6.2 manual to auto swap

[STOCKISH]

I am changing the sm 465 in my crew cab to an automatic. It has 35 inch tires and 4.10 gears. Will i be okay with a turbo 400 or do I need an overdrive to be able to run happily at 70 miles an hour on the interstate? I don't want to over rev the 6.2 diesel to the point where I am hurting it or killing my gas mileage. Anyone who has experience with these please help me out. Does anyone know what is the optimal
cruising rpm for the 6.2 diesel? Thank you guys for all your help ahead of time.
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[GM72K10]

This gets talked about on the steelsoldiers site all the time in the CUCV section. Take a look there and do some reading. I have both manual and auto with 6.2s, both stock tires, both 4:56s, they aren't speedsters but mine aren't meant for long rides of 70 mph.

[GmtGmt]

Nv4500

[ponytail]

my truck has the 3 speed automatic. i also have a well built 355. 33" tires. anything over 60-70 is just too much as a cruising speed. i am thinking about swapping for an overdrive myself. it is just nice to be able to get on the interstate if i choose to and roll out!

[STOCKISH]

Originally Posted by GmtGmt

Nv4500

Switching to an automatic because I tore a ligament/tendons in my ankle, thanks though.

[rcbildr]

My diesel burb is set up with 4.10 gears, 35" tires, and a TH-400. I had an SM-465 in it and converted to the auto so my girfriend could drive it...she has arthritis pretty bad.

Anyways, before I rebuilt the TH-400, I didn't notice any change in mileage and 70mph is about as far as I would push it...but I drive like an old man too. Since I had the tranny rebuilt, my mileaqge went up a bit. I know 65mph is a nice speed for the diesel and I think 70 wouldn't be too bad either, but it's been a while since I've driven it at 70....all the highways near me top out at 60. I went with the TH-400 when I did the conversion because my Burb is also my tow rig.

[STOCKISH]

Thanks buddy.

[lindstromjd]

Might as well point out the obvious here... you're going to be running the EXACT same RPM's with the TH400 as you are with the SM465. It's the same final drive of 1:1 on both transmissions. Are you happy with your current RPM's at 70 mph? If not, then go for the 700r4. I have a 3.40 rear end, and had a TH350 behind my 6.2 and HATED listening to the RPM's at anything over 70 mph. I went ahead and got a 700r4. And my fuel mileage was around 17 mpg's at 70, and 14 at 75 with the TH350. Haven't had it on the interstate yet with the 700r4.

[Jonboy]

I would go for the 700R4 because it has a lower 1st and 2nd gear than a TH400 also. That's a heavy truck to get moving.

[thirdstreettito]

With a TH400, 4.10's and 35's you would be turning 2952 of the 3600 total rpm's the 6.2 has. That's at 75mph. Same with the current SM465.

I would recommend a 700R4 or even better a 4L80E. The 700R4 has a 8600GVWR. The 4L80E has a 16000GVWR. Pick the latter.

At 75mph the 700R4 would be turning 2066rpm. The 4L80E would be turning 2214 rpm. Big difference over the TH400 and SM465.

My suburban at 75mph turns 2122rpm. She isn't screaming. I've hit 110mph and she still doesn't scream.

They'll run wide-open for years. But never the less, I would get the 4L80E if I were you.

This guy has good stuff.

http://www.transmissioncenter.net/4l80e.htm

[STOCKISH]

Originally Posted by lindstromjd

Might as well point out the obvious here... you're going to be running the EXACT same RPM's with the TH400 as you are with the SM465. It's the same final drive of 1:1 on both transmissions. Are you happy with your current RPM's at 70 mph? If not, then go for the 700r4. I have a 3.40 rear end, and had a TH350 behind my 6.2 and HATED listening to the RPM's at anything over 70 mph. I went ahead and got a 700r4. And my fuel mileage was around 17 mpg's at 70, and 14 at 75 with the TH350. Haven't had it on the interstate yet with the 700r4.

I know thw RPM will be the same with the th400 as the sm465. Thats why I am asking about the overdrive. I have never owned a 6.2 diesel before and was only curious about where they are happy on the interstate. I do not want to run a 700r4 in a 1 ton crew cab truck with 35-38 inch tires, it just isnt going to last. I have had a few "built" 700s in larger trucks and the sunshell (even the Beast sunshell) just doesnt hold up. I am also going to swap in a Cummins once the 6.2 craps and the 700 sure wont hold that. I was looking in to the 4l80e controller from the diesel truck or something like that. I would love to keep my np205 t-case also so I would love to find the 91 4l80/np205 combo but theyre hard to find (and stupid expensive). I will probably swap in the 400 and keep it off the highway for now I guess???

[thirdstreettito]

You can get an adapter for the 4L80E to t-case. $500-700. Yikes.

Here's a trans and some other parts. http://raleigh.craigslist.org/pts/2337914791.html

http://raleigh.craigslist.org/pts/2346699464.html

http://www.summitracing.com/parts/ADD-50-0410

[STOCKISH]

I'm like you on the adapters, Yikes! I am pondering a 2wd 4l80e(cheaper) and a divorced transfer case. I am just trying not to have to swallow $2000 for a auto trans swap!

[thirdstreettito]

It'll save you that in fuel over the next few years the way the prices are going.

[lindstromjd]

Originally Posted by 1972SuperCheyenne

I know thw RPM will be the same with the th400 as the sm465. Thats why I am asking about the overdrive. I have never owned a 6.2 diesel before and was only curious about where they are happy on the interstate. I do not want to run a 700r4 in a 1 ton crew cab truck with 35-38 inch tires, it just isnt going to last. I have had a few "built" 700s in larger trucks and the sunshell (even the Beast sunshell) just doesnt hold up. I am also going to swap in a Cummins once the 6.2 craps and the 700 sure wont hold that. I was looking in to the 4l80e controller from the diesel truck or something like that. I would love to keep my np205 t-case also so I would love to find the 91 4l80/np205 combo but theyre hard to find (and stupid expensive). I will probably swap in the 400 and keep it off the highway for now I guess???

Fair enough. I found that my 6.2 was happiest at 65 mph when I was on the interstate with the TH350. I was getting 20 mpg's at that speed. It didn't have any problems at all going 75-80 mph, but to me the speed vs fuel cost just wasn't worth it.

[STOCKISH]

Thanks, do you know what RPMs you were turning? I know I can use a RPM calculator but I dont know your gear ratio or tire height.

[lindstromjd]

Originally Posted by 1972SuperCheyenne

Thanks, do you know what RPMs you were turning? I know I can use a RPM calculator but I dont know your gear ratio or tire height.

My rear end ratio is a 3.40 and tire size is 275/60r15. Don't know exactly what RPM's I was at, because my tach isn't hooked up right now.