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Old 09-27-2021, 08:39 PM   #1
cornerstone
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C50 5 speed?

I've recently transformed a 1968 C50 grain truck into a dump truck and plan on driving the behemoth on the highways fairly regularly. It still has all of its original equipment, a 327 with a 4 speed manual and a split rear differential. 58 mph is all she's got. (downhill with a tailwind) Every time I run through the gears I wish there was one more gear to grab. My thoughts are to swap out the 4 speed gearbox with a 5.

Has anyone done this? Am I asking for something I'll regret? Any help or advice appreciated!
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1972 C10, "Loyd", LWB to SWB, 5.3, L83/6L80e, 4:11 Tru Trac, Air Ride, VA, DD, 20" Coys, 4 wheel disc, A quick LS swap turned into a 6 year frame off resto-mod.
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Old 09-28-2021, 07:16 AM   #2
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Re: C50 5 speed?

If I am wrong, hopefully someone will correct me.
I don't think a 5 speed will do you any good for achieving a higher "mph" as the final drive is 1 to 1, just as it is on 4 speeds unless you find something like a Clark V0 overdrive 5 speed - which the final drive is 1 to .8, or another form of overdrive.
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Old 09-28-2021, 08:39 AM   #3
C10 - C90 Bill
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Re: C50 5 speed?

Right, the regular 5-Speed will still be 1 to 1. It will just give you 2 extra gears in-between and most likely a much lower Granny Gear.

Brian, when you say "one more gear to grab" which gear would you be referring to?

If you are desiring another last gear, you would need an Overdrive as lexadmn has mentioned.
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Old 09-28-2021, 09:44 AM   #4
cornerstone
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Re: C50 5 speed?

Yes, thanks guys, an overdrive of sorts. I remember I had a 6 speed manual once that had a .67 final ratio, if my memory serves me correct.
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Old 09-28-2021, 09:59 AM   #5
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Re: C50 5 speed?

Almost all of the older 5 speeds were 1:1 final. There were a few with OD and if I remember correctly they had weird shift patterns. Some achieved OD by swapping the gears on shaft cluster. So a 1,2,3,4,5 became a 1,2,OD,3,4 3rd was revered to become OD.

The reason I tell you this is the old OD transmissions weren’t very impressive, look for a modern 5 sp out of a more modern med duty truck, or used a nv4500. In a 2wd format they are easy to find, and if you get one from a 3500hd it will have a parking brake on the tail shaft.
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Old 09-28-2021, 10:19 AM   #6
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Re: C50 5 speed?

Either that or go with a Brownie with an OD. An Auxiliary Trans that you mount in back of your present trans. You will then have 2 Shifters, but all the gears you will need with OD to boot. Although they are not that easy to find and a little work to install.
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Old 09-28-2021, 11:00 AM   #7
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Re: C50 5 speed?

If an aux trans is an option, I use to have a truck with a ranger od unit, advanced adapter makes them. It performed well. It would be alit complicated tho with a ranger and a 2sp rear end. Thief proof
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73 k5 gm crate 350-265 / sm465 / np205 3.73 posi
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Old 09-28-2021, 11:42 AM   #8
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Re: C50 5 speed?

If an aux trans is an option, I use to have a truck with a ranger od unit, advanced adapter makes them. It performed well. It would be alit complicated tho with a ranger and a 2sp rear end. Thief proof
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73 k5 gm crate 350-265 / sm465 / np205 3.73 posi
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Old 09-28-2021, 08:14 PM   #9
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Re: C50 5 speed?

read up on the military 2.5ton 5speed . there o.d. on 5th but funky shift pattern . also they basicly bolt up to a gm bell housing that had a 5 speed factory . ( i have a whole extra bell setup from a med duty gas 5 speed )

otherwise browny box / aux box and another lever on the floor to shift .

keep in mind the brakes and tires and steering on these old girls was NOT ment for 70+ mph use so watch what mods you do and be prepared for the next round of upgrades .
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Old 10-02-2021, 11:19 AM   #10
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Re: C50 5 speed?

Quote:
Originally Posted by lexadmn View Post
you find something like a Clark V0 overdrive 5 speed - which the final drive is 1 to .8, or another form of overdrive.
I agree, the Clark 280 VO was the optional overdrive back in the day with the .8 overdrive, which IMO, would be perfect. Modern overdrives, like the NV, are more common, but are around .7 overdrive ( larger step down in rpm ). Like ky-donzi mentioned, the 1 ton 3500HD version has the much needed parking brake drum. Make sure the NV4500 is a good unit first, many have noisy bearings that need a professional rebuild.
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Old 10-02-2021, 12:02 PM   #11
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Re: C50 5 speed?

Curious if the NV4500 will bolt right in. If not, what mods would be needed to make a complete swap?
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Old 10-02-2021, 09:56 PM   #12
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Re: C50 5 speed?

Here is a good write up on the installation in a 1 ton http://67-72chevytrucks.com/vboard/s...t=nv4500+1+ton
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Old 10-02-2021, 10:51 PM   #13
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Re: C50 5 speed?

Is there an option to incorporate a two speed rear into a C30?
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Old 10-03-2021, 12:50 PM   #14
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Re: C50 5 speed?

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Is there an option to incorporate a two speed rear into a C30?
Not without installing a 2-Ton Rear and even then it would still be 1 to 1.

But if you are talking aftermarket, that would be a great idea. An Electric 2-Speed Rear with the high gear being high enough to be like an Overdrive.
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