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Old 02-20-2021, 08:39 AM   #1
ortho stice
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Default G80 does not lock up

1994 940 Turbo wagon with ~240k miles on it. Only modifications are a 16t at 12psi and T5 blue injectors. Iíve owned the car for almost one year exactly and it has always made a strange knocking noise on deceleration from the rear end, not sure if thatís related.

Anyway I got stuck in my driveway the other day and had my girlfriend in the car while I pushed. I noticed that it just spun one rear tire and made a sort of crunching/clicking noise. What fails on the G80 typically? Is it serviceable or should I be looking for a new differential?
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Old 02-20-2021, 12:06 PM   #2
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A "new" (used) G80 is certainly not expensive, so I would replace it. I don't know what breaks in there if anything did, but I do know using the incorrect lube will destroy the clutches and create one-tire-fire. So if a previous owner used lube with an LSD friction modifier, that would do it.

Replace it and take the old one apart and post pics of what you find.
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Old 02-20-2021, 10:21 PM   #3
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I hadn't thought of that, that's a distinct possibility. I admit I still don't totally understand how these things work and didn't even realize there was a clutch pack in there. I'll start the hunt for a G80. Hasn't been a '91+ 940 in the local yard in almost a year.
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Old 02-20-2021, 11:24 PM   #4
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THe clutches are metal and your not supposed to put any limited slip additive in there or it will slip then. Straight gl-5 gear oil synthetic.

OTHer then that check the little paw gears break then it won't ramp up and lock so you'd need new little paw gear thingy. Gotta take it out to check or might be able to see if you take the back cover off and turn the wheels to see. The paw gears are near the counter weight thingy. I've seen them stripped out before. Also there is a beefier G80 it's the 1041K found in the rear of early 960 wagons.
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Old 02-20-2021, 11:51 PM   #5
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I'll drop the $100 or whatever the going rate for a G80 these days is before pulling the diff. If there's carnage, I'll be able to put that in and hopefully have no down time for the car.

I'd never heard that about the 960's, there's a sedan at the upull right now but of course that will have the independent rear.
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Old 02-21-2021, 02:02 AM   #6
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Quote:
Originally Posted by ortho stice View Post
I admit I still don't totally understand how these things work and didn't even realize there was a clutch pack in there.
Ah, Youtube...

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Old 02-21-2021, 02:26 PM   #7
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I have a couple GM G80's on the bench. I wonder if the clutches are compatible with our old Volvo ones....
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Old 02-22-2021, 12:58 AM   #8
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Quote:
Originally Posted by sbabbs View Post
Also there is a beefier G80 it's the 1041K found in the rear of early 960 wagons.
So, I'd read that in the past, and tried to cross check it and had people say it was rubbish. Is there any proof that it's in any way stronger and if so, what is that proof? I have one, but I have my doubts about it being any different.
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Old 02-22-2021, 01:58 AM   #9
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Originally Posted by ZVOLV View Post
I have a couple GM G80's on the bench. I wonder if the clutches are compatible with our old Volvo ones....
If anyone has a Volvo one outside the car, you could take some dimensions and compare notes.

I've heard that products designed for the Jeep Dana 30 can be made to fit but I've not seen specifics.
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Old 02-22-2021, 04:58 PM   #10
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I have a spare working G80 that I removed from a '93 940.

Message me if you want it.
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Old 02-23-2021, 06:44 AM   #11
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Ah, Youtube...

nice video. I always wondered if the G80 can engage in both directions. I seems it can.
I have a G80 in my 780. I must say the engagement while demanding traction on snowy/icey surfaces is not what i would call subtle. It locks with a clunck. But it works.
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Old 02-23-2021, 02:29 PM   #12
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Quote:
Originally Posted by Khrrck View Post
If anyone has a Volvo one outside the car, you could take some dimensions and compare notes.

