I just bought an 87 Firebird and I've already run into a few problems. The speedometer stays at 0 or sometimes will climb to 20 or 50mph only to drop back to 0. The temp gauge waves back and forth. The gas gauge may or may not be working (I only got the car yesterday and have driven it very little so far). Everything else looks ok.

I'm a novice but I'm ready to roll up my sleeves and put some work into fixing up this car if someone can just point me in the right direction.

Thanks!

 

Welcome to the fold.

So, you're ready to tackle this one? Fortunately, it probably won't take a lot of special equipment or tools. You will need some means of getting under the center of the vehicle. There, on the left side of the tailshaft housing of the transmission, you will find the Vehicle Speed Sensor (VSS). Camaros of that vintage had them incorporated into the rear of the speedometer, while Firebirds had them on the transmission since 1985. Camaros caught up in about 1989 and moved them to the transmission as well, eliminating the cable drive to the speedometer.

The VSS is a cylindrical "can" about two inches in diameter and 2" long.



Carefully remove the electrical connector and inspect the pins and sockets for contamination and corrosion. Clean up anything you find, and apply a dab of silicone dielectric grease (often called "Tune-Up grease") to the contacts and rubber sealing boot of the connector. Place it aside, and loosen the single bolt that holds the large forked clip in position. Note the position of the sensor in relation to the clip, and how the clip shoulders against the plastic tabs on the VSS to prevent its rotation.

Place a catch pan beneath the area in case any transmission oil leaks out when you remove the VSS. Remove the bolt and clip, and gently twist the VSS to aid in removing it. Do not use pliers, since distorting the VSS can ruin it. If necessary, use a strap wrench to start turning it or very carefully use pliers cushioned by an old cloth or leather belt. The VSS should just pull out, but may be stuck from a few years of corrosion. Remove it carefully and straight, since they is a very thin 'O' ring on the base of the VSS to prevent leakage of transmission oil. There is also a plastic gear on the shaft of the VSS, inside the transmission, and you'll want that to come out with the sensor without damage.

Once you have the VSS it out of the transmission, and have the pan in place to catch any drips, get back out from under the vehicle with the VSS and inspect the plastic gear. The gear teeth should be regular, uniform, and symmetrical. If there is any damage, it should be evident. The gear is simply pushed onto the VSS shaft, and can be removed by pulling. The gear is keyed to the shaft by a flat in its bore that mates the flat in the 'D' shaped shaft. Make sure they are aligned before you reassemble them. If the gear is damaged, you'll need a replacement. You'll have little luck getting one anywhere but a dealership parts department. Make sure you have the VIN number of the vehicle, engine, transmission, and axle information when you go to order one. You'd be VERY lucky indeed if they happened to have one in their stock. Make a note of the color of the plastic gear as well, since it can be significant.

If there is no apparent damage to the VSS gear, reconnect the VSS to the electrical connector, turn on the ignition, have an assistant watch the speedometer, and twirl the plastic gear by hand. The speedometer should respond by displaying a speed, regardless of the direction you turn the shaft.

1. If the speedometer responds, the VSS is generating signal. If so, shut off the ignition, get a good lamp, and look inside the hole where the VSS was removed. You should notice a mating gear on the tailshaft, and it should be aligned almost dead center in the hole. If it has moved in one direction or the other, that could explain the intermittent signal. Sometimes, the gear can be moved back into position through the hole with a small prybar, sometimes not. If your's is out of alignment, pray, then pry.
2. If the speedometer is not responding to manually turning the VSS, the sensor itself may be failing, or the wiring or signal buffer between the sensor and speedometer could be failing. Unfortunately, I know of no good way to test the VSS without an oscilloscpe. Short of replacing the VSS or beginning diagnosis of the wire harness, there is little else to do.

Hopefully, you find only a corroded electrical connector. That should keep you busy for a few minutes.

 

Welcome Aboard!

If you don't feel like diving right under there like the Wizard outlined, you might want to check the 10A GAUGES fuse and power circuit first. The speedometer & VSS, temperature and oil pressure gauges, voltmeter, and several other circuits on the vehicle, like most of the sensors are powered by this fuse and circuit.



If the GAUGES fuse in the panel is intact, make sure the contacts are not damged in the fuse panel.

If you've found no problems to that point, you may need to dig into the instrument panel There are two electrical connectors at the upper and lower edges of the instrument cluster that connect the cluster to the vehicle circuits.



The foil contacts can become corroded over time, and the mating contact fingers in the instrument panel can become distorted. If the panel insert is loose in the dash, connections can be marginal. Removing the instrument panel is not difficult, but can take some time. Confirming cood connections there can solve several of your problems. It may also be a good opportunity to refresh all the backlight and indicator lamps in the cluster, and generally clean up the dash. Plan on having a box of #194 lamps on hand just in case. There are 14-15 of them.

 

Thanks for all the help! Looks like I've got plenty to keep my busy during the holiday weekend. I'll let you know how I come out (and I may come back begging for more help ).