hey im lost i have an 86 2.8 firebird it used to be a factory automatic but now it has a borgwerner 5 speed in it i didnt do the swap the guy who had it befor the guy i got it from did the swap it had the cruise control stuff under the hood when i got but i took it out so now that the history is out heres my problem my speedo dont work it hasnt since i got it no cable how do i fix this the cable dont plug in to the speedo like on my 85 where did the cable go on the ato with cruise control or would i save my self the hedache and put in a aftermarket mechanical speedo any insight

 

Do you have the full gauge package on that '86? If so, the speedometer's really electric, even though it has a needle. To get that electric speedo to work, you need to get a Vehicle Speed Sensor for that transmission. Your full gauge package goes to a yellow VSS buffer box by the computer- and that expects to get a VSS signal from the tailshaft of the transmission.

VSS installs easily in the trans; you'd remove the speedo gear from the transmission (fluid will probably pour out) and put the VSS + VSS gear in its place.

The only problem is finding a VSS in a junkyard that will fit that trans (unless all speedo holes are the same size?).

Oh also there should've been a single wire from the back of the engine going to the trans to hook up into the VSS. So that might be problem #2, trying to find the wire. I bet the guy just cut it off.

 

thanks i figured it out though the cruise control had two parts to it the control box and the diaphram that ran the throtle cable to maintain speed the speedo cable ran the the control box on the cruise and the vehicle speed sensonr was in that unit my car didnt have that part of the cruise on it when i got ahold of it so im missing that part so im gonna check around to see if i can find one cheap and if i cant im just gonna put in a aftermarket mechanical speedo

 

Okay, I'm gonna have to hijack this, since it is along the lines of where I'm at. But, rather than having NO speedo, mine reads high. It's got to be somewhere between the buffer box and the speedo head (yes, the speedo is off, so is the odometer). I have tested the system with the OLD VSS, running both with a drill running at the same input RPM (550 RPM), and BOTH are off, according the Equations page (reading 45 when they should be reading 34). I don't know if I can get another yellow buffer box, but I DO know that I can pick up a mechanical speedo unit from my favorite yard. I have the mechanical VSS parts already (were in the T5 when I bought it), and I'm sure getting a cable is going to be a walk in the park. But, I DO know that I NEED a working VSS signal to the ECM, otherwise, I'm going to have to deal with the SES light.
The question is this: Should I put in the mech speedo unit, or get a yellow buffer box and see if that fixes the problem?

 

it would probably be easier to do the new box first cause if you buy a mechanical speedo youll have to mess around with the gears until you get it calibrated right

 

AFAIK, the trans came with the right gears, and its the rest of the system that's FUBARED. All I did was to swap out the speedo cable adaptor on the 85 trans (bought 85 trans to replace my broken 84, which had a cracked case and leaked ATF like nobody's business) for the VSS I bought for the 84 trans (also was mechanical as it was pulled from an 84 Camaro, had to switch to electric for the 87). The gears are proper: 7T drive, 18T driven, counted by hand two or three times.

BTW, between the speedo cable and the cost to pick up the mech speedo, it's less than GM wants for a NEW buffer box ($40 or so vs $65 without shipping).