|The MGA With An Attitude
Limited Slip Differential (LSD) - PHANTOM LOCKER - RA-302B
On 26 August 2009 at 22:49:57 UK time, Mike Ellsmore in Victoria, Australia, wrote:
"Has anyone had experience with a Phantom Grip LSD in a MGA banjo housing differential"? (Click for Phantom Grip web page).
Phantom Grip LSD parts, including springs for two different friction levels.
On 27 August 2009 at 03:22:04 UK time, David Lieb in Illinois, USA, wrote:
"Not in an MGA, but I have one in my Midget's 3.9 diff. If you expect a Quaife, buy a Quaife. If you want $300 worth of LSD-effect, you will get it with the Phantom Grip.
This plus race rubber plus 3/4" ARB in my Midget equate to the ability to do a skid pad on two wheels... not necessarily a good thing, but it demonstrates that the Phantom Grip is effective.
Mine is NOT the "track-only" version, it is the street version and does not have any negative effect on the streetability of the car that I can detect. I have been autocrossing a Sprite with open diff this year and severely missing my Phantom Grip".
Notes on general application of a friction type LSD:
This device is a cheaper rudimentary form of a clutch type LSD, without the clutch parts. It uses the original sun gear thrust washers as clutch discs as well as the steel to steel interface between the sun gears and the new center device. This does work, but it can encounter a substantial amount of wear with time and mileage and may need some expensive disassembly and replacement parts at closer intervals than you may like. If you don't put too many miles on the car you might like this one.
This device works by applying strong force against the sun gears in the differential, thereby creating considerable friction between surfaces on both sides of the sun gears. Traveling in a straight line on hard surfaces nothing happens. As long as the tires are same diameter all differential parts rotate together with no relative motion inside. If one tire is slightly smaller (like low on air) the resistance to relative motion in the differential may tend to push the car to track in a wide arc (very large circle). Result could be a slight pull to one side in the steering while driving in a straight line. This has generally NOT been a problem with friction type limited slip differentials in street car applications.
There will be relative motion at the friction surfaces when the car goes around a corner, or any time one wheel turns faster than the other. Friction is the desirable (in this case) force that makes the two wheels want to turn together, so if one wheel goes light or hits a slick surface it will NOT free-wheel (spin freely), and the other wheel will take up the driving work. This is often referred to as transferring torque to the wheel with better traction.
Relative motion and friction combined will dissipate energy in the form of heat, same as clutch disc or brake linings. If all goes well the heat is carried away by the lubricating oil and will transfer to ambient air by conduction through the differential housing (same as normal differential heat). Friction and motion will also cause wear on the mating surfaces. In this case that would be the sun gear thrust washers (soft bearing material), both faces of the sun gear (hardened steel), and the outboard surfaces of the LSD shell (hardened steel). What wears first and how fast remains to be seen, but hopefully the wear will be reasonable (minimal?) and may be treated as a long term periodic service issue. Depending on how much you drive the car these parts might never wear out.
It is however subject to abuse. If you have one wheel on hard pavement and one wheel on ice or in mud, and you stand on the throttle to make one wheel spin continuously, you could induce some serious overheating and abnormal wear in short order (same as with any friction type LSD unit, but more so with this one). Since this device does not have formal friction discs it may be subject to more rapid wear when used heavily for competition. It may work well for normal street use, and it may serve well for occasional autocross work (rare weekend runs). Since this device is relatively cheaper than a full formal LSD, it may deserve a trial run before spending more money on a more expensive unit. If it works out well for you it may serve the purpose appropriately with considerably lower cost. If you use it enough to ultimately wear it out, then you might consider footing the bill for a more traditional type LSD unit.