Rear Differential Oil - The 1947 - Present Chevrolet & GMC Truck Message Board Network

domano 68 · 12-07-2019, 12:13 PM

Going to put a new gasket on my rear diff on my 71 C10 307 V8 Automatic. Leaking pretty bad and I don't know the history so I figured I'd fresh'n it up. What are the specs on the gear oil, 75W-90, ... etc? Non synthetic I assume.

Service manual says GL5, not sure what that translates to in a 75w, 80w, .... Also, how many quarts? Any special additives?

Example: Ok to use this?
https://shop.advanceautoparts.com/p/...lvoline+80w-90

Thanks in advance!

Andy4639 · 12-07-2019, 12:21 PM

Get the gear oil gasket maker for sure to have no leaks. This stuff works great and is much better than the normal stuff. I use the Valvoline 80-90 gear lube in all of mine.

https://www.autoserviceprofessional....desktop-view=1

**Stocker** · 12-07-2019, 12:39 PM

^^ Andy beat me to the punch with that Permatex. It's called Gasket Maker but I smear a thin coating on both sides of a gasket. No leaks, great stuff, made to use with gear oil.

I typically use Mobil-1 75W-90 synthetic, but any good gear oil will work fine. If you have an open diff you don't need any additives.

I'd get 3 quarts and you'll probably have some left over.

domano 68 · 12-07-2019, 12:44 PM

Thanks for the responses, just what I was looking for!

Not sure if open diff or not. It is a 12 bolt though.

The brake line is attached to one of the bolts. It appears to be very rigid. I assume it will easily move out of the way once I remove the bolt that attaches it to the diff cover. Not much space with the panhard bar being close also, but I assume just enough room to get cover off and back on. Thanks again!

**truckster** · 12-07-2019, 01:38 PM

There will be enough room once you take the bolts out.

I agree with the recommendations so far, but if you discover it's a positraction, I like to use Royal Purple in those. No friction modifiers are needed with Royal Purple.

While you're in there, snap a pic of the numbers on the ring gear. At some point you might want to know for sure what your rear ratio is, and that will tell you.

**Wrenchbender Ret** · 12-07-2019, 03:21 PM

The GL 5 is not the viscosity. It is a anti friction rating. You must use gl5 in differentials.
Practically all gear lubes are rated for GL 5. If your seals are old you might use 85w140 in the rear end unless you are using it in extreme cold.
If it is a Posi-trac you need to put an additive in it.
George

ManNamedJed · 12-07-2019, 09:01 PM

I put 'Lubelocker' gaskets on mine. No sealant needed and you can reuse them if you have to pull the cover again. No leaks ever.

**CS1972** · 12-07-2019, 10:15 PM

I used LubeLocker for both my front Dana 44 and the rear 12 bolt and NO LEAKS ! Quite honestly it's my first time not using the typical gasket / sealer and after doing so I don't know why anyone would mess with smearing it all on equally and dealing with the mess. Sure the Lubelockers are more, but remember you don't have to buy the sealer.

Take pics of your ring gear so you'll know what ratio you have FOR SURE.

I used Mobil1 75W-90 Synthetic Gear Lubricant LS which will work for BOTH limited slip and non limited slip rear ends.

**53burb** · 12-07-2019, 11:13 PM

I used the Right Stuff by Permatex on my rear diff on my Ram....no gasket...worked great!!
I learned about it from this site....surprised no one has mentioned it yet....

https://www.amazon.com/Permatex-3369...a-448741432246

**Stocker** · 12-08-2019, 12:55 AM

Lubelockers are new to me but sound intriguing. Summit lists 43 different gaskets, unfortunately none to fit my K20's rear diff.

57taskforce · 12-08-2019, 02:24 AM

Quote:

Originally Posted by 53burb

I used the Right Stuff by Permatex on my rear diff on my Ram....no gasket...worked great!!
I learned about it from this site....surprised no one has mentioned it yet....

https://www.amazon.com/Permatex-3369...a-448741432246

Same here I get the big aerosol can of the right stuff for jobs like this. Never had a leak using it and it cleans up pretty easily when it’s time to change the oil again. In use 80w90 for oil.

**special-K** · 12-08-2019, 08:50 AM

I use Purple Power, too. I have a posi rear and also use it up front w/o posi. No harm in using better than called for.

Bigdav160 · 12-08-2019, 10:25 AM

Quote:

Originally Posted by Wrenchbender Ret

The GL 5 is not the viscosity. It is a anti friction rating. You must use gl5 in differentials.
Practically all gear lubes are rated for GL 5. If your seals are old you might use 85w140 in the rear end unless you are using it in extreme cold.
If it is a Posi-trac you need to put an additive in it.
George

Just for clarity, GL5 is a SAE test sequence that certifies a fluid to meet a standard.
It is normal for an older standard be replaced by a newer standard.

But there is nothing to prevent an oil blender from marketing an lubricant without pursuing the expense of certification.

**70STOVEBOLT** · 12-08-2019, 09:45 PM

Make sure to use a thread sealer on the bolts that pass thru the housing into the oil or it will
leak in those areas. I forget which two they are but you can look at them and tell.

Happy_dan · 12-09-2019, 10:29 AM

If you have a posi and you want to use Royal Purple there is one that end in LS, that means limited slip. I use that in my ZL1 Camaro and rear is nice and quiet.

