"I belive that many people
are going to be taking this route from now on and it will answer most if
not any of the question that people might have: and now for
the long awaited gs400 differential swap thread:
Hey guys, been some time since i could sit down and put together some
useful info for you, but here it is:
*****THIS SWAP IS FOR LSD EQUIPED NA SUPRAS!!!! if you
have an open diff and are buying a separate LSD (trd, ect.) you just
need to follow half of the steps which include taking out the diff form
the gs400 pumpkin and taking off its ring
gear, you do not have to touch the na differential*****
*****keep in mind that you also could just put in the gs400 pumpkin and use it as an open lsd untill
you buy one, in that case you just simply put the differential INTO THE
CAR and everything bolts up, no taking apart required****
(***please keep in mind that i used a 2000 gs400
differential, i am not yet aware of what year lexus gs400's have come with the same differential)
(***also, another member used an LS400 differential with very minor
adjustments from mine and made it work***)
***and one last thing before i start*** MAKE SURE THAT YOU UNTIGHTEN THE
COMPANION FLANGE BOLT WHILE THE DIFFERENTIAL IS STILL IN THE CAR IF YOU
ARE ALREADY USING A TT AUTO COMPANION FLANGE TO MATE TO A TT AUTO REAR
HALF DRIVESHAFT, if you take down the differential that bolt is really
hard to break loose and takes some thinking 
)
To ease everyones mind, this swap is just
about as direct as it can get while upgrading your NA-t. Everything is
pretty much interchangeable and bolt-in, and quite simple if you have
the right tools @ hand.
to get teh differential out of your car, (its very
simple, just need some stregth) follow this simple instructions from the
toyota manual under STEP 2:
http://www.mkiv.com/techarticles/aut...ial/index.html
here is what the casing of the gs400
differential looks like (this is just an empty casing, the insides have
already been taken out):
the stubs seen on the right are the first to come out from the differential when you have everything taken out, you simply "bang" them out, we used a peice of wood and a hammer and tapped it out of place around the circumference of the stub:
After both stubs are out, the bearing cap (seen on the left in the above
picture) is taken out by unscrewing the 8 bolts that hold it in place.
After both of the caps are taken out, the differential simply pulls out
of the casing, here is the GS400 OPEN
differential:
the take-apart process for the Supra differential is the same exact way, except the LSD out of the supra needs to be turned in order to be taken out. here is the picture of my LSD that was taken out at the same time :
here is the picture of the pinion that is left inside of the casing (you do not touch this part at all!):
next step is to take of the ring gear from the differential, this is done by using a special "Start" socket (12mm I THINK!, im not exactly sure), there is 10 of them:
once they are removed (it takes some muscle) the ring gear just comes off :
this ring gear is reinstalled onto the LSD and the reverse process if
followed to get the differential back together. only thing different is
that if for those who are using the NA LSD, the NA LSD Axle stubs that
were taken out from the NA pumpkin will have to be put into the gs400 pumpkin, other than that everything else
is in reverse!
here is what it looks like:
on the star bolts that hold the ring gear to the LSD, make sure to use
some THREAD LOCKER from Autozone, use the Red kind (the toughest kind)
its only 9 bucks and will keep sure bots nice and tight.
once everything is assembled you simply follow the reverse step and
reinstall the differential into your car.
the drive shaft combination that was used previously works exactly with
this swap, so you have nothing to worry
about.
here is the gs400 pumpkin with the LSD,
we also sanded and painted the housing, looks brand new !!!:
here is the verdict on the differential:
Major gearing reduction form the v160-na rear end combo.
this is not yet AEM varyfied, but after i got the speedometer corrected
with the DAKOTA DIGITAL unit (www.dakotadigital.com) my tach read approx. 2650rpm @
70 mph as apposed to 3600rpm @ 70mph last time
top speed is not yet varyfied with this swap,
but stay tuned, please feel free to ask any questions."
- Thanks to Ravan17 for the writeup/pictures
Other important facts/swaps:
refill the GS400 diff. with 1.5 quarts of oil (I am using Redline Heavy Duty Shockproof)
the GS400 ring and pinion uses a 3.26 gearing, tt 6spd is a 3.13, TT auto rear end has a 3.76 gear
the actual LSD inside the NA/TT AUTO/GS400 differential is the same exact size
If you start out with a TT Auto complete diff & GS400 complete diff to perform this swap, you can use either (Auto TT or GS400) stubs (refer to the second picture) to put back into it. You need to swap the auto TT ring gear for the GS400 ring gear when using the auto tt LSD in the GS400 pumpkin. The auto TT ring gear is slighter thicker than the GS400's and will rub.
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ABOUT MKIV REAR DIFFERENTIALS
There are 2 differential sizes in the JZA80, the most common is the A
series which runs a 200mm crown wheel which was found in the 2JZ-GE
manual and automatic as well as the 2JZ-GTE automatic and in the manual
2JZ-GTE from 5/96 up until 7/02 when the JZA80 was no longer produced.
The following ratios are available for the A series diff - 3.266, 3.769
& 4.083.
Then there is the B series which runs a 220mm crown wheel. It was found
in the 6speed 2JZ-GTE from 5/93 up until the 5/96 where it was
discontinued and replaced with the smaller A series. There was only ever
2 ratios offered on the B series diff - Export JZA80's received the
3.133 whilst the JDM ran a slightly shorter 3.266 ratio.
Both of the A & B series run a Type 1 Torsen differential up until
the 5/96 when the Type 2 Torsen was introduced.
B Series dimensions
------------------------------
Differential Case OD 133mm
Element Gear Length 61.90mm
Spur Gear OD 36mm
Worm wheel OD 33mm
Side Shaft OD 37.80mm
Side Shaft spline count 35
A Series dimensions
-------------------------------
Differential Case OD 123mm
Element Gear Length 57.1mm
Spur Gear OD 33.3
Worm wheel OD 30.5mm
Side Shaft OD 33.70mm
Side Shaft spline count 30
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