How twitchy will a rear sway bar make a '74 without one currently?
 

Hi guys - My '74 does not have a rear bar on it currently but I have a 20mm rear bar on hand. This is a fast road and touring car, and I am wondering if I am asking for trouble by stiffening up the rear of the car. By trouble I mean the "I am not actually as good of a driver as I think I am and the rear bar might catch me out unexpectedly" sort of trouble.

Any coaching to pass along?

Thanks!

Made a huge improvement on my '74. If anything, made it tighter and more predictable. The rear stays planted better.

Well that is encouraging. Makes sense I suppose.

20 is bigger than stock so you might want to use the beefier aftermarket welded mounts not the stock ones.

Thanks - she doesn't have rear bar at all at this point. Think going with a 20 is too big of a jump?

Thanks for the reminder on needing to reinforce the rear mounts.

What size is the front bar? 6x15 all around?

I am running upgraded torsions as well (22 front and 28 rear.)..but the factory Konis and 7x15 inch wheels. I think the sways are stock. Handles much better than my previous '74.

What Flintstone said. When I put mine on it all got more predictable. Mine had lost one of it's mounts, so I retrofitted to Wevo's and an SC bar. Chase the link in my signature line on the process.
-C

Don't worry about it. Put it on, drive it slowly. It won't bite you at under 75. Think about how it feels when you go around a corner. In short, start conservatively and build your confidence over time. Some people will be comfortable in ten minutes. Others will take a few drives. You'll like it.

My '74 came with the "S" suspension option and the rear sway bar is 18MM. Don't know what a '74 drives like without a rear sway bar but I can't imagine that adding one would make it "twitchy"... just the opposite, more planted and stable.

Thanks Jack, I am sold

And I would use the matching front sway bar.

Let me double check what I have on the front.

Thanks for the coaching.

Contemplating doing the same except my chassis does not have the mounting brackets. Anyone have the exact locating for the mounting brackets? See the approximate location in pictures but don't want to weld in wrong position.

When Dad's 74 passed to me, it had no rear bar at all. One of the rear mounts looked like it had been trimmed off with a sawzall.
Driving the car home, gently, (no sliding through turns, the car had 20 year old Pirellis on it) it seemed to handle just fine.

The original window sticker said the car was optioned with "Carrera" bars, that is 20mm ft and 18mm rear. The rear bar mount probably failed and my Dad's mechanic probably said "you're not driving the car hard enough to need this so we will just take it off".

So, I bought Wevo rear mounts and installed them an a used bar, links and poly bushings. I also installed Dunlop direzzionales, so it is hard to put all of the handling improvement to just the rear bar.

The car seems to corner flatter and feels more poised.

I am going through a front end, (brakes, steering and suspension), overhaul and just a couple of days ago decided to upgrade the torsion bars too.

If you are going to drive the car hard enough to get the tail out a bit, you might want to consider a bigger front bar, preferable one that is adjustable, so you can tune the oversteer/understeer balance.

The stock 74 comes with 18.8mm front T bars and 12.4 rear T bars. The strength the bars is calculated by taking the diameter to the fourth power, so going from the stock 18.8 to a whopping 21mm shows a 55% increase in stiffness.

Looking at the Carrera bars 20 to the fourth divided by 18 to the fourth give us a relative front to rear stiffness of 1.5 to 1, that is the front bar stiffness is 50% stiffer.
So, if we carry out the Carrera bar analysis, you might need a 22mm front bar to balance the 20mm rear bar. If it is adjustable you can shorten up the effective arm length and crank up the front roll stiffness.

All of this balance is assuming you have stock T bars and that the factory got the 20/18 Carrera bar option well balanced.

Alas, all of this is still theoretical, because I haven't had the 911 back on the road much less on the track, but I have been around a few turns on the track.

Best,
chris

These might help.

Pelican Technical Article - Porsche 911 (1965-1989) - Standard and Adjustable Drop Link Replacement

Pelican Technical Article: Replacement of Sway Bar Bushings and Brackets - 911 (1965-89) - 930 Turbo (1975-89)

If you are missing rear brackets, I would have the the WEVO reinforced ones as the factory ones tend to break. Also, remember that if you use factory sways, they changed in '78 so you would need to mount later ones a bit differently. Described here: http://blog.dietersmotorsports.com/?page_id=172

http://forums.pelicanparts.com/uploa...1425400797.jpg

Fintstone thanks for the info but I'm trying to locate the exact position the rear brackets need to be welded to the frame. I have a 70T and it came without them. I plan on using the 78 rear control arms so if needed I can use a heavier sway bar. Just need to be sure where to weld.

