From my notes ...
Differential Fluid -
***
Differential, Rear......GL-5
All TEMPS......80W-90 [5]
SAE 80W-90 Synthetic Gear Lube (AGLQT)
SEVERE GEAR 75W-90 Synthetic EP Lubricant (SVGQT)
75W-90 Synthetic Long Life Gear Lube (FGRQT)
SEVERE GEAR 75W-110 Synthetic EP Lubricant (SVTQT)
Rearend Fluid Capacity:
4.1 pints *** rev-les and LeeAnn says 1.5 qt ***
***
How to tell what diff you have?
Look for the "Service Parts Codes" sticker. It may be on the inside of the "glove box" or on the passenger door jam.
Service Parts Code Sticker GU5 =
3.23 open gears (mine)
All RPO codes =
GU2 2:73 ratio
GU4 3:08 ratio
GU5 3:23 ratio
GU6 3:42 ratio
GT4 3:73 ratio
GT5 4:10 ratio
GQ1 Open Differential Rear Axle
G80 GOV-LOC Rear Axle
If you don't find that, or in case someone has replaced your rearend and it's now different than the one that came with the van, look on the axle itself. The characters are stamped into the axle. Covered with dirt, rust, gunk. Clean it off and look for :
Axle Code Stamp. Passenger side, FRONT of axle, near diff. (pre-90, Driver's side)
All Axle Code Stamps, first three chr:
FAA: 7.5", 2.56 open (1985-1986 Astro)
FAF: 7.5", 2.73 open (1988 Astro)
***: 7.5", 3.08 open (1988-1989 Astro)
FAH: 7.5", 3.42 open (1988-1989 Astro)
FAJ: 7.5", 2.73 posi (1988 Astro)
FAK: 7.5", 3.08 posi (1988-1989 Astro)
FAL: 7.5", 3.42 posi (1988-1989 Astro)
FAM: 7.5", 3.73 open (1988-1989 Astro)
FAN: 7.5", 3.73 posi (1988-1989 Astro)
FAP: 7.5", 4.10 open (1988-1989 Astro)
FAR: 7.5", 4.10 posi (1988-1989 Astro)
FAS: 7.5", 3.23 open (1988-1989 Astro)
FAT: 7.5", 3.23 posi (1988-1989 Astro)
FBA: 7.5", 2.56 posi (1985-1986 Astro)
FCA: 7.5", 2.73 open (1985-1987 Astro)
FCB: 7.5", 2.73 posi (1985-1986 Astro)
FFA: 7.5", 3.08 open (1985-1987 Astro)
FFB: 7.5", 3.08 posi (1985-1986 Astro)
FMA: 7.5", 3.42 open (1985-1987 Astro)
FMB: 7.5", 3.42 posi (1985-1986 Astro)
FRA: 7.5", 3.73 open (1985-1987 Astro)
FRB: 7.5", 3.73 posi (1985-1986 Astro)
FSA: 7.5", 4.11 open (1985-1986 Astro)
FSD: 7.5", 4.11 posi (1985-1986 Astro)
GWH: 7.5", 4.10 open (1985-1987 Astro)
GWJ: 7.5", 4.10 posi (1985-1986 Astro)
HZA: 7.5", 2.73 posi (1987 Astro)
HZB: 7.5", 3.08 posi (1987 Astro)
HZC: 7.5", 3.42 posi (1987 Astro)
HZF: 7.5", 3.73 posi (1986 Astro)
HZG: 7.5", 4.11 posi (1986-1987 Astro)
KJM: 7.5", 2.73 open (1987 Astro)
KJN: 7.5", 3.08 open (1987 Astro)
KJP: 7.5", 3.42 open (1987 Astro)
KJR: 7.5", 2.73 posi (1987 Astro)
KJS: 7.5", 3.08 posi (1987 Astro)
KJT: 7.5", 3.42 posi (1987 Astro)
KJU: 7.5", 3.73 open (1987 Astro)
KJW: 7.5", 3.73 posi (1987 Astro)
KJX: 7.5", 4.10 open (1987 Astro)
KJY: 7.5", 4.10 posi (1987 Astro)
KRK: 7.5", 2.73 open (1987 Astro)
KRL: 7.5", 3.08 open (1987 Astro)
KRM: 7.5", 3.42 open (1987 Astro)
KRN: 7.5", 2.73 posi (1987 Astro)
KRP: 7.5", 3.08 posi (1987 Astro)
KRR: 7.5", 3.42 posi (1987 Astro)
KRS: 7.5", 3.73 open (1987 Astro)
KRT: 7.5", 3.73 posi (1987 Astro)
