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Gear Ratio Codes?

uchi

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uchi Enthusiast

uchi

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i saw another post that said the codes are listed in the glovebox of the truck, but it was for older gen gmc trucks, wondering if its the same for the gmt800 trucks and if the codes are the same for the different years?

revrnd Senior Enthusiast

revrnd

Posted
Posted

The RPO codes usually are similiar thru the years.

 

GT4 = 3.73

GT5 = 4.10

 

Some options haven't changed in 30 years KC4 = Block heater

uchi Enthusiast

uchi

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one last thing, well two, where can i find a complete listing of the codes im looking for? theyre called rpo codes right? and also are the codes specific to where theyre located on the sticker? or if say gt4 is in one location its gear related but if its in another ont he sticker it means something else?

Chris Senior Enthusiast

Chris

Posted
Posted

rpo's are rpo's. gt4 means the same on eery truck no matter where on the sticker it is. and if you have the locker, you will have gt4 gu6 and so on and then an additional g80 code

dlstewart01 Senior Enthusiast

dlstewart01

Posted
Posted

GQ1 -- AXLE REAR, STD RATIO

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, HD locking differential

 

GM does not put a limited slip in trucks with the exception of the Quadrasteer whick could have a G86 limited slip.

 

http://www.youtube.com/watch?v=-sw9DwurQAs

dlstewart01 Senior Enthusiast

dlstewart01

Posted
Posted
ok, i have a picture of my sticker, i see a gt4 followed by a g80. ill just upload it tonite to make things easier

 

You have a G80 Eaten locking diff..heres how it works..

 

When the wheel-to-wheel speed difference is 100 RPM or more, the flyweights of the governor will fling out and one of them will contact an edge of the latching bracket. This happens because the left cam side gear and cam plate are rotating at a speed different, either slower or faster, than that of the ring gear and differential case assembly. The cam plate has teeth on its outer diameter surface in mesh with teeth on the shaft of the governor.

 

As the side gear rotates at a speed different than that of the differential case, the shaft of the governor rotates with enough speed to force the flyweights outward against spring tension. One of the flyweights catches its edge on the closest edge of the latching bracket, which is stationary in the differential case. This latching process triggers a chain of events.

 

When the governor latches, it stops rotating. A small friction clutch inside the governor allows rotation, with resistance, of the governor shaft while one flyweight is held to the differential case through the latching bracket. The purpose of the governor's latching action is to slow the rotation of the cam plate as compared to the cam side gear. This will cause the cam plate to move out of its detent position.

 

The cam plate normally is held in its detent position by a small wave spring and detent humps resting in matching notches of the cam side gear. At this point, the ramps of the cam plate ride up on the ramps of the cam side gear, and the cam plate compresses the left clutch pack with a self-energizing action.

 

As the left clutch pack is compressed, it pushes the cam plate and cam side gear slightly toward the right side of the differential case. This movement of the cam side gear pushes the thrust block which compresses the right-hand side gear clutch pack.

 

At this point, the force of the self-energizing clutches and the side gear separating force combine to hold the side gears to the differential case in the locking stage.

 

The entire locking process occurs in less than 1 second. The process works with either the left or right wheel spinning, due to the design of the governor and cam mechanism. A torque reversal of any kind will unlatch the governor, causing the cam plate to ride back down to its detent position. Cornering or deceleration during a transmission shift will cause a torque reversal of this type. The differential unit returns to its open diff function.

 

The self-energizing process would not occur if it were not for the action of one of the left clutch discs. This energizing disc provides the holding force of the ramping action to occur. It is the only disc which is splined to the cam plate itself. The other splined discs fit on the cam side gear.

 

If the rotating speed of the ring gear and differential case assembly is high enough, the latching bracket will pivot due to centrifugal force. This will move the flyweights so that no locking is permitted. During vehicle driving, this happens at approximately 32 km/h (20 mph) and continues at faster speeds.

 

When comparing the effectiveness of the locking differential, in terms of percent-of-grade capability to open and limited-slip units, the locking differential has nearly 3 times the potential of the limited-slip unit under the same conditions.

Chris Senior Enthusiast

Chris

Posted
Posted

damnn that was a long read. maybe u should write encyclopedias

uchi Enthusiast

uchi

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sweet thanks for the help guys and the write up. perhaps he does write encyclopedias? lol. ill check that link shortly, ended up just passing out last night and now im getting ready to go to work for a bit.

 

im surprised that gm would put actual lockers into their vehicles. i know theyre stronger than lsd setups but didnt think anyone these days used a locker as a factory option anymore.

Chris Senior Enthusiast

Chris

Posted
Posted

i think gm is he only one that does in half tons

uchi Enthusiast

uchi

Posted
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right on, i guess it makes more sense than an lsd maintenance wise. btw love your sig pic, ive been buried like that beofre but in a much bigger truck :thumbs:

i think gm is he only one that does in half tons
uchi Enthusiast

uchi

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Posted

well good news and bad, the bad is this

 

 

TIRE FRONT P275/55R20-111S BW TL ST AL2 TIRE(XSS)

and mine has 17s on it, wondering if they were swapped out at some point? who knows.

 

but the good is this :thumbs:

 

AXLE,REAR,POSITRACTION,LIMITED SLIP POSITRACTION L/SLIP R/AXL(G80)

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