That's always better than hanging out in these forums _wishing_ I was working on or driving my cars.I read the thread from the guy who has a Phantom Grip unit on order. My experience was much the same. I beat on them regularly. I sent them a diff carrier. I gave them credit card info for billing to get started. I begged. I called regularly (email were almost always ignored or respones came weeks later) and left messages as seldom did a human answer the phone. Typically, a voice mail was the only option. Finally, I got the unit. It always seemed like they were too busy to talk with a customer. Maybe if I wanted something for a Honda they would have been more interested. And it seemed like the guy's teenage son was who returned the calls. It wasn't confidence building.
I got two units. One was for my car the other was for a customer's car. (I build engines and transmission for racing and performance street customers) Materials and workmanship looked good. It came with no instructions. It did come with fancy "Phantom Grip" stickers
Anyway... the PG unit is very simple in operation. There are basically three types of Limited Slip diffs (and because there are descriptions of their operation I won't go into detail here). A true locker mechanically locks the two axles together (like a spool) under acceleration. A gear type or torque sensing (like a Quaife or Torsen/Gleason) direct torque to the loaded wheel and a clutch or viscous type that uses a clutch to limit the difference in rotation between the two axles. The clutch allows some slip depending on how much clutch action is applied.
The PG unit is basically a variation on the clutch type limited slip. Where as a true clutch type actually has a stack of clutches between the axles the PG unit uses a spring loaded block between the two spider gears so that the block and spider gears have some "clutch" type action to limit the rotation differences in the two axles.
I have pics of the PG unit installation on my yahoo picture page at:
http://photos.yahoo.com/steve020361
Click on the Phantom Grip album.
You can see in the pics that the side gears are machined flat where they mate with the PG unit. The PG unit is basically a block of aluminum with a hardened coating. This coating protects the aluminum from wear and gives some amount of friction to the spider gears. The block is split in two and inserted between the two spider gears. The block sandwiches a set of four springs which force the two halves apart to apply pressure and therefore friction on the spider gears. Since the spider gears are splined onto the axles, this is how the slip is regulated.
The PG unit is designed to have a certain amount of clearance between the block and spider gears. The amount of clutch action is determined by the spring pressure and different springs of varing stiffness are available. The springs can also be shimmed for more preload. Surface area of the spider gears is also important, the more surface area the more grip.
PG recommended a spring set and installed it in the unit I got. Once installed the performance wasn't that good. I tested heavier springs and ended up with the stiffest springs, no shims and a much greater surface area on the spider gears. The PG guys had never tested machining the spider further to increase contact area.
You do have to pull the diff carrier out of the transmission to install the PG unit. This means that the installation requires pulling and disassembling the transmission. If you want to make any changes, you will have to pull it back out.
Notes from testing in my DSP X1/9 autocrosser: Unlike a true clutch type, if you break it loose (get one tire spinning) it will not lock back up until you let off the throttle. It works pretty good until you break it loose and then its gone. The amount of preload didn't solve this problem, it only raised the threshold. Like a clutch type, it noticably alters the cars handling. It makes the car slower to turn in and want to either push the front under throttle or power oversteer. And it can snap from one to the other quickly. Under very hard braking it would sometimes cause wheel-hop and try to kill the motor. A slight brake bias adjustment usually fixed this.
Conclusion: I am no fan of LSDs in most mid engined cars. I tested a true clutch type LSD in my X and found I didn't like what it did to the handling. The PG unit behaves somewhat like an LSD in its effect on handling but not as severely as the LSD. But then it wasn't as effective as the LSD either. I have a clutch type TRD limited slip in my D Prepared MR2 and it works quite nicely. Its set a little on the loose side to prevent handling problems but does a pretty good job of curbing wheel spin.
I had learned to tune out most of the wheel spin (using an open diff) with chassis setup. Setting the car VERY stiff with a heavy bias toward front roll stiffness and keeping the rear roll center below the front works great. But as developement increased grip I would still sometimes spin the inside rear off the corners. My X was capable of more than 1.3 g on a good surface and would spike much higher than that. Photos of the car at those cornering loads would show the inside front tire in the air and the inside rear with a contact patch about the size of a quarter. I only wanted enough LSD effect to keep the wheel spin under control right at corner track-out where the g numbers spiked. It was partially successfull.
Bottom line, you get what you pay for. Its a poor man's LSD in every sense.
I am sure there will be questions, I will be glad to answer.
Thanks for the great info!