Good posi diff gearing? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

KilroyWasHere · 06-18-2016, 08:16 PM

So after my car shows today, I was inspired to really start thinking about what I'd like done with the truck. The one thing that I cannot find good advice on is a good gear ratio for a posi diff. I still want the truck to have some towing power, but I'd love to still be able to moonlight as a proper street machine. What would be best?
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**The Rocknrod** · 06-18-2016, 08:29 PM

that depends on much, tire size, transmission gearing and how many RPM's your looking for at highway speed. Add you info here and get an idea of what you want: http://www.dennysdriveshaft.com/pote...alculator.html
There are quite a few sites like that online.

KilroyWasHere · 06-18-2016, 09:10 PM

Quote:

Originally Posted by The Rocknrod

that depends on much, tire size, transmission gearing and how many RPM's your looking for at highway speed. Add you info here and get an idea of what you want: http://www.dennysdriveshaft.com/pote...alculator.html
There are quite a few sites like that online.

That's a very helpful website, thanks. Looks like maybe a 3.83:1 would be best for what I need
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racecougar · 06-18-2016, 09:39 PM

You'll have a far easier time finding a 3.73:1 ratio.

KilroyWasHere · 06-18-2016, 10:49 PM

Quote:

Originally Posted by racecougar

You'll have a far easier time finding a 3.73:1 ratio.

Ah should've known lol. Any good places to buy new ones, or perhaps a good donor vehicle to try and find one?
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**Captainfab** · 06-19-2016, 12:17 AM

I would suggest taking a look to see what gears you have now. Your truck could very likely already have 3.73's. That was the most common gear ratio.

Quote:

Originally Posted by KilroyWasHere

Ah should've known lol. Any good places to buy new ones, or perhaps a good donor vehicle to try and find one?
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KilroyWasHere · 06-19-2016, 12:08 PM

Quote:

Originally Posted by Captainfab

I would suggest taking a look to see what gears you have now. Your truck could very likely already have 3.73's. That was the most common gear ratio.

I'll have to look again, but I think I'm running 4.10s. Whenever I peel rubber I only get one tire fires. Plus it's a C20, so I think it's a heavier duty diff
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**Classic v6 GMC's** · 06-19-2016, 01:58 PM

Quote:

Originally Posted by KilroyWasHere

I'll have to look again, but I think I'm running 4.10s. Whenever I peel rubber I only get one tire fires. Plus it's a C20, so I think it's a heavier duty diff
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With a c20 you will have the eaton rear axle and the only gears are 4.10 and 4.57.

KilroyWasHere · 06-19-2016, 02:12 PM

Quote:

Originally Posted by Classic v6 GMC's

With a c20 you will have the eaton rear axle and the only gears are 4.10 and 4.57.

In that case I'll probably have to replace the whole rear axle then. Well my plans won't go into effect for some time, but it's nice to know where to start
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**Classic v6 GMC's** · 06-19-2016, 02:16 PM

Quote:

Originally Posted by KilroyWasHere

In that case I'll probably have to replace the whole rear axle then. Well my plans won't go into effect for some time, but it's nice to know where to start
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Yeah check out this thread
http://67-72chevytrucks.com/vboard/s...d.php?t=624445

**Captainfab** · 06-20-2016, 12:07 AM

Being a C20 makes a BIG difference. There are no gears or new posi units available for the Eaton HO52/72. In fact bearings and seals may be difficult to find and $$ when you do. Your best option is to change the entire differential as shown in the link as Classic v6 GMC posted.

Quote:

Originally Posted by KilroyWasHere

I'll have to look again, but I think I'm running 4.10s. Whenever I peel rubber I only get one tire fires. Plus it's a C20, so I think it's a heavier duty diff
Posted via Mobile Device

06-18-2016, 08:16 PM	#1
KilroyWasHere Registered User Join Date: May 2016 Location: Leavenworth, Kansas Posts: 18	Good posi diff gearing? So after my car shows today, I was inspired to really start thinking about what I'd like done with the truck. The one thing that I cannot find good advice on is a good gear ratio for a posi diff. I still want the truck to have some towing power, but I'd love to still be able to moonlight as a proper street machine. What would be best? Posted via Mobile Device

06-18-2016, 08:29 PM	#2
The Rocknrod Moderator Join Date: Aug 2011 Location: China Spring, TX Posts: 7,280	Re: Good posi diff gearing? that depends on much, tire size, transmission gearing and how many RPM's your looking for at highway speed. Add you info here and get an idea of what you want: http://www.dennysdriveshaft.com/pote...alculator.html There are quite a few sites like that online. __________________ Master Chief, US Navy, Retired 1964 C10 Step-side Short Bed - In Progress 2009 2500HD Duramax LTZ 1948 GMC Panel 1956 Big Window Stepside 1953 5 Window Chevy Stepside 1932 Coupe New Seat Foam for Bench Seats?

06-18-2016, 09:39 PM	#4
racecougar Registered User Join Date: Jan 2013 Location: Imperial, MO Posts: 1,003	Re: Good posi diff gearing? You'll have a far easier time finding a 3.73:1 ratio. __________________ Rod @ AzzKicker Cars 1965 C10 SWB - Build Thread



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