Kicking around doing an LS swap

[Bruce Wingate]

I'm trying to figure out if an LS swap would be worth the effort. I have a 1984 K10 with a 350 and 700r4 trans and, I think, an NP205 transfer case. I'm not sure of my rear end gearing. I'm struggling with getting only 8 mpg no matter how I drive. I think an LS swap would give me between 12 and 16 mpg. I'm going to try to figure out what some of my problems might be (if there are even problems. 8 seems to be on the low end of normal)

Anyway, if I do an LS swap, I'm looking at a 5.3 or 6.0 drive by wire setup with a 4l60e transmission. This should be one of the most straightforward swaps (famous last words). My questions are: 1) Would be easier to to get the donor transfer case or an adaptor for between the new transmission and the old transfer case? I'm curious about length and drive shaft compatibility. 2) What about the speedo? Its cable driven off the 700r4 right now if I'm not mistaken.

 

[Vbb199]

1: the 4L60e is 27 spline output as is a gm np208 (cable driven) or sometimes you can find the super ultra rare 90-91 np208 with a vss for a speedo.

I have peronally confirmed , a gm np241 and gm np208 will fit on at least a gen 1 4L60e as long as you have the 4 bolt to 6 bolt adapter.


On the cable driven speedo cases, you'll need a Dakota digital adapter to convert it to vss which the LS and 4L60e needs for torque management and transmission shifting.
There also exists np241 transfer cases from 1990-1991 which are "easier" to find than the unicorn vss driven np208.

In terms of length, the 4L60e and 700r4 are about the same.

The cases probably are different lengths from a np205 to a np241/np208

I wanna also say there's some 27 spline np205s out there, but you'll need an adapter an the vss signal converter to run it behind the 4L60e.


2. Yes. Your speedo is cable driven, so you will need also an aftermarket gauge set or a 1990-1991 vss speedometer. For speedo signal

 

[Bruce Wingate]

Thanks - I have to do some digging on my truck. It sound like the speedometer is driven off the transfer case and not the transmission like I thought.

 

[Vbb199]

2wd speedo is driven at the transmission output, 4x4 speedo is driven at the t case output.

 

[Bruce Wingate]

2wd speedo is driven at the transmission output, 4x4 speedo is driven at the t case output.

Just did a visual confirmation. That's correct and makes sense.

 

[Vbb199]

1: the 4L60e is 27 spline output as is a gm np208 (cable driven) or sometimes you can find the super ultra rare 90-91 np208 with a vss for a speedo.

I have peronally confirmed , a gm np241 and gm np208 will fit on at least a gen 1 4L60e as long as you have the 4 bolt to 6 bolt adapter.


On the cable driven speedo cases, you'll need a Dakota digital adapter to convert it to vss which the LS and 4L60e needs for torque management and transmission shifting.
There also exists np241 transfer cases from 1990-1991 which are "easier" to find than the unicorn vss driven np208.

In terms of length, the 4L60e and 700r4 are about the same.

The cases probably are different lengths from a np205 to a np241/np208

I wanna also say there's some 27 spline np205s out there, but you'll need an adapter an the vss signal converter to run it behind the 4L60e.


2. Yes. Your speedo is cable driven, so you will need also an aftermarket gauge set or a 1990-1991 vss speedometer. For speedo signal

Bruce, I meant to tell you, this information is only valid for 1/2 ton stuff.

The 3/4 and 1 ton cases will be 31 spline in a 208 and 241 I believe.

Or at least a th400 and 4L80e is 31 spline.

So you'll need to make sure you source your chevrolet drivers drop cases from a k5, k10, or 4x4 1/2 ton suburban

But the immediate swap solution is a 1990-1991 np241c. Good luck!

 

[Bruce Wingate]

Bruce, I meant to tell you, this information is only valid for 1/2 ton stuff.
<<snip>>
So you'll need to make sure you source your chevrolet drivers drop cases from a k5, k10, or 4x4 1/2 ton suburban

But the immediate swap solution is a 1990-1991 np241c. Good luck!

I'm still in the early planning stages for this, but I think the plan is to source a pull-out engine and trans from a 2004 or so truck/suv. This should give me an LQ4 or LQ9 with a 4l60e transmission which should connect relatively easily to my NP208 transfer case (confirmed 208 and not a 205). With the Dakota digital adapter for the speed sensor, I should be good to go.

BTW - what do you mean by "driver's drop cases"? I have a 4wd K10 right now, so I should have that right?

 

[Vbb199]

I'm still in the early planning stages for this, but I think the plan is to source a pull-out engine and trans from a 2004 or so truck/suv. This should give me an LQ4 or LQ9 with a 4l60e transmission which should connect relatively easily to my NP208 transfer case (confirmed 208 and not a 205). With the Dakota digital adapter for the speed sensor, I should be good to go.