12-07-2019, 12:13 PM	#1
domano 68 Registered User Join Date: Nov 2014 Location: hsv al Posts: 89	Rear Differential Oil Going to put a new gasket on my rear diff on my 71 C10 307 V8 Automatic. Leaking pretty bad and I don't know the history so I figured I'd fresh'n it up. What are the specs on the gear oil, 75W-90, ... etc? Non synthetic I assume. Service manual says GL5, not sure what that translates to in a 75w, 80w, .... Also, how many quarts? Any special additives? Example: Ok to use this? https://shop.advanceautoparts.com/p/...lvoline+80w-90 Thanks in advance! __________________ 1971 C10 127 in wheelbase Model Number-CS10934 Body Type & Seating-Fleetside 8 ft. Original Factory Price-$2,854 Shipping Weight-3,605 lbs Total Production-206,313 Last edited by domano 68; 12-07-2019 at 12:25 PM.

12-07-2019, 12:21 PM	#2
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Rear Differential Oil Get the gear oil gasket maker for sure to have no leaks. This stuff works great and is much better than the normal stuff. I use the Valvoline 80-90 gear lube in all of mine. https://www.autoserviceprofessional....desktop-view=1 __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

12-07-2019, 12:39 PM	#3
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,495	Re: Rear Differential Oil ^^ Andy beat me to the punch with that Permatex. It's called Gasket Maker but I smear a thin coating on both sides of a gasket. No leaks, great stuff, made to use with gear oil. I typically use Mobil-1 75W-90 synthetic, but any good gear oil will work fine. If you have an open diff you don't need any additives. I'd get 3 quarts and you'll probably have some left over. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

12-07-2019, 12:44 PM	#4
domano 68 Registered User Join Date: Nov 2014 Location: hsv al Posts: 89	Re: Rear Differential Oil Thanks for the responses, just what I was looking for! Not sure if open diff or not. It is a 12 bolt though. The brake line is attached to one of the bolts. It appears to be very rigid. I assume it will easily move out of the way once I remove the bolt that attaches it to the diff cover. Not much space with the panhard bar being close also, but I assume just enough room to get cover off and back on. Thanks again! __________________ 1971 C10 127 in wheelbase Model Number-CS10934 Body Type & Seating-Fleetside 8 ft. Original Factory Price-$2,854 Shipping Weight-3,605 lbs Total Production-206,313

12-07-2019, 01:38 PM	#5
truckster Senior Member Join Date: Jan 2001 Location: Orem, Utah Posts: 7,791	Re: Rear Differential Oil There will be enough room once you take the bolts out. I agree with the recommendations so far, but if you discover it's a positraction, I like to use Royal Purple in those. No friction modifiers are needed with Royal Purple. While you're in there, snap a pic of the numbers on the ring gear. At some point you might want to know for sure what your rear ratio is, and that will tell you. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

12-07-2019, 03:21 PM	#6
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,190	Re: Rear Differential Oil The GL 5 is not the viscosity. It is a anti friction rating. You must use gl5 in differentials. Practically all gear lubes are rated for GL 5. If your seals are old you might use 85w140 in the rear end unless you are using it in extreme cold. If it is a Posi-trac you need to put an additive in it. George

12-07-2019, 09:01 PM	#7
ManNamedJed Registered User Join Date: May 2018 Location: Reno, NV Posts: 232	Re: Rear Differential Oil I put 'Lubelocker' gaskets on mine. No sealant needed and you can reuse them if you have to pull the cover again. No leaks ever.

12-07-2019, 10:15 PM	#8
CS1972 Senior Member Join Date: Jun 2018 Location: Austin Texas Posts: 449	Re: Rear Differential Oil I used LubeLocker for both my front Dana 44 and the rear 12 bolt and NO LEAKS ! Quite honestly it's my first time not using the typical gasket / sealer and after doing so I don't know why anyone would mess with smearing it all on equally and dealing with the mess. Sure the Lubelockers are more, but remember you don't have to buy the sealer. Take pics of your ring gear so you'll know what ratio you have FOR SURE. I used Mobil1 75W-90 Synthetic Gear Lubricant LS which will work for BOTH limited slip and non limited slip rear ends. Attached Images __________________ Ron 1972 Cheyenne Super 1/2 ton LWB 4x4 - Grapefruit Yellow / White

12-07-2019, 11:13 PM	#9
53burb Registered User Join Date: May 2004 Location: Queen Creek, AZ Posts: 1,004	Re: Rear Differential Oil I used the Right Stuff by Permatex on my rear diff on my Ram....no gasket...worked great!! I learned about it from this site....surprised no one has mentioned it yet.... https://www.amazon.com/Permatex-3369...a-448741432246

12-08-2019, 12:55 AM	#10
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,495	Re: Rear Differential Oil Lubelockers are new to me but sound intriguing. Summit lists 43 different gaskets, unfortunately none to fit my K20's rear diff. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

12-08-2019, 08:50 AM	#12
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,862	Re: Rear Differential Oil I use Purple Power, too. I have a posi rear and also use it up front w/o posi. No harm in using better than called for. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

12-08-2019, 09:45 PM	#14
70STOVEBOLT Senior Member Join Date: Jun 2005 Location: Winona Lake, IN Posts: 6,208	Re: Rear Differential Oil Make sure to use a thread sealer on the bolts that pass thru the housing into the oil or it will leak in those areas. I forget which two they are but you can look at them and tell. __________________ 70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Power windows Power Locks Coming soon: EFI 2015 Silverado 1500 LS 4.3/6L80/3.23

12-09-2019, 10:29 AM	#15
Happy_dan Registered User Join Date: Jul 2019 Location: New Boston, NH Posts: 456	Re: Rear Differential Oil If you have a posi and you want to use Royal Purple there is one that end in LS, that means limited slip. I use that in my ZL1 Camaro and rear is nice and quiet. __________________ 1968 C-20 CST Vermillion http://imageevent.com/happy_dan/dantoys/68c20 2019 Silverado 2012 Camaro ZL1



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