Speedometer

[unbludictable]

How can u tell if u need a new speedometer cable or guage?

I know the print circuit thing on the back of that cluster still works b/c the light still work and the oil pressure guage works and the rpm guage works.

But that darn speedometer won't move an inch!

I've got a cruise control, but I don't need no cruise control! I need some help!!

my truck is a '76 GMC High Sierra!

Help!

[Redneckchevy]

If its not working its more then likely to be a bad cable...These trucks snap cables like no ones business

[ccz145a]

Check the cable first... take out the screws holding the dash bezel and guage cluster, then reach back and unhook the speedometer cable, then pull the cable out. It should be smooth and free of kinks and have squared-off ends. It will be easy to tell if the cable is broken.

[unbludictable]

I look at the cable and it the end is squared! I see two cables that look the same, the only difference is that one looks like it screws on and the other just slides on! I tried to slide it on but it just won't stay! I got tired of fooling with it and didn't even try to screw it on!

Will the speedometer  work if the cruise control doesn't?

I really don't want the cruise control b/c I don't know if it works! Before I buy a new cable, I want to see will it work if the cruise control doesn't!

[ccz145a]

with the cruise control there are 2 cables. the speedometer will work even if the cruise does not as long as the cables are intact. you need to check both ends of both cables.

[locdogg]

i had problems with the speedometer on my 79
turned out to be the ratio adapter (found out after replacing both speedo cables)

see my post earlier http://forum.73-87chevytrucks.com/smforum/index.php?topic=6118.0

the ratio adapter turns and looks to be fine but i can't get the speedometer to work when i have this ratio adapter on.  I'm sure the speedometer is way off without the ratio adapter but at least the needle moves

when it gets warmer, I'll play with it some more to see if I can get the speedometer to work with the ratio adapter so my speedometer will be displaying the correct speed.

[choptop]

The speedo cable on these trucks with cruise, runs the the cruise control module the out to the tranny. It almost sounds like your cruise module is missing. You should have a cable from the firewall on the left to a aluminum module ( I can';t think of the right term) on the driver side inner fender. Then another from the module to the transmission. If it is there, then there may be a gear stripped in it, or there is a plastic gear in the transmission (ratio adapter) they stripout , if the cable is intact all the way to the tranny, remove the cable from the tranny and carefully hooked up a cordless drill to the cable and spin it. This will not only tell you if the speedo works, but will also give you an idea of where the cable is broke. If the speedo doesn't work, reverse the drill and try again. If it works, then it is the gear in the tranny, which I don 't believe is hard to change. If it doesn't then check where the cable goes into the gauge. It snaps in, and if not careful, will pop out when the gauge is re-installed

[VileZambonie]

pull the cable off the trans b4 you rip the dash apart and drive it with a drill. If it works you know the cable and the speedo are working so need to look at the driven gear

[choptop]

Right, check the cable visually under hood to make sure it is connected all the way, and check with drill first. Thanks Vile

[Hank Hill]

Sometimes it is the speedometer, probable most of the time it isnt, but for me it was. This morning I actually replaced mine. My speedometer needle was jumping around quite a bit. Replaced the cable and it didnt make any difference. But when I replaced the speedometer it fixed it.
Something else, my truck originally came with 308 gears which I replaced with 410s I also went with bigger tires. My old speedometer was way out. However with the new speedometer it seems not to be out as much. Got me wondering so I got looking at my old speedometer. On it there is a spring that returns the gauges needle to zero. Well then I noticed that the spring tension on this needle is adjustable. Just wondering but depending on how this spring tension is adjusted wont this calibrate your speedometer? Make it read differently?

[choptop]

I would like to know that one myself, I have never paid it any attention. I do know that the gear swap will change the reading, but the larger tires can set it back closer to right. Depending on how big a tire you went to, may have been closer to the right ratio for the tranny, but the old speedo didn't work well enough to use it. To many change tire sizes and not gears, then complain about performance. I hope someone knows about the spring. I can use that info.

[Hank Hill]

I only went from 28" tires to 33" tires but with the gear change my old speedometer was way off. Like it read 140kph when I was actually only going 100Kilometers per hour. The slower you went the less it was off.
But with the new speedometer the first thing I noticed was the shift points in the auto transmission. Now it shifts at about 10kph slower than it used to with the old speedometer.
If you look at those speedometers and at that spring adjustment that I was talking about its definately adjustable and it even has reference marks for whatever adjustments that you make. I would bet we can calibrate them from this point. Be easy to do once you had everything apart. Then road test it with a buddy in another truck and talk back and forth on your cell phones to find out your speed.

[choptop]

i will be trying it soon on my ext.cab when I get the new wheel setup. I have a GPS that I use to calibrate reprogrammed trucks speedos, so, i will try it then, and let you know

[Fordeatinz71]

ehh, the 2 cables thing must have went away by 1983...because my '83 K1500 has cruise and is all-original and doesn't have 2 cables...i just replaced mine.  it's only like $10.

[choptop]

Right, I think it changed in81 or 82. I have them on my pre 80s trucks, but my newer ones have the diaphram