Changing Rear End Fluid - The 1947 - Present Chevrolet & GMC Truck Message Board Network

skokie · 12-14-2003, 03:30 AM

I was planning to open up the rear end and see what gear ratio I have and while I was in there change the fluid. I realize that removig the fluid is the easy part but how do you put more in? How much does a 1/2 ton 12 bolt take?

Thanks

lost wages · 12-14-2003, 03:47 AM

should be a plug about halfway up the diff cover, it will take 3-4 bottles of gear oil, not real sure fill it till it runs out the fill plug, if you have a limited slip make sure you have some fritction modifier, you can get it at parts store or tranny shop/

skokie · 12-14-2003, 03:50 AM

Facing the rear of the truck is the plug on the left or the right? Not sure if I have limited slip or posi. Thats another reason I am opening this up. Plus I am pretty sure the previous owner didnt change it.

Thanks

1969 GMC · 12-14-2003, 04:24 AM

I'm not sure what side the plug should be on a 12 bolt, but there should be only one drain plug on a diff cover, it's a big square headed plug that sticks out.

lukecp · 12-14-2003, 04:31 AM

There isn't a drain plug on a stock 12 bolt cover (unless someone has modified it).

The fluid goes in on the passenger side of the differential, on the same side as where the driveshaft goes in. Look around and you will find it...it comes out with a 3/8" ratchet.

skokie · 12-14-2003, 04:39 AM

Ok sounds good. Thanks again

1969 GMC · 12-14-2003, 04:45 AM

d'oh my bad...i'm used to my dana 60. sorry

lost wages · 12-14-2003, 04:45 AM

yup yellow is right, i changed my oil in my dodge today and thats why i thought of it being on the cover, my 68 has a ford 9 inch so i havent seen a 12 bolt in a while! heres a link i found for you. http://www.sporttruck.com/techarticl...03/index1.html

Longhorn Man · 12-14-2003, 11:58 AM

If you have the cash and do any seriouse RPMs (like high speed cruising) or tow any heavy loads in a regular basis...sythetic is not a bad idea.
Many will scoff at the idea, but our lab shows that it does indeed help more than most ppl would ever think.
Acording to our lab, if your oil is original in there, and it has the typical 3.73 or numeracly higher gears, and asuming you have over 100K on the clock..your oils is only working at about 25%- 45%.
This is an independent lab that we deal with all the time for the past 12+ years.

**old Rusty C10** · 12-14-2003, 12:24 PM

anyone have a certain brand that they swear by when changing the gear oil im thinking mine has over 200K on it and it may not be a bd idea to change it

**MJN** · 12-14-2003, 12:46 PM

I would use Mobil 1 if you go with synthetic, otherwise Mobil or Valvoline 80w-90 will work fine. If it is a factory posi and has the little clutches in the diff, then you will need GM's friction modifier. It comes in a 4oz bottle andyou just dump it in with the oil. I found this out the hard way, I tried using a friction modifier from Napa but kept getting a clunk when the diff would engage, after putting in the GM stuff the clunk went away and never had another problem. Hope this helps.

70c10 · 12-14-2003, 11:05 PM

My Eaton Posi came with instructions NOT to use synthetic. I wanted to use it anyway but figured I would just go with the regular stuff.

Longhorn Man · 12-15-2003, 01:23 AM

Good point. I guess I would say to look into it if you have a posi or locker.

**MJN** · 12-15-2003, 04:57 PM

I replaced the rear end oil in our '94 Jimmy and it has a locking differential in it and the Moblil 1 synthetic hasn't hurt it one bit, made sure to get the GM additive too.

skokie · 12-15-2003, 08:14 PM

Ok its drained man that stuff was nasty. Barely any in it at all and there was no gasket either. So now its all filled up with a new gasket on it and here are the numbers that I pulled off of the ring gear.

381777811:41 GM168219-1

lukecp · 12-15-2003, 09:00 PM

If those numbers mean 11:41, you have 3.73 gears.

Quagmire · 01-17-2004, 03:55 PM

somebody mentioned 4 or 5 bottles, does that mean quarts?

cableguy0 · 01-17-2004, 04:24 PM

just fill it untill it starts leaking out of the hole your putting it into. then put the plug back in

lukecp · 01-17-2004, 04:31 PM

It is about a quart and a half...buy two bottels and you will be good.