KRU: 7.5", 4.10 open (1987 Astro)
KRW: 7.5", 4.10 posi (1987 Astro)
PZK: 7.625", 4.10 open (1990 Astro)
PZL: 7.625", 4.10 posi (1990 Astro)
RHB: 7.625", 3.23 open (1990 Astro)
RHC: 7.625", 3.23 posi (1990 Astro)
RHD: 7.625", 3.42 open (1990 Astro)
RHF: 7.625", 3.42 posi (1990 Astro)
RHG: 7.625", 3.73 open (1990 Astro)
RHH: 7.625", 3.73 posi (1990 Astro)
RHL: 7.625", 3.23 open (1990 Astro)
RHM: 7.625", 3.42 open (1990 Astro)
RHN: 7.625", 3.73 open (1990 Astro)
RHP: 7.625", 3.23 posi (1990 Astro)
RHR: 7.625", 3.42 posi (1990 Astro)
RHS: 7.625", 3.73 posi (1990 Astro)
RHT: 7.625", 4.10 open (1990 Astro)
RHU: 7.625", 4.10 posi (1990 Astro)
SGF: 7.625", 3.23 open (1991 Astro)
SGG: 7.625", 3.23 posi (1991 Astro)
SGH: 7.625", 3.42 open (1991 Astro)
SGJ: 7.625", 3.42 posi (1991 Astro)
SGK: 7.625", 3.73 open (1991 Astro)
SGL: 7.625", 3.73 posi (1991 Astro)
SGM: 7.625", 4.10 open (1991 Astro)
SGN: 7.625", 4.10 posi (1991 Astro)
SGS: 7.625", 3.23 open (1991 Astro)
SGT: 7.625", 3.23 posi (1991 Astro)
SGU: 7.625", 3.42 open (1991 Astro)
SGW: 7.625", 3.42 posi (1991 Astro)
SGX: 7.625", 3.73 open (1991 Astro)
SGY: 7.625", 3.73 posi (1991 Astro)
SHD: 7.625", 3.23 open (1990 Astro)
SHF: 7.625", 3.23 posi (1990 Astro)
SHG: 7.625", 3.42 open (1990 Astro)
SHH: 7.625", 3.42 posi (1990 Astro)
SHJ: 7.625", 3.73 open (1990 Astro)
SHK: 7.625", 3.73 posi (1990 Astro)
SHL: 7.625", 4.10 open (1990 Astro)
SHM: 7.625", 4.10 posi (1990 Astro)
SHR: 7.625", 3.23 open (1990 Astro)
SHS: 7.625", 3.23 posi (1990 Astro)
SHT: 7.625", 3.42 open (1990 Astro)
SHU: 7.625", 3.42 posi (1990 Astro)
SHW: 7.625", 3.73 open (1990 Astro)
SHX: 7.625", 3.73 posi (1990 Astro)
SHY: 7.625", 4.10 open (1990 Astro)
SHZ: 7.625", 4.10 posi (1990 Astro)
TZD: 7.625", 3.23 open (late 1995 Astro)
TZF: 7.625", 3.23 posi (late 1995 Astro)
TZG: 7.625", 3.42 open (early 1995 Astro)
TZH: 7.625", 3.42 posi (late 1995 Astro)
TZJ: 7.625", 3.73 open (late 1995 Astro)
TZK: 7.625", 3.73 posi (late 1995 Astro)
USN: 7.625", 3.23 posi (1993-early 1995 Astro)
UTM: 7.625", 3.23 posi (1991-1992 Astro)
UTN: 7.625", 3.42 posi (1993-early 1995 Astro)
UTP: 7.625", 3.42 posi (1991 Astro)
UTR: 7.625", 3.73 open ('91-early '95 Astro)
UTS: 7.625", 3.73 posi ('91-early '95 Astro)
UTT: 7.625", 3.23 open (1991-1992 Astro)
UTU: 7.625", 3.23 posi (1991-1992 Astro)
UTW: 7.625", 3.42 open (1991-1992 Astro)
UTX: 7.625", 3.42 posi (1991-1992 Astro)
UTY: 7.625", open (1991-1992 Astro)
UTZ: 7.625", 3.73 posi (1991-1992 Astro)
VAC: 7.625", 3.23 open (1996-1997 Astro)
VBC: 7.625", 3.23 posi (1996-1997 Astro)
VCC: 7.625", 3.42 open (1996-1997 Astro)
VDC: 7.625", 3.42 posi (1996-1997 Astro)
VFC: 7.625", 3.73 open (1996-1997 Astro)
VGC: 7.625", 3.73 posi (1996-1997 Astro)
VKA: 7.625", 3.42 posi (1995 Astro-Export)
VKC: 7.625", 3.42 posi (1996-1997 Astro-Export)
VLA: 7.625", 3.73 posi (1995 Astro-Export)
VLC: 7.625", 3.73 posi (1996-1997 Astro-Export)
Lump