3/4 Ton K10

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Tiny dime

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Hello guys,

I am fairly new to the forum. Im needing a truck for pulling a trailer. I was hoping to be able to set mine up to do it. I have read where the frames are a tad bit lighter gauge steel on a 1/2 ton vs 3/4 and 1 ton. I don't think that would be an issue because my frame is solid. I have a 14 bolt full float rear axle and a dana 44 front axle, both geared in 4.10 ratio. I currently have 2.93. It will be a huge difference I know but it won't be on the highway very much. Im curious as to how much trouble it will be (driveshafts, universal joints, mounts, etc.) I have the 3/4 ton leaf springs, I will get some shocks in the future. I would appreciate all info. Also if someone could point me in the direction of another thread that would be great! Im sure this has been done many times before.

Thanks guys!
Jonah
 

dvdswan

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Welcome to the site.

3/4T axle swaps are pretty common. You will need new u-bolts and a plate for the top of the leaf springs in the rear. The rear u-joint will need replaced as the yoke on the axle is larger than the 1/2T axle. When I did this swap on my Blazer years ago they made an u-joint that was 1/2T one way and 3/4 / 1T the other way. This got me by until I updated the driveline. Front axle should be direct bolt in. Brake lines will bolt right in.
 

HotRodPC

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It's fairly easy to do if it's a long bed. The frame will be punched for both sizes of springs. 3/4 ton 4x4 Springs come in both lengths. I prefer the longer ones so you just move the rear spring hangers back and put in the 52 in 3/4 ton springs. Gives you a better ride and more strength. AKA the C6P spring pack.
 

HotRodPC

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I found you a pic. This shows the 48 inch rear spring hanger location, then the holes you'll move that bracket back to and use Grade 8 hardened bolts and lok-tite to bolt them on, maybe even throw a tack weld on if you wish. Some claim the rivets are stronger.

I haven't swapped my C6P Springs in yet, but I have bolted up the 14b Full Floater.

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SirRobyn0

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I've only been on the forum for a few months and I've already seen this topic come up a few times. I have no practical experience with the modifications that you are about to perform, and I'm not trying to discourage you with this statement, but keep in mind that no mater what you change, even if 100% proper your hauling and towing capacities will never be anymore than is listed on the door card. I only bring it up because if you live in a state or travel into a state that weighs pickups that are towing or if involved in an accident ever if your not at fault you could have some trouble. With that said I totally get what you're doing, and while I have C20 already, I'll be beefing up the rear end and springs in the future.
 

Tiny dime

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Thanks for all the replies guys! I forgot to say but I do have the 3/4 ton lwb driveshafts. What I don't like about the rear one compared to the one on my 86 is its standard size on one end then it tapers down VERY small on the transmission end. I will definitely drill out those spring hangers and move them back. I appreciate the pics too!

As for towing with this truck I'm mostly going to be hauling small cars and trucks (a 1967 Pontiac Firebird and a 1964 Farmall Cub tractor). I believe its got 6,500Lbs on the door. The trailer has a 7,000lbs rating. So its all pretty close together. Ive wanted to do this for a while. Even without a load behind you those 2.93 gears are terrible in mountain country!
 

Craig 85

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I did it to my '79 K15. Here's the rear U-joint I used. My truck was lifted before I bought it. I installed a SF 14 bolt and had to shorten the rear drive shaft. I also switched to a 3/4 master cylinder. I was going to add an adjustable proportioning valve for the rear brakes as they would lock easily, but I sold the truck prior to doing that. I also removed the speedometer adapter from the transfer case when I went from 3.08 to 4.10. FYI with 33's and no OD I was turning about 3K RPM at 65-70 MPH.

Rear U-joint: Spicer 1310-1350 Part# 5-460X or O’Reilly’s – Precision U-joint Part# 348
(3.219 / 1.062 to 3.625 / 1.188)

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HotRodPC

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How much did you have to shorten the driveshaft @Craig 85 ? The 14b FF has a shorter pinion gear so it may not have to be shortened going to a FF. It's about 1.5 inches shorter than the SF. I plan on just finding a driveshaft out of a 3/4 ton because I want the bigger rear U joint too instead of going with a conversion joint.
 

Craig 85

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@Craig 85 thanks for the info! What did you do about your speedometer?

I didn't do anything. By just removing the speedo adapter, I was within 3-4 MPH at 65 MPH. I also did the same swap to my '77 K5. Also 3.08's to 4.10's, but I was running 36" tall tires, up from 31's. On that truck I had to buy a new adapter. This was in 1991, so they were easy to find locally.

@HotRodPC I think it was in the 1-2" range.
 

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@Craig 85 thanks for the info! What did you do about your speedometer?
You can also change your drive and driven speed gears. We have the forumulations here on this site. You do the math then it'll tell you what color gears you need for that ratio and tires size and should accurate within the 5% range which would mean you could be off 5mph at 100mph, or 2.5mph at 50mph or 1.25mph off at 25mph which is pretty damn close, and that's worse case scenario. I prefer doing it that way than using adapters. I've used adapters before then they break and you have no speedo at all.
 

HotRodPC

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I didn't do anything. By just removing the speedo adapter, I was within 3-4 MPH at 65 MPH. I also did the same swap to my '77 K5. Also 3.08's to 4.10's, but I was running 36" tall tires, up from 31's. On that truck I had to buy a new adapter. This was in 1991, so they were easy to find locally.

@HotRodPC I think it was in the 1-2" range.
Good to know. So if you went to a 14b SF, then going to a 14b Full Float should be no cutting necessary.
 

Tiny dime

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Thanks again for all of the replies guys! When I do the swap Ill take pics and post them. Also I will bring this thread back up if I need more help. Thanks!

Jonah
 

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