Best Automatic tranny for cummins swap

[olblue1978]

Planning to put a 1990 12v cummins into my 78 f250 4x4 automatic. A little overwhelmed at all of the transmission variables with this swap. Anyone have any suggestions? Would really like to stick with an automatic, and plan to tow a 6-7000 lb trailer on occasion. Is there a clear winner here? Thanks in advance!

[Kuskoal]

Well ideally a transmission that came behind the cummins, thats easy. but a FORD transmission look at destroked for some adapter plates to mate most popular trannys to it. i'm pretty sure the 6bt cummins shares the same bell housing pattern as the smaller 4bt, and the 4bt was a repower for vans like fedex trucks, they used a TH400 or a SM420 manual. I do think the np 435 or t-18 was used behind the 4bt as well in ford powered vans, not too sure about that.

[olblue1978]

So if I find an automatic tranny out of an old cummins, in theory I would not need to buy the adapter plate/kit from destroked or fordcummins.com? Any particular tranny model numbers that are best suited? And a dumb question, what about using the C6 that is in it?

Thanks again.

[olblue1978]

Sounds like 3.55 gears and larger tires will allow a C6 to work. Anyone have any experience with that? Also, could you keep the 4.10 gears and use a gear vendor overdrive to get the top speed up and rpm's down?

[ChaseTruck754]

read this for the c6
http://www.ford-trucks.com/forums/87...a-cummins.html

Many people will say an Allison is the best auto - but then the model varies by person.

Heck - you'll get TONS of DIFFERENT opinions on what is best.

I'd weigh out the options and see what looks best for YOU.

[mistakenID]

I have 4:10's C-6 and a gear vendor OD. Tires are 33x12.50x16.5. Freeway speed 75 mph has the engine maxed at the factory 2500 rpm setting. The engine is a cummins recon bought direct from cummins and is a 93'. Truck is an 86' F250 4x4 regular cab.

Power and fuel mileage are terrible above 60 mph. Engine really needs to be around 1600 rpm at freeway cruising speed. With a load on, any hill I hit, the truck slows till the rpm's get back into the torque curve and then it'll hang there without having to shift unless it's a real long, 6% or better grade hill. I tow a 27 ft fifth wheel and atv trailer behind that. No idea what it weighs.

[olblue1978]

Thanks for all of the replies. Some very good info to know. Not sure I know which one to get, but it sounds like my C6 with the 4:10's is not it, even with a GV overdrive.

Anyone know what pros/cons I would face with the 4L80E GM tranny? I would imagine the transfer case would have to be replaced with a divorced model?

Thanks again for all of the replies.

[mistakenID]

Any electronic over drive you install is going to need a computer to shift correctly. Baumann engineering has electronic controls for most but a bit pricey at $500 plus.

My opinion the 4L80E is one of the strongest OEM autos till you get into the Ford torque shift. The E4OD can be made into a good, reliable trans, cost is $3000-$4000 at a good shop and you still need the controls with either option.

[ChaseTruck754]

Yup - and at that point the c6 with a gear vendors doesn't look all too bad!

Especially because you can grab them used for like $800!

[olblue1978]

Yeah...trying to figure out what made me think this would be a good idea to start with...seems like quite the money pit even without the labor. I could build a pretty gnarly 460 to drop in to tow with and still have plenty of gas money ;-)

[ChaseTruck754]

Yeah - but with gas costing MORE than diesel (around here even the lowest octane costs MORE than diesel) and the fact that the diesel gets DOUBLE the mileage or more and I think you might run out of gas $$ pretty quick

[bradyracing]

I'm switching to autos from manuals in mine. I think I'm going to the Allison. And I'm going to go big like maybe a 545. I've just never seen one that was for four wheel drive. I do have one divorced 205 from a 76 3/4 ton Ford left in the pile that I could make work. I don't know. I saw an ISB with an Allison 1000 like is used behind the Durapad on Ebay so that could be a possibility if you found the 4x4 version.
On Ebay type in Cummins and Allison or Cummins and transmission. There is some interesting parts and combos on there, all it takes is money.
It also helps that GM and Dodge started putting the front driveshaft on the left. Now trans and transfer case options a limitless.

[fordman67]

I have an Allison at545 going into my 64 2wd. Let me tell you something.It is LONG.I had to cut some of the carrier bearing cross member out to clear the parking brake.I was hoping to someday throw a front axle under and a divorced transfer case.BUT i dont think that would work since the transfer case would be under the bed.

[F-250 WARHORSE]

I think that you guys could switch the governor springs in those rotary pumps to obtain a solid 3000 rpm, cummins will easily handle this (mine does with 250k and I beat on it) and that will get your torque curve up. I run 285/75/r16 on my 12 valve with a five spd and i have 4.10s I can run 75 mph at 2300-2500 (in there) and easily 65 in 4th gear (same as high in a c6) I would run a 34-35 inch tires with a gear vendor and do away with that 2000 rpm governor get a 3000-3200 rpm spring and advance the timing (really easy on those older ones) then get a good air intake and a good exhaust, that would let you use the c6 I would presume. You might be limited to the 80 mph range but that is plenty in my opinion for a 35 year old truck. My dad had a 4.10 dodge with a gearvendor and a 5 spd and the stock donut tires It would make 65-70 in 4th get the rpm up and add some taller tires no prob seeing 75-80 but this IS coming from a guy who can't seem to make a 460 perform but can make his wore out dodge tow a tractor and a load of straw on a trailer over the passes as fast as I can take the corners. I would stick with the C6 even put 3.73s or 3.54s in the rear end that cummins will make more that enough power to deal with that.

[fordman67]

where ya find a gear vendors for 800? I need one.