What is the Axle Ratios of My 89 4x4 Suburban?

plance1 · 04-08-2009, 09:01 AM

this is not a 3/4 truck, just standard. Any idea what the stock ratios were? Thanks.

94Dodge Truggy · 04-08-2009, 09:15 AM

I am not into chevy's but I would guess 3.55? Spin the wheels and count the driveshaft revolutions to get the ratio or look for a tag on either the front or rear diff. covers. The vin. tag can tell you also. Dodge has them on a label in the glove box.

blazerbrad · 04-08-2009, 10:40 AM

Assuming it's still there and readable, the RPO (regular production order) code list should still be taped/glued inside the glove box. This will tell you what the truck came with from the factory. However, unless you are 100% confident it is still all original you need to double-check in case parts had been swapped at some point in the last 20 years.

The most common in an '89 1500 series Suburban typically were 3.42 or 3.73, while 3.08 or 3.23 may be possible. Anyway, here are the codes to look for:

GT4 -- AXLE REAR, 3.73 RATIO
GT5 -- AXLE REAR, 4.10 RATIO
GU4 -- AXLE REAR, 3.08 RATIO
GU5 -- AXLE REAR, 3.23 RATIO
GU6 -- AXLE REAR, 3.42 RATIO
G80 -- AXLE REAR, LIMITED SLIP (POSITRACTION)

To double-check just pull the diff cover off (probably wouldn't hurt to have fresh gear lube anyways). Most gears sets will have a series of numbers stamped along the edge of the ring gear...rotate it around until you see it and write down the numbers. Likely have some data codes and other numbers, but should show the number of teeth on the ring and pinion in the series (example: XXXX XXX 11 41 XXX). This means 41 teeth on the ring, and 11 teeth on the pinion, so 41/11 = 3.73. If the stamping is not available, you can physically count the teeth on the ring gear and then the pinion.

KargoMaster · 04-08-2009, 11:04 AM

*shudder*

G80... (aka - Gov Lock, or Gov "bomb") yeah, that was fun...

Great descriptions Brad... Sometimes I look up parts on AutoZone's website (not the user-friendliest, but sometimes helpful) and I've found some production percentages (97% - 5.7L... whatever) that I have used to guess, but don't think it would get down to that level of detail...

plance1 · 04-08-2009, 02:11 PM

guys thanks, this info is perfect.

04-08-2009, 09:01 AM	#1
plance1 Join Date: Jun 2007 Location: Northern Kentucky Posts: 25	What is the Axle Ratios of My 89 4x4 Suburban? this is not a 3/4 truck, just standard. Any idea what the stock ratios were? Thanks.

04-08-2009, 09:15 AM	#2
94Dodge Truggy EX-Vice President Join Date: Jan 2007 Location: Fairfield, Ohio Posts: 3,048	I am not into chevy's but I would guess 3.55? Spin the wheels and count the driveshaft revolutions to get the ratio or look for a tag on either the front or rear diff. covers. The vin. tag can tell you also. Dodge has them on a label in the glove box. __________________

04-08-2009, 11:04 AM	#4
KargoMaster Cleaning off the rust... Join Date: Jan 2007 Location: Cincinnati, OH Posts: 1,009	shudder G80... (aka - Gov Lock, or Gov "bomb") yeah, that was fun... Great descriptions Brad... Sometimes I look up parts on AutoZone's website (not the user-friendliest, but sometimes helpful) and I've found some production percentages (97% - 5.7L... whatever) that I have used to guess, but don't think it would get down to that level of detail... __________________ brad 5.0L \| 435 \| 203 \| 300 \| 4.10 \| 39.5 Buildup BACK underway...

04-08-2009, 10:40 AM	#3
blazerbrad - CORE Member - Join Date: Feb 2007 Posts: 831 Images: 6	Assuming it's still there and readable, the RPO (regular production order) code list should still be taped/glued inside the glove box. This will tell you what the truck came with from the factory. However, unless you are 100% confident it is still all original you need to double-check in case parts had been swapped at some point in the last 20 years. The most common in an '89 1500 series Suburban typically were 3.42 or 3.73, while 3.08 or 3.23 may be possible. Anyway, here are the codes to look for: GT4 -- AXLE REAR, 3.73 RATIO GT5 -- AXLE REAR, 4.10 RATIO GU4 -- AXLE REAR, 3.08 RATIO GU5 -- AXLE REAR, 3.23 RATIO GU6 -- AXLE REAR, 3.42 RATIO G80 -- AXLE REAR, LIMITED SLIP (POSITRACTION) To double-check just pull the diff cover off (probably wouldn't hurt to have fresh gear lube anyways). Most gears sets will have a series of numbers stamped along the edge of the ring gear...rotate it around until you see it and write down the numbers. Likely have some data codes and other numbers, but should show the number of teeth on the ring and pinion in the series (example: XXXX XXX 11 41 XXX). This means 41 teeth on the ring, and 11 teeth on the pinion, so 41/11 = 3.73. If the stamping is not available, you can physically count the teeth on the ring gear and then the pinion.

04-08-2009, 02:11 PM	#5
plance1 Join Date: Jun 2007 Location: Northern Kentucky Posts: 25	guys thanks, this info is perfect.