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Old 08-03-2018, 10:17 PM   #1
Farm_Truck
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Two speed rear end in a P/U?!

Alrighty folks. new to the website and new to the trucks older than '72. (Save for a '55 3100 but that's besides the point.) Anyway. Looking at picking up a '63 C20 with a 4 speed and the 2(71?) small block. It's cheap, and halfway buried in the ground, but mark my words I'm gonna try and get it roadworthy. I know it's probably the least of my worries, but I was wondering if it was possible to stick a two speed rear end from a '58 dump truck under the pickup. It's only got a 4 speed, but it would be the only one around. If it is possible, how hard is it to hook up? Does it need vacuum or positive air pressure? Do I need to change the driveshaft or frame? And, is it possible to change the hubs on them, or would I have to stick with the huge effin tires and rims? Or, would there be a better option for it? Thanks for the help- in advance of course.
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Old 08-03-2018, 11:48 PM   #2
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Re: Two speed rear end in a P/U?!

The medium duty truck differentials are much larger physically than a Eaton HO52/72. Plus the high gear in those 2 speed differentials are a much lower gear than what is in the HO52/72. They do need vacuum to shift and yes you will be stuck with using the original hubs and 20" wheels. I see really no point is making this swap. If you want a higher gear in the C20, either change the trans to a OD trans, or change the differential to a 14 bolt or Dana 60 with higher gears.
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Old 08-04-2018, 09:58 PM   #3
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Re: Two speed rear end in a P/U?!

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Old 08-05-2018, 01:32 AM   #4
Farm_Truck
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Re: Two speed rear end in a P/U?!

Quote:
Originally Posted by Captainfab View Post
The medium duty truck differentials are much larger physically than a Eaton HO52/72. Plus the high gear in those 2 speed differentials are a much lower gear than what is in the HO52/72. They do need vacuum to shift and yes you will be stuck with using the original hubs and 20" wheels. I see really no point is making this swap. If you want a higher gear in the C20, either change the trans to a OD trans, or change the differential to a 14 bolt or Dana 60 with higher gears.
Got any clue what would be the best OD tranny to throw in behind it? The engine is stuck, so I might just tear it out and drop the cheapest SBC I can find into it.
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Old 08-05-2018, 10:25 AM   #5
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Re: Two speed rear end in a P/U?!

The 700R4 is popular, the latest version that still has the cable is probably the best. You would also need to do a cross member modification. Finding a 350 from an old P/U (year? ) with tranny attached would be a good score.
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Old 08-05-2018, 11:23 PM   #6
Captainfab
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Re: Two speed rear end in a P/U?!

If you want to stay with a manual trans and use your C20 as a truck, a NV4500 would be the best choice IMO. If you want to go with an auto trans a 700R4 will work in a C20 if it is built right. If this is mainly a cruiser, then a NV3500 or a T5 will work for a manual trans. And again if a auto trans is desired a 700R4. The 4L80E is much heavier duty trans, basically a TH400 with OD, but they can be $$$ to retrofit. From a budget perspective, changing the differential will be much cheaper.

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Originally Posted by Farm_Truck View Post
Got any clue what would be the best OD tranny to throw in behind it? The engine is stuck, so I might just tear it out and drop the cheapest SBC I can find into it.
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Old 08-07-2018, 09:15 PM   #7
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Re: Two speed rear end in a P/U?!

Quote:
Originally Posted by vince1 View Post
The 700R4 is popular, the latest version that still has the cable is probably the best. You would also need to do a cross member modification. Finding a 350 from an old P/U (year? ) with tranny attached would be a good score.
Not really looking for an auto.

Quote:
If you want to stay with a manual trans and use your C20 as a truck, a NV4500 would be the best choice IMO. If you want to go with an auto trans a 700R4 will work in a C20 if it is built right. If this is mainly a cruiser, then a NV3500 or a T5 will work for a manual trans. And again if a auto trans is desired a 700R4. The 4L80E is much heavier duty trans, basically a TH400 with OD, but they can be $$$ to retrofit. From a budget perspective, changing the differential will be much cheaper.
As much of a sin as it is, I'd devote it to more of a fixer/beater truck. The kind that you don't worry about dings and scratches, yet at the same time put rocker panels in. Kind of a conflict of interest, but whatever.
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Old 08-08-2018, 12:59 AM   #8
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Re: Two speed rear end in a P/U?!

Put a road ranger gear splitter between the engine and trans.
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Old 08-08-2018, 09:50 AM   #9
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Re: Two speed rear end in a P/U?!

Or you could go with a Gear Vendors Overdrive - http://www.gearvendors.com/cg2wd3s.html
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