Tranny or rear end ?


The "Hot Rod" version of the K and KB truck

Yard Art
Yard Art

Posts: 70

Joined: Fri Dec 29, 2017 8:55 pm

Location: Roseville, Calif.

Post Thu Dec 19, 2019 11:08 am

Tranny or rear end ?

I have a 48 KB1, Sitting on a Dodge Dakota Chassis W/ a Chevy 5.7 with a TH400. At 65 miles per Hour tach reads about 3000 RPM, To much for me but it will get down the road.

This is what I'm thinking, Change tranny to a overdrive tranny or Have the rear end ratio change to a higher gear, Leaning towards rear end gears. I'm more of a cruiser than hot rodder. :t3901; Either way its going to cost.

Lefty 1948

Golden Jubilee
Golden Jubilee

Posts: 5171

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Thu Dec 19, 2019 11:27 am

Re: Tranny or rear end ?

I have re-ratioed vehicles. I would strongly recommend planning it out on paper 1st. Plot the ratio and transmission ratios you have now, at idle, torque peak, desired cruising RPM and at hp peak. Next play around with available transmission and rear axle ratio's to see where you'll end up. Don't forget to look at low end starting ratio.
It takes a lot of math and plotting but when you are done, and made your choice, you'll have no surprises when the truck is on the road.
Using an auto trans, makes low end starting less critical, but still important. Some "fudging" can be done with convertor stall speeds.
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Golden Jubilee
Golden Jubilee

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Location: Bothell, Washington

Post Thu Dec 19, 2019 3:24 pm

Re: Tranny or rear end ?

put a 700r4 in it, goes right in where 400 is, need to move rear tranny mount, and redo driveline,
Gentle Men! you can't fight in here! This is the war room!

Golden Jubilee
Golden Jubilee

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Joined: Thu Dec 27, 2012 12:45 pm

Location: Canada's left Coast

Post Fri Dec 20, 2019 3:52 pm

Re: Tranny or rear end ?

Do yourself a flavour. Google tranny and rear end. Then click on images.
I would rather have tools I do not need than to need tools I do not have
Thinking risks being controversial and possibly being offensive

Golden Jubilee
Golden Jubilee

Posts: 5171

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Fri Dec 20, 2019 6:28 pm

Re: Tranny or rear end ?

Nope, not me, I know what he was talking about.

Golden Jubilee
Golden Jubilee

Posts: 8938

Joined: Thu Dec 27, 2012 12:45 pm

Location: Canada's left Coast

Post Fri Dec 20, 2019 7:16 pm

Re: Tranny or rear end ?

I never doubted you, CB89.
Language changes. Nipples have become zerks. Packages have become cellphone contracts or parcels from the post office. The package has been sent to where the sun never shines. And so it goes.
I would rather have tools I do not need than to need tools I do not have
Thinking risks being controversial and possibly being offensive
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Golden Jubilee
Golden Jubilee

Posts: 630

Joined: Fri Nov 30, 2012 10:04 pm

Post Mon Oct 05, 2020 4:20 pm

Re: Tranny or rear end ?

I would go with the 700R4, just make sure you do the TV cable correctly so the trans pressure rises right off of idle so you don't burn the trans up. I have installed 5 of these for friends and they love it. With the lock-up converter your running temps will go down. 700R4 has a deeper 1st gear for good take off and a .75 overdrive for fuel economy and lower rpm. Mine was running at 3100 with my 3.54 gears at 65, now it runs at 2300 at 65.
KB owner since 1972 and still loving it.
Retired Lineman, mechanic, fabricator, retired motorcycle racer.
South Amherst, Ohio

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