Identifying rear diff on 1980 C20. LSD or not? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Reese Allen · 09-05-2019, 08:11 PM

My truck has a 14-bolt rear differential. I've removed the cover and drained the oil, and am about ready to button it all back up and refill with fresh oil. However, I can't figure out if this truck has an LSD or not, and therefore whether to add LSD additive into the oil.

Picture: https://imgur.com/VLqjWER

With the rear end jacked up, and transmission in neutral, when I spin one wheel, the other stays stationary. But if I put in gear and spin one wheel, the other spins the other way.

I'm inclined to think this means it does NOT have an LSD, but I'm getting so much conflicting information after searching extensively that I am not feeling very confident about this. Help?

**AussieinNC** · 09-05-2019, 08:45 PM

The diff described and pictured is not an LSD...it is an open or standard diff...

sweetk30 · 09-05-2019, 09:21 PM

4 windows and see spider gears = open

4 windows and see coil spring and block of steel = detroit locker ........... do NOT pull apart a detroit type unit unless you bolt the unit together inside or it will pop open good on you and might hurt .

3 pins on the center of case were the ring gear bolts and no windows = gov-loc posi unit .

3 pics in order as i typed above .

**mongocanfly** · 09-05-2019, 09:46 PM

("3 pins on the center of case were the ring gear bolts and no windows = gov-loc posi unit .")
what k30 posted is what you have.....G80
it is not a open diff..it the GM version of a posi

sweetk30 · 09-06-2019, 10:18 AM

forgot to add also . the strongest of the gov-loc posi units is the 14ff . i have run them stock to built 400 sbc engines with 38" tall super swamper mud tires and no problems .

Reese Allen · 09-06-2019, 03:12 PM

Quote:

Originally Posted by sweetk30

4 windows and see spider gears = open

4 windows and see coil spring and block of steel = detroit locker ........... do NOT pull apart a detroit type unit unless you bolt the unit together inside or it will pop open good on you and might hurt .

3 pins on the center of case were the ring gear bolts and no windows = gov-loc posi unit .

3 pics in order as i typed above .

This is helpful. Mine looks just like the first one. Four windows with small gears visible through them. So I assume this is an open diff and therefore I shouldn't put anything but gear oil into it.

Here's a better pic, you can see one of the windows and small gears: https://imgur.com/a/7u0Z6Hv

**mongocanfly** · 09-06-2019, 04:52 PM

I think i see the windows now...so that changes my opinion...couldn't see them in the other pic...looks open

sweetk30 · 09-06-2019, 05:49 PM

open diff or gov-lov both call for std gear oil in these axles .

and yes you have open diff .

09-05-2019, 08:11 PM	#1
Reese Allen Registered User Join Date: Feb 2015 Location: Seattle Posts: 14	Identifying rear diff on 1980 C20. LSD or not? My truck has a 14-bolt rear differential. I've removed the cover and drained the oil, and am about ready to button it all back up and refill with fresh oil. However, I can't figure out if this truck has an LSD or not, and therefore whether to add LSD additive into the oil. Picture: https://imgur.com/VLqjWER With the rear end jacked up, and transmission in neutral, when I spin one wheel, the other stays stationary. But if I put in gear and spin one wheel, the other spins the other way. I'm inclined to think this means it does NOT have an LSD, but I'm getting so much conflicting information after searching extensively that I am not feeling very confident about this. Help?

09-05-2019, 08:45 PM	#2
AussieinNC Moderator Join Date: Jun 2017 Location: Cherryville, NC Posts: 2,204	Re: Identifying rear diff on 1980 C20. LSD or not? The diff described and pictured is not an LSD...it is an open or standard diff... __________________ Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox

09-05-2019, 09:21 PM	#3
sweetk30 Registered User Join Date: May 2012 Location: horseheads,ny rust belt Posts: 2,794	Re: Identifying rear diff on 1980 C20. LSD or not? 4 windows and see spider gears = open 4 windows and see coil spring and block of steel = detroit locker ........... do NOT pull apart a detroit type unit unless you bolt the unit together inside or it will pop open good on you and might hurt . 3 pins on the center of case were the ring gear bolts and no windows = gov-loc posi unit . 3 pics in order as i typed above . Attached Images __________________ 77-k30lb BIG truck build . 87-k30lb budget beater build . 85-k30lb the plow machine build . 85-c10sb summer fun toy . ----------------------------- HOLLEY SNIPER efi = worst case of p.i.t.a i ever had . EDELBROCK pro flo 4 = best deal going so far . love my setup works great.

09-05-2019, 09:46 PM	#4
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,670	Re: Identifying rear diff on 1980 C20. LSD or not? ("3 pins on the center of case were the ring gear bolts and no windows = gov-loc posi unit .") what k30 posted is what you have.....G80 it is not a open diff..it the GM version of a posi __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

09-06-2019, 10:18 AM	#5
sweetk30 Registered User Join Date: May 2012 Location: horseheads,ny rust belt Posts: 2,794	Re: Identifying rear diff on 1980 C20. LSD or not? forgot to add also . the strongest of the gov-loc posi units is the 14ff . i have run them stock to built 400 sbc engines with 38" tall super swamper mud tires and no problems . __________________ 77-k30lb BIG truck build . 87-k30lb budget beater build . 85-k30lb the plow machine build . 85-c10sb summer fun toy . ----------------------------- HOLLEY SNIPER efi = worst case of p.i.t.a i ever had . EDELBROCK pro flo 4 = best deal going so far . love my setup works great.

09-06-2019, 04:52 PM	#7
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,670	Re: Identifying rear diff on 1980 C20. LSD or not? I think i see the windows now...so that changes my opinion...couldn't see them in the other pic...looks open __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

09-06-2019, 05:49 PM	#8
sweetk30 Registered User Join Date: May 2012 Location: horseheads,ny rust belt Posts: 2,794	Re: Identifying rear diff on 1980 C20. LSD or not? open diff or gov-lov both call for std gear oil in these axles . and yes you have open diff . __________________ 77-k30lb BIG truck build . 87-k30lb budget beater build . 85-k30lb the plow machine build . 85-c10sb summer fun toy . ----------------------------- HOLLEY SNIPER efi = worst case of p.i.t.a i ever had . EDELBROCK pro flo 4 = best deal going so far . love my setup works great.



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