BTW - what do you mean by "driver's drop cases"? I have a 4wd K10 right now, so I should have that right?

I somewhat messed up on that one. My bad.

Squarebodies are passenger side drop, but your aforementioned Lq4 + 4L60e + np-whatever will be drivers side drop.

That's what I meant, my bad.

If you intend on keeping your front axle in your truck, you'll need to also keep a passenger drop case, necessitating a np208, np241, or np205

(I don't think any np203's are 27 spline)

 

[Bextreme04]

You should keep your current transfer case. Its a direct swap between the 700R4 and 4L60e.. they are basically the same transmission. A newer LS will require VSS from the T-case in order for shifting to work correctly on the 4L60 while in Low range. Make sure you get the adapter with the highest output. I'm not keeping my mechanical speedo so I'm using the 128k one, which is the same as the stock speed sensor. Some of them that have the lower number(like 8k) don't have the resolution that the computer needs at low speed. If you are mostly concerned with mileage, you should get a 5.3. It will get better mileage than the 6.0 and has WAY more power than your stock engine.

 

[Bruce Wingate]

You should keep your current transfer case. Its a direct swap between the 700R4 and 4L60e.. they are basically the same transmission. A newer LS will require VSS from the T-case in order for shifting to work correctly on the 4L60 while in Low range. Make sure you get the adapter with the highest output. I'm not keeping my mechanical speedo so I'm using the 128k one, which is the same as the stock speed sensor. Some of them that have the lower number(like 8k) don't have the resolution that the computer needs at low speed. If you are mostly concerned with mileage, you should get a 5.3. It will get better mileage than the 6.0 and has WAY more power than your stock engine.

Target engine is a 5.3, but when the time comes to pull the trigger, it will really depend on what I can source easily. I might even go for the 4.8l LR4, but the 5.3/4l60e combo seems so plentiful that I shouldn't have trouble getting one.

The VSS issue is new to me, so I have to do some research about what is available.

 

[Originalthor]

I'm in the same boat as you in the fuel mileage and doing a ls swap. What i have learned so far is that if you go with a 6.0 you are going to want to go with a 4l80e. You can sometimes get lucky and find a 6.0 and a 4l65e combo on a escalade but not the easiest things to come around.

I'm going the 4.8l with a 4l60e cause I was able to buy the hole setup for 300 bucks so far cause not to many people who do ls swaps are looking for a 4.8. I figured if it doesn't have the power or fuel mileage I want it would be easy to sell for what I got into it.

 

[CalSgt]

Target engine is a 5.3, but when the time comes to pull the trigger, it will really depend on what I can source easily. I might even go for the 4.8l LR4, but the 5.3/4l60e combo seems so plentiful that I shouldn't have trouble getting one.

The VSS issue is new to me, so I have to do some research about what is available.

From what I have read the Dakota Digital adapter to convert cable speeedo to electric signal is not accurate enough to control an E type tranny through the PCM.

I was able to rob a 40 tooth reluctor wheel from a late model NP241 and adapt it onto the output shaft of my NP-208.

There's some notes in my build thread: Posts 34, 40, 59, and 61
https://www.gmsquarebody.com/threads/80-k-10-squircle-build.34732/

Advance adapters makes a VSS adapter that goes between trans and trasfercase that will get the job done also.

Your donor PCM should also have a wire to inform it when it is in 4 low to change the shift patterns

 

[Bextreme04]

Your donor PCM should also have a wire to inform it when it is in 4 low to change the shift patterns

The 4-lo sense changes the tables(shift points, engine braking, etc...), but the values in the tables will not be accurate if you aren't taking the speed signal off the T-case output. Lots of guys use the adapter between transmission and T-case or use the OSS on the transmission and this will cause issue in 4-lo shifting due to the output not reading correct vehicle speed.

I have also read about people having issues with the 8k pass-through sensors. I am using the 128k sensor and have a 91 suburban speedometer installed so I don't need the mechanical cable anymore.

 

[wlwarnke]

NP208 doesn’t have the switch to tell the PCM your in low range. You’d have to rig something off the shift linkage perhaps.

The advanced adapter works great between the. 4L60e and NP208. You can then keep your cable speedo functional until you upgrade gauges, at which time you can take VSS from the PCM (low range will read high).

4L60e 4x4 output shaft is longer than 700r4. Adapter makes up this difference so don’t worry about loss of spline engagement.

I used to 2wd 4L60, then swapped in a 4wd output shaft during my rebuild.

 

[Camar068]

I've got a NP208 and I used the adapter that came with the 4l60e. My 5.3/4l60e came out of a 2006 silverado.

As for your speedo, it maybe coming off the transfer case. Run with it if thats the case. For the VSS signal, I drilled and tapped a hole for a camaro sensor in the adapter mentioned above and put a reluctor wheel on the output shaft of the trans. Look for clamp on reluctor wheels, or you could press on one.