Posted by & filed under 240sx, Automotive.

The lowdown on 240 rear end swaps:

with legal LSD


First things first, what is an LSD? 
It stands for Limited Slip Differential, 
why is this important? Because it allows your car to get an incredible
holeshot due to increased traction.   The
differential is the thing in the rear of the car that splits the power coming
from the driveshaft up between the 2 rear tires.  

Now the factory 240 (with a few exceptions) use what’s called an ‘open
rear end’.  In this setup both tires
are basically free to spin at whatever speed they want to, this has one good
side and a bad side.  The good side
is that when going around a turn the tires don’t ‘scrub’ or ‘hop’ around since
they will be traveling at different speeds (outside tire has farther to go so it
spins faster).  If you had a solid
axle (or welded the 2 halves of the differential together) you would have killer
grip in a straight line but handling would be extremely bad.  
The bad side of the open rear end is that since both tires are free to
spin at whatever speed they want, whichever tire has less grip (the one
spinning) will get more power transferred to it which will cause it to spin
more, which will cause it to loose more grip and spin more which………….
anyhow it’s not a good cycle. 

The LSD comes into play right here, LIMITED SLIP comes to the rescue by
stopping the loss in grip by recognizing that one tire is spinning and then
transferring the power to the other wheel that has grip.  
The type of rear end I’m using is called a Viscous LSD which means it
uses silicone and 2 plates to operate.  
The simplified explanation of how this works is that there is a plate
stuck on the end of each shaft.  These
plates spin at the same speed as the wheel they are attached to.  
When one wheel looses grip and starts to spin faster it creates friction
between the two plates due to the difference in speed. 
This friction heats up the silicone floating around causing it to expand. 
When the silicone expands it pushes on the other plate ‘locking’ it to
the one that’s spinning.   This
locking is what causes the other wheel to push.   

The fact that both wheels are now pushing is VERY apparent while driving. 
My friend’s turbo 240 dropped a full second off his quarter mile time
after I installed an LSD from an Infiniti J30 into it. 
My car can be launched at 5,500 RPM’s by sidestepping the clutch and
flooring it with almost no wheelspin.  
But this isn’t just useful to dragracers, the difference while
autocrossing is even more pronounced.  The
car can start accelerating earlier and harder out of corners than you could ever
hope to do with an open differential.  
Lastly the car is much smoother to drift (but it dose take a lot more
power to get the rear end to start coming around).

Now that you know what an LSD is I’m sure you want to know where to get
one.  The easiest way is to find a
240sx with one on it already and take it.  
There is a lot of talk about what year and options a 240 has to have to
be equipped with an LSD.  From what
I’ve heard SE’s with ABS, HICAS, or S14 5 lug SE’s w/ ABS all should have the
LSD.  Canadian 240’s also have VLSD
(all of them).  The easiest way to
check is that  the LSD will have an
orange sticker above the fill hole that identifies it as an LSD. 
Also if you turn one side the other should turn the same direction.  
You’ll also notice that the LSD is harder to spin by hand than the open
differential.    If your
like me you can’t find a 240 in a scrap yard anyplace with an LSD in it, so you
have to improvise………. here comes the fun part.  
The R200V (VLSD) differential is used in the Infiniti J30, and Z32 300zx.  
The Infiniti one has an ABS sensor at the front which adds about an inch
to the length of it.  The flanges
for the halfshafts (the shafts that go to the wheels) are the same pattern for
the 95 and up J30’s (pre ’95 used a different pattern at least on the ones I saw
in the yard)  Also if you own an S13
(89-94) you will need to get a new differential cover gasket and swap the rear
cover off your R200 (stock diff) onto the new one.   The S13’s used a different bolt pattern (4 bolts) than
the S14 (2 bolts).    The
90+ 300zx one also fits but takes more work. 
First thing DO NOT get the twin turbo diff, it’s got different gear
ratio’s in it and it will really slow your car down (3.86) 
The NON turbo has the same ratio as the 240 (4.06).  
The 300sx also uses the 2 bolt rear cover so if you own an S13 you’ll
need to switch it.   The biggest problem with the 300zx  is that the output flanges are different. 
The look like a ‘5 star’ flange where the 240sx uses 3 sets of 2. 
The parts to convert a 300 to a 240 can be had for around 200-300 new.  
I got mine at a scrap yard for 150. 

The M30 and Q45 diff’s also work with the same basic modifications I
mentioned earlier.   The big
thing to look for is the flanges, they need to be the 3 sets of 2 or you will
have to replace them.

I have heard rumors that the J30 differential requires you to shorten the
driveshaft by an inch due to the position of the ABS sensor but my buddy hasn’t
had any problems with his when he installed it in an S14.   It’s only been on for 2 weeks and the fit is tight but
it works.

The install is pretty straightforward, just unbolt the stock diff and
then stick the new one in.  The hard
part is getting the new diff up and in place so you can bolt it on (these things
are HEAVY).  I needed another guy to
help me and 2 jacks to get the thing where I wanted it.   
Care must be taken when tightening it down that it’s level when you start
tightening so that you don’t’ crack the cover.   I hung it in the back by sticking the studs on the
cover through their holes and then lining up the bolts in the front and
tightening them down then I put the nuts on the rear. 
After that put on the 6 bolts on each side that holds the flanges to the
driveshaft.  Finally bolt the
driveshaft to the differential.  

While you have it out I highly recommend changing the fluid in diff while
you have it out since it’s a major pain to do it while it’s still in the car. 
You MUST use either a fluid designed for LSD (royal purple or Redline) or
add the LSD additive (this additive contains the silicone I mentioned earlier
that heats up to make the differential lock up).  
Another thing you might want to do at this point is take the bottom drain
plug off the stock diff and put it on the new one at the filler point. 
The bottom plug has a magnet on it that picks up metal shavings floating
around in the case, it’s not really necessary but since your throwing the other
diff out anyhow you might as well keep the magnet for the new one to help keep
stuff from floating around the case.

and modifications required:

240sx W/ LSD
No mods needed if it is NON ABS
300ZX  90+ Non Turbo Needs new output flanges
90+ Turbo
Needs new output flanges and gears are
J30 95+
No mods needed*
J30 pre 95
Needs new output flanges
No mods according to Infiniti of
Melbourne FL*
Infiniti Q45 No mods according to Infiniti of
Melbourne FL*

*might need to have driveshaft shortened one inch due to ABS sensor but
this isn’t’ confirmed and my
friend has no problem with this setup

Written by Paul 

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