I've heard that products designed for the Jeep Dana 30 can be made to fit but I've not seen specifics.
I think I will pull one of them apart. I think its from a 2017'ish Sierra.
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Old 02-23-2021, 02:52 PM   #13
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Okay here is the 1041K is beefier picture proof. It has a solid tube in the center. Smaller holes in the sides of the case.




Left is the rubbish 1041k with smaller hole, see the smaller hole harder for rubbish to get inside your rear. Anybody else wanna say it's rubbish now, if so you should go rubbish one out! You think it's the same as all the 1040's? Why did volvo make it different and call it 1041K and put it in 960's only place I've ever found them???? Why is the side of the case beefier with smaller little tight hole??? Why does it have a solid thick metal tube in the center where the axles meet??? Questions to BS around the tea pot while pondering rubbish holes to fish.







But the best is welded rear diff for sure! When I had a welded diff I broke about 6 axles. Put in the 1041K, haven't broke an axle yet.. Maybe the 1041K axles are better then 1041 rubbish ones??

Last edited by sbabbs; 02-23-2021 at 03:04 PM..
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Old 02-23-2021, 04:59 PM   #14
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Chill out sbabbs! Rubbish the way I used it simply meant "untrue". British English thing, probably.

Interesting photos. My spare non-K 1041 G80 is on the bench and IIRC looks different to both of those, but perhaps I don't recall correctly.

I wasn't very interested in whether the G80 aspect was stronger, more whether the ring gear and pinion were compatible or a different size/bigger/stronger. I guess you've answered that: Same diff gear strength, different G80 core. Cool :-) Thanks!

The reason I wanted to know that is because I want to swap a 240 3.783 ratio set into the 960 wagon so it can accelerate a bit better without losing too much fuel economy like a 4.1 would.

I'll have mine open sometime soon and will post some higher quality/resolution photos here of it and maybe the other one on my bench, too, if I can dig it out.
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Old 02-23-2021, 05:02 PM   #15
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Plenty cold here, just razzin' ya.. Didn't you notice the tea pot reference? Har har har. I got rubbish here parked out back, it's a 240. Har har har.. That beech will slide into anything.

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Old 03-12-2021, 12:08 PM   #16
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I'm pretty sure they have a centrifugal weight that is designed to open the diff at 25mph. It doesn't take much to get over the 25mph when you have no traction.
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Old 03-12-2021, 12:27 PM   #17
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When did Sbabbs turn into JohnV?



Is the diff in the IRS 960 the same?
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Old 03-12-2021, 01:05 PM   #18
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I miss John V.
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Old 03-12-2021, 01:21 PM   #19
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Me too. It was fun to get drunk and try to understand him.
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Old 03-12-2021, 02:42 PM   #20
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Ha, the diff in the IRS g80 is the same, but it has different number of splines for the axle shafts so won't work in a solid axle rear. This has been stated over and over and recently in that other g80 thread the other day..

BAck to my cigs and coffee.. Har, har, har..
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Old 03-12-2021, 03:21 PM   #21
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Quote:
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I'm pretty sure they have a centrifugal weight that is designed to open the diff at 25mph. It doesn't take much to get over the 25mph when you have no traction.
Sort of. It has a weight that keeps the diff from locking at speeds over 25. The function is not quite the same as you describe. If the G80 locks and you keep the power to it the G80 will not unlock. Once you let off the gas it will unlock. Remove the centrifugal weight and it will lock at any speed. That's the way the G80 is set up in Gregervin's 740.
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Old 03-24-2021, 02:42 AM   #22
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Sort of. There's a strong force trying to free one dog from the other over that speed. I found my first G80 to be highly disappointing without the mod, it was nearly impossible to enjoy it as you could get it to spin up higher than the disengage speed faster than the dogs flung out, so when they did, they'd just miss. It would also do weird walking from one to the other as the locking is directional/sided. With the mod, totally consistent. Also both with and without the mod sometimes it just stays locked and it's like you have a welded diff until you apply enough force in the unlock direction and it snaps free. But I am a bit of an animal to it
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