Differential Gears
Japanese
Early corollas (KE1x, 2x, 3x) all had banjo-type front-loading differential centers, commonly called the Jap diff. KE1x and some 2x had 5.7" ring gears, other KE2x and 3x had 6". There are two different pinion flanges for these diffs, but the tailshaft unis are the same, so it's no big drama if, for example, you put a 6" KE30 center in your 6" KE25 diff and the pinion is different.
I am pretty sure you can put a 5.7" center into a 6" housing as well. The difference is in the ring gear only, not the carrier.
Borg Warner
KE5x and 7x Corollas in Australia had Borg Warner differentials, you can't change these centers as easily as in a Jap diff. KE5x have 6" ring gears, KE70s have 6.38". Apparently some KE1x cars had a Borg-Warner type diff as well, limited info available on these. KE20s have Borg Warner diffs from when they were made in Australia. All KE25s were imported, so they all have Jap diffs.
Comparison
So which is stronger? It really depends who you talk to. I personally would prefer a Jap diff, because even if you do destroy a center, it's bloody easy to change. I have seen both types of diff stand up to a decent amount of punishment (traffic light launches, weekend racetrack action, etc) behind a 96kw 4AG in a KE30.
Both factory diffs take 1L of oil. A common trick is to park your car on a downhill slope, so you can put more oil in, useful if you have a worn center or are running thinner oil or are just giving your car a hard time.
Upgrades (different housing)
Common upgrades are a Celica/T18/Corona T series 6.7" diff (clutch-type TRD LSD centers available AU$1200 ex-Japan, Cusco and Kaaz also available for more money), R31 Skyline diff (factory 4-pinion clutch-type LSD and disc brakes), 8" Hilux diff (many ratios and LSD available, rumored to be quite heavy), Mitsubishi Scorpion (LSD and good ratios available out of some L300 vans, but rare), even live-axle Datsun 1600 (wagon).
Depending on the car you are putting it into (obviouly KE3x, 5x and 7x are a bit wider than KE1x and 2x) just about any bigger diff you want to use is going to have to be shortened and have leaf mounts welded onto it. If putting into a KE3x, 5x or 7x, then Celica/T18 diffs will fit without shortening, but with the correct mounts welded on. With any of these, you'll obviously need to do something about your tailshaft.
Limited Slip (without changing housing)
Yes, there is a limited slip center that bolts into a Corolla housing, they were used in American KP Starlets. Sometimes you can find them in 4.1 or 4.3 ratio, more often than not they are the ridiculously low 2.928. Option1Garage on the Gold Coast import these for around $880. There are also people who "make" a sortof limited slip conversion, one such company in America is Phantom Grip. Tayell Automotive in Bentleigh East (Vic) advertise a similar service for around $250.
Ratios
Borg Warner diffs have the ratio written on a plate at the bottom of the diff center, facing the rear of the car. For Jap diffs, read the plate on your firewall, and relate to the list below. Most are U292 or U282, sometimes U209 or U211, rarely U231.
from Helene & Matti's page http://www.geocities.com/MotorCity/Pit/9975/dataBySubject/AxleCodes.html
first digit: ring gear diameter
A 138mm B 145mm C 6.25" D 6.62" E 7.1" F 7.5" G 8" H 9" J 9.25" K 9.5" L 10.5" M 12.5" N 13.5" P 14" Q 12" R 162mm S 6.38" T 6.7" U 6" V 10.6" W 15.5" X 142mm Y 158mm Z 202mm - no ring gear = FWD
Second, third digits: gear ratio
01 3.30 02 3.36 03 3.545 04 3.556 05 3.70 06 3.889 07 3.90 08 4.111 09 4.222 10 4.375 11 4.444 12 4.625 13 4.79 14 4.875 15 5.125 16 5.286 17 5.60 18 5.714 19 5.833 20 6.167 21 6.667 22 6.78 23 6.833 24 7.64 25 4.556 26 5.571 27 3.364 28 4.30 29 4.10 30 3.727 31 3.909 32 6.591 or 4.807 33 7.503 or 5.583 34 6.781 or 4.786 35 7.636 or 5.60 36 4.778 37 3.583 38 3.417 39 3.154 40 5.375 41 3.308 42 6.500 43 3.550 44 3.214 45 3.533 46 2.928 47 3.944 48 3.356 49 3.729 50 3.400 51 3.736 52 3.722 53 3.250 54 3.941 55 3.333 56 2.821 57 4.058 58 3.238 59 3.234 60 3.519 61 2.724 62 2.892 63 2.655 64 4.312 65 3.837 66 3.071 67 3.526 68 3.095 69 4.176 70 5.857 71 2.962 72 3.949 73 4.285
Fourth digit: no of pinions, ltd slip-yes/no
Code pinions LSD 2 2 no 3 2 yes 4 4 no 5 4 yes
Application guide
based on a table from Helene & Matti's page http://www.geocities.com/MotorCity/Pit/9975/dataBySubject/diffSize.html
5.6" (X) Starlet KP61 81-82
5.7" (B) Corolla KE1x Corolla KE20,25,26 70-74
6.0" (U) Corolla KE2x (some) KE30 77-79 Starlet KP61 83-84
6.25" (C) Corolla TE21,27,28 (some) 71-74
6.38" (S or R) Corolla TE21,27,28 (some) 71-74 Corolla TE31,37,38,71,72,75 75-82 Corolla AE71,72 83 Tercel AL10 80
6.62" (D) Carina TA12 72-73 Corona RT62,72,63,73,83,93 70-72 Corolla TE27 (some) 74
6.7" (T) Celica ALL 71-85 (RWD) Corona RT85,95,104,114,105,115,119,134,32,34,36 72-82 Corolla TE37,51 75-79 Corolla TE27 (some) 74 Corolla AE86 83-87 (?)
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