Do all the VSS units put out the same pulses throughout the 3rd gen years? I have an electronic 86 T/A speedo that I wanted to use on a 91 Z28 TPI engine/700r4 and factory wiring harness. I sold my 91 cluster and want to make a custom guage pack using the FB 140 speedo. Is this possible or do I need to use a different VSS? If the 86 speedo will not be a plug in what years of speedometers would work with the 91 VSS? I may find something neat in the boneyard from another car.

IIRC, the early VSS units were magnetic pulse output, and the later versions were optical. Or, maybe I have that backward. You could solve it by installing the '86 VSS in yout '91 transmission.

The buffer module may be expecting that '86 signal too.

Thanks for the response, maybe I worded my question wrong. From reading here I believe the VSS buffer splits outputs to both the cruise control and the speedo, both with different output signals. I cant remember what the output count was for the 91 speedo (was it 4000 counts per rev or something similar?) and I was wondering if the 86 FB speedo would accept that input or if it used a different input signal count to work.

Oh, the rate. The later speedos (and VSS) were 4,000 pulses per mile (even though the signal was buffered so the ECM only received 2,000 pulses per mile). 1989 and earlier Firebirds used a 2,000 pulse per mile VSS, if memory serves me.

thanks, so a 90 up speedo should work with the 91 Z buffer output. I will do some research and see if the change was across all GM lines, I want to make a custom guage setup and I am not sure what speedo I want to use. I like the firebird one so maybe I will just use a 90 up one. Thanks again!