04 LM7 into 87 K5

K5Rob said:

Can you dumb this down for me? Are you saying 4 high (and 2 high) will behave like 4 low? Or are you saying 4 low will not shift correctly? I thought with the use of a switch, i could tell the pcm “hey i am in 4 low” and it would use 4 low shift tables?

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You have to think about what the PCM is seeing compared to what the vehicle is actually doing. If you have the VSS at the transfer case, then the VSS will always show the actual vehicle speed. The engine RPM will be MUCH higher for a given vehicle speed when in 4lo than it is in 4hi, which is why you need to have a separate 4lo shift table(the shift table gives a mph at the vss that an upshift or downshift is started).

If you are reading VSS at the transmission output, then it doesn't matter what the ACTUAL vehicle speed is or what the transfer case position is. The transmission will still shift at the right engine RPM depending on throttle position, regardless what the transfer case position is. If you want your shift RPM to be different in 4-lo, then you can still use the 4lo tables and wire up a switch, but it should drive just fine in 4lo without that.

A VSS on the transfer case output with no 4lo switch will drive TERRIBLY in 4lo as it will want to rev to the moon before shifting even at idle throttle position. In most cases it will just never shift in 4lo because the first shift is commanded at ~11mph at 0%TPS, which is going to be ~3500RPM if you have 4.10's and 35's. If you go up to ~25% TPS reading, then your shift point moves to ~20mph... which would put your engine at redline(6500RPM) before it would try to initiate the shift. Here's what the shift tables look like for a stockish 4L60 in an 0411 ECU.

Drauka99 said:

The VSS in the trans (before the Tcase) will read the same speed regardless of the T-case being in high or low. The ECM(PCM) uses VSS for shift tables. I don't think you can use a switch to adjust that.

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You can... that's what the 4lo switch is for. You can also set "normal" and "performance" shift points using a tow/haul type momentary button. I have wiring schematics at home that call out what pins those connect to. They actually change the tables that the PCM is using for the shift points and pressures.

Pin 71 on the blue connector(C1) can be provided with a momentary ground to trigger Tow/Haul maps and Pin 16 on the green connector(C2) can be provided with a constant ground when in 4lo to trigger the 4lo tables.

As stated above, if you are using the sensor off the adapter for VSS and you don't have the ability to do your own tuning... I would not use the 4lo switch and would just drive it as-is on the standard tables. If you are going to mess with things, you can use the Bluecat trans tool to get table values and then fine tune it once you get it running using a cheap-ish tool and free software. The tool has gotten a lot more expensive, but is available for ~$80-120 https://obdxpro.com/product/obdx-pro-vx-obd2-diagnostics-and-tuning/

You can do any minor adjustments with universal patcher or TunerproRT for free. Alternatively, HP Tuners is more expensive, but definitely easier to use. I use a combination of both on my swaps and HPTuners exclusively on my newer vehicle.

Bextreme04 said:

If you are reading VSS at the transmission output, then it doesn't matter what the ACTUAL vehicle speed is or what the transfer case position is. The transmission will still shift at the right engine RPM depending on throttle position, regardless what the transfer case position is. If you want your shift RPM to be different in 4-lo, then you can still use the 4lo tables and wire up a switch, but it should drive just fine in 4lo without that.

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Thanks for the time for explaining this. So much incorrect info out there or yes/no with little explanation. This is my first ls based build. So you are saying the adapter i am using with the vss at the transmission output shaft will allow the pcm to shift correctly at all ranges

Bextreme04 said:

As stated above, if you are using the sensor off the adapter for VSS and you don't have the ability to do your own tuning... I would not use the 4lo switch and would just drive it as-is on the standard tables. If you are going to mess with things, you can use the Bluecat trans tool to get table values and then fine tune it once you get it running using a cheap-ish tool and free software. The tool has gotten a lot more expensive, but is available for ~$80-120 https://obdxpro.com/product/obdx-pro-vx-obd2-diagnostics-and-tuning/

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I have a tuner lined up to get me started but feel i need to do my homework as well. Which hasnt been easy. I expect to get into some basic tuning once i have everything put together. I am ls ignorant but proficient around a carb/distributor setup. This is the next step for me so i appreciate the help for sure.

K5Rob said:

Thanks for the time for explaining this. So much incorrect info out there or yes/no with little explanation. This is my first ls based build. So you are saying the adapter i am using with the vss at the transmission output shaft will allow the pcm to shift correctly at all ranges

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Yes. The issue would be if you are planning on using an electronic speedometer. If you are keeping the mechanical speedo on the output of the transfer case, then you will be fine as-is all the way around. No need for a 4lo switch and everything will just work.

Damn this whole thread outta be pinned for any future 60e 4x4 swappers haha

Vbb199 said:

Damn this whole thread outta be pinned for any future 60e 4x4 swappers haha

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No doubt. Gotta be the most comprehensive one i’ve found yet. I appreciate you guys. I had my 700 all ready to go and i wasnt gonna look back but i can sell it. The 4l60e will have way better manners. I think having to ratchet shift everywhere would get old

There is not a lot of information regarding VSS in a 4x4. Definitely makes an LS swap more difficult.

Ricko1966 said:

IDK so throwing this out for someone who might shed some light. I'm pretty sure Camaros starting in 1984 used an adapter at the mechanical speedometer location that went in just like a mechanical drive but put out vss for electric speedo. Anyone,anyone,Bueller, Bucket.

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yes you can use a pass-through adapter that will give the signal and still use the cable driven speedo.

I put a reluctor wheel on the output shaft of the 4l60E and drilled/tapped a hole in the trans adapter. Pretty sure I used a camaro speed sensor.

K5Rob said:

Thanks vbb. Could anyone touch on the high/low range switch? I know ppl are using a switch that they either epoxy or screw to the shift gate so it is actuated when put in low. What pins on the pcm do I wire this switch to?

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I think if you put the reluctor on the transmission output shaft, you don't have to have the "4LO" signal to the ecm. I don't use 4LO much. I didn't have an issue when I did.

Found the post:

LS 4WD

Per LT1, Green pin 16 is used if using the VSS from the transfer case. Otherwise, remove. That's what I did.

LT1 pinouts.

Camar068 said:

I think if you put the reluctor on the transmission output shaft, you don't have to have the "4LO" signal to the ecm. I don't use 4LO much. I didn't have an issue when I did.

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I think this is correct. Thank you

K5Rob said:

I think this is correct. Thank you

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Also, I deleted the trans range sensor. One less thing to fail later and was a simple programming for 1 signal wire on pin 34 for park/neutral (utilize trucks single wire....think it's purple).