WRMZ71 · 01-17-2004, 08:31 PM

somebody correct me if i'm wrong but i think the 3:73's were in pretty much all of these trucks. Mostly one wheel wonders if you had 2 wheel drive

lukecp · 01-17-2004, 08:55 PM

I would guess 3.07 to be the most common (for C10's anyway). , but i don't have any numbers. Just about every 350/auto truck has 3.07's...and that is what most of these trucks are. 3.73 is an easy second...with all inline trucks coming standard with 3.73's and most 307/283 trucks too.

I've seen like one in person with factory posi, lol.

Quagmire · 01-19-2004, 05:32 PM

thx guys just trying to get an idea, i order all my oil, etc. just didn't want to order to little or too much. that stuff is pricey

skokie · 01-19-2004, 05:51 PM

Yep and it smells great to

Quagmire · 01-19-2004, 06:42 PM

yeah, my garage has been stinking for a week now

67dragtruck · 01-19-2004, 09:43 PM

If my memory is correct it takes between 3-4 bottles (quarts)

Tom

12-14-2003, 03:30 AM	#1
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,354	Changing Rear End Fluid I was planning to open up the rear end and see what gear ratio I have and while I was in there change the fluid. I realize that removig the fluid is the easy part but how do you put more in? How much does a 1/2 ton 12 bolt take? Thanks

12-14-2003, 04:24 AM	#4
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	I'm not sure what side the plug should be on a 12 bolt, but there should be only one drain plug on a diff cover, it's a big square headed plug that sticks out. __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650

12-14-2003, 04:31 AM	#5
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	There isn't a drain plug on a stock 12 bolt cover (unless someone has modified it). The fluid goes in on the passenger side of the differential, on the same side as where the driveshaft goes in. Look around and you will find it...it comes out with a 3/8" ratchet. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

12-14-2003, 04:45 AM	#7
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	d'oh my bad...i'm used to my dana 60. sorry __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650

12-14-2003, 12:24 PM	#10
old Rusty C10 Robert Olson Transport Join Date: Oct 2002 Location: recent transplant to NC USA Posts: 20,326	anyone have a certain brand that they swear by when changing the gear oil im thinking mine has over 200K on it and it may not be a bd idea to change it __________________ Bob 1951 International running on a squarebody chassis "If a man's worth is judged by the people he associates himself with, then i am the richest man in the world knowing some of the fine people of this board" http://67-72chevytrucks.com/vboard/a...t.php?f=25&a=9 (you can review the site rules here!) PM Me for your vehicle/parts hauling needs in the North East US or see my Facebook page Robert Olson Transport Live each day to the fullest.. you never know when fate is going to pull the rug out from under you... I hate cancer!!

12-14-2003, 03:47 AM	#2
lost wages Registered User Join Date: Apr 2001 Location: jefferson city, mo Posts: 1,364	should be a plug about halfway up the diff cover, it will take 3-4 bottles of gear oil, not real sure fill it till it runs out the fill plug, if you have a limited slip make sure you have some fritction modifier, you can get it at parts store or tranny shop/

12-14-2003, 03:50 AM	#3
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,354	Facing the rear of the truck is the plug on the left or the right? Not sure if I have limited slip or posi. Thats another reason I am opening this up. Plus I am pretty sure the previous owner didnt change it. Thanks

12-14-2003, 04:39 AM	#6
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,354	Ok sounds good. Thanks again

12-14-2003, 11:58 AM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	If you have the cash and do any seriouse RPMs (like high speed cruising) or tow any heavy loads in a regular basis...sythetic is not a bad idea. Many will scoff at the idea, but our lab shows that it does indeed help more than most ppl would ever think. Acording to our lab, if your oil is original in there, and it has the typical 3.73 or numeracly higher gears, and asuming you have over 100K on the clock..your oils is only working at about 25%- 45%. This is an independent lab that we deal with all the time for the past 12+ years.

