I'm putting the finishing touches on an LT1 swap. I've got a 94' LT1 bolted to a TH350.

The LT1 computer is stock programmed to run the T56. The TH350 has no speed sensor, just the cable for the speedo.

Does the computer need a signal from the T56 speed sensor to run/drive properly? Or is the speed sensor (for the T56) just for the 94's speedo and ABS system?

I understand that the 4L60E transmission NEEDS a VSS... thats because its electronically controlled by the PCM and needs to know how fast the car is going.

BUT... does the T56 need a VSS for the PCM because you (the driver) change the gears at what ever speed?

Thanks in advance!

 

The VSS keeps you from stalling when coming up to stop lights. Some will argue that a VSS isnt needed and a good tuner can fudge it enough to prevent drivability problems. Fine and dandy for some, but not every tuner is the worlds greatest

Fixing it is pretty simple. Find a 2WD truck/van/Fbody with a 4L60E trans in it and take the VSS and 40 tooth reluctor ring. Any trans will do from early to late 90's. If the VSS has a gear on it, you've got the wrong sensor

Next find a large VSS tailhousing for your TH350. BOP cars were much more often to be found with these than Chevy cars, keep in mind the different tailhousing lengths. An electric VSS 700R4 tail will do in a pinch, but it doesnt cover the tip of the output shaft completely

Pull the old tail off, slide the drive gear off, press the reluctor ring on, new tail with newer VSS (fits only the large VSS tailhousings), wire the VSS to the PCM and use the PCM speedo output to drive a Cable-X box

 

Ok, I was under the impression that the 4L60E has a 40 tooth reluctor ring with 40 pulses with each drive shaft revolution and the T56 Uses a a setup that runs 17 pulses per driveshaft revolution. Pricing the parts new there are different part numbers and a huge price difference between the auto and manual sensors leading me to believe that there is a difference and if my PCM thinks there is a T56 bolted to the motor and the sensor is one of a 4L60E it may give false readings to the PCM... Is there a difference in the auto/manual sensors?

Oh, the TH350 is all mechanical, no electronics... if that makes a difference, if there are electronic Th350's... are there?

 

Missed the output signal part

The 4L60E does have a 40 tooth reluctor while the T56 uses an 11 or 17 tooth based on the year. The output shaft diameters are different along with the VSS itself so you MUST use the 4L60E reluctor and change the speedo conversion factor in the PCM

No TH350's were electronic, but some came with the large housing VSS(still mechanical) that just happened to be the same size as the newer electric VSS'