Limited slip or locking

Rick Wojtkowiak · August 29, 2019

I have a 2005 Silverado. I can't find anywhere what rear differential it has. Do any of you know how to find out? I'm looking to buy a different truck and I want to get the same diff I have now.

davester · August 29, 2019

Look in the glove box for a sticker with a list of 3 digit codes. If "G80" is in that list, the truck should have a G80 locking diff, if it's missing, it should have an open diff. Note, if you bought the truck used, it may or may not still have the G80 in it, as it isn't unusual for them to fail, and some people will fix them and others will just swap in an open diff.

Brian715 · August 30, 2019

Yes the G80 is prone to failure. The RPO codes are the sticker you are looking for. They can tell you a lot about a vehicle. https://www.newgmparts.com/decoding-general-motors-rpo-codes

Rick Wojtkowiak · August 30, 2019

Brian, I looked at the website you suggested. It says G80 is positraction,limited slip.

Rick Wojtkowiak · August 30, 2019

I know it's not an open differential. Those are horrible in snow.

davester · August 30, 2019

Here's info on the G80 by the manufacturer: https://www.eaton.com/us/en-us/catalog/differentials/mlocker.html

Rick Wojtkowiak · August 30, 2019

So if it is a locking differential would I no the difference in handling if I went with a limited slip in a different truck? This truck I have now is great in snow or even soft sand. I very seldom have to put it in 4wd. I did buy it used so not sure if the diff was changed.

Brian715 · August 30, 2019

How a G80 works. Its a limited slip. Slip is allowed up to a 120rpm difference between the tires. Then the rear wheels are locked together. Alot of people use these terms interchangeably. It's not a spool which is no slip allowed ever, or a selectable locker which can be turned on or off like an air locker or an e-locker. I consider the G80 a limited slip.

Rick Wojtkowiak · August 30, 2019

26 minutes ago, Brian715 said:

How a G80 works. Its a limited slip. Slip is allowed up to a 120rpm difference between the tires. Then the rear wheels are locked together. Alot of people use these terms interchangeably. It's not a spool which is no slip allowed ever, or a selectable locker which can be turned on or off like an air locker or an e-locker. I consider the G80 a limited slip.

Just about every 2010-2013 silverado or gmc ive been looking at says automatic locking. I'm not a mechanic I just drive the truck.

I know this is a gmc forum. But a Ford has either a open,limited slip or electronic locking knob. And I thought most chevy/gmc we all automatic locking.

diyer2 · August 30, 2019

So do both rear wheels pull when it starts spinning tires?

Or put another way, does it lock both rear wheels?

If you have had it on snow an sand you would know.

Brian715 · August 30, 2019

Ya the GMC/Chevy's are only G80 Limited slip/posi/ automatic locking(All the same end result of both rear tires getting Powe), or open(one wheel peel). I don't think they have a electronic locker that is factory for the GMC like the Ford. The G80 works great, they are just prone to breaking. My 06 G80 doesn't work properly. I don't think you would notice a difference as long as your new truck isn't and open diff. You will end up needing to put it in 4wd in someone's driveway with 6 inches of snow on it because it's stuck. Lol ask me how I know...

Rick Wojtkowiak · August 30, 2019

I know mine isn't an open. I had one of those on a Ford I use to have.

You are saying limited slip and locking are the same but how can that be if a Ford has limited slip or pull button locking.

That's why I'm so confused.

Lets say I buy a Ford that has limited slip would that be the same as gm automatic locking.?

carl1783 · August 31, 2019

The Eaton locker option in GM rigs is a locker, not a posi-trac rearend. But it locks and unlocks automatically, unlike an electronic or air locking diff. It is meant to be used in low speed situations. They get a bad rap and guys blow them up when they lock them up at high speeds in the sand and snow. When used properly they work great. I have it in my suburban.

Grumpy Bear · August 31, 2019

11 hours ago, diyer2 said:

So do both rear wheels pull when it starts spinning tires?

Or put another way, does it lock both rear wheels?

If you have had it on snow an sand you would know.

G80 is a wheel speed delta sensitive FULL locking differential. Once locked it behaves the same as a spool. Not nearly as strong. Air lockers use an air piston. Electric lockers use a solenoid and a G80 uses flyweights and centrifugal force to engage the locking device. None of these require a friction modified lubricant. Unlike an E-Locker or an Air-Locker which can be engaged at rest the G80 requires a speed difference to engage. That IS it's weakness. Shock!!!! This is not a drag race friendly set up.

A true limited slip with clutches 'limit' wheel speed difference but do not eliminate it. Does require a friction modified lubricant. The amount of difference can be tuned with spring rate, clutch material and count and fluid composition. They have a an average service life between rebuilds of about 30-40K miles. It's not a huge deal to replace clutches but most people never service them and run basically open for the remainder of it's life. They were the GM 'go to' in the 60's - 70's. My 76 Corvette was so equipped.

You could tell the difference then by raising the rear of the car/truck and turning by hand one wheel. If the other wheel turned the same direction, it was a limited. If it turned opposite it was open. The G80 will act like a open however.