Would a locking differental option be the same as a posi. in 85 c10?

[72farmer]

I just got a 85 Silverado and I was looking at the sticker in the glove box.It has a locking diff. listed on it.So I want to check it out immediately.I tried it in my gravel driveway and it left 2 marks.I then try it on the payment and it only spun one side.As we know in 28 years a lot of things get changed on these trucks.It also had a auto 4 speed trans. on option sheet.What ratio would the rearend be if it is original?

[4x4k30]

no the factory option is a locking diff that has clutches and springs it will only lock both wheels up to bout 35mph and it will only lock if its senses loose traction they are also prone to bust in pieces with no warning most 85s came with 308 gears posi like Detroit lockers lock both wheels at all times the chevy 1/2ton rears imhop are not fit to survive with any abuse I have learned the hard way but now I only run the 14 bolts with Detroit and dana 60 front .

[Keith Seymore]

Originally Posted by 72farmer

I just got a 85 Silverado and I was looking at the sticker in the glove box.It has a locking diff. listed on it.So I want to check it out immediately.I tried it in my gravel driveway and it left 2 marks.I then try it on the payment and it only spun one side.As we know in 28 years a lot of things get changed on these trucks.It also had a auto 4 speed trans. on option sheet.What ratio would the rearend be if it is original?

There's a lot here so let's break it down a bit:

a - If the truck was originally equipped with RPO G80 then it had a "non-open" differential. Within GM the terms "locker" and "posi" are both used colloquially to describe a non-open diff, even though the technology is different ("locker" has an engaging pawl; "limited slip or Posi usually means stacked friction plates). Some of the noun names for the RPOs, like G81, are even assigned incorrectly within GM. As 4x4K30 alludes - a lot can change in 30 years so whether the original rear axle is still in the truck could be up for debate.

b- The rear axle ratio may or may not be defined on the SPID label. If the base ratio was installed then the label will show "GQ1" and not define the ratio numerically. If an optional ratio was chosen then it will show the RPO and the number (ie, GU6 = 3.42; GT4 = 3.73).

https://www.gmheritagecenter.com/doc...olet-Truck.pdf

The base ratio is defined by model, series, engine, emissions equipment (Federal vs California) trans and GVW. We would need to know all of that to determine what the base ratio was.

And again - who knows what's in there now. The only way to really really be sure is to pull the cover and count teeth. That's a good time to change the gear lube while you are at it.

K

[D13]

There are many different types of 'posi'. The most likely form in a square body truck is the 'gov-lock'. This uses a weight and pawl mechanism to lock the shfts together, at speeds under 25mph or so, when the axles hit a certain difference in rpm (I want to say it is about 200rpm). This is designed to give you full pulling power at low rpm, such as when your truck is trying to start a heavy load on a slick surface. I have one in my 8.5 half ton axle and one in my 9.5 3/4 ton axle. They do not survive sudden massive torque differentials (like when you are mudding at a bazillion RPM and all the sudden one of the extra large tires finds traction) or shock loads (like dropping the clutch at 5000RPM on your 454 with the slicks warm). This failure, due to operator behavior, is what earned them the name 'gov-bomb'. I have 200, 000+ miles on one and 15 years of farm abuse on the other with no issues.

The other main GM type is a 'limited slip' or 'Eaton' or 'clutch' type which limits the amount of slip between the axles, using essentially clutches and preload springs. These will slip under severe load but basically work all the time. These were more common in cars, particularly in 60's and 70's where some 'racy' behavior was expected.

Then there are helicals, ratcheting, etc, none of which woudl be stock in the square bodies.