Technical Whats going on with my old (38 Chev) trucks speedo?

Before I start buying parts I wanted to get a second opinion.

-The problem:

When driving occasionally my truck start making an odd noise that I can only describe as 'a handful of marbles in an old coffee can being swirled'. When this noise starts the speedo needle starts jumping randomly from 10mph to 70 and back (*while driving at a consistent 35 or so).

Here is the speedo in question:



After hitting it with some degreaser you can see the cable going into the trans past the master.



Truck




I am ***uming this is just a bad cable.
If this is accurate how hard is this to replace? (I have seen instances where things like a broken speedo cable required cracking the transmission; I just want to know what I am looking at).


THanks for any advice!

~JH

 

Might try removing the cable from the speedo, and adding a drop or two of oil to the part that turns, then spin it around a bit. Might help, for a little while, at least.

The speedo is worn out, is the real problem.

(yes, I've had this problem plenty of times)

 

You can try lubing the cable. Take the housing off the back of the speedometer, pull the inner cable out, lube it up with some white lithium spray and WD40. When you put it back in you will have to turn it until it goes into the transmission.

If that doesn't help there might be a speedometer repair shop near you. This one is near me.
http://stenesspeedometer.com/speedometer-service/

 

Most likely the internals of your speedometer are worn out if the bearings that carry the spinning magnet that spins within that spring loaded cylinder get off-center they will hit the spring loaded cylinder and make the needle go crazy or if you're lucky there's just some junk between that magnet and the spring loaded cylinder

 

The jewel in the magnet is worn causing the