D400 - Should I convert from Manual to Auto?

Hi, folks. I have a clean 1970 D400 from Oklahoma. Currently has a /6 NP435. I have a nice 440...all done, from a different project.

I've already ditched the 6.6:1 rear axle in favor of a Dana 70HD. Retained the nice 20" wheels.

Since I need to use this truck for hauling and moving stuff around (highway driving long distances), I thought the 440 would be a better way to go.

Finding all the pieces to retain an NP435 (hydraulic clutch) behind the 440 is pretty close to building a decent 727.

Any thoughts, opinions on this move?

A D400 is a pretty big truck that can carry a big load. If you intend to load it up, it might get pretty rough on the 727. Most modern big trucks with an auto trans has an Allison, and they are a lot more heavy duty then a 727.
The NP435 has a low 1st gear to get things moving from a dead stop.

My concern with the 727 would be about the life expectancy. Be sure its build for pulling a heavy truck with a heavy load, unless you don't intend to load the truck very heavily. Gene

lets see that beastie

I think the 727 would work if built properly and big trans cooler and right rear ratio. I think the NP435 would work better however. The NP435 is rated for low 20k lb gross weight from memory... a good medium duty truck transmission. The low 1'st is great for slow running on rough ground or to get her rolling when heavy.

i always heard an automatic can start a bigger load on a hill than a manual-----from what you guys are saying maybe they meant starting downhill---and dont forget the 727 stood up to the cummins and the OD variants after that are based on the venerable 727.....

i have a 727 out of a motor home with a 440,it needs a rebuild ,ive always been told they were the heavy duty units?,its a short tail shaft unit

Check prices on a wrecker to tow you home when the 727 craps out...and it will.

jmho.



Wouldn't a 12 valve & NV4500 be a better fit?

435 over 727 in that app. I know where a BB hydrabell is if your looking.

boy i cant believe all the nervous nellies here talking crap about automatics------makes you wonder how stupid the guys are that are racing with automatics in all classes of truck racing---strip--off road--pulling contests-----a friend, butch brooks, builds performance automatics and has about 30 teams that run his trannys-----a few years ago in the world championship rock crawling event in moab utah his trannys placed 1-2-3-5 with 4th place going to a nv4500-----the only real advantage of the manual is holding the unit back going down a colorado mountain pass----yep i do have an nv4500 in my cummins truck and a getrag in my 71 govt truck but still not scared of an automatic in a truck application.....

That 440 won't put out any more power in your D400 than it will in a 10 seccond race car. The motorhome trans usually have good internals if you can find one. ALso use a big trans cooler.

I have to agree, if a 4WD 2000 horsepower diesel truck can use a torqueflight to run high 7's there is no reason to be worried.

A 727 can take the abuse... if you want an auto go for it

I would keep the stick. I hate towing with automatics. Unwanted downshifts, no downshifts when you want them and always worrying about when it's going to puke. No thanks.

I have no doubt that a 727 can be built to do the job, but at what cost?

There is a pretty signigifent different difference between a high power motor abusing a trans for 7-12 seconds, or rock crawling at very slow speeds and a 6 mile 6% uphill grade pulling 20,000 lbs.
Ask Rhinodart how those 727s and their derivatives hold up dragging heavy loads across the country. Gene

Rhino dart is not a good example. If he had an anvil for a trans he could tear it up.

Here's my girl. By now, the /6 is running well... and I need to start moving stuff so... It's gonna be a 6 cylinder truck for a little bit until I can get the trans question(s) sorted out

love it! Hard to imagine a truck that size having a Slant.

It is all in the gearing and torque multiplication..
What do you think all truck companies engineered back in the 30's,40's and early 50'S before offering OHV V8's??
The slant six is more efficient than its flathead it replaced and has a stronger bottom end.

It may not have much horsepower but makes enough torque to do the job.
People say that today about some diesel engines.

The 440 upgrade is a great idea with the right cam to suit the heavy truck application.
727's survived underneath giant Travco RV's yet I would stick with the stick if it were my truck.
Cheers

Sell that 440 and put a Cummins in that beast!

Much better idea!

I have to agree a Cummins 12V would be the way to go, you'd have to gear it up though. They're about done at 2000RPM.

@handygun ...I sent you a PM. I am looking for a hydrobell and (of course) B/RB engine mounts

I know a 48RE is a 727 derivative but throwing all the electronic garbage and weak overdrive is what killed mine! Don't forget I lunched 5 NV4500's and 2 G56 Mercedes transmissions too! I am still contemplating what to put in my D700 as it has a 361 big block and I believe a 435 now.

I like that vintage Dodge truck... both the 400 and 700 are nice.

Does the 700 have a 2 speed rear?

Turbocharge the slant!

I believe it is a 5-speed, I haven't had it on the road yet and it doesn't have the extra switch for the 2-speed rear...

An NV4500 with hydraulic clutch would be interesting, too. I see where the Lakewood bell can be used behind B/RB but I can't seem to figure out if a certain McLeod hydraulic throw out bearing can be used to make it all work together

OK, so...final note on this topic from me: cutting out the bellhousing crossmember and somehow trying to fashion a replacement which leaves room for the Lakewood bell OR a 727 is not on my list of things to do.

I'm gonna keep searching for the one-year-only bellhousing which permits me to run a six-bolt flywheel with the hydraulic clutch bellhousing. I know Bud Thorp has some...

Thanks for the thoughts and suggestions. I love Moparts.