I was wondering if anyone has any information regarding the differantial and in particular the method used to obtain the required preload. Does it utilize a bevel washer to hold tension on the plates and has anyone ever experimented with reducing the preload? The preload setting seems to be quite high (about 40ftlbs) and I thought 20 to 25ftlbs would reduce some of the under steer felt in tight corners. If anyone has any experience etc I would be very gratefull for your input. Thanks for your time
brian, are you refering to the pre-load on the tapered roller bearings that hold the carrier assembly?
Difaz, if its the limited slip differencial that you are refering to, then I,m afraid I can't help you there Gary
The best guy to probably answer your question is Phil Hughes (aka. ferrarifixer). He has a lot of experience and ran 'Fluffer' in a 360 Ferrari in Australia. Good luck with it. Rob Calisi
Robert Nuvolari !! How do you know Allan then. The fluffer nickname is from the Palmer school isn't it...?? Anyway, the diff. The static preload is actually quite low I think at around 40lbs slip, and tightening it up further by re-arranging the clutch plates order, or fitting thicker ones can help traction a fair bit. It is too low to cause understeer, and I'd say that's more a wheel alignment / tyre thing in most cases. Total lock will cause low speed understeer, but that's a long way from where the std Ferrari units runs. The clutch plates / static lock can be adjusted by changing the number of friction surfaces that work against each other. The more faces the tighter it gets. But it's not an exact science, and much time can be absorbed for very little gain. New plates always settle a LOT, and it's better to re-use old ones for consistency, so long as they're healthy of course. The dynamic lock (on/off power) is controlled by the ramp angles on the cross spider shaft, where it locates to the housing. Typically, most Ferrari diffs are quite good, in that they have a fairly loose overun slip, and tighten up nicely under power. Frank Capo of Modena Engineering (here in Melbourne) makes really nice diffs, of adjustable (by dismantling) locking, and can be configured just about any way you like, from open to fully locked, and just flip the cups/housing over to reverse the torque loading direction. In short, unless you're racing VERY seriously on slicks, a std Ferrari diff in good condition works very well. You may gain some traction by upping static slip to around 65-75 lbs, but you'll probably need thicker clutch discs or shims to do this. On 246 and early GT4, there is no static slip preload, and locking is achieved solely by more aggressive ramp angles. I think static preload became the norm around late '75, but as always with Ferrari, there are no doubt exceptions out there.
PMA1010 / Philip Differential preload is what I am questioning as I can't seem to find any specifiacations on this. The percentage lock on power I believe is 40% from what I can see in my workshop manual. Thanks Ferrarifixer Phil for the info, I didn't know what the std preload setting was supposed to be. Difaz
Is the push during overun entry/mid corner on power apex out? Changing the overun ramp angles will help entry push but as the guys mentioned above, it sounds like the diffs in these cars are well balanced to start with. Reducing the power on ramp angle should help exit push but may make it a bit loose. If the problem is more like a lack of entry rotation, I'd start by taking some rebound out of the rear dampers. Might unsettle your braking a little, but like any chassis tuning, it's a matter of balance and driver style...
I build them with new discs on the bench with oil, then spin them until they seem to settle, (or as long as I can be bothered to stand there and do it), then strip, clean and rebuild again. It usually settles about 10lbs, but it can vary wildly depending on many things.
