My Dad restored/mildly customized a '63 GMC 1/2 ton about 20 years ago. The speedometer doesn't work because the "adapter" between the speedo cable and the trans is shot. It's got a 305ci V-6, and a 4-speed deep low manual trans. Does anybody know where to find this part? Is there cross-reference part that will work? Could it be repaired/rebuilt? I tried LCM Trucks and they had no clue. While it is kinda fun to play stupid with the cops on the speeding, occasionally one has no sense of understanding. Thanks in advance for any help.
A good transmission shop will either make one for you or know who does. You can get any reduction ratio imaginable to accomodate your tire size, etc. So you're not stuck with the original factory ratios.
I'll need Dad to show me to be sure, but I don't think it's the gear in the tranny. I think it's a "connector" between the speedo cable and the tranny. Idk.o No: I'll try to get a pic of it tomorrow and post it.
Here's what you need. Once you open the site, click on RATIO ADAPTERS. http://www.transmissioncenter.net/speedometer_calibration_______va.htm#gm ratio adapter No doubt they can help you figure what ratio you need if you tell them the rear end gear ratio, the overall height of the tire and what the tooth count is on the speedo gears currently inside of the transmission.
What a great website. Thanks, John... I put a "Certified Police Speedometer" in my 68 Cutlass back when it was new. Partly because my speedo got noisy, but also to keep the odometer low as it had a 5 year/50,000 drive train warranty. It read about 30% high, and GM had a right angle reducer I got for it...Drove by the tach most of the time anyway, so was only a "reference. With my 3.91 gear and G70x14 Polyglas, it was easy to predict the speed in 4th gear.....3000 RPM was 60MPH, 4000 was 80, etc. Had it mounted on the steering column in front of the tach anyway....:laugh:
Math and theory is fun, but the simplest way to make your speedometer/odometer accurate is to simply measure what percentage fast or slow it is over, say, a 20-mile stretch of highway. That's how the shop I used worked it. He didn't care what gears or tires I had; he just wanted to know that my odometer read 21.6% high, then he built an adapter to counter that.
John, thank you so much! I just showed my Dad the link. Quote:"I'll be gaw-d@mm'd. That's the animal I've been looking for!":TU: Now we just need to order and install.
