Chassis wiggle.....strut brace?

I have never experienced shaking on my car, even on rough roads, so i will suggest you have another problem, most likely related to worn suspension or steering components.

Doug

 

The cowl shake comes from an open top design, specifically, flexing of the chassis between the area of the front of the doors to the rear of the doors. A front (or rear) strut brace between shock towers won't do anything to lessen this. All you can do is add chassis bracing - a full roll cage helps, but even if you added further bracing of the chassis tubes you're still left with an open box configuration that isn't going to be that rigid anyway compared to a coupe.

The 308 is pretty rigid for an open top configuration compared to many full convertibles. If you have a lot of cowl shake then you should first look for accident damage or corrosion damage to the chassis tubes.

 

Resurrecting this old thread, and had the same question. Lots of aftermarket braces available for the 911 Targas. Anyone come up with anything to improve the GTS?

 

911s have Macpherson struts, 308s don’t.

 

I've never heard of any aftermarket chassis braces for the 308, and I don't know of anyone who had added anything for this. It's an open car, it has cowl shake. It's better than some, worse than others.

I think the 308 doesn't have this for a lot of reasons. One is that it isn't that bad. Compared to my old Alfa Spider or Triumph Spitfire it is nice and stiff! In my Alfa you had to hang on to the steering wheel over railroad tracks because it would hop around in your hands. The Mercedes SL I drove was much stiffer. The 308 is in the middle. It is too good for someone to provide aftermarket support for it. It just doesn't suck enough. Secondly is that the GTS isn't a serious enough sports car. They aren't really raced, autocrossed, etc. If you want a stiff 308 for serious handling performance just start with a GTB or GT4. And the GTS doesn't need more weight.

Derekw - he's not asking about a strut tower brace, he's asking about a whole chassis brace. Some open cars have (or you can add) a giant X brace across the entire bottom of the car to stiffen the frame and try to eliminate the cowl shake. Cars that were designed as a coupe can have these from the factory. Some cars have these as aftermarket pieces available. The best way to eliminate this is to add some sort of structure above the open cockpit to tie the front and rear of the car together. A roof works really well for this but a full race cage can also work.

 

Under certain conditions - like the railroad tracks mentioned - I can certainly tell that my '89 GTS is not as stiff as a coupe. But frankly, other than some RR track crossings or occasional washboard road sections, I never really notice any cowl shake/flex and I do try to "stress" the car handling-wise in the twisties every chance I get. I had it on a track in NV the day after I bought it, in '08 hitting speeds of 145+ and it was very stable/comfortable at that speed. IMO, it does what it was designed to do very well with no drama at all. But it is NOT a race car.

Obviously you can get stiffer bushings/etc that may help a bit but those won't eliminate the inherent flex that exists in the body style. Certainly, if you want to seriously race it, there are ways to stiffen the chassis though, as noted, it would have to be done by shops that do such things since there are no stiffening "accessories" produced for the car.

 

Stiffer bushings are the last thing you want on a flexible body I would think. You are just going to be putting more energy into the body because you are absorbing less in the bush. Didn’t the GTSs came with softer spring rates for this reason?


Regards
David

 

Thanks guys. Appreciate the responses. I agree with all that you’ve said - I’m not interested in changing the character of the car with roll bars or cages- I bought it as a back road, sunny day car (plus as a piece of living automotive art). I have a 964 race car with a full cage, and it’s amazing how stiff the car becomes. Great on the track - not so much on the street. You actually want a little bit of flex on the street.

The Porsche crowd is full of engineers and they can’t help themselves. There are tons of mods and bolt-on solutions to just about any issues you could have with an old 911. Many of them work well! I was just curious if anyone in the 3xx universe may have stumbled across anything.

First world problem - I love my 328!

 

Per the parts diagram/part numbers, from what I can see, there is no difference between the GTS/GTB suspension, Stiffer bushings are a pretty common change though I wouldn't put them on my 328.

 

Must just be the 308 then. Those definitely have different spring rates between the B and S. The 308 GTB/GTS suspension sub assemblies were labeled differently on the production line to identify the difference.

Thanks for the correction.


Regards
David

 

The 911 like 914 are a unibody. Very different than what is underneath the panels on a 308. Unless you want to go this far.
http://build-threads.com/build-threads/makela-ferrari-308-gtb-group-4/
http://www.mat.fi/projects

 

If you don't think that there is a lot of flex in the 328 GTS just listen to the squeaks of the roof. It could be helped by putting braces inside the door that go from high area to latch, would be invisible and add only a few pounds , you could make them out of room bar tubing with a plate at each end, would even make your car safer for side impact.

 

TIL - the springs between the GTB and GTS have different part numbers. I knew the GT4 had different part numbers but I didn't know the GTB and S also had different springs. The shocks have the same part numbers so valving is the same, but with different springs they will have different behavior. I wonder if this is just to compensate for the extra weight of the GTS or if the GTB got a "sportier" ride with stiffer springs.

 

Possibly consider placing a very attractive Lady in the passenger seat, back firmly against the seat, knees against the dash, elbow resting top of door and hand keeping her hair from sunglasses and face? Bound to make something in the car more Ridgid . Lol

 

GTS springs are softer to reduce chassis flex. A brace or two inside the door and tapered pins into holes/slots in brackets on the rear door post would work well.

 

I think you have to face facts here, these cars have very low torsional stiffness - just enjoy them unless you want to spend a ton of money and time making stiffer via rollcages, additional chassis braces.

 

Easiest way to get a stiffer chassis is to buy a GTB A stiff drink also works as you won’t notice the flex as much... as you go into the ditch

 

Afternoon all,
I have a 328 GTS and it does wiggle on bumpy roads, not a lot, but if you put your finger between the union of the targa top and the windshield frame while driving, you certainly notice a movement.
If you look at the workshop manual and observe how the chassis is put together, this torsion should be expected. The only thing holding the front and back of the car together are the oval shaped tubbing below. In my opinion, this arrangement will flex when twisted, not saying it's good or bad, just saying what it is.

John.

 

Silicone grease on the top's rubber gasket will stop the annoying squeaks! Not hearing the squeaks will automatically improve the handling.

 

The lower rocker sills on the GTS are much larger than the GTB, that's where most of the extra weight comes from.

 

I saw this thread and thought of your project, Simon. I do wonder about the hidden triangulation bracing you put in under the floor and how much it helps torsional rigidity by itself. That's about all you could do on a GTS.

 

Out of interest MAT did some FEA on the Group 4 cars;
http://www.mat.fi/gallery/59