bars.
I will post pics tonight. I have both digital and mechanical calipers and both read the same.
Please keep in mind that I am only trying to rule out if the diameter of the bar is in fact the size of the bar, then why does the rear "factory" bar decode as an 18mm but measures 23mm?

Hewh! Glad that's over.


So what year are those "stabilizers" from?

You're so funny.....

These are all names for the same device:

anti-roll bar
roll bar
sway bar
anti-sway bar
stabilizer bar
stabilizer

The term "anti-roll bar" is generally preferred by chassis/suspension engineers. Note that they are never called "torsion bars".

Scott

Let's hope we will see his issue posted tonight.

Here is a picture of an early Porsche 911 Front Through-Body Sway Bar. I have no idea what size it is because I sold it ten years ago. I'm posting the picture just for reference.

http://forums.pelicanparts.com/uploa...1351796397.jpg

Here is a picture of Porsche 911 Front & Rear Torsion Bars. I would not call these thru body because they don't actually go thru the body - they do however go thru the suspension.

http://forums.pelicanparts.com/uploa...1351796706.jpg

Here's a picture of three girls "Planking". This has nothing to do with sway bars or torsion bars however, there is a car in the parking lot that uses sway bars.

http://forums.pelicanparts.com/uploa...1351796861.jpg

The point is: Original Poster, you need to post photos when talking about something that is confusing like this: swar bars marked 15 but measure 23 but factory never made these but front and rear are mis-marked and somehow ended up on my car by the factory?

Wow! I feel so stupid right now that I really did not want to even post this, but since so many of you tried to help me, I am going to admit fault. So my caliper was set at 32nd's, 19/32 = 15mm and 23/32 = 18mm. So the bars are correct based on what is stamped on them. Now I need to contact the person I bought them from and discuss that I was sold a 19mm bar and ended up with a 15mm.

Just out of curiosity, anyone running larger rear sway bar than front?

I upped my OEM 85 stabilizers to 87's, both front and rears, larger id bushings had to be installed as well.

Don't sweat it brother we all done similar, ;-)

No worries. We all make stupid little mistakes like that...even if we don't admit to them in public!!

It is not at all uncommon to use a larger anti-roll bar at the rear. But, it all depends on your setup. I prefer to use adjustable anti-roll bars of the same size front and rear. I don't even know where to start using Factory anti-roll bars. Anyone would need to know what size torsion bars you are running front and rear.

Scott

Yes. Same species, both examples. They work on the same principle, both examples.

Sherwood

Actually, torsion springs are coil springs that work in bending but act in a rotary manner. Torsion bars work in torsion and a torsion bar mounted in a certain way can be used to resist roll and one-wheel bump but not heave. An anti-roll torsion bar with the levers reversed is called a Z-bar and works in heave and one-wheel bump but not in roll.

You can add roll resistance independent of heave in many ways. Bellville washers, coil springs, bending of blades, etc.

Torsion bars are also torsion springs. Look here:

Torsion Springs

Or here:

http://www.wisegeek.com/what-is-a-torsion-spring.htm

Scott

Thanks for understanding. I want to share my set up with you guys and see if you can point me in the right direction. The car is a 1967 912, the car was not original by any means, so dont get upset when I explain the mods. I swapped the motor with a EJ2.5 Subaru, Stinger ECM, making around 200hp. The car has been flared in the back. Running 16x7 with 205/50 in the front and 16x8 with 225/50 in the rear. Stock torsion bars but I lowered it, added a strut brace. It has RS bumpers and has been lightened throughout. It has a 4 point roll bar. It was not equipped with sway bars so I thought I would run a 19mm up front and a 18mm in the rear. I bought the bars used online and the seller sent me a 15mm for the front by mistake. I notice that everyone seems to run a larger bar upfront, but I am curious if anyone runs larger bars in the rear. I am guessing with the light Subaru motor in the rear and SWB a larger bar might end up with excessive oversteer. Any thoughts?

Will you be tracking or street only? DO you know your front and rear weights?

This was my point.

It also brings up the point that coil springs are actually torsion bars!!

OP I think you've been hi-jacked :-o

Its a weekend street car but I want to take it to track days at Thunder Hill

Okay parttime AX/DE er, okay do you happen to know front and rear weights or at least total weight?

After suspension upgrades, you should consider corner balancing to optimize the mods.

What was your point??

Scott

What size?

Scott