4l80e vss and iss

[eran tomer]

Doing an ls swap with psi harness on 95 k2500 suburban. The harness has iss and vss plugs. I understand that the iss is the front sensor, isn’t it? But there’s no rear sensor on the tranny. So where does the vss plug go?

 

[Scooterwrench]

In the transfer case?

 

[NickTransmissions]

Doing an ls swap with psi harness on 95 k2500 suburban. The harness has iss and vss plugs. I understand that the iss is the front sensor, isn’t it? But there’s no rear sensor on the tranny. So where does the vss plug go?

In '94 they started putting the vss in the Tcase on most 4WDs though there were some that still had it through '96...

 

[Schurkey]

In '94 they started putting the vss in the Tcase on most 4WDs though there were some that still had it through '96...

Where else would the VSS go on a 4WD but in the transfer case? My '88 K1500 has the VSS in the transfer case.

On any transfer case with a low-range, you'd need the VSS able to see actual output shaft/driveshaft RPM, to get a proper speed reading no matter which "range" the transfer case was in.

Or do some of them use the DRAC to adjust the pulse count based on which range the transfer case is in?

 

[NickTransmissions]

Where else would the VSS go on a 4WD but in the transfer case? My '88 K1500 has the VSS in the transfer case.

On any transfer case with a low-range, you'd need the VSS able to see actual output shaft/driveshaft RPM, to get a proper speed reading no matter which "range" the transfer case was in.

Or do some of them use the DRAC to adjust the pulse count based on which range the transfer case is in?

Good question as I'm not exactly sure how GM managed vehicle speed back then in those early 90s 4wd 4L80Es and unfortunately it's been forever since I did an early 4x4 4L80 (91-93 vintage). But last one I do remember doing was a 92 4wd and it had both speed sensors installed and the reluctor on the output carrier (rear planet) for the sensor to read. Its also possible there were three speed sensors (ISS, OSS and VSS) including the one in the TC which would be the VSS, if so. I never see the vehicles themselves so wouldnt have had the opportunity to view the entire set up.

I'll dig through my records in the next couple days or so to see what other info I may have about the rest of the drivetrain including the tcase on that deal. Will also ask a couple builder friends next week if I can't find answers before then...

 

[Schurkey]

Its also possible there were three speed sensors (ISS, OSS and VSS) including the one in the TC which would be the VSS

THAT I'd believe, although I didn't know they were using input and output sensors that early.

 

[NickTransmissions]

THAT I'd believe, although I didn't know they were using input and output sensors that early.

Yea its an interesting question...hopefully I can find out more in the next few days and relay here, unlesss someone else can chime in sooner with the facts on those early 4x4 speed sensor set ups...

 

[Dropped88]

The psi harness are pre-wired for 4l80 so when you hook it up too a 4l60 you just zip tie the iss out the way and usually you'll use the original patch cable that will extend vss to transfer case

 

[Scooterwrench]

Where else would the VSS go on a 4WD but in the transfer case? My '88 K1500 has the VSS in the transfer case.

On any transfer case with a low-range, you'd need the VSS able to see actual output shaft/driveshaft RPM, to get a proper speed reading no matter which "range" the transfer case was in.

Or do some of them use the DRAC to adjust the pulse count based on which range the transfer case is in?

In my research on DRACS they only have one VSS input and it comes from the driveshaft.

 

[tayto]

In my research on DRACS they only have one VSS input and it comes from the driveshaft.

no. drac uses a 40 tooth wheel usually in tail shaft or transfer case