I bought a 92 RS 305 TBI, (110mph speedo), about a month ago and have been working out a lot of bugs. I was able to get cruiz to work fine by re-running some vac lines that had been plugged up by who knows. All gauges are working fine, except the speedo. Sometimes it stays burried one direction or the other. Sometimes it pings around erratically. Every great once in a while it works fine for a second or two. If I have a cruiz controll, odometer, and trip that work fine, I don't know where the speedo issue could be, but in the gauge itself. On this car, the vss is on the driver's side rear end of the tranny. There is a gear on the vss that looks okay. I pulled that out the other day and almost got a face full of fluid. I pulled the gauges and they are all enclosed. There are just connects that kinda plug in when you screw the gauge assembly in place. contacts do not appear to be dirty. Again, cruiz, odometer, and trip seem to all work fine. I was in the 12 volt field for about 5 years at one point in time and don't have any issues with taking stuff apart and re-soldering any contacts/traces/components/replacing electronic components. I just wonder if I should try or go looking somewhere else first. Thanks for any help!

 

If you know anyone with datalogging capabilities, you can see if the ECM is getting a speed reading, it would really help to point you in one direction or another. If you don't, it only takes an ALDL/USB cable, a laptop, and some shareware to do it yourself.

I have the same problem and have narrowed it down to the plastic film circuit on the back of the instrument cluster. Just haven't gotten around to replacing it as I am still finishing an engine swap.

Best of luck!

 

I pulled the gauge cluster out again, and am currently testing continuity between all traces / connections. I'll let ya know if I find anything interesting.

 

I didn't find any bad traces/connections. circuit board that has a 4 pin connector that goes to needle mech didn't have anything bad/burned that jumped out at me.

 

I guess question is now does VSS control cruiz, odometer, or trip meter. If it does then I know not to buy $125 VSS.