I have a '67 Firebird with a 326 and 2-speed automatic. When I got the car, the speedometer cable was loose at the tranny connection. I tightened that but still have a problem. The speedometer reads consistently about half the actual speed. In other words, if I'm going about 45 mph, it reads 22mph...if I'm going about 65 mph, it reads 30 or 35 mph. The needle doesn't "bounce" or look abnormal other than the speed is reading about half of what it should. I think everything is original but I'm not 100% certain.
Any ideas as to what this could be or where I should start looking for the problem? I've only had the car a month or so and am still getting familiar with her.
The only logical problem / solution would be a bad speedometer head which means replacing the speedo. Another choice - which seems remote - is that the wrong gear was put in the speedo cable adapter. You need one with half as many teeth.
It's unlikely (but not impossible) that your car had a rear end in it at one time that would have required the gear combination it has. Pull out the speedo cable adapter from the transmission and count the number of teeth on the drive gear at the end of the cable.
The adapter is attached to the trans. It's the thing the cable is inserted into. You need to pull the whole assembly out, not just the cable.
Thanks for the quick response. I had a feeling it was probably the speedo unit and found one in a wreck-yard for about $30. I was waiting to send for the used unit until I had time to further investigate. Seems logical that I pull the adapter and count the teeth before proceeding, though. The car is so original in every respect that I seriously doubt anyone ever messed with the drivetrain.
The only odd thing I've found regarding the originality of the car is that the code stamped on the block XI indicates a 326 with a 2 barrel carb. This car has a 4-barrel Carter carb on it. Maybe I misunderstood some code deciphering somewhere but I'm pretty sure I double-checked it and the numbers I pulled from the car indicated a 326/2-barrel w/ California emissions. Other than that, the car appears to be very original.
It sounds like it is NOT the speedo unit itself. Either different rear end, different tires, different trans. Speedo itself is probably OK. Should be able to correct with right tires or change the speedo gear in the tranny.
68' Firebird 400 convertible, numbers matching, solar red w/ deluxe parchment interior. 66' Pontiac Ventura Hardtop 66' Pontiac Catalina Convertible
Some decoders I've found say it's a 6-cylinder and others say an 8-cylinder. I wouldn't be surprised to find it's not the original engine but why leave the 2-speed tranny if you're swapping an 8 for a 6? (money comes to mind)
Hmm. Well, regardless, I want a speedometer that works. I'm probably going to replace the 2-speed with a Turbo 350 or 400 and put a floor shifter in it so I assume that will change things again ;-)
It was originally a V-8 car. The number after the "U" is a "1." That's a V-8 car. If it was a "6" after the "U", then the car would have been an OHC-6 car.
In 1967, the TH400 only went on 400 cars, otherwise the ST-300 (which is what you really have, not a Chevy powerglide) went with the 326.
