Rear end info-

 

Engine/Tranny/RearEnd/Gear Ratio Combos

S10 Pickups
1995 s10 2wd 8.5 rear, (LB4,L35,M30,GU6)
1995-1997 s10 2wd 8.5 rear, (LN2,M30,GT5)
1996-1999 s10 2wd 8.5 rear, (L35,M50,GU4,G80)
2000-2002 s10 2wd 8.5 rear, (M50,GU4,G80)
2003 s10 2wd 8.5 rear, (LU3,M50,GU4,G80)

S10 Blazers
1995-1997 s10 blazer 2wd 8.5 rear, (L35,M50,GU6,G80)
1998-1999 s10 blazer 2wd 8.5 rear, (L35,M50,GU6,G80)
2000-2001 s10 blazer 2wd 8.5 rear, (L35,M50,GU6,G80)
2001-2004 s10 blazer 2wd 8.5 rear, (M50,GU6,G80)
2003-2005 s10 blazer 2wd 8.5 rear, (M50,GU6)

So... for example if you are looking for a 8.5 rear end with 3.42 gears and posi, you can find it in a v6 blazer 2wd with a manual 5spd trans...

There are also 8.5 rear ends in 4x4 s10's but i did not list them...  Hope this helps you  find the rear end you want.

Axle Codes/Engine Codes

These are some of the axle RPO codes and should be the same for all GMs with either of these axles.(these codes are located in the glove box on s10)

GU4=3.08
GU5=3.23
GU6=3.42
GT4=3.73
GT5=4.10
HC4=4.56

G80= locking differential

LB4- 4.3 V6 TBI
LN2- 2.2l 4cyl MFI
LU3- 4.3 V6
L35- 4.3 V6 CPI
M30- Auto 4 speed trans

M50- Man 5 SPEED trans


Heres a pic of the standard 3.73 gear rear end with drum breaks,

Heres a pic of what the g80 locking diffs look like this one has disc breaks.3.42 gear

-Additives-

This subject comes up often enough I thought I'd post this service bulletin

There's a lot of conflicting info about whether or not to use a posi or limited-slip additive to the gear oil when filling a G80 (Eaton Gov-Loc) differential in a GM truck.

Much of the confusion likely comes from the fact that the G80 RPO code is also used to indicate posi or limited slip differentials in car applications, but in trucks it is the Eaton Gov-Loc. It doesn't help when someone goes to Eaton's site and finds statements like:

"What type of lubricant and limited slip additive should I use with my newly purchased Eaton Limited Slip Differential? Eaton strongly recommends utilizing an API-GL5 approved Mineral-Based 80W-90 Axle Lubricant and one 4-oz bottle of Limited Slip Additive (GM or Ford)."

Note that the Eaton Gov-Loc is NOT a limited slip; the information in the above paragraph does not apply to the Eaton unit used by GM for the trucks!

Here's the service bulletin from GM about the proper lubricant and use of additives (I added the bold and underline):

  • GM Said:
LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION) #91-4-109
SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)
VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS
Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.
This condition of alternate engagement and disengagement of clutches in differential assembly is usually caused by contaminated axle lubricant.
To correct this condition, drain and refill the rear axle with SAE 80W-90 GL5 (P/N 10950849).

The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life.

VEHICLES/COMPONENTS INVOLVED: ------------------------- ---- Some light duty trucks equipped with locking rear axles, RPO G80.
SERVICE PARTS INFORMATION:
Part Number Description ----------- ------------------ 10950849 Lubricant, Rear Axle (1 litre)