th400 questions

[twojoints444]

I am in the middle of a transmission crisis. How high of rpm's will my 350 be turning @ 60mph on the freeway with a th400 np205 4.10 gears and 37's? my truck used to have a 700r4 until i grenaded it. I am kinda in the middle of getting the parts together to swap my truck to a sm465 but i am runnig out of money and am thinking about aborting and going with a th400 instead? is my fuel mileage gunna goto S#IT with the th400 np205 4.10s and 37's or will it all work out?? thanks for any info guys!!!

Adam

 

[warwgn]

3rd gear is 1:1 so depends on what you had before,I think .64:1? Anyway I hope your good cause thats what I am gonna be runnin too!

 

[76zimmer]

I think the 700/4L60's are .70 OD

I would think with 37's and 4.10...a 1:1 final would be great at 60mph.


but you realize you will be changing a few other parts too right?

 

[Adventurous 4x4]

I changed 2 of my K5's from a 700r4 to a th400. 1 of them went to a 400/205 the current one is a 400/241. You will lose some bottom end due to the 1st gear ratio's in the trans. I didn't lose alot of gas milage but I never checked exactly how much. I was running 4.56's in the 1st one and running 4.10's and 37's in the current one. I have been running the current one since 2002. After putting the 400/205 in the first one I vowed never to do something like that again. The low range flat out sucked for crawling. In the mud and faster stuff it was fine though.

 

[twojoints444]

Adventurous4x4:
so u dont recomend the 400/205 for crawling but dailey driving is ok? I do alot of hunting in the truck and a lil friday night fun so CRAWLING isnt a big issue.

 

[Adventurous 4x4]

Nope. Even with my 241 I want more low range so that is why I ordered a Atlas 4spd. The 205 is fine for general use and even better when doing a Doubler but if rocks are your thing then, no I would not recommend a 400/205.

 

[blazin' j]

so back to the 1st question, what rpms should he be turnin w/his set up @ 60mph???

 

[whyth20rydn]

according to 4lo.com calc your gonna be turning 2234rpm@60mph

 

[76zimmer]

according to 4lo.com calc your gonna be turning 2234rpm@60mph

perfect!
You should be getting into the best part of the torque band right about there.

 

[Adventurous 4x4]

Before you figure out RPM's measure the actual tire hight.

 

[Silver84k5]

http://www.grimmjeeper.com/gears.html

 

[scrappyk5]

according to 4lo.com calc your gonna be turning 2234rpm@60mph

hhmmm, I wonder if my tach is off. I am running 37" hummers with 3:73 gears and I am at about 2250 rpms @ 60mph.

 

[whyth20rydn]

Might be, though Wayne/Adventurous 4x4 has a good point. Measure your tires, even if you start at 37" they do wear.

Maybe clean contact at distributor?

 

[4X4HIGH]

To answer your question you would be turning 2234 RPM @ 60 MPH based on a true tire diameter of 37" (tires rarely measure the stated size, usually smaller by anywhere from 1/2" - 1 1/4") and also not accounting for convertor slippage.