The Stovebolt Site Forums Welcome! Welcome Centre Do It Yourself (DITY) Gallery 1947 GMC EC152 - "Love at Last"

And finally... does anyone recognize this rear end? It appears to be a Dana, but I can't place it.

Rick - It sounds like the lube in your speedo is kinda dried out??? This 2024 thread on a 1941 speedo problem (speedo is the same design as used in your early '47 truck) I think will offer some helpful info on your issue and solution. If you want to see other previous threads on the topic, use the Stovebolt Search to help you find them. I did a search using "Speedometer Repair 1941-47 trucks" and found lots of existing threads that are on topic and could help you with that.

You can also use that search to find previous posts on steering wheel removal and horn repairs, among most any other topics you come across. Happy hunting!

Rick - Using the info from this Dana/Spicer axle identification guide, it could be a Dana 44. That's just from comparing the rear cover pics with yours, which are a little rounder on the bump out than the 50/60 series axles. The decoding info at the top of the page should be helpful, assuming you can find/read the stampings on your axle?

nice heater

You are a wealth of information.

Problem solved... the needle seems to have fallen off, so it's no longer stuck at 10 MPH. I'll see about taking the instruments back out to see if I can find the needle and get this working.

Horn: I confirmed power to the horn. I cleaned the horn and can hear it making some movement. But it's unclear why it's not working - but I admit I know little about how the horn is meant to operate.

Stock horn had battery power to one terminal (call it A) at all times. Actually, both terminals (A and B) should read battery power when the horn button isn't pushed. Inside the horn there is a normally closed switch connecting terminals A and B. Terminal B has a wire that goes back into the steering column and attaches to the brass ring at the top of the steering column. The steering wheel has a brass contact that connects one side of the switch under the steering wheel cap to the brass ring.

When the horn button is pushed it provides a ground for terminal B which activates an electromagnet inside the horn, moving a diaphragm in one direction and compressing a spring. Once the diaphragm moves a short distance it opens the switch in the horn, stopping electrical flow, turning off the electromagnet and allowing the spring to push the diaphragm back to its original. The process repeats until you let go of the horn button.

Quick troubleshooting steps:

You've already confirmed power to the horn, so ...

1. Confirm power to the other horn terminal. It should be there if the horn button is not being pushed.
... If power, skip to step 2.
... If no power, the contacts or wiring inside the horn are defective.
...........SOME horns can be opened and the contacts could be cleaned with VERY FINE abrasive.
...........Reassemble and try again.

2. Remove one wire from the horn. Check the wire for power.
... If power, reinstall the wire to the same terminal which we will call X.
... If no power, reinstall the wire to the same terminal which we will call Y.

3. Use a short piece of wire, a screwdriver, or practically anything metal to short terminal Y to ground on the engine nearby. The horn should HONK LOUDLY.
... If the horn honks loudly, the problem is between the terminal B wire and the ground provided by the horn button.
... If the horn makes little or no noise the contacts or wiring inside the horn are defective.
...........SOME horns can be opened and the contacts could be cleaned with VERY FINE abrasive.
...........Reassemble and try again.

Thanks Bill. I had already confirmed power. The truck is re-wired to 12v with a negative ground. This is the American Auto-wire harness - it's pretty awesome. I was able to trace the whole thing out and I have power to the horn (via a relay inside the cab). I can ground the horn wire which closes the relay, providing 12v to the horn. The horn does make a relay click sound - but that's it.

I attempted to clean the contacts, but this didn't seem to do much. I suspect the contacts are shot.

I am trying to make sure I understand the mechanism... Since sound is produced by vibration, the horn must be creating a pulsation or vibration. I'm guessing the contacts inside are meant to energize the coil, pulling the bar which moves the metal diaphragm and opens the contact (disconnecting the coil). Once the contact is broken the contacts close again the coil re-energizes... Is this about right? If this is correct, then my contacts are fine - otherwise the coil couldn't energize and make that relay sound. It also implies that the distance of the gap is very important - it would effectively set the frequency of the horn.

I ask about the inner workings because this would help me diagnose.

@Gdads51 - So when I got the pickup the guy said the axle was a 1957 (I know; too much information). Using the info provided above, it appears it's a Dana/Spicer 45 axle - in use in GMC pickups from 1957 to 1959. The stamped codes are nearly too hard to read...

So I ordered a gasket. Given the things I find on this old pickup, I wonder what the fluid looks like in the rear axle... if there is any. Wish me luck.

Rick - Glad the info helped a little. If you are really interested in confirming the axle details, you might try some of the tricks and tips in this Tech Tip written by Stovebolter "Woogero" (long time member and Co-Moderator of the engine Shop). Knowing the details of the axle will improve your chances of determining and sourcing parts like bearings and seals etc. that you may find yourself in need of.

Wishing you luck that you have good findings when you open that pumpkin up.

Rick: Next time please let us know at the original post of a problem that the electrical system has been highly modified. That would have kept me from my totally useless post on how to troubleshoot a stock horn system.

Your understanding of how a horn works is correct.

It's earlier in this chain. Thanks though.