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Discussion Starter · #1 ·
I am about to begin converting my 1985 GMC k30 to a 12 valve cummins and i have a few questions

1. Where can i buy the center crossmember with the motor mounts

2. Where can i get an adapter kit for a 12 valve cummins to chevy turbo 400 trany

3. I have a 3 inch body lift and an 8 inch skyjacker suspension lift but i will need to upgrade my leafs right? and what about the leaf mounts? Is there anyone who sells the stonger leaf springs?

4. Will i need to trim the a/c box on the firewall or just put a heat shield tape on it?

5. Other than that is there any other major mods ill need to do?

Thanks all help is much appreciated
 

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Discussion Starter · #3 ·
Thanks man im pretty sure i can beef up my leaf mounts but does that avalanche place sell custom 8" lift springs that can withstand the weight of the cummins or is there somewhere else?

Thanx - I hope mine looks as good as yours when im done
 

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i dont know about that. i know on my 87 with 8 inch springs my boggers didnt rub with the smallblock but they did with the big block so i can imagine a cummins would lower it a little bit more so maybe go with some 10 inch springs or drop the spring mounts down a couple inches or somethin.

Thanks but my truck dont look too good right now, it got in a little fender bender/bedside bender whatever you wanna call it lol
 

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Discussion Starter · #5 ·
yea the front of my truck sits a little higher than the back now, so im not to worried about sag, but i dont want the weight to crack the leaf springs.

I will try just adding a stack of leafs to add strength
 

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Discussion Starter · #7 ·
Thanks man but im in north carolina

I saw the pics of ur spring stack and I think i can fab up some that will work for mine but i dont know how long they will last
 

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not trying to hijack the thread here, but i'm looking into doing something similar in the next year with my grandfathers truck. its a 85 chevy c20. i'd like to swap it over to a dually and was originally thinking of replacing the old 6.2L with a 6.5L. maybe the optimizer or p400 from am general...but there are few things in life that are better than a cummins...so i'm looking into putting in a 4bt now. i'm not a big fabricator, but i want to do it right, and clean. i'd like to use a nv4500 behind it as well. where do i start once i've got an engine/trans? i know the front end will need beefed up, potentially even boxing in the frame along with some more stout coils. any help is welcomed. BTW i dig your handle tbird....its my callsign in army aviation.
 

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6bt not a 4bt...oops
 

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Discussion Starter · #11 ·
Thanx man its all anyone calls me anymore and 69 is my race car number
And an update on my progress i just got my 12 valve that i will be putting in my truck and i have begun dissasembling it to have it machined i plan on having the block bored 20 over. I am having the head o-ringed and im upgrading the valvesprings and having the head milled for bigger valves. I plan on running around 200hp injectors and twins to go with all the other fuel system upgrades
 

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Discussion Starter · #12 ·
would it be worth the money to buy the trans adapter for the cummins to my th400 or should i just use a dodge tranny? :confused013:
 

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I am about to begin converting my 1985 GMC k30 to a 12 valve cummins and i have a few questions

1. Where can i buy the center crossmember with the motor mounts

Fab your own, the "Kit" crossmembers normally use the GM6.2 rubber mounts which rattle away fast with the weight of the Cummins

2. Where can i get an adapter kit for a 12 valve cummins to chevy turbo 400 trany
4BT Cummins out of a Bread Truck,,,, try Ebay....
3. I have a 3 inch body lift and an 8 inch skyjacker suspension lift but i will need to upgrade my leafs right? and what about the leaf mounts? Is there anyone who sells the stonger leaf springs?
Ditch the body lift, too unstable at high speeds/corners.... The springs will have to be replaced in the front to handle the weight, I ran Superlift 3.5" for 1ton K30... they lasted about a year with the Cummins,,, Alcan Spring out of Grand Junction CO built me a set of 4" springs with 1900lbs capacity and they have been in for about a year now with no droop.... Atlas Spring can do the same... prepare for some$$$$$$$

4. Will i need to trim the a/c box on the firewall or just put a heat shield tape on it?
The A/C box may have to go..... get a Retro A/C unit which slicks the firewall.... making room for the BHAF, and puts the A/C under the dash behind the glove box.

5. Other than that is there any other major mods ill need to do?
as before.... prepare for this to take way longer than you expected and cost twice as much as you expected..... Auto tranny or Manual... if manual,,, go find the manual hump out of a manual truck and weld it in, makes pulling the tranny later much simpler.

Side note.... start with at least a 3/4ton or preferabley a 1 ton truck chassis if you plan on using this thing for anything more than a pavement princess.... the 1500 chassis physically will not run the longevity.

Thanks all help is much appreciated
My frame is welded and reinforced in the front to keep the front engine cradle area from flexing and allowing my engine or fan to come in contact with anything that it can destroy.
 

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Discussion Starter · #14 ·
My truck is a 1 ton already with the d60 and the corp. 14 with 4.10 's and spring benders said they could make a set of springs for me that are 6 inch lift that will handle the wieght for a decent price. ive been looking for the adapter plate but in not sure if i should stick with the th400 or go with the dodge tranny.

thanx for all the info
 

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Personally,,,,, Id go with the Dodge NV4500, or a Manual with OD,,, those 4:10s are really gonna suck the diesel above 55mph,,,, 2,000RPM is the majic number for these engines.... I run 3:73s (which nets me 2,[email protected]) and the Dodges ran 3:54s. Figure out the equivalent for the tire size that your gonna run, and get a tach that is mounted off the Harmonic balancer,,,, Isspro makes one for the GM6.5, the same kit can be used for the Cummins. this is what I use and it gives me an accurate acount of true engine RPM, versus the alternator mounted ones which tend to read inaccuratly as voltage spikes.
 

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Do you have a part # for the isspro balancer tach sensor?
Will any tach work with that, or an Isspro tach only?
Thanks, I have been trying to figure out a tach system for my swap for a while.
 

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Discussion Starter · #17 ·
thanx man i will most likely be runnin around 36 in tires and what do u think would be the best automatic tranny for this swap? i was told a non electric 4l80e woul work great
 

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Do you have a part # for the isspro balancer tach sensor?
Will any tach work with that, or an Isspro tach only?
Thanks, I have been trying to figure out a tach system for my swap for a while.
I dont have the part # handy right now... the sensor kit is about $65 and the tach itself is the really expensive part... just look for the Isspro tach kit for GM6.5 or 6.2 (the one that mounts on the Harmonic balancer) and you will find it,,, if not call Rapid Diesel in Rapid City SD, Gail the parts manager knows exactly which one you will be asking for. (thats where I got mine.)

thanx man i will most likely be runnin around 36 in tires and what do u think would be the best automatic tranny for this swap? i was told a non electric 4l80e woul work great
as for an auto tranny,,,, check your local trash can.... all joking aside, I cant stand autos...... the 4l80 was a good auto but its still an auto. regardless of what trans you go with, here are the breaks.... you WILL NEED an OVERDRIVE, and you WILL NEED the durability that comes from and old Rockwell.... 700R4s when properly built have been known to stand up. TH400s have been known to stand up. and 4l80s have been known to stand up... then again, I know of one TH400 that was built billet to the gills and a 502 with no spray continues to break its cases in half,(this one isnt even putting out the torque and power that is capable out of the Cummins... It really boils down to what YOU want to do with the truck.... if drag racing is in the mix,,, build it for such, if pavement pounding is in the mix, then a stock trans should be fine. However once your used to the Cummins you WILL start pushing the envolope..... we all have..... I know, Im not much help......
 
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