Chevy pickup limited slip differential (viscous coupling?)

[Sodo]

Was at the chevy dealer yesterday, looking for a 4WD truck with a rear locker. They had some but one of them had a limited slip ( 2013 low miles, 1/2 T fleet model). 3 salesmen did not have the slightest idea even what a differential did period. Had to wait (hours?) for the --->one guy<--- who knew more about drivetrains than anybody in the dealership.

So I asked him "what kind of 'limited slip' is in this pickup?". He said its a viscous coupling. That was the first I'd heard of that in a differecntial. I've seen those in a primary drivetrain but never after the ring and pinion after the speed goes down and the torque goes up (by a factor of 3 or 4). Well anyway he went on to explain that if there is more than 100RPM difference between the rotational speeds of the left and right wheel, it locks up. Incidentally, that means the driveshaft is spinning or 4 times faster.

hhhhhhh o-o-o-o kayyyyy?. That sounds like "already stuck" to me. 10 RPM difference sounds stuck to me. I did not get the impression this guy knew enough to be consulted about drivetrains so I'm asking here.

Does anybody know about this Chevy "limited slip"? What does Ford use for their "limited slip"? (not referring to "electronic lock" option, but "limited slip")

 

[k0ua]

Was at the chevy dealer yesterday, looking for a 4WD truck with a rear locker. They had some but one of them had a limited slip ( 2013 low miles, 1/2 T fleet model). 3 salesmen did not have the slightest idea even what a differential did period. Had to wait (hours?) for the --->one guy<--- who knew more about drivetrains than anybody in the dealership.

So I asked him "what kind of 'limited slip' is in this pickup?". He said its a viscous coupling. That was the first I'd heard of that in a differecntial. I've seen those in a primary drivetrain but never after the ring and pinion after the speed goes down and the torque goes up (by a factor of 3 or 4). Well anyway he went on to explain that if there is more than 100RPM difference between the rotational speeds of the left and right wheel, it locks up. Incidentally, that means the driveshaft is spinning or 4 times faster.

hhhhhhh o-o-o-o kayyyyy?. That sounds like "already stuck" to me. 10 RPM difference sounds stuck to me. I did not get the impression this guy knew enough to be consulted about drivetrains so I'm asking here.

Does anybody know about this Chevy "limited slip"? What does Ford use for their "limited slip"? (not referring to "electronic lock" option, but "limited slip")

I assume you are talking about the G80 RPO coded "govlock" locker made my Eaton. Look in the glovebox for the G80 RPO code to be sure the truck is so equipped. Or it may be on the window sticker if it is still attached.

It has nothing viscous, or vicious about it. It is an mechanical system. You can learn all about it here in these links

https://www.youtube.com/watch?v=AjymmXvBYsI

https://www.youtube.com/watch?v=MCxqUJCZGNU

https://www.youtube.com/watch?v=tTGZOJQQBeE

 

[Sodo]

Yes, "a viscous coupling in the differential" sounded fishy.

If I go back I'll look for that G80 code. Thanks very much for that video James! I like automatic locking, but a delay that causes loss of momentum is not very appealing. And having to stop to apply any lock is disruptive too but I suppose that our world now.

Does anybody know if the Ford has "speed limitations" on their electronic locker and if it locks only in 4L?

 

[Clint S]

They should use the term viscous coupling very and I mean very loosely for there system. Many of the early posi units needed a special "friction modifier" for the clutch plates to work properly, thus the fluid aided the coupling so viscous coupling. My old firebird would chatter and slip when I did not add the modifier to the rear end. When I did the axle seals on dads truck (2003) the dealer said I needed to use "their" rear end oil for the locker to work properly. I just assumed that it was due to the modifier being added to their oil. I really do not know but that is my half witted guess to their term of "viscous coupling" when dad bought his truck they used that term too. My S10 had it too and it really is a good rear.

Those videos are very good thanks for posting.

 

[Sodo]

James that last vid was interesting. Looks like they put a lot of effort into making it so it can't lock up at speed. Looking at this vid https://www.youtube.com/watch?v=xr_00EQBx7I the G80 appears to remain locked if it gets locked while slow.

Not sure what they mean at the video end when they guy says "oh what's that sound - I don't know" but the title is called "exploding G80".:confused3: and it doesn't sound like a good sound.

Clint a "viscous coupling" is an entirely different device than a 'clutch type' limited slip that need a special gear oil because the clutches run in the gear oil. The Eaton G80 is a "clutch type" thus I bet it requires and appropriate type of gear oil.

I guess "viscous coupling differentials" do exist (somewhere?) or at least in theory. The presenter doesn't explain the "fluid" used in a viscous coupling, which is a very special fluid that "solidifies when disturbed" then softens again when undisturbed. Kind of like the opposite of quicksand.

I found a whiteboard explanation of a viscous coupling limited slip differential. https://www.youtube.com/watch?v=w2bRb17jJ1U It doesn't mention whether these differntials actually exist (for example in a 2013 chevy).

 

[Diamondpilot]

The GM G80 locker has limitations so be careful. It automatically disengages and engages as needed which causes wear. You also have a speed cutout where the fly weights mechanically unlock it.

The Electric Lockers like I have in my Titan and F150 will work in 4 Low or 4 High. Is said that on the Ford's the locker disengages at 25 mph but have had no need to verify.

Chris

 

[Sodo]

Excellent info, thanks Chris. I think I'm OK with a locker disengaging at 25 mph. Going to look at trucks again today.

Been to 3 Ford dealers so far, who have nobody in staff knowing anything more than what the user manual states. Found one with a 30-year tech who is too busy to help sales, but I'm gonna try to bug him anyway.

 

[Clint S]

Clint a "viscous coupling" is an entirely different device than a 'clutch type' limited slip that need a special gear oil because the clutches run in the gear oil. The Eaton G80 is a "clutch type" thus I bet it requires and appropriate type of gear oil

I guess "viscous coupling differentials" do exist (somewhere?) or at least in theory. The presenter doesn't explain the "fluid" used in a viscous coupling, which is a very special fluid that "solidifies when disturbed" then softens again when undisturbed. Kind of like the opposite of quicksand.

I found a whiteboard explanation of a viscous coupling limited slip differential. https://www.youtube.com/watch?v=w2bRb17jJ1U It doesn't mention whether these differntials actually exist (for example in a 2013 chevy).

I should of worded my post differently. I was trying to be a bit sarcastic, but give them a far fetched reason (use of viscous fluids) to use the term. I think Subaru uses them maybe this type of diff. Again thanks for the links I watched them all

 

[k0ua]

Another G80 demo:

https://www.youtube.com/watch?v=f31WBscnFh0

I would not give my G80 equipped truck as much abuse as shown in the vid, but I have needed it a few times, and I have had no problems with it. It if pretty smooth and does keep you moving. Mine is a 2010 4wd Silverado.

I don't think the G80 is the strongest diffy out there, but if used like 99 percent of "normal" people use it for street use and moderate trail use to get you unstuck, I think they are excellent. If you are a rock crawler, or "heck" raiser, then no.. there are better things out there for your use.

 

[Sodo]

No abuse here, I would never bust any diff (now I drive like an old fart). But I dont like the way you have to lose your momentum for the diff to lock up. Just 1or 2 mph momentum makes a huge difference, if you stop, its a huge disadvantage.