GMPP LS3 (E38) w/ 4L70E in square body 4x4

I am doing an 80 chev 4x4 with a GM Perf LS3 and a GM Perf 4L70E with a 205 transfer case.

The trans controller that came from GM Perf says that a TISS (Transmission Input Speed Sensor) is not required to be connected for 4L6x and 4L70 trans it is only required for a 4L80. It does show an OSS (Output Speed Sensor) for all 4Lxx trans. Is the OSS the VSS for trans shift control? What is the deal with the ISS, what is it used for on the 4L80.

Next challenge is the 4L70 is being adapted to the TCase an adapter housing which has a sensor it it but the tailshaft has no reluctor ring on it. And the TCase being out of the 80 Chev 4x4 has no electronic speed output only a cable for the speedometer. In a 4x4 where should the VSS signal come from the output of the trans or the output of the TCase. How is VSS dealt with when the TCase is in Hi vs Lo.

Thanks

ISS is used to detect TCC slip (by comparing engine speed to input shaft speed) and slip while gears are engaged (ISS to output shaft with gear ratio). Someone correct me if I'm wrong.

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What tells the Trans Controller if the TCase is in Lo or Hi range so that the shift curves or TPS vs Speed are correct.

Is the VSS supposed to be in the TCase or Transmission on a 4x4

Isn't the sensor on the tail housing that is replaced by the transfer case? If so, it should come out of the transfer case. You should be able to replace the cable driven output with a reluctor and sensor setup if I remember correctly; atleast it's done on TH350-400; or use a pulse generator using the cable output. Not really sure, just throwing ideas out there.

Correct on ISS vs VSS to detect slippage.

OSS is VSS...

the difference is that OSS is in RPM, while VSS is in MPH.


The Shift tables are based on TPS vs VSS.

Hi Joe
Thanks :)
Should the VSS be in the Transfer Case or Trans Output for a 4x4.
When the TCase is in Hi it would be 1:1 but when it is shifted into Lo will now it will shift at the same VSS but the engine RPM will be skewed by the ratio of the Lo gear in the TCase how is this addressed.

I'm not sure where VSS/OSS is picked from when transfer case is present...

if it is picked from after the TC gears then it represents driveshaft speed, so it won't be affected by Hi/Lo selection;

if it is picked from before the TC gears, then it will be affected as you said... in this case, I'm not sure how this is taken care of, may I see your tune file.

Hi Joe
I haven't got the hardware yet am trying to ensure I dot the i's and cross the t's before I pull the trigger.
As far as I can determine it is standard E38 w/ a T42 controller set up for a 4L70E.
I have looked through some 4x4 calibrations and don't see anything different in the 2wd vs 4x4.
Eldon

can you use something like this to get a speed sensor output?

https://www.carid.com/dorman/vehicle...gaAm58EALw_wcB

Also looks like the speed sensor is at the output shaft of the transfer case, so no matter what the gear and range, it'll still show true wheel speed if given the proper size wheel and gearing.

https://www.justanswer.com/chevy/14b...mc-2500hd.html