84 Cabriolet rigidity questions...
 

Hello All,

I recently purchased an 84 911 Cab and for the most part, it feels pretty solid but there are times when I hit certain kinds of bumps that I can REALLY feel the body flex. I want to tighten the car up and despite my best efforts, can't seem to find any real difinitive answers on how to accomplish this aside from the obvious such as installing a roll bar. I was thinking that perhaps installing strut braces would be a good first step. Could you guys please offer some good suggestions on how to fix this? I'd appreciate any advice you can give as I'm brand new to P-cars.

Thank you,
Aaron

A strut brace (tying the front struts together laterally) won't help the cab/targa flex issue.

The issue is that there is no tie from front to rear other than the pan. No roof.

If you're good at 'feeling' the car, you'll notice that it's a tiny bit better with the top up (helps slightly in tension, not compression). Same with a targa.

There is NO way for it to be as rigid as a coupe.

The only way to stop it is a full cage that ties front and rear together, WITH side bars across the door openings front to rear.

Just enjoy it like it is. I do with my targa.

I would have to take a look at the underside of the car to check for any signs of damage or rust on the bottom of the tub. The Cabs and Targa models had extra supports engineered and added to strengthen the body, to insure that there was minimal body flex.

I know on mine, I can jack up either side at the front, and there is no distortion from side to side, as both front wheels will come up. I have also had the rear up on jackstands, and the front still on the ground, and there was no change in the gap on the doors, nor any problems with opening and closing either door. Maybe it is just the way mine is, but there is virtually no flex at all from side to side, or from front to back. Be sure to take a good look at the underside, and the extra factory bracing, to make sure that there is no damage to allow more flex than it should have. Good luck with it, Tony.

I have an '86 cab and everything 3.2 Cab says is exactly as mine is too. I had a '69 Firebird with a rusty floor and that car would flex like a bamboo pole going over bumps so I know how flex feels but I don't feel any flex in my Porsche 911 cab at all.

Yes, mine's the same, no change in door gaps, etc.

But the car IS more flexible than a coupe. Period.

A good driver can absolutely feel the difference. (or a mediocre one like me).

Yes there is more bracing, but it's all in the pan.

Anyway, a strut brace won't help.

My Targa is weird. A tiny bit of flex when I jack it up from the left, rather more when I jack it up from the right. My '69 flexed as well, but less than this '82 does. My conclusion is that they're all just a little different.

I have a coupe and my friend has both a 73 Targa and a 86 Cab. The Targa bothers me when going over a bump with one side of the car (rust free, solid and well set-up club car) since it definitely twists, the Cab also twists but not so bad and the coupe doesn't display anything that I can discern.

Everything flexes, period; except at absolute zero. Flexure in our cars is combination of torsion about the long axis plus flexure about the cross axis and to be complete, flexure about a vertical axis; resulting deflections of all (three axis system of coordinates) are additive. Consider this flexure as part of your suspension system if it makes you feel better.

Wow! I have to say you guys are awful kind to give me such good, thorough and consistent answers!

Taken into account what I read, I'm beginning to gather that it's not the chassis that's flexing, but perhaps the suspension is what needs work. As I said before, it's only on certain kinds of bumps in the road that cause my concern. Head on bumps don't seem to provoke what I'm thinking to be body flex so much as a wavy, unevenly paved road (if that makes any sense) or bumps only on one side of the car. I'm still feeling the car out, though. Unfortunately, I can always tell when something isn't right when others seem to think everything is fine. Given the car has 134k miles and I just replaced the ORIGINAL plug wires, chances are everything suspension is original. It does steer straight as can be despite it all.

One thing I did notice when the car was on a lift is that the sway bar mount on the passenger side had broken loose. I had the guy weld it back together but the car handles the same as it did before (which is why I didn't bring it up earlier). Is this a common problem and/or cause for concern? Is there a solution to this problem that any of you know of aside from simply welding it back?

3.2 Cab (Tony) - I'll do as you suggested and take a closer look at the underside. I did see some surface rust on the very front of the pan near the condensor but nothing else under there caught my eye.

Again, thank you all SO very much for your help! It's much appreciated. I hope I can offer some assistance in the future.

Welcome to the madness...
 

Aaron

Not that it will do much for the body flex but it's mainly for engine vibration dampening, confirm that you have Vibration Damper, on the photo you can see (barely) the top of it just left of the fan pulley.

Ok, for a proper welcome, you should do an intro posting (info abou how you got the Porsche illness, got the car along with many pics.

J.J.

http://forums.pelicanparts.com/uploa...1285146325.jpg

look like a small shock absorber

http://forums.pelicanparts.com/uploa...1285146479.jpg

Driver Status...
 

[QUOTE=tcar;5574405]Yes, mine's the same, no change in door gaps, etc.

But the car IS more flexible than a coupe. Period.

A good driver can absolutely feel the difference. (or a mediocre one like me).

Yes there is more bracing, but it's all in the pan.

Anyway, a strut brace won't help.[/QUOTE]

Not sure I buy your driver description :D:):D

Anyway, i met a Targa guy last week-end who had torsion bar, very much like the front tower strut, installed between the shoulder seat belt point and the lower one. Not sure which driver category he fall in but he said he does fell the difference after he installed them.

JJ,

I do have the damper for sure (I like your air filter set up by the way).

Don't confuse being a 'good' driver with someone who can tell when somethings wrong :) I consider myself to be mediocre or maybe just a bit better than average. I've worked on and owned MANY cars in my life, though, and can always tell when something is amiss. It's more the mechanic in me than anything.

I'll check into the torsion bars as you mentioned. I've looked all over Pelican and the internet altogether trying to find solutions for strengthening the chassis and wasn't able to come up with anything which is why I resolved to asking you guys.

Being a past 1987 Cabriolet owner that also tracked his car extensively - I can vehemently say that most people could not tell the difference between a coupe/targa/and cabriolet by just driving one.

I can also say that the strut brace with integrated monoballs made a difference in the driving dynamic of my car.

By many accounts the 911 cabriolet and targa are miles ahead of other convertible cars. I know my garage floor is not completely level. I know when I put my car on jack stands - it will tripod - with the driver's side front being free about 1/4 of an inch.

My cabriolet would tripod - the same as my current 1974 non-sunroof coupe that I currently have. If there were major structural issues with a cabriolet - it would have sagged that 1/4 inch and closed the gaps. It didn't.

So - will a 911 cabriolet give a little cowl shake going over major road imperfections? You bet - just as just about any convertible will (My old alfa romeo spider got the nickname flexible flyer for a reason) Is it reason to be concerned? No, not really. Check out the rockers for rust - the rockers are paramount in the integrity of the cabs and targas.

Thom Fitzpatrick welded in some tubes to increase the structural integrity of his heavily tracked car - Dave at TRE makes a rollbar system specifically for cabriolets = check that out.
(thom's car) http://rennlight.com/thomn8r/2101081c.JPG

As far as the sway bar mounts - the porsche originals were designed at a time with smaller and less sticky tires - I recommend ditching the factory mounts and welding in a set of WEVO mounts and your trouble goes away.

Sorry for the long winded response -

I agree... If you never drove a Cab before you got nothing to compare it to.

I went over some badly maintained railroad crossing, flexing was not my problem, airborning was... My mirrors stop working after that one (plug on the drivers side adjust switch became unplugged).

2 Months ago I installed a Kirk Roll Bar that use the 4 rear seat belt bolts and is plate sandwiched through the floor. I barely notice any difference. The Cab is production car #10 (Nov 82) and the doors gap are still perfect, so they had their design nailed down.