I've got a set of SC front/rear sways with end links if you're interested. PM me if you are.

I'm running Carrera sways and Tarrett end links plus sport hardness bushings...I've tracked my car and done thousands of canyon carving miles with the stock rear sway mounts, so it's definitely not a requirement to upgrade those mounts (assuming you already have stock mounting points on your chassis)

Cheers

Although I am not an expert on this, I am pretty sure that you hang them and then bolt up the brackets (no bushings), mark where they are, tack them on, drop the bar and finish welding the bracket and then install.

Random thoughts:

Add'l rear roll stiffness increases oversteer. Thus, the front end bits also enter into the proper equation.

A 911 with factory sway bars (some or none) and torsion bars handles differently than one with upgraded versions. Suspension mods for a 911 follow a proven path that includes torsion bars, sway bars, shocks, ride height and alignment specs.

Doing so gradually is fine. Merely doing one item may create some negative results and isn't recommended.

Sherwood

Craig thanks for the offer but already have all the parts. My concern is where to weld the brackets.

Fintstone I kind of thought that would be the way to go about it but I thought maybe someone could confirm it or lead me in another direction. Thanks for your input.

If I remember right, this clip addresses install in an early car...but, I don't have the bandwidth here to view it...so I am not sure. It used to be quite common though. If we keep bumping this to the top, one of the pros will eventually chime in.

http://youtu.be/QjceX92qPb0?list=PLPDtxlBvsuA-uLh4oC92fTUpTa3I00XTj

Fintstone excellent video but I'm not so sure that it applies to the 70T. Peter installed the brackets on a 68 SWB car that had a special indentation on the body that lined up with the brackets. Will try and check that out on my car in the next couple of days and get back with the results. I know the brackets are different than the ones I have. Thanks for the heads up on the video.

Replacing my 74 torn rear mounts
 

Here is an old thread dealing with replacing damaged 74 rear bar mounts, along with a fuel pump relocation.

Once cleaned up, we assembled the bar, drop link and brackets and offered it up to the chassis to see where it wanted to mount. This wound up right about where the outlined area on the chassis was. We clamped the bracket to the chasis after hosing everything with weld through primer.
As you can see from the photo, the rear fuel pump mount makes working on the left mount a bit awkward, so we decided to a front relocation fortuitously, this also made for better pictures.

Hope this helps,
chris
http://forums.pelicanparts.com/porsche-911-technical-forum/617072-replacing-rear-bar-mounts-74-911-a.html

Here are a few shots of the processhttp://forums.pelicanparts.com/uploa...1425481005.jpg
http://forums.pelicanparts.com/uploa...1425481030.jpg
http://forums.pelicanparts.com/uploa...1425481064.jpg
http://forums.pelicanparts.com/uploa...1425481106.jpg
http://forums.pelicanparts.com/uploa...1425481132.jpg
http://forums.pelicanparts.com/uploa...1425481183.jpg

Way back when I had an '86 944, I ran mis-matched front/rear sways. For about 50 miles.

PO had replaced the front sway with a smaller one, and removed the rear entirely. (sways smaller/rear optional on earlier cars - figured they probably swapped sways with a buddy before selling the car).

Sourced some late turbo sways (bigger again), fitted the rear first - but ran out of light working on the car. So big rear sway, small front when driving home.

This combination induced oversteer. To the point where you'd be using opposite lock/throttle steer driving round on/off ramps at legal/responsible speeds... Whilst it was entirely controllable & predictable - not to mention kind of fun :D - fitted the matching front sway PDQ.

Whole car felt stiffer/cornered flatter afterwards. The rear much more so.

Chris exactly what I was trying to figure out. Fintstone and I both thought that was the way to go about it but were not sure.Thanks for the pics and input.

Spuggy like you said my car had the capability for the fronts but none for the back. Hence the problem.

Great conversation guys, thanks for the input and hope it helped some other people as well.

PSA
If you have a '74, and you move your fuel pump to the front of the car, you WILL need to replace the tunnel fuel line to one that can take the full pressure of your fuel pump. In '74 they used vinyl tubing which WILL NOT handle the pressure, and should be replaced (regardless of the pump location).
We now return to your regular scheduled programming....

Great info (and reminder). Thanks!

Hi Charles,

I was thinking the same thing too, so we ran a 5/16 id stainless line inside the old vinyl line because I was worried about not only the pressure but getting tangled up in the clutch and or throttle cables in the tunnel.

It is covered in the thread I referenced and the parts were available through Napa.

regards,
chris