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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: masonjenkins5 on February 23, 2016, 09:55:30 am

Title: Making a K20 a better highway cruiser
Post by: masonjenkins5 on February 23, 2016, 09:55:30 am

I have a '76 K20 with a 400 small block powering a TH350 auto that hooks into either 4.10s or 4.11s in the rear end. I'm running a 2.5" lift with 33" tires. I'm thinking about changing the rear end gear to something higher, maybe like a 3.73. I want my truck to be a better cruiser. I'm not looking to roast the tires at the green light, but I also want something I could still have the option to tow light loads with. Anybody have any ideas how to make my truck better on the highway?

Title: Re: Making a K20 a better highway cruiser
Post by: Blazin on February 24, 2016, 05:32:12 am

Personally I would look into swapping a quality built 700R4 transmission in instead of changing gears. Swapping two gear sets is costly. with an overdrive trans you would still have the low gear for get up, & go, plus 4th gear / over drive for highway cruising.
You sure its a TH350? Being a K20 is should be a TH400.

Title: Re: Making a K20 a better highway cruiser
Post by: roundhouse on February 24, 2016, 05:51:11 am

3.73 wont lower the RPM much
Plus you gotta change the front axle too
Although everyone has 3.73 and 3.08 so finding a Set of axles  won't be to hard
You could try fitting 35's   That would be cheaper than regearing both axles


We have the opposite problem
Running 35s with 3.73 axles.   Like to have 4.56


I have 4.11s in my bronco and I run 33s and sometimes 35s.  And that's about as good a combo as you can get


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Title: Re: Making a K20 a better highway cruiser
Post by: Irish_Alley on February 24, 2016, 07:13:10 am

if you swap trans like blaz said you will turn your 4.1 into something like 3.08 in OD. its the best of both worlds

Title: Re: Making a K20 a better highway cruiser
Post by: masonjenkins5 on February 26, 2016, 02:33:34 pm

Quote from: Blazin on February 24, 2016, 05:32:12 am

Personally I would look into swapping a quality built 700R4 transmission in instead of changing gears. Swapping two gear sets is costly. with an overdrive trans you would still have the low gear for get up, & go, plus 4th gear / over drive for highway cruising.
You sure its a TH350? Being a K20 is should be a TH400.

I'm fairly sure it's a TH350. The trans pan is just a square.

Title: Re: Making a K20 a better highway cruiser
Post by: Boonie on February 26, 2016, 08:08:02 pm

My 74 K25 has a turbo 350.  Surprised me the first time I rolled under it.  Expected a t400, especially considering how granddad used it. 

Title: Re: Making a K20 a better highway cruiser
Post by: Irish_Alley on February 26, 2016, 08:39:14 pm

Th350 is a square with one corner cut off

Title: Re: Making a K20 a better highway cruiser
Post by: FlatBlack77 on February 26, 2016, 08:52:26 pm

(http://www.nastyz28.com/pictures/transpan.gif)