The Stovebolt Site Forums The Shop Area Engine Shop non-standard 69 C-20 rear

Folks,

Got a 69 C-20 longbed stepside with what amounts to a 1-ton suspension and drive-train with eight-lug wheels and standard three-speed tranny. Looking for advice on options about swapping out rear and wheels to get a standard C-20 rear and six-lug wheels -- possibly five. Idea is to get a different gear ratio for highway speeds while still keeping the stock three-on-tree. My mechanic down in Georgia advises the existing rear is of a type rarely used on C-20s -- and that seems like both a problem right now in terms of a torquey gas hog and down the line if that rear ever goes.

3/4 tons of that vintage were standard with 8 lug and a full floating rear as you describe. common was the eaton HO52, especially with chevy. highway gears are hard to find. i 'think' GMCs were slightly more likely to have a dana 60.

Welcome to the 'Bolt! Some explaination is in order. There's no such critter as a 6 lug C 20,all 3/4 and 1 ton GM trucks from '47-current (excluding some '88-'98 light duty models) are 8 lug, full floating axles. There is a 4.10 gear that was used in some automatic equipped trucks fom that era that is a direct bolt in, but it is somewhat rare. Sounds like you have the std 4.56 gear. You mention that you have the 1 ton suspension, I take it that yoou're truck is leaf spring in the rear? That may make swapping in a later diff easier, perhaps one from a late '70s or '80s truck. You couls also swap in a 1/2 ton rear, if that is the way you plan to go, but you should also swap out the front spindles and balljoints to the later 1/2 ton components to keep things matched.
One more question, does your truck have the Eaton style diff (removable center section) or the Spicer/Dana style (integral center section)? If it has the Spicer/Dana, commonly found under GMCs and Camper Special Chevies, that does open up easily available aftermarket gearsets in many ratios, as that axle was used up to current production on many trucks, as well as being a very popular axle with the off road crowd.

Bill,

Very helpful info for a guy who ain't a wrench, but loves old iron. When I say one-ton suspension, that's my mechanic's description. If I recall correctly -- truck's down at my mom's in Georgia, I'm in N.C. -- it has both leaf and coil. Which may make swapping more difficult, but I may be dead wrong on that point. We're at the point where we either find out whether we can change out gearsets or have to swap in a 1/2 ton rear, with the accompanying swap out of front spindles and balljoints. Two questions here -- will the 1/2 ton rear stand up to load and is there aftermarket gearsets available for same? As to your final question -- since posting the original note, I've done a little surfing and found mention of the Spicer/Dana style diff. I take it the Eaton has fewer aftermarket options? And given my mechanic's pessimism -- and the fact I bought a rig that, typical for me, isn't vanilla simple -- I'd bet on the Eaton.

But you've given me great questions to ask my man down South. And a much firmer understanding of what I'm dealing with and what he's talking about. May be a situation where I have to ease her up the two-lane backroads to Raleigh and get a mechanic here to work with. Friend of mine had her father's 49 Ford restored by a guy who does excellent work, so I'm considering a move to Plan B.

Thanks again,

Jim

Bill,

One other thought occurs -- mechanic mentioned rear is of an older type not in production any more, making me think it's more likely to be the Eaton HO52 mentioned by another fella in this string. I'm kinda old-school and would love to keep the 8-lug standard of that vintage. I've tried to keep everything else stock, resisting urge to 'hot rod' it out.

Regards,

Jim

Bucket,

I take it I can't swap in the Dana for the Eaton. But it does sound like I might try finding a GMC rear -- or does that open another set of problems. Forgive the dumb question.

Jim

The 1/2 ton rear will hold up fine to relatively light loads, but not well to going with the full load that the 3/4 ton can hold. If it is an Eaton, than the available gearsets are very limited. I'm not even sure if anything is available in the line of gears for them, mainly soft parts like seals and gaskets. If it has the Spicer/Dana (most likely a 70) that opens up a very good gear assortment, running from 3.54s up to the 6.00s range. Just from what you describe, it has the std coil spring rear with the single helper leaf. My Dad had a '71 with that setup with the Eaton rear. My Granpa (Moms side) had a '69 Camper Special w/ leaf springs, it had the Spicer/Dana 70. A later diff (like a 14 bolt full float) coild be swapped in, you would just need to swap the mounts for the springs to the new axle, which will require some welding. For the front, you can do the same swap as a 1/2 ton disk brake/spindle swap, just use 3/4 or 1 ton parts. I think the lower balljoint is the same, it's the upper that is different. I've heard that the outer tie rods are different, too, so those may have to be swapped as well.
Oh, one more thing, yes, lots of hear choices for the 1/2 ton axle. GM used the 12 bolt up into the '70s, so there are parts available for it.

not a dumb question. if you can find a dana for a coil setup that would be easiest and yes, it would be a direct swap. don't know about any differences in drive shaft length though.

otherwise, i know guys have fabbed the appropriate brackets to make a dana fit the coil/trailing arms like the eaton.

go to here for lots of info regarding what you are exploring: http://67-72chevytrucks.com/vboard/

Bucket,

Further info from my mechanic -- an exchange that convinces I need to creep this rig slowly up to North Carolina and quit trying to do this by remote. Good barbecue on the back roads between Georgia and here. He describes the diff as a front-load 12-bolt, similar to a Ford nine-inch, lacking an inspection cover. As Bill aptly describes in post above, the rig has coil springs with leaf spring 'helpers.' Talked to a fella with a Washington state outfit called Randy's Ring and Pinion who mentioned swapping out what I've got for a later model 14 bolt for a 3/4 or 1 ton with a 6 bolt pinion support, free floating axles, stay away from the C-clips. I'm told I ought to be able to get one for $250 or so, then get the ring, pinion, etc. to get me where I want to go. I think I want to try to keep the extra strength of a 3/4 rather than go the 1/2 ton route, if I can avoid same.

Again my thanks to you and Bill for walking me through this.

Jim

You've got the Eaton, but there should be a removable cover on the back, unlike the ford. The 14 bolt full floater will be an exellent diff for your truck.

your welcome. sorry i can't give more info on a swap. i've kept the 4:11 in my 67 eaton for the "farm feel". if i want to go fast, i drive my 07 5.7 tundra

Bucket,

If I were still living down in Augusta, I'd probably keep it 'as is.' It's fine for weekend chores and tooling around town. But driving it up here might get me killed by a Beltline Bandito. You and Bill have given me some excellent advice on my options. Allows me to guide a mechanic -- either the one I've got or one I go to up here.

Jim

I've run into the same problem on my 1946 chevrolet 3/4 ton truck is to also has a Eaton 12 bolt rearend