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Replacing a 400 with a 4L80e?

dbreid

dbreid

1/2 ton status
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Dec 26, 2005
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San Mateo CA
All,
I have a 3/4 ton 1989 Suburban with a 350 (serpentine belt 5.7L crate motor from about a mid 90's truck), bolted to a 400 Transmission and an NP241 (the mechanical speedo one).

Everything is fine with this setup, and when I drive locally, the truck is excellent. It has 35's on it, and it has good power, and the transmission is good.

HOWEVER... I REALLY wish it had overdrive for highway driving. Lately, the truck has morphed more and more into an adventure rig and sees some long highway drives and trails, etc. I do tow with it (not SUPER extensively, because it has a 350..) so I'd prefer a 4L80e to a 700R4, I think.

Will they bolt up? Do I need a specific one? I know you need to either convert them to full manual or get a standlaone control box, but would I need a different transfer case adapter? Will the splines work?

Are the lengths the same (driveshaft changes?).

Thanks in advance.

-Dan
 
Wow, you are close to me. I'm in fremont. What gears do you have? I'm guessing 4.10's. If you do this swap, i am curious as to how your truck performs with that gear/trans setup. I have a 4l80e in my 91 wiht stock height tires.
 
I would think that converting the 241 to VSS and running a later ECM/trans harness would solve all your problems with a 4L80E swap.

I wouldn't be surprised if a 4L80E/241 adapter is shorter than a 400/241 adapter though. I'm sure the info is out there, I just haven't followed the 241 side of things.
 
The bellhousing, and 6-bolt pattern on the output side are identical to the TH400.

You'll find that the overall case length (minus any bolt on adapters for the xfercase) is 1.5" longer than the TH400.

I'm not 100% sure on the stickout lengths for the 4L80E, but they are 32-spline like the TH400. You can even bolt on the existing TH400 output adapter to the 4L80E case...

The only two minor things to worry about are the stickout (don't want to bottom out in the xfercase side) and moving the xfercase crossmember(s) back 1.5" to compensate for the extra length.... (I suppose you could also consider moving the engine crossmember forward to achieve the same effect)



:usaflag:
 
dhcomp said:
Wow, you are close to me. I'm in fremont. What gears do you have? I'm guessing 4.10's. If you do this swap, i am curious as to how your truck performs with that gear/trans setup. I have a 4l80e in my 91 wiht stock height tires.
Click to expand...

Yeah, the truck has 4.10's. I am trying to figure out where to draw the line. My 241 just started leaking from a couple of the seals, and I probably need to pull it and change the seals anyway, so I was thinking about potentially swapping in a transmission with another gear for fuel economy. I drive the truck a lot, and I get about 10-12mpg fully loaded on the highway (roof rack, rocketbox, heavy bumpers, full of gear and fuel).

Part of me wants to just take a later 8.1L motor (with tranny and transfer case, etc) and see if that makes more sense.

I know Kevin at Pac Fab is excellent at that swap, and then I could tow quite a bit better.

Just thinking out loud.

-Dan
 
I've got a 4l80e and 4:56s on 35s+. I don't have a tach in the suburban so I don't know what RPM it's running on the hwy but it doesn't seem to be all that bad.
 
I put a 4L80E in my 87 K5.

After all adapters are on and everything there is a difference of 3". You will have to have the front drive shaft lengthened and make the rear shorter.

If you are going to want to get a 95 or 96 transmission. Because in 97 they moved the cooler lines to a different location and went to the quick disconnect style. You can make that style work, but the 95 or 96 is more of a direct bolt up with some minor tweaking on the lines.

Also like said you will have to move your cross member back. Since you have a burb, i dont know if the fram tapers at the crossmember like the k5s do. If it doesnt then you will be able to use the 2 rear holes for the front holes of the crossmember and only have to drill the 2 rear ones.

My transfer case bolts right up with no problems at all.

You will also have to lengthen the shifter rod and the transfer case linkage.

Hope this helps
 
I'd say go for the 8.1, 4l80E swap. I'm running a 6.0L, 4L80E with a 241 case (SYE on back) and love it. I just kept the crossmember in the same place and welded a piece of rectangular tubing on the back for the mount. On my K5 the frame starts to widen too much to just have moved it back. Will be fabbing up a new crossmember soon to clock the NP241 up and make a skid plate also.
 
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