A member recently asked me the difference between a 2 way diff and a 1.5 way diff and here is my explanation about the different types of rear axle Differential and what they will do to the way your car goes around corners.
First of all the reason we have these differentials fitted is because as you turn a corner the inner wheel attempts to rotate at a different speed and without a “differential” that will allow one wheel to go faster than the other, the inside tyre that is turning into the bend will wear out VERY quickly as it will scrub and “hop” whilst the vehicle is in the corner.
Another side effect of this scrubbing is a detrimental effect on the vehicles handling, but more of this later.
To now come back to the original question, these 2 way and 1.5 way diffs made by Kazz and Cusco are not as some may think new technology indeed they are just basic old style Salisbury LSD’s (limited slip diff ) that were used on Jaguars and Triumphs etc in the 1950s’ and the name Salisbury came from the company that manufactured these diffs.
These diffs work by the fact that as one wheel attempts to spin faster than the other when you are on the throttle the LSD diff locks up to then transmit equal power from your engine to both wheels.
This action is carried out by the “cross shafts” that locate the planet gears which operate the speed differential climbs up a ramp cut in the differential housing and exerts pressure on the plates that are on either side of the planet gears that are in the centre of the diff assembly and this in turn locks the diff to transmit the equal power. (See attached picture for explanation)
Now what is the difference between the 1.5 and 2 way, well the 1.5 on entering a corner will allow the inner wheel to turn and the differential to operate till you put the power on thus making the diff clamp or “lock” itself together.
The 2 way “diff” however already have the plates under preload effectively locking the diff almost completely as you turn into a corner; the side effect of this is that because both wheels are still locked and the inner is scrubbing into the corner understeer IS induced and understeer in its worst form means the car will not want to turn into a corner and will want to go straight on, which is why it is called understeer.
Then once you have got the car into a corner and try to exit because the diff is already locked up, then “snap” oversteer is induced both of which will make a car overall go slower around a corner on the road and on a race track, however this is why the Drift guys love these 2 way diffs literally because of the way they screw up the handling and make the back “step out” as soon as you go near the throttle.
On the other hand a 1.5 way diff will operate in the same way as a normal diff that has no lockup capability and will not screw up the handling of the car providing that preload on the plates that were described earlier is not too great.
I know the above because when I raced in my early years I could not afford LSD or as you know them, 1.5 way diffs and used to weld my diffs to lock them up solid but suffered from evil handling cars that never won a thing, but in later years I even worked out that by stripping the LSD diffs and swapping the plates around thus making the preload less than it should be as standard and guess what I then won lots of races. ( I used to set the preload at just 80lbs)
Now we have talked about Sailsbury LSD’s, 1.5 way and 2 way diffs its worth knowing there are other way of making both your wheels transmit power.
There’s a diff that’s called a spool type diff which is where there is no diff but just a lump of billet steel to locate the crown wheel and the only purpose of these is for Drag racing where you want both the wheels to turn the same time all the time.
Another is a pawl type diff where lumps of metal inside the diff throw out centrifugally to lock it.
The last and in my opinion the best without going to computer controlled hydraulic diffs is the Torsion diff as used in RX-7’s and RX-8’s that have Limited Slip Diffs.
These diffs are ideal because they work purely on gears and worm drives within the diffs and need no preload thus letting the wheels turn correctly upon entering a corner but then making both wheels turn together when leaving the corner on power with no detrimental effect on the vehicles handling.