I think it's a...? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

stllookn · 08-05-2002, 02:05 PM

C30 dually rearend casting number is 3883379. I believe this is a GM 12 1/4 inch ring gear. Anybody have a clue? I need to replace the pinion seal. I have a diagram of 1977 GM 12 1/4 that looks similar but mine has no ring gear thrust pad. Any help would be appreciated.

jku72 · 08-05-2002, 02:08 PM

Sounds like a HO 72 to me. My 1970 C30 has that.

stllookn · 08-05-2002, 02:32 PM

HO 72...I'm not familiar with that one. What can you tell me about it? I am trying to replace the pinion seal and it looks like the entire pinion assy. can be removed from the front. I guess I can just remove the pinion nut, then the universal joint yoke and pull the seal out the front. It looks like it can be removed by tapping on the back side of the oil seal retainer. Maybe I have to pull the entire pinion assy. It takes a thin wall socket...my standard 1 5/8 won't fit inside the yoke. I might just turn mine down.

**COBALT** · 08-05-2002, 04:48 PM

Yeah, it looks like you can remove the pinion yoke out the front. I know the whole 3rd member can come out, but that doesn't help you very much. Not sure about the socket size, but it reminded me of the front hub nuts, which are at about 1 1/4".

I assume you'll have to pull the cover and drain it first.

Here's a snap-shot of mine. The codes are located at positions 1-4. Your casting number is either at 1 or 4 I don't remember, but there is a set of pressed-in numbers that actually tell you specific info about the axle.

stllookn · 08-05-2002, 05:45 PM

That very close to mine except I do not have the ring gear adjustment nut at location 4. Mine does not have a cover on the rear, everything comes out the front. My casting number, 3883379, is located at position 4 and the casting number,3883654, for the pinion assembly is located on the flange at 12 o'clock. I can't find any other numbers but there is a ton of dirt on it and I will keep looking. I may just pull the entire pinion assy. if I can't find a socket to fit inside the yoke.

It seems to run fine and does not make any noise so I am thinking it will be ok for now if I just repalce the seal and wiper.

jku72 · 08-05-2002, 05:58 PM

The not well known 11000 lb and or 13000 pound axle looks very much like the HO 72(7,200 lb) axle, but does not have a removable rear cover. On a dually, this is likely the case.
In any event, replacing the seal involves removing the pinion nut(not easy) and sliding the yoke off, then you can unbolt the little cast plate from the front of the pinion, and replace the seal, and also the little plate gasket. Be sure to proper torque everything upon reassembly, I did not get quite enough and oiled my body.
The hardest part for me was removing the pinion nut, that took a huge airgun at the highest setting to hammer it loose, but maybe yours will not be so tight. Good luck aside from the nut it is an easy job.

stllookn · 08-05-2002, 07:59 PM

jku72, Thanks that is just what I needed. Since I do not have that thin wall socket I will have to wait. By unbolting the cast plate do you mean the one that holds the entire pinion assembly? If that is the case I guess I could pull the assy out and take it to the shop. I was hoping the seal would come right out the front after the yoke came off. I may have to pull the yoke too...but sure I can figure it out from here. Thanks again.

jku72 · 08-06-2002, 09:32 AM

Several points:
The thin wall socket that I used was a craftsman socket, no other brand seemed to work.
And, the "Cast plate" I was talking about "should" come out once the yoke is off. I ended up removing the whole pinion since I did not have the airgun big enough to remove that stubborn yoke nut. It should come out with a slide hammer, once you remove the 5(6?) bolts. Dont damage the bearing, it cost me 300 bucks for a new one. The seal itself was like 5 or 10 bucks.
Also, my another problem was the truck wanting to roll when I was wrenching the nut. Be careful. Also, if you dont have an e brake, you life will be even more difficult.

stllookn · 08-07-2002, 09:56 AM

jku, Thanks for the lead on the socket. Hopefully I can pick that up today and get on with this project. I hate to see the truck just sitting there with a leaky seal. Makes it hard to drive anywhere when you leave a big oil spot when you stop...LOL!

08-05-2002, 02:05 PM	#1
stllookn Saving 1 truck at a time! Join Date: Aug 2001 Location: Kent, WA Posts: 6,465	I think it's a...? C30 dually rearend casting number is 3883379. I believe this is a GM 12 1/4 inch ring gear. Anybody have a clue? I need to replace the pinion seal. I have a diagram of 1977 GM 12 1/4 that looks similar but mine has no ring gear thrust pad. Any help would be appreciated. __________________ '68 C20 Longhorn 50th Anniversary 400/TH400 '68 C20 Longhorn 50th Anniversary 468/TH400w/buckets '72 C20 Halfhorn (Longhorn w/o cab and front clip) '69 Flxible Cruiser (look up ugly in the dictionary)

08-05-2002, 02:08 PM	#2
jku72 Registered User Join Date: Jan 2002 Location: cornville, maine Posts: 659	Sounds like a HO 72 to me. My 1970 C30 has that. __________________ jku Cornville, Maine 68 C10 burb 42 Willys MB 46 Dodge WF-32 1.5 ton 53 & 56 Olds' 60 Cadillac 22 Dodge Brothers

08-05-2002, 02:32 PM	#3
stllookn Saving 1 truck at a time! Join Date: Aug 2001 Location: Kent, WA Posts: 6,465	HO 72...I'm not familiar with that one. What can you tell me about it? I am trying to replace the pinion seal and it looks like the entire pinion assy. can be removed from the front. I guess I can just remove the pinion nut, then the universal joint yoke and pull the seal out the front. It looks like it can be removed by tapping on the back side of the oil seal retainer. Maybe I have to pull the entire pinion assy. It takes a thin wall socket...my standard 1 5/8 won't fit inside the yoke. I might just turn mine down. __________________ '68 C20 Longhorn 50th Anniversary 400/TH400 '68 C20 Longhorn 50th Anniversary 468/TH400w/buckets '72 C20 Halfhorn (Longhorn w/o cab and front clip) '69 Flxible Cruiser (look up ugly in the dictionary)

08-05-2002, 04:48 PM	#4
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	Yeah, it looks like you can remove the pinion yoke out the front. I know the whole 3rd member can come out, but that doesn't help you very much. Not sure about the socket size, but it reminded me of the front hub nuts, which are at about 1 1/4". I assume you'll have to pull the cover and drain it first. Here's a snap-shot of mine. The codes are located at positions 1-4. Your casting number is either at 1 or 4 I don't remember, but there is a set of pressed-in numbers that actually tell you specific info about the axle. Attached Images __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

08-05-2002, 05:45 PM	#5
stllookn Saving 1 truck at a time! Join Date: Aug 2001 Location: Kent, WA Posts: 6,465	That very close to mine except I do not have the ring gear adjustment nut at location 4. Mine does not have a cover on the rear, everything comes out the front. My casting number, 3883379, is located at position 4 and the casting number,3883654, for the pinion assembly is located on the flange at 12 o'clock. I can't find any other numbers but there is a ton of dirt on it and I will keep looking. I may just pull the entire pinion assy. if I can't find a socket to fit inside the yoke. It seems to run fine and does not make any noise so I am thinking it will be ok for now if I just repalce the seal and wiper. __________________ '68 C20 Longhorn 50th Anniversary 400/TH400 '68 C20 Longhorn 50th Anniversary 468/TH400w/buckets '72 C20 Halfhorn (Longhorn w/o cab and front clip) '69 Flxible Cruiser (look up ugly in the dictionary) Last edited by stllookn; 08-05-2002 at 05:49 PM.

08-05-2002, 05:58 PM	#6
jku72 Registered User Join Date: Jan 2002 Location: cornville, maine Posts: 659	The not well known 11000 lb and or 13000 pound axle looks very much like the HO 72(7,200 lb) axle, but does not have a removable rear cover. On a dually, this is likely the case. In any event, replacing the seal involves removing the pinion nut(not easy) and sliding the yoke off, then you can unbolt the little cast plate from the front of the pinion, and replace the seal, and also the little plate gasket. Be sure to proper torque everything upon reassembly, I did not get quite enough and oiled my body. The hardest part for me was removing the pinion nut, that took a huge airgun at the highest setting to hammer it loose, but maybe yours will not be so tight. Good luck aside from the nut it is an easy job. __________________ jku Cornville, Maine 68 C10 burb 42 Willys MB 46 Dodge WF-32 1.5 ton 53 & 56 Olds' 60 Cadillac 22 Dodge Brothers

08-05-2002, 07:59 PM	#7
stllookn Saving 1 truck at a time! Join Date: Aug 2001 Location: Kent, WA Posts: 6,465	jku72, Thanks that is just what I needed. Since I do not have that thin wall socket I will have to wait. By unbolting the cast plate do you mean the one that holds the entire pinion assembly? If that is the case I guess I could pull the assy out and take it to the shop. I was hoping the seal would come right out the front after the yoke came off. I may have to pull the yoke too...but sure I can figure it out from here. Thanks again. __________________ '68 C20 Longhorn 50th Anniversary 400/TH400 '68 C20 Longhorn 50th Anniversary 468/TH400w/buckets '72 C20 Halfhorn (Longhorn w/o cab and front clip) '69 Flxible Cruiser (look up ugly in the dictionary)

08-06-2002, 09:32 AM	#8
jku72 Registered User Join Date: Jan 2002 Location: cornville, maine Posts: 659	Several points: The thin wall socket that I used was a craftsman socket, no other brand seemed to work. And, the "Cast plate" I was talking about "should" come out once the yoke is off. I ended up removing the whole pinion since I did not have the airgun big enough to remove that stubborn yoke nut. It should come out with a slide hammer, once you remove the 5(6?) bolts. Dont damage the bearing, it cost me 300 bucks for a new one. The seal itself was like 5 or 10 bucks. Also, my another problem was the truck wanting to roll when I was wrenching the nut. Be careful. Also, if you dont have an e brake, you life will be even more difficult. __________________ jku Cornville, Maine 68 C10 burb 42 Willys MB 46 Dodge WF-32 1.5 ton 53 & 56 Olds' 60 Cadillac 22 Dodge Brothers

08-07-2002, 09:56 AM	#9
stllookn Saving 1 truck at a time! Join Date: Aug 2001 Location: Kent, WA Posts: 6,465	jku, Thanks for the lead on the socket. Hopefully I can pick that up today and get on with this project. I hate to see the truck just sitting there with a leaky seal. Makes it hard to drive anywhere when you leave a big oil spot when you stop...LOL! __________________ '68 C20 Longhorn 50th Anniversary 400/TH400 '68 C20 Longhorn 50th Anniversary 468/TH400w/buckets '72 C20 Halfhorn (Longhorn w/o cab and front clip) '69 Flxible Cruiser (look up ugly in the dictionary)



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