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Old 06-24-2017, 01:31 AM   #1
BigRandy
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Look for a differential or a set of gears?

My project is a running 74 C-10 Cheyenne, 454 with a TH400 and 3.73 gears. I'm guessing it 60 is a comfortable speed for the motor as it sounds like it's turning around 3 grand at that speed. The 3.73's are quick but the truck runs out of fun once I hit 3rd gear so I'm thinking about getting rid of them.

I've never done any work on a differential and would like some opinions.

Should I try my hand at installing some 3.42's, 3.08's, or find a complete unit from a junk yard and go with that? What's a fair price for a salvage yard rearend?

Thanks!
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Old 06-24-2017, 06:42 AM   #2
b454rat
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Re: Look for a differential or a set of gears?

What size tires? I've had many 454s in different variations and vehicles. In less you have really small tires your not running 3k with 3.73s. I had a Malibu with 4.10s and 27" tires and was barely 3k at 60mph. Last one had 3.42s and still pulled good and didn't scream too bad on the highway. Verify your tach (if you have one) and double check speed.....
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Old 06-24-2017, 01:08 PM   #3
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Re: Look for a differential or a set of gears?

If you're not doing any towing I would go with the 3.08s. If you're not comfortable swapping them out, have it done by a competent shop. The big block will pull the truck without any problems. In my 3/4 ton that I haul with, I've got 3.73s, SM465 with a Ranger Overdrive and 31'' 8 ply tires. Freeway at 60 mph I'm about 22-2300rpm
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Old 06-24-2017, 05:07 PM   #4
B. W.
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Re: Look for a differential or a set of gears?

My DD is a 79 k25 that's still full time 4wd. I'm running 4.10's behind a T400 & I run the speed limit (70). Yeah, I'm wringing it & I'll admit the engine likes 65 better. The fuel gauge doesn't like any speed!

Kwmech, not trying to hijack the thread, the 70 I'm building has a ranger with 3.73s. How do you like it?
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Old 06-24-2017, 10:50 PM   #5
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Re: Look for a differential or a set of gears?

60 mph is holding up traffic. I pull full size cars on car trailers easily with my little K10 with 350 and 308's. It still revs high enough for me at 75 mph. If your hauling stuff bigger than a car trailer then you may or may not want the 308's. It is a 454 after all so it should have some torque.
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Old 06-25-2017, 01:37 AM   #6
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Re: Look for a differential or a set of gears?

Thanks for the replies. I have no plans to tow very much or very often. I like the zip when I hit the gas but I don't have the money to get both.

I don't have a tach and I think the speedo is off. At 50 it feels like 60-65 and the motor is starting to wind up. The current tires are 275/75/15's The tires that will be going on it are going to be a bit shorter. 265/60/15's and, if I can find them, some old style 8.5" or 10" slotted aluminum mags.

On another note I had some success with the truck today so I'm feeling better about buying it. It's been randomly firing on 5-7 cylinders since I got it two weeks ago. The plug wires looked like what you would find in a dollar store if dollar stores sold wires. I change the plugs (R44T), got a decent set of DENSO wires and swapped the points distributor for a GM HEI that I got from a scrap yard. Had .050 play in the shaft so I shimmed it to about .020 and it fired up on the first try, and after setting the timing it runs exceptionally smooth. OP is 32PSI at warm idle and 45+ at highway speed. Overall not a bad way to spend a rainy day in the garage.

Next on the list is the starter. It has a new on on it but something's not right. There's a harsh engagement with the ring gear when starting. The PO used 6 with the new starter and I've never seen that many used before. I found that removing them made it better. I ended up removing all shims and while it did improve slightly it still engages way too rough. The teeth are't sheered off the flex plate but they do have marks where the starter drive is biting in hard.

I bought this new in 77 and my goal is to eventually have it again in the 74 when I'm done. It will take years.


Last edited by BigRandy; 06-25-2017 at 01:58 AM. Reason: Added a pic
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Old 06-26-2017, 12:04 AM   #7
Ironangel
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Re: Look for a differential or a set of gears?

Nice truck! A 3:08 gear behind a 454 is plenty, especially on 15" wheels. These trucks were the last of the "cheap gasoline" dinosaurs, if you were getting 10+ miles to the gallon you were good, especially if you had a big block. The 400 Turbo will drink gas on the highway but it's reliability is second to none. I'd install a 3:08 gear set and call it good.
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