cummins in 71' chev longhorn

[dlefebvre]

I have a 71 chev longhorn 3/4 ton. Has a 402 big block with a beefed up 700r4 automatic and 3:54 rear end LS. I love this old truck- it has every factory option, but is very thirsty-especially when pulling my fifth wheel. I now use my 91 E350 dually CTD. I would love to put a 6 cyl cummins into it. Has anyone ever heard of anyone doing this or has any info about it? The transmission cost me big bucks to have built -extreme duty clutch packs,torque conv,shift kit and a few other mods. The mechanic told me it would take alot of torque, even if the 402 was opened up from its stock 400 ft ponds of torqe. I don't know if the transmission would be applicable for this application or not. Any advice appreciated. Thanks in advance. Dean- whitecourt, alberta, canada

 

[Hutchew]

6 of 1, 1/2 dozen of the other....

It would take a long time to pay for the conversion as far as the increase in mileage goes. Of course, there is no telling what the conversion will actually cost, sometimes you can find parts cheap, sometimes not. It comes down to whether or not you really want a Cummins, with the associated mileage and power, in that old truck, and the coin to make it happen.

I have been told that you can purchase the adaptors to run a 700r behind a CTD from the Chevy dealer. I don't know if it's true, my buddy here was looking into it for a conversion into a 90 GMC CC 4X4, but he happened across a 518/205 so he went with that instead. I understand the sprag in those trannies is the weak part, but there are racing parts being manufactured that are pretty strong. For a tow rig, my preference would be a NV4500 or NV5600 Manual.

First step I guess would be to start measuring, see if you have enough room in the bay for the Cummins. You may have to modify the firewall for enough room to run an intercooler and large radiator.

Keep us posted on your project... ... ... ... .

 

[fredflinstone]

I would think that you should be able to use one of the bellhousings from a 4bt in a bread truck with the automatic transmission to mate to your transmission since all gm transmission's use the same bellhousing. But I would guess the hardest part would be finding a torque converter to hold up, I would suggest one from behind a gm diesel since they are setup with a different stall speed than the gas version. As far as room I know of several guys who have put them in cheverolets form 74 to present body styles and have plenty of room to do so. As a matter of fact I know a gentelman who owns a shop about 30 miles from me and they do these kinds of swaps into gm's all the time except they use a manual transmission, and he currently has a late 90's suburban for sale that they just put a cummins in.

Good luck Seth

 

[AWM]

sounds like my kinda' swap !. Bob

 

[jlast]

700r4

I do not, nor would not put a 700r4 behind a cummins, I probably still would not put one behind a 4bt. I have and have seen these trans Blow up, consume themselves inside out, and that is on basically mild SBC. My friend scrap his 700r4 after replacing it twice, but he had a more modified bbc. I dont know how "built" you trans is but far as I have seen no mods can keep it held together. IF and Only if that trans is under warrenty I might try it just to see if it would hold, if it would be replaced!



I have seen many people with cummins chevys and sure they would be glad to help out, just try PM and see if the respond.



Also 14 bolt rear will hold, but the front D44 will only take mild abuse, have to upgrade springs for sure.



AWM,

is yours 4x4? any pics or website?



My suggestion as I am looking to possibly doing this swap would be, (alot depends on what it is used for and what HP output are you happy with),



if you use the GM frame would be 6bt, nv5600 and go with 1st gen np205 transfercase.

Or try 6bt, th400, to GM np205 and look into gear vendors o/d, depending on you driving.



And finally you could slap a GM truck body on a Dodge frame, just do the measuring and little body mount and wiring and be done!

Addressed in the new tdr mag!!!!!!!!!!!!!



TY,

Jlast

 

[fredflinstone]

dlefebvre,

I'm assuming the truck your wanting to do the conversion to is a two wheel drive? If this is the case I would agree with jlast that you don't have to worry about the rear end it would deffinatelly hold the cummins as long as it's in good shape, and if it's a four by the front end might need some attention but that all depends on how hard you use it and what type of driving you do. Many people say that a dana 44 won't hold much power but I put a 460 in my 76' ford with a six inch lift and 38 inch tires and abuse the heck out of it with a dana 44 up front. You just have to be carefull to take care of it. And if you abuse one with high torque expect that it will eventually explode a gear set. As far a the transmission I know of at least one gentalman in colorado who put over 200 thousand miles on a well built one in a lifted suburban with a 6bt in front of it and then he swapped in a 24 valve engine a kept going until he recently sold it. They are a weak transmission from the factory and even a built one will explode if abused but with a certain amount of reserve while driving it and not giving it full throttle in overdrive it should be ok at least until you can afford to have one really built strong. I have a friend who has one that was built and gauranteed to hole up to 1000 ft lbs of torque, so they can be built to last it's just a matter of how much you want to spend. I look forward to seeing the finished product when your done with the truck!! Seth

 

[AWM]

jlast; yes 4x4, divorced 205, dana 60 front end. I've just about got the picture thing figured out. Bob