Speedometer doesn't work.

[emil77]

Hi guys,

I had a previous thread, where I was having a problem with transmission leak, it still leaks, but I've given up. http://67-72chevytrucks.com/vboard/s...d.php?t=458282

Anyways, so I changed the bullet, it worked fine for awhile, but now my speedometer doesn't work. I went under the truck and played around with the speedometer correction/calibration box, it's not sitting tight, should the box be tight on where it's mounted? I looked at the cable coming from the box, it seems to be ok. Once in awhile the speedometer needle will jump up and down, but mostly it stays at 0mph.

Any suggestions on what to look for?


The box I'm talking about is right above the black circle.

[bosco200]

Have you checked the connection behind your Gauges?

[emil77]

I don't think it's that because it was working fine until we did the work on the above mentioned part.

[LockDoc]

-
Did you have the cable disconnected from the box? It sounds like the cable or the shaft in the box to transmission connector is not in the square hole, either in the speedo gear or where the cable connects to the box. It may have slipped out of the back of the speedometer also. If you don't find anything down below I would disconnect the cable from the speedometer head and re-seat it like bosco200 suggested.

LockDoc

[emil77]

Thanks for the help!

[LockDoc]

Originally Posted by emil77

Thanks for the help!

No problem, hope you get it sorted..

LockDoc

[emil77]

Update: Speedometer still doesn't work. We took apart the box today, checked the gears and greased it up nicely again. Took her out for a test drive, worked fine for a mile or two, but then the speedometer stopped working again. I don't know what else to check for. Should I just change the cable? What length is the speedometer cable? The parts store computer shows different lengths.

[68gmsee]

I'm not familiar with the box you have but what if you remove it and connect the cable directly to the bullet? It will be off on the speed but at least you will
know if the problem is inside the transmission, the box or the speedometer itself.

Another trick: Take the bullet out with the cable attached and see if you can twirl the cable with your fingers at the trans side. You should see the speedometer bounce. If it doesn't, speedometer may be bad.

[emil77]

Thanks for the additional info. I took her out for another drive, sometimes if I go over a bumpy road the needle will bounce and sometimes the needle will bounce up to 40mph.

I will try your tips later this week.

[68gmsee]

If it bounces that much it's possible the bouncing is allowing the cable to engage occasionally. Broken cable or cable not engaging properly and slipping.

It could also be the speedometer not working correctly -so still a tossup. I'd try hooking it up directly to see what happens.

Disregard this if you already are aware of the way a speedometer moves but in case there may be some others that don't know...

The needle moves when the cable rotates a permanent magnet inside a metal cup or ring. The magnet creates eddy currents which in turn move the needle.

[emil77]

Great info, thanks so much.

[emil77]

For future reference what is the length of the speedometer cable?

[slikside]

I've never had the need to know this, but from reading other threads about tranny stuff, seems the best way to know the length of cable for your application is to take yours out, and buy one the same length.