348 highway instability

I'm sure you've covered it but are your tires recent and matched and at the correct pressure and have you had a full alignment done ?

 

Alignment, ride height.
Mine used to do that but now is rock stable.

Kai

 

What is alignment like?
What tires fromt rear?
How old?
What is chassis rake?
Stock wheels?
Which rear subframe?
When last shocks rebuilt?
When a arm bushings changed?

 

I recall test driving at the Ferrari dealer an (early model) low mileage 348 when they were only 5 years old and felt an instability on the highway at around 65+ mph.
The F dealer suggested there was some instability on the early models at elevated highway speeds that was addressed at the end of the model run by wider rear wheel spacing.
I had read about the same issue in road tests at the time.....so not sure if worn rubber components have made the issue worse or the addition of wheel spacers on the rear (if your 348 is an early model) would help the situation.

 

I have a 93 348ts and the handling is rock solid, even going around sharp corners at speed. No twitching or unnerving at all. I’ve had 4 911’s from the 3.2 to the 996 anniversary which could not be driven the way i can the 348.

I understand that there was suspension mounting point changes and shock absorber updates over the production time. When i bought my car last July I noticed that all the bushes were also replaced by the previous owner for the poly type which probably help.

 

This has been a LONG time ago, but not long after I purchased my old 348 (2000), I installed a new pair of Bridgestones, in original size, on the rear only. Pressures set to factory specs. No unusual wear patterns. The fronts had over 50% tread remaining. The car instantly became alarmingly undriveable, wandering all over the road. I started a thread here on FChat about it, and learned that it happens all the time with just two tires replaced. I purchased another pair for the front, and it was fine again.

So Chuck, do you have a matching set of tires on your car, same age? If not, you're probably never going to make it track correctly.

And just in case, is it possible that you have tires with directional tread, and they are mounted on the wrong sides of the car? The wheels (if stock 348's) are also directional and belong in their own proper location on the car.

 

Ditto the above, I replaced the REAR only on my 328 with new Bridgestone. The car at speed was all over the place, even got an alignment at Les Schwab .... Still squirrly, then got a 4 wheel alignment at a quality race shop .... Better but still funny.
Talked to the dealer maint manager ... He just smiled and asked if I had changed/replaced any tires recently. Put 4 new tires on and PERFECT. The maint manager said he had spun a 348 on the highway a few months back, a customers car no damage. But the 348 owner had just replaced the rear tires only ..... Same result.
This was like 15 years ago, my front tires were still 50% plus so I thought why change them ......

 

Here is my opinion on the twitchy handling of the 348.

The factory alignment specs SUCK.

Here is what I did to improve the handling of my 348.

1) lowered it via the stock coil overs, and did my best to set the front to rear rake as close to the specs as I could manually. (thanks goes to fatbillybob for helping me with that) It really should get corner weighed to have it balanced properly.

2) I dialed OUT as much negative camber as I could in the rear, and then had the front aligned to drive straight (meaning basically no toe in or neg cam). I also had a whole bunch of the negative camber removed from the front.

3) I put on a set of wider 355 wheels, and spacers. Though currently I'm running the stock 348 wheels.

4) I run wider tires than what the factory recommends. 225/45 front, 275/40 rear and if I can find them 285 rear.

5) almost forget, I have also replace all the wheel bearings

The result is my 348 no longer has the wandering issues it had when I first bought it. I drove it across the country last year and I had zero wandering/twitchy/darty issues.

 

I still haven't sorted mine out fully. Gets light at high speed.

Putting 355 underfloor panels on the car in the next few weeks. Hopefully that will give it some additional stability.