Drivetrain swap.1972 to 2001

[terry b]

Hi everyone. I have a 1972 C-20 with leaf spring rear end and a factory 402 with a turbo 400. I want to remove the L-31 vortex 350 and 4l80 transmission and disc brakes rear end out of the 2001 3500 express van I bought from our church and put them in my truck. Low miles and well taken care of!! Has anyone ever tried this combination? Will I need to change motor mounts? Can I use the one piece drive shaft? Want to keep the fuel injection and factory computer. Please help me out if you can. Thanks Terry.

[truckster]

I put an L31 in my Blazer using the stock motor mounts. I'm not sure about the towers, because mine was originally a SBC. I'm guessing the drive shaft will have to be shortened.

Out of curiosity, why are you doing this particular swap?

[terry b]

Deliverability. Modern drivetrain with overdrive. Modern rear differential with four wheel disc brakes. This is a real 3/4 ton truck. I have owned it for over twenty years. The body and interior are completely restored. I left the drivetrain swap for last because I don't want it to be covered in over spray. It will be able to do anything I ask of it tow a camper or boat. It is a two owner numbers matching Cheyenne Super. That is the only downside. I am going to keep the big block and turbo 400 together so when I sell it some day it could be put back to stock but I think it is going to be a better truck this way.

[truckster]

In that case, I would seriously consider a cam upgrade. The stock cam is pretty anemic. I used a GM HT383 cam and I'm pretty happy with it.

[burnin oil]

I am not versed in the van rears but they are a little different than trucks. If you are happy with the van brakes no problems. Upgrades are not bolt on so you will have to do some research on them.

[terry b]

I will be looking into a cam swap. I am going to be detailing everything so it will be a good time to do it. Both rear differential are leaf spring mounted and close to the same dimension. Thinking I my have to move spring pads and adapt emergency brake and proportion valve disc front and rear. Maybe if lucky use the one from the van.
Thank you all for your support!!

[95 S_Trucker]

Double check your rear end on the van. A 2001 will still have drum brakes. Disc brakes didn't come on the rear of the vans until 2003.

[Ziegelsteinfaust]

Originally Posted by burnin oil

I am not versed in the van rears but they are a little different than trucks. If you are happy with the van brakes no problems. Upgrades are not bolt on so you will have to do some research on them.

Aren't they a good bit wider then a typical truck rear end?

[b454rat]

I have a van rear from an 02, it has the huge drums on it. And, as mentioned it's a touch wider than a stock rear. Using this style rear in 4wds will make the tires track the same, or be the same width, so the rears won't be tucked in. The disc rears came out in 03, and a 3/4 ton will have a semi float Dana 60, 1 ton will be full float Dana 70.

[b454rat]

Also, I'd keep the 402 if you wanna tow with it. Either way your gonna have wiring and computer BS, but an L31 isn't gonna pull like a 402. Modern fuel systems are above and beyond what even the 0411 can do, plus they can run the 4L80 too.

[57taskforce]

Originally Posted by b454rat

I have a van rear from an 02, it has the huge drums on it. And, as mentioned it's a touch wider than a stock rear. Using this style rear in 4wds will make the tires track the same, or be the same width, so the rears won't be tucked in. The disc rears came out in 03, and a 3/4 ton will have a semi float Dana 60, 1 ton will be full float Dana 70.

I thought GM had gone pretty much full AAM by the early 2000’s?? Interesting I didn’t realize the vans had Dana’s in them.

[gmc684x4]

Even if you do not do a cam swap replace the intake gaskets as they are prone to fail and leak

Van diff is a fair bit wider then a 72 i am guessing eaton diff, a good swap diff is the tried and true 14 bolt out of 73 87 trucks

you can do a disk brake swap easy on the 72 or a 1 ton drum brake swap from a 14 bolt to it

Look up Lt1swap site he has posted how to re work your wiring harness there


I was going to do this route I picked up a 99 express van last year for its L31 Sold it and the 350 in my 72 C20 and picked up a 5.3 and a 6 liter LSX for swapping kept the van 4l80e

The L31 is a Gen 1 small block the only difference is it takes a 1 peice rear main flywheel

[garyd1961]

Don't listen to what everyone says about the stock cam. I have the L31-R in my truck with the stock cam and it runs great. I'm running a 770 Holley carb and long tube headers though. If you want a bigger cam you need to mill the bosses in the heads or run beehive springs in order to run a cam big enough to make a real difference. You will lose low end torque if you do. The stock cam will idle smooth and still have plenty of get up and go.