Rear Gears?

[junk4cash]

Been working on my 66 c10 and noticed the rear end is out of an earlier truck. Replaced my clapped out 230 with a fresh 292. Still have the stock 3 on the tree and noticed that on the hwy in 3rd gear it really sounds and feels like its wound up at only 60 mph. I can't imagine pushing it to 70 or 75mph. Just curious if this is normal with these older trucks or should I check the rear end gears and see what I have? I am going to put a tach in this weekend and see where I'm at. Family friend has a muncie 3 speed with overdrive that is recently rebuilt and he is looking to unload it.

[1969K10]

my 72 had 4.11 gears, and spun about 3200 at 70. I didn't go 70 very often. 60 was about as fast as it went normally. Same 3 on the tree.

[junk4cash]

Originally Posted by 1969K10

my 72 had 4.11 gears, and spun about 3200 at 70. I didn't go 70 very often. 60 was about as fast as it went normally. Same 3 on the tree.

I think I'll pull the cover and see what I have. That Muncie with overdrive sure would be nice.

[jtrichard]

junk all you need to do is jack up one side and turn the tire one turn and count the revolutions on the drive shaft and divide by 2 and that will tell you what gears you have

[junk4cash]

Originally Posted by jtrichard

junk all you need to do is jack up one side and turn the tire one turn and count the revolutions on the drive shaft and divide by 2 and that will tell you what gears you have

I heard something about doing that. Thank you for clearing it up. I will do that.

[junk4cash]

What do most stock trucks have?

[Captainfab]

In my experience the 3.73 gear is the most common.

Originally Posted by junk4cash

What do most stock trucks have?

[Clyde65]

that OD trans would be a plus for sure. I bet you have 4.10's by what you said. If you have the lower gear, it would work fine with the OD or an Auto OD.

[66Submarine]

Tires make a big difference, too. My C-30 with a 4.10 rear runs about the same as my C-10 with a 3.73 and shorter tires. Looks like you have pretty short OE style rear tires; I have 31x10.50r15 4x4 tires on the back of my 1/2 tons. With those tires 70 is about 3,000RPM; with a 215/75r15 tire 70MPH would be about 3,250RPM.

[Irishbleueyes]

When I was a kid all those old trucks had really big back tires and stock front tires and thats why, they all had low rear ends in them. Don't know why JT said to divide by 2. Just make one full rotation with a rear wheel and count how many times the driveshaft turns and thats the gear ratio. 4 driveshaft turns plus a little is 4.11, 3 and 3/4 turns is a 3.73. Jack the entire rear axle up when you rotate and see if both tires turn the same direction, that will tell you if you have positraction.

[jtrichard]

irish if he has limited the you have to jack up the entire axle and count the shaft turns if no locking rear then jack up one wheel and divide by 2 because of the differential

[Irishbleueyes]

Originally Posted by jtrichard

irish if he has limited the you have to jack up the entire axle and count the shaft turns if no locking rear then jack up one wheel and divide by 2 because of the differential

Thanks Jt

[Dillon Rock]

Anyone ever run across a rear GM axle on the trucks that was a solid casting, not a three pice rear? My '64 C20 has a solid, cast rear axle and I've never seen anything like it before, no markings, no nothing on it. Maybe a staping number. Anyone have any axle plant codes by chance? It looks heavy duty so I'd expect it to take some payload for a 3/4 ton.

[T Smith]

Pictures...

[66Submarine]

It's probably a later rear someone swapped in for taller gears.

[Captainfab]

The original differential under your '64 C20 was likely the Eaton HO52. The housing for those is welded together 2 piece stamped steel. The weld is on the front and back of the axle tubes. It does look like it is one piece, but it is not cast iron, The third member is, but not the housing.

Originally Posted by Dillon Rock

Anyone ever run across a rear GM axle on the trucks that was a solid casting, not a three pice rear? My '64 C20 has a solid, cast rear axle and I've never seen anything like it before, no markings, no nothing on it. Maybe a staping number. Anyone have any axle plant codes by chance? It looks heavy duty so I'd expect it to take some payload for a 3/4 ton.

[Dillon Rock]

Tahnks CaptainFab, much appriciated. Like I said in my earlier post, I'll try to get some pics up of the truck when I get back from deployment soon. I'm just trying to solve some mystery out about the ol' girl. I have all the original paperwork from when the first owner bought it at the South Tacoma Motorways south of Seattle, all the reciepts from what he did, including a reciept for a valve guide re-knurling in '77 or '79, plus original shop manual.

[Dillon Rock]

By the way, is it somewhat uncommon to come across the Eaton model HO52 rear axle?

[66Submarine]

Eaton HO-52/72 was the standard rear axle for Chevrolet 3/4 and 1 tons, and was used from 1947-72. If that's what you have, it's easy to ID. Here are a couple pictures of the one under my '65 C-30 (with leaf springs).

[Clyde65]

If it is a 10bolt and 6 lug,it's quite possible it is an HO33, if it is, find you a 12bolt and get rid if the HO. It only has two gear ratios and rebuilding is expensive.
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[66Submarine]

Originally Posted by Clyde65

If it is a 10bolt and 6 lug,it's quite possible it is an HO33, if it is, find you a 12bolt and get rid if the HO. It only has two gear ratios and rebuilding is expensive.
Posted via Mobile Device

He said C-20; so it would be the HO-52. '64 was the early 12 bolt, anyway; they started using the 12 bolt in '63.

[Captainfab]

No, they are very common just as 66Submarine said. And as Clyde65 said, they are expensive to rebuild and there are no higher gear ratios available. Youre more than likely has 4.57 gears. If you're lucky it has the 4.10 gears. Either one is not very highway friendly, even with a tall tire. If you plan to keep your truck a C20, I would recommend finding either a 10.5" 14 bolt or possibly a Dana 60. Those have much better parts availability including higher gear ratios.

Originally Posted by Dillon Rock

By the way, is it somewhat uncommon to come across the Eaton model HO52 rear axle?

[Dillon Rock]

Thanks guys, and yes 66submarine, My c-20 is an early year, made in April of 64 so it's more than likely the H0-52. Also, appreciate the pictures 66submarine, helpful indeed.

[66Submarine]

Glad I could help. BTW; CaptainFab isn't a big fan of them, but I don't see any reason not to run a good one. They are real tough, and unless someone has done something really stupid like run all the oil out of it; it's probably just fine. (They have a small 4x4 crawler following to prove their durability) Mine is a 4.10:1 ratio, and I personally don't find it bad at all. Here's what my speeds work out to with a 32" tire:

45MPH=2,000RPM
50=2,200
55=2,425
60=2,650
65=2,875
70=3,075

It's not geared for 90MPH empty commuting or anything, but I like it for an all-around working/towing/driving truck. My 2 cents.