I own a 1988 camaro tbi with Borg Warner M 39 5 speed manual transmission. Problem- speedometer/ odometer do not work. Upon further investigation my transmission serial numbers match the vin number. However there is not a vss (vehicle speed sensor) attached to the tranny, rathera speedo drive housing with gear in place of where the vss would normally mount towards left rear of tranny. Also, the 2 prong vss harness is disconnected and just hanging there. I'm aware the vss must communicate with the ccm (computer control module). Otherwise check engine code 24 will be thrown.
Please note that the new vss I purchased (AC Delco # 10456088) is approx. 2 inches across the round mounting/ sealing area which is supposed to attach to the tranny via y clamp with bolt. My existing speedo drive housing with gear that is currently fitted to my t5 tranny measures approx. 3/4 inch across the opening, thus the vss I purchased will not fit my tail housing.
All I can think is that the tranny tail housing may have been switched previously before I purchased the camaro? Any help would be greatly appreciated.
Thanks

 

The VSS on an 88 Camaro is on the back of the speedometer. They didn't go to an electronic speedometer until 1990. You bought an automatic trans VSS. The one for a T5 is obsolete.

 

The extension housing is the same, whether for cable or VSS.

As Drew said, your VSS is on the back of the speedo, and there's a cable that goes from the trans to the speedo. You need the cable type "bullet" and the right speedo gears to match your rear end gears, which would originally probably have been 3.08.

https://transmissioncenter.net/shop/...-gear-housing/
https://transmissioncenter.net/shop/...-7-or-9-teeth/
https://transmissioncenter.net/shop/driven-gear/

Most likely you need the 9 & 21 combo.

Look at the color of the wires on that connector. If they're blue and green, then it's for the backup lights, not a VSS.

 

Sounds like your cable 88 IROC has the proper sending unit installed in the tranny, but it's missing the speedo cable. Since the tranny is original to the car, the speedo DRIVE and DRIVEN speedo gears are PROBABLY correct. The VSS you bought is made for a 90-92 automatics; might as well ship that thing back ASAP so you can focus on finding a replacement Speedo Cable.