swathdiver

I thought my front differential was howling, time for a new ring and pinion until I changed out the old KO2s for Michelin Defenders. Might be time for some wheel bearing work.

The G80 in a trucks since the mid 1980s is not the same as a 1970 Chevelle or a 1980s Monte Carlo SS G80. The truck G80 is a combination of a locker and limited slip. It requires no limited slip lubricant. From the shop manual: The optional locking differential (RPO G80) enhances the traction capability of the rear axle by combining the characteristics of a limited-slip differential and the ability of the axle shafts to "lock"together when uneven traction surfaces exist. The differential accomplishes this in 2 ways. First by having a series of clutch plates at each side of the differential case to limit the amount of slippage between each wheel. Second, by using a mechanical locking mechanism to stop the rotation of the right differential side gear, in order to transfer the rotating torque of the wheel without traction to the wheel with traction. Each of these functions occur under different conditions. Limited-Slip Function Under normal conditions, when the differential is not locked, a small amount of limited-slip action occurs. The gear separating force developed in the right-hand clutch pack is primarily responsible for this. The operation of how the limited-slip function of the unit works can be explained when the vehicle makes a right-hand turn. Since the left wheel travels farther than the right wheel, it must rotate faster than the ring gear and differential case assembly. This results in the left axle and left side gear rotating faster than the differential case. The faster rotation of the left-side gear causes the pinion gears to rotate on the pinion shaft. This causes the right-side gear to rotate slower than the differential case. Although the side gear spreading force produced by the pinion gears compresses the clutch packs, primarily the right side, the friction between the tires and the road surface is sufficient to overcome the friction of the clutch packs. This prevents the side gears from being held to the differential case. Locking Function Locking action occurs through the use of some special parts: A governor mechanism with 2 flyweights A latching bracket The left side cam plate and cam side gear 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 limited-slip 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. Locking Differential Torque-Limiting Disc The locking differential design was modified in mid-1986 to include a load-limiting feature to reduce the chance of breaking an axle shaft under abusive driving conditions. The number of tangs on the energizing disc in the left-hand clutch pack was reduced allowing these tangs to shear in the event of a high-torque engagement of the differential locking mechanism. At the time of failure of the load-limiting disc, there will be a loud bang in the rear axle and the differential will operate as a standard differential with some limited-slip action of the clutch packs at low torques. The service procedure, when the disc tangs shear, involves replacing the left-hand clutch plates and the wave spring. It is also necessary to examine the axle shafts for twisting because at high torques it is possible to not only shear the load-limiting disc, but to also twist the axle shafts.

Missed this post! I've got 166K on my stock truck and 110K on my lifted Sierra and the locker works just fine in both. Even did a burnout a few weeks ago at the drag strip. You'll like that new Truetrac.

Wow, they got mighty proud of them, I bought a 14-bolt for about $300 earlier this year with 3.42s in Fort Myers. I just looked, found one with 3.23 gears for $433 and some 3.73s and 3.42s and even 4.10s in 9.5" 14-bolts when changed the year to 2006 and used GMC Sierra. I know for my generation, all of the GMC trucks have the G80, not sure about yours.

Good to know thanks for that. Diesels like to pull on a gear!

Thanks, I didn't know there were two different 2500s. I knew about the heavy half tons, boy they had a lot of options back then. I've got one on my work bench too, with 6 lug axles.

You need enough air to exceed your axle capacities. 43 psi puts a pair of tires at 4366 pounds. I initially ran mine at 49 psi and after 40K miles, they were wore down 1/32 more in the center. 42 was perfect for mine.

3.73s? When I do "Build Your Own" for GMC Sierra CCSB with NHT the axle ratio is 3.42 with the 6.2 and 10-speed.

Looks like you have a 10.5" full floater according to the blurry picture. Like Cam says, no need to go inside the pull the shafts. 2500s in that generation didn't run the 14-bolt 9.5" semi-floater.

Go to LKQ online and look for an entire axle with the G80. They only blow up when you do donuts and burnouts in them constantly. Stick with your generation to keep it plug and play.

GM foolishly shut down their chip making plant and off shored production to Communist China. Only a fool trusts Communists. They opened the plant again to make ventilators and are ramping up chip production again.

Happened before we bought the truck. Nuts and bolts are always tight during periodic inspections.

I sent in a sample of trans fluid for Blackstone Labs to analyze. At 36K they said it had about 10K of life left in it. So 36-42K for me from now on. That was GM ACDelco Dexron VI full synthetic too. Those 8-speeds take different fluid I think.

Zone is a subsidiary of BDS and we have had their 6.5 lift on our Sierra for about eight years now. One of the phenolilc cv-shaft spacers broke and was replaced with an aluminum one a few years back. This version has the longer struts, not strut spacers.

Thanks Brian. Did you happen to pull the torque converter inspection cover and see if the bolts were loose? Did you say in the video that the oil leaking was new? Have you checked the level? I'm no expert on all LS engine noises so let's get some folks to have a listen and get their input. @doubeleive@Grumpy Bear@Black02Silverado@shakenfake Brian, bump this thread around 10 am or so and more folks will get to see it as well.

I just remembered, when you replaced the computer module, did you program it? A new one has to be programmed to the truck.

Look like this?

Could you possibly record a video, post it to youtube and link it here for us to see and listen to?

Not in New York!

First thought is, how old is your battery? Second, you need to put your bi-directional scan tool on it to look for parasitic loss and any internal BCM codes. Do check your cables and grounds as well. My Daddy taught me to never buy a first year model. Let other folks work out all the kinks with the factory.

I've compared the truck's fuel efficiency on different brands and we also mix fuels, running different blends of gasoline and ethanol to find that sweet spot of power and economy.

They look a normal to me, maybe a little slow and not going the full range, watched them a couple of times. I'm going to ask some other fellas to stop by and read the thread and watch these videos. Hey Fellas, Can you check this thread out and render an opinion please? @doubeleive @Grumpy Bear @shakenfake@diyer2@GrumpyGhost@Black02Silverado

Eleven cents ($.116) was my lowest ever! My 5 year average is $.199 CPM. Last 3 months have averaged a quarter per mile. The Sierra has average thirty two cents a mile since August! My daughter calls it, "Smile per Gallon"! LOL

If I lived and worked in an area with public transportation, where they make auto ownership a hardship, I'd move! I cherish freedom more than publlc transportation or a high salary. My family in New York disagrees; they love being nannied. For the most part, we buy used and keep them until the scrap man tows them away. With the Yukon and Sierra, we'll endeavor to keep them running until our last days and pass them down to the next generation. Lots of fun and memories.

748UU or 19351579 Yes, I know this is an old thread, just adding to the knowledge base.