Engine, Trans, Rearend (REVISITED) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

JOJABOY · 02-10-2013, 05:04 PM

I have been reading and reading and still not sure what I want to do. I have a 69 C20 with 350sbc, Th400 and Dana 60 with 4.10 out of a 1972. I do not have a tach but the truck has to wind up pretty hard to hold 65 mph. I don't tow or haul heavy. I do drive on the freeway quite a bit. I would like to be able to cruise at 70 mph comfortably.

What should I do? Trans swap or Rearend?

Tx Firefighter · 02-10-2013, 05:21 PM

A 3.54 rearend swap would unwind the engine a whole bunch at highway speeds. I had a 72 C20 with 3.54 and it was real pleasant combo to drive on the road.

Personally, I steer toward a rear end swap since you don't tow much and you currently have a very quality transmission, the TH400.

SS Tim · 02-10-2013, 05:31 PM

A 3.54 rear end would be the easiest swap but.... What rear end and suspension do you have?

Ho52 (eaton/chevy 5200# with drop out carrier) or Dana 60 (5500# fixed carrier)?

Coil springs or leaf spring suspension?

JOJABOY · 02-10-2013, 05:51 PM

Leaf with Dana 60 from a 1972

**jocko** · 02-10-2013, 06:12 PM

since it is named "empty wallet" project in your signature - seems a self-answering question. Best bang for the buck is a 3.54 D60 from a big block truck in a yard somewhere. The big block is probably long gone from the yards, but the 3.54 rears should be plentiful (look at C20s in the yards).

I do believe there are width differences in the rear ends over the years? But you already have a 72 rear, so no real changes...

SS Tim · 02-10-2013, 06:44 PM

Then you have it easy, look for an axle from a big block leaf spring C20 and it is probably a 3.54 Dana 60.
Or if you wanted to a set of gears and probably a carrier would allow you to keep your axle...but that is going to cost a lot more.

JOJABOY · 02-10-2013, 08:02 PM

I thought about that. Would bee the cheapest and easiest thing. Just roll 4.10 rear end out and roll new one in and bolt up. Would 3.54 relax the RPM on th highway at 70 or will it still feel like it's gonna blow?

If the right answer is 4-speed trans than that is what I am going to do. I'm sorta at a less than $500 budget but I want to be able to drive my truck on the freeway comfortably.

Tx Firefighter · 02-10-2013, 08:08 PM

A 3.54 rearend will unwind your truck significantly at highway speeds. Since you're running a 3/4 ton truck, I'll assume you're running typical 16 inch tires (about 30-31 inches tall) which when combined with the 3.54 will make it a nice highway driver.

My 72 3/4 ton had a factory 402 big block, TH400 and 3.54 with 265/75/16 tires and it was a really pleasant driver on the road.

JOJABOY · 02-10-2013, 08:11 PM

I'm on 245/75-16 tires. Lots of grip and rip off the line but........I live in L.A. lol

**leddzepp** · 02-10-2013, 08:13 PM

Quote:

Originally Posted by Tx Firefighter

A 3.54 rearend will unwind your truck significantly at highway speeds. Since you're running a 3/4 ton truck, I'll assume you're running typical 16 inch tires (about 30-31 inches tall) which when combined with the 3.54 will make it a nice highway driver.

My 72 3/4 ton had a factory 402 big block, TH400 and 3.54 with 265/75/16 tires and it was a really pleasant driver on the road.

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Tx Firefighter · 02-10-2013, 08:18 PM

I just ran your numbers.

Your tires are 30.46 inches tall. Going from a 4.10 to 3.54 gear will lower your cruise RPM by 440 rpm at 70 miles per hour.

JOJABOY · 02-10-2013, 08:20 PM

(sounding ignorant) is that alot?

Tx Firefighter · 02-10-2013, 08:23 PM

It's a quite noticeable difference.

luvbowties · 02-10-2013, 08:31 PM

Quote:

Originally Posted by JOJABOY

I thought about that. Would bee the cheapest and easiest thing. Just roll 4.10 rear end out and roll new one in and bolt up. Would 3.54 relax the RPM on th highway at 70 or will it still feel like it's gonna blow?

If the right answer is 4-speed trans than that is what I am going to do. I'm sorta at a less than $500 budget but I want to be able to drive my truck on the freeway comfortably.

Hi, JOJABOY, altho' prolly not the cheapest, in our area, we can just about buy/install a used 700R4 overdrive for $500.

With its 70% o/d ratio, it should work nicely with a 4.10--would drop your final ratio to 2.87 when in overdrive.

For comparison, a 3.54 would drop rpm's at any given speed approx 14% (3.54/4.10 = .86.....1.00-.86 = .14!); the 700R4 would drop the rpm's at any given speed approx 30%.

HTH,
Sam

02-10-2013, 05:04 PM	#1
JOJABOY Registered User Join Date: Sep 2012 Location: Factory Posts: 681	Engine, Trans, Rearend (REVISITED) I have been reading and reading and still not sure what I want to do. I have a 69 C20 with 350sbc, Th400 and Dana 60 with 4.10 out of a 1972. I do not have a tach but the truck has to wind up pretty hard to hold 65 mph. I don't tow or haul heavy. I do drive on the freeway quite a bit. I would like to be able to cruise at 70 mph comfortably. What should I do? Trans swap or Rearend?

02-10-2013, 05:21 PM	#2
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Engine, Trans, Rearend (REVISITED) A 3.54 rearend swap would unwind the engine a whole bunch at highway speeds. I had a 72 C20 with 3.54 and it was real pleasant combo to drive on the road. Personally, I steer toward a rear end swap since you don't tow much and you currently have a very quality transmission, the TH400.

02-10-2013, 05:31 PM	#3
SS Tim Registered User Join Date: Aug 2010 Location: Edwards, CA Posts: 7,503	Re: Engine, Trans, Rearend (REVISITED) A 3.54 rear end would be the easiest swap but.... What rear end and suspension do you have? Ho52 (eaton/chevy 5200# with drop out carrier) or Dana 60 (5500# fixed carrier)? Coil springs or leaf spring suspension? __________________ Thanks, Tim * VIN/Model Decoders * Power Team Charts (engine/transmission/gear ratio) * Post Your Pickup SPID Blazer SPID Suburban/Panel SPID * RTFM ... Read The Factory Manuals... download 'em here Highlanders Do you have a 1972 Plaid Pickup? Plaid Blazer ** Plaid Suburban

02-10-2013, 05:51 PM	#4
JOJABOY Registered User Join Date: Sep 2012 Location: Factory Posts: 681	Re: Engine, Trans, Rearend (REVISITED) Leaf with Dana 60 from a 1972

02-10-2013, 06:12 PM	#5
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,975	Re: Engine, Trans, Rearend (REVISITED) since it is named "empty wallet" project in your signature - seems a self-answering question. Best bang for the buck is a 3.54 D60 from a big block truck in a yard somewhere. The big block is probably long gone from the yards, but the 3.54 rears should be plentiful (look at C20s in the yards). I do believe there are width differences in the rear ends over the years? But you already have a 72 rear, so no real changes...

02-10-2013, 06:44 PM	#6
SS Tim Registered User Join Date: Aug 2010 Location: Edwards, CA Posts: 7,503	Re: Engine, Trans, Rearend (REVISITED) Then you have it easy, look for an axle from a big block leaf spring C20 and it is probably a 3.54 Dana 60. Or if you wanted to a set of gears and probably a carrier would allow you to keep your axle...but that is going to cost a lot more. __________________ Thanks, Tim * VIN/Model Decoders * Power Team Charts (engine/transmission/gear ratio) * Post Your Pickup SPID Blazer SPID Suburban/Panel SPID * RTFM ... Read The Factory Manuals... download 'em here Highlanders Do you have a 1972 Plaid Pickup? Plaid Blazer ** Plaid Suburban

02-10-2013, 08:02 PM	#7
JOJABOY Registered User Join Date: Sep 2012 Location: Factory Posts: 681	Re: Engine, Trans, Rearend (REVISITED) I thought about that. Would bee the cheapest and easiest thing. Just roll 4.10 rear end out and roll new one in and bolt up. Would 3.54 relax the RPM on th highway at 70 or will it still feel like it's gonna blow? If the right answer is 4-speed trans than that is what I am going to do. I'm sorta at a less than $500 budget but I want to be able to drive my truck on the freeway comfortably.

02-10-2013, 08:08 PM	#8
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Engine, Trans, Rearend (REVISITED) A 3.54 rearend will unwind your truck significantly at highway speeds. Since you're running a 3/4 ton truck, I'll assume you're running typical 16 inch tires (about 30-31 inches tall) which when combined with the 3.54 will make it a nice highway driver. My 72 3/4 ton had a factory 402 big block, TH400 and 3.54 with 265/75/16 tires and it was a really pleasant driver on the road.

02-10-2013, 08:11 PM	#9
JOJABOY Registered User Join Date: Sep 2012 Location: Factory Posts: 681	Re: Engine, Trans, Rearend (REVISITED) I'm on 245/75-16 tires. Lots of grip and rip off the line but........I live in L.A. lol

02-10-2013, 08:18 PM	#11
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Engine, Trans, Rearend (REVISITED) I just ran your numbers. Your tires are 30.46 inches tall. Going from a 4.10 to 3.54 gear will lower your cruise RPM by 440 rpm at 70 miles per hour.

02-10-2013, 08:20 PM	#12
JOJABOY Registered User Join Date: Sep 2012 Location: Factory Posts: 681	Re: Engine, Trans, Rearend (REVISITED) (sounding ignorant) is that alot?

02-10-2013, 08:23 PM	#13
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Engine, Trans, Rearend (REVISITED) It's a quite noticeable difference.



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