Speedometer accelerating in neutral
Thread Starter
Staging Lane
Joined: Oct 2009
Posts: 50
Likes: 0
From: Perrysburg, OH
Speedometer accelerating in neutral Hey all, I just installed a 255lph fuel pump and the Racetronix upgraded wiring harness in my 1995 Z28. I put my exhaust back together, but not the axle yet as I wanted to see if the car would start properly. Sure enough, it works! I had my T56 in neutral, gave it some gas, and noticed the speedometer needle rose with the RPM. When I pushed the clutch in, the speedometer needle dropped back down, but when I let the clutch out (still in neutral), the speedometer went back up. I don't have a driveshaft in at the moment, just an old yolk to keep fluid from getting all over. I searched and saw sometimes a loose ground can cause weird issues like this, but the harness relay is properly grounded on the brake bracket where the instructions say to put it. None of the other gauges seem to have an issue. I even added the extra ground strap between the battery and the body (despite already having a strap there). I also saw a thread where this is normal behavior for GM vehicles.
Is this normal and somehow I've never noticed this in the 18 years I've owned this car?
I have the Racetonix wiring harness zip-tied to the T56 wiring to reach the engine compartment. Could it be getting interference from the wiring harness power wire and thinking it's a speed signal? Speedo drops back to 0 when the clutch is disengaged.
Any help on this would be most appreciated. I was going to put the rear axle back on but now I'm worried this is some kind of a ground issue in the tank itself and will have to drop the tank again to see.
Is this normal and somehow I've never noticed this in the 18 years I've owned this car?
I have the Racetonix wiring harness zip-tied to the T56 wiring to reach the engine compartment. Could it be getting interference from the wiring harness power wire and thinking it's a speed signal? Speedo drops back to 0 when the clutch is disengaged.
Any help on this would be most appreciated. I was going to put the rear axle back on but now I'm worried this is some kind of a ground issue in the tank itself and will have to drop the tank again to see.
Thread Starter
Staging Lane
Joined: Oct 2009
Posts: 50
Likes: 0
From: Perrysburg, OH
After reading some more I discovered that this wasn't an electrical issue at all. While in neutral, the T56 input shaft and main shaft provide enough friction together that the main shaft will spin without any load on it. I started the car and looked underneath and sure enough the bare yolk in the transmission was spinning away so the speedometer was reading correctly. I hope this helps anyone else with a similar problem in the future.
