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Old 10-19-2013, 09:05 PM   #1
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Question GM locking rear diff.

I bought a used GMC 2500 and finally got around to checking all the RPO's and I found that the truck has a locking rear differential. Any towers out there have one and can give me your thoughts?
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Old 10-19-2013, 10:15 PM   #2
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Old 10-20-2013, 04:39 AM   #3
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Make sure you change the rear ends gear oil with proper oil and additive for the GM Locking rear axle.

As the gear oil get older, the rear locking clutches will start popping when you make a turn and the oil is hot or is the axle being used under a load.
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Old 10-20-2013, 06:48 AM   #4
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I have it and love it... just change your rear diff fluid on a regular basis. I use Royal Purple it already has the friction modifier added.
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Old 10-20-2013, 07:45 AM   #5
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GM locking rear diff.

I have it also and love it. Like said above keep the fluid changed every 50,000 miles and they will go for ever. The nice part is when changing the lube is you don't have to remove the cover. You will find a drain plug on the bottom and that makes it so easy and fast. All the the rear axles use 75/ 90w synthetic lube and then you will need a bottle of friction modifier. Add the friction modifier first when filling then it will take 3 qts of lube and you will be good to go.
You can use any brand that you like as i have seen no difference in performance of different brands when serviced at regular basis.
Hope this helps.
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Old 10-20-2013, 12:50 PM   #6
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Old 10-20-2013, 05:44 PM   #7
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I thought friction modifier was only for limited slip differentials??? OP has a locking diff.
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Old 10-20-2013, 05:58 PM   #8
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I have the G80 locking rear on both my Chevy trucks. No issues towing or not. The 04 2500 has the drain plug on the bottom which is nice, but my 04 1500 does not, have to remove the cover to drain.

Also found this on a search:

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)
Parts are currently available through CANSPO.
WARRANTY INFORMATION:
As specified in Light Duty Truck Maintenance Schedules, locking rear axle fluid drain and refill is required owner maintenance at the first engine oil change. Failure to drain and refill the rear axle as specified may contribute to a later axle chatter condition. Refer to the appropriate Light Duty Truck Maintenance Schedule or service manual, section OB, for further details on change intervals.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
© Copyright General Motors Corporation. All Rights Reserved.
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Old 10-21-2013, 06:50 AM   #9
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GM locking rear diff.

Quote:
Originally Posted by tls001 View Post
I thought friction modifier was only for limited slip differentials??? OP has a locking diff.
You are correct. Guess i should learn to read better. Lol my bad
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Old 10-21-2013, 11:51 AM   #10
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I have always used Mobil 1 synthetic 75W-90 in all GM trucks with the G80 Eaton and never had a problem. My last Avalanche went 140K with no issues. I also use it in the front Diff. Now my TBSS uses the friction modifier as she has a limited slip, not a locking..
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Old 10-21-2013, 12:51 PM   #11
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Everyone who said to use a friction modifier on a G80 is probably having issues...DON'T use the friction modifier; as the correct people have chimed in and stated...it is not for the locking diff but rather a limited slip and those do not exist on any current 4WD Chevy/GMC trucks as far as a I know. I have the G80 also and love the way it performs in slick conditions. I've changed the lube in it 3 times and currently have the Amsoil 75w90 Severe Gear lube in it. No problems. There is are several good youtube videos on how it works...search Eaton G80 and you'll get several vids.
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Old 10-21-2013, 02:24 PM   #12
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I have the G80 and don't love it, and I don't hate it. It can actually cause you issues sometimes, other times its awesome.

My manual calls for fluid changes every 30k. Every 3rd party documentation I've read says to stick with the GM recommended fluid. My truck has 150k on it and no troubles with the drive train. Just keep up with the maintenance.
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Old 11-14-2013, 11:13 AM   #13
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GM locking rear diff.

What don't you like about the G80? I've only had trouble with mine once. It locked when I clipped a curb with the back tire (my fault) and I couldn't get it to unlock. I finally had to drive in reverse and steer back and forth until it opened up again.
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Old 12-04-2013, 07:03 PM   #14
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GM locking rear diff.

BTW, I am using Amsoil in my diffs, tranny and T-case...there's more than 30k between service changes. It protects the best...
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Old 12-05-2013, 02:10 PM   #15
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What don't you like about the G80? I've only had trouble with mine once. It locked when I clipped a curb with the back tire (my fault) and I couldn't get it to unlock. I finally had to drive in reverse and steer back and forth until it opened up again.
Didn't see your question until today. The locking rear end is only as good as the grip the tires can get. If both tires are on a slippery surface all your back end does is slide around and you go no where. In fact you can end up in a worse spot if that happens and you aren't ready for it. I've slip backward down hill because of this. Not a good feeling. But its like I said, its also awesome sometimes. Like when towing up a hill that has loose gravel.
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Old 12-05-2013, 07:46 PM   #16
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With this winter storm we have, I'm finding the locking diff pretty handy especially in 4wd. With the open diffs on my old suburban, in 4wd I would spin one tire on each axle. With the new pickup, in 4wd, once the back locks up I have three tires churning. Conclusion, one more tire working to get me in deeper!
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Old 12-06-2013, 11:29 AM   #17
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4 wheel drive, locking diffs, limited slip just means you can get farther into the yuck before you get stuck.
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