12-14-2003, 12:46 PM	#11
MJN Registered User Join Date: Feb 2000 Location: Maquoketa, Ia/ Orr, Mn Posts: 3,072	I would use Mobil 1 if you go with synthetic, otherwise Mobil or Valvoline 80w-90 will work fine. If it is a factory posi and has the little clutches in the diff, then you will need GM's friction modifier. It comes in a 4oz bottle andyou just dump it in with the oil. I found this out the hard way, I tried using a friction modifier from Napa but kept getting a clunk when the diff would engage, after putting in the GM stuff the clunk went away and never had another problem. Hope this helps. __________________ '51 South Bend Model "9A" '56 Chevy 3600 NAPCO '74 Chevy Cheyenne Super K20-restored on 37's '72 GMC Sierra Custom K2500- in progress '08 GMC Envoy Denali '12 GMC Sierra 2500HD Denali '17 GMC Yukon XL VCCA member #58596 http://www.nohrco.com

12-14-2003, 11:05 PM	#12
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,856	My Eaton Posi came with instructions NOT to use synthetic. I wanted to use it anyway but figured I would just go with the regular stuff. __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

12-15-2003, 01:23 AM	#13
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Good point. I guess I would say to look into it if you have a posi or locker.

12-15-2003, 04:57 PM	#14
MJN Registered User Join Date: Feb 2000 Location: Maquoketa, Ia/ Orr, Mn Posts: 3,072	I replaced the rear end oil in our '94 Jimmy and it has a locking differential in it and the Moblil 1 synthetic hasn't hurt it one bit, made sure to get the GM additive too.

12-15-2003, 08:14 PM	#15
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,354	Ok its drained man that stuff was nasty. Barely any in it at all and there was no gasket either. So now its all filled up with a new gasket on it and here are the numbers that I pulled off of the ring gear. 381777811:41 GM168219-1

12-15-2003, 09:00 PM	#16
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	If those numbers mean 11:41, you have 3.73 gears. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg



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01-17-2004, 03:55 PM	#17
Quagmire A splendid one to behold Join Date: Jan 2004 Location: moore, ok Posts: 251	somebody mentioned 4 or 5 bottles, does that mean quarts? __________________ 67 swb 02 wrx

01-17-2004, 04:24 PM	#18
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	just fill it untill it starts leaking out of the hole your putting it into. then put the plug back in __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

01-17-2004, 04:31 PM	#19
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	It is about a quart and a half...buy two bottels and you will be good. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

01-17-2004, 08:31 PM	#20
WRMZ71 Cause the Chicks DIG IT!! Join Date: Nov 2003 Location: Beaufort SC Posts: 509	somebody correct me if i'm wrong but i think the 3:73's were in pretty much all of these trucks. Mostly one wheel wonders if you had 2 wheel drive

01-17-2004, 08:55 PM	#21
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	I would guess 3.07 to be the most common (for C10's anyway). , but i don't have any numbers. Just about every 350/auto truck has 3.07's...and that is what most of these trucks are. 3.73 is an easy second...with all inline trucks coming standard with 3.73's and most 307/283 trucks too. I've seen like one in person with factory posi, lol. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

01-19-2004, 05:32 PM	#22
Quagmire A splendid one to behold Join Date: Jan 2004 Location: moore, ok Posts: 251	thx guys just trying to get an idea, i order all my oil, etc. just didn't want to order to little or too much. that stuff is pricey __________________ 67 swb 02 wrx

01-19-2004, 05:51 PM	#23
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,354	Yep and it smells great to __________________ RIP to my son Dylan. 5/17/2002 - 8/18/2018 If you want to know more about rare forms of pediatric cancer or if you want to help fund pediatric cancer research, please check out the website for the non-profit I started. https://slothforpedcancer.org 68 build thread http://67-72chevytrucks.com/vboard/s...d.php?t=223234

01-19-2004, 06:42 PM	#24
Quagmire A splendid one to behold Join Date: Jan 2004 Location: moore, ok Posts: 251	yeah, my garage has been stinking for a week now __________________ 67 swb 02 wrx

01-19-2004, 09:43 PM	#25
67dragtruck Registered User Join Date: May 2001 Location: Bethlehem, GA, USA Posts: 389	amount of fluid If my memory is correct it takes between 3-4 bottles (quarts) Tom

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