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**COBALT** · 05-22-2002, 06:00 PM

I have two of those bad-boy rear-end differentials. One under my daily driver and one under my parts truck. Both were originally set up with 4.10 gears. They carry spiders (unless the original owner opted for an eaton posi unit or one of the earlier lockers).

This was my first major problem with my C20 after I bought it. I noticed that a dull roaring noise would happen around 50 mph (2500-3000 rpm). It would only make noise if my foot was on the gas petal. At first it was just anoying, but over time it got so bad that the vibration could be felt through the steering wheel. At the time I was a dumb-a$$, and should have pulled the pan, but I was a whimp. I wouldn't have hesitated now...

Anyway, I took it to Randy's Ring & Pinion in Everett, WA. because I heard a lot of good things about them. Turns out 1 of the 4 spiders had blown its bearing, heated up and welded itself to the carrier cross-pin. The remaining 3 busted the teeth off of it and kept turning. Over time the carrier bearings ate themselves up, and that's the roaring noise. Ironically, the 4.10 gear set was flawless!

I had it completely rebuilt with new carrier bearings, 3.90s and a detroit locker. Now it kicks serious a$$, but it cost me a bundle but oh well. I didn't want to go searching for a new axle, driveline, etc. etc....

These are known as 10 bolt GM Corporate differential. They exist with 8 and 10 lug axles. The carriers were made by eaton corp, and at the time were the best around. They just don't wear very good over 35 years. HO52 (5200lb) axles were supposed to be the only coil sprung axle of this type for 3/4 ton trucks, and HO72 (7200lb) axles were supposedly leaf sprung only and under 1 tons. I don't believe this because the codes on my C20 indicate an HO72, it's coil sprung like yours, and the GVW of the truck is 7500lbs!

Anyway, here are the locations of the codes if you want to do your own homework:

------------------
'69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed!
'69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast).
Seattle, WA.

*See pics of my trucks and project at www.webshots.com!

05-22-2002, 06:00 PM	#17
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	I have two of those bad-boy rear-end differentials. One under my daily driver and one under my parts truck. Both were originally set up with 4.10 gears. They carry spiders (unless the original owner opted for an eaton posi unit or one of the earlier lockers). This was my first major problem with my C20 after I bought it. I noticed that a dull roaring noise would happen around 50 mph (2500-3000 rpm). It would only make noise if my foot was on the gas petal. At first it was just anoying, but over time it got so bad that the vibration could be felt through the steering wheel. At the time I was a dumb-a$$, and should have pulled the pan, but I was a whimp. I wouldn't have hesitated now... Anyway, I took it to Randy's Ring & Pinion in Everett, WA. because I heard a lot of good things about them. Turns out 1 of the 4 spiders had blown its bearing, heated up and welded itself to the carrier cross-pin. The remaining 3 busted the teeth off of it and kept turning. Over time the carrier bearings ate themselves up, and that's the roaring noise. Ironically, the 4.10 gear set was flawless! I had it completely rebuilt with new carrier bearings, 3.90s and a detroit locker. Now it kicks serious a$$, but it cost me a bundle but oh well. I didn't want to go searching for a new axle, driveline, etc. etc.... These are known as 10 bolt GM Corporate differential. They exist with 8 and 10 lug axles. The carriers were made by eaton corp, and at the time were the best around. They just don't wear very good over 35 years. HO52 (5200lb) axles were supposed to be the only coil sprung axle of this type for 3/4 ton trucks, and HO72 (7200lb) axles were supposedly leaf sprung only and under 1 tons. I don't believe this because the codes on my C20 indicate an HO72, it's coil sprung like yours, and the GVW of the truck is 7500lbs! Anyway, here are the locations of the codes if you want to do your own homework: ------------------ '69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed! '69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast). Seattle, WA. *See pics of my trucks and project at www.webshots.com! __________________ '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.