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#1 |
Registered User
![]() Join Date: Sep 2012
Location: Factory
Posts: 681
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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? |
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#2 |
Watch out for your cornhole !
![]() Join Date: Jun 2003
Location: Azle, Texas
Posts: 14,162
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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. |
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#3 |
Registered User
Join Date: Aug 2010
Location: Edwards, CA
Posts: 7,503
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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 |
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#4 |
Registered User
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Location: Factory
Posts: 681
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Re: Engine, Trans, Rearend (REVISITED)
Leaf with Dana 60 from a 1972
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#5 |
Senior Member
![]() Join Date: Oct 2009
Location: Godley, TX
Posts: 17,962
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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... |
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#6 |
Registered User
Join Date: Aug 2010
Location: Edwards, CA
Posts: 7,503
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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 |
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#7 |
Registered User
![]() Join Date: Sep 2012
Location: Factory
Posts: 681
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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. |
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#8 |
Watch out for your cornhole !
![]() Join Date: Jun 2003
Location: Azle, Texas
Posts: 14,162
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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. ![]() |
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#9 |
Registered User
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Location: Factory
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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
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#10 | |
Moderator
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Location: Southern Cal
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Re: Engine, Trans, Rearend (REVISITED)
Quote:
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1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man |
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#11 |
Watch out for your cornhole !
![]() Join Date: Jun 2003
Location: Azle, Texas
Posts: 14,162
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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. |
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#12 |
Registered User
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Location: Factory
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Re: Engine, Trans, Rearend (REVISITED)
(sounding ignorant) is that alot?
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#13 |
Watch out for your cornhole !
![]() Join Date: Jun 2003
Location: Azle, Texas
Posts: 14,162
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Re: Engine, Trans, Rearend (REVISITED)
It's a quite noticeable difference.
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#14 | |
Registered User
Join Date: Feb 2009
Location: southeasternfoothillsofusa
Posts: 1,557
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![]() Quote:
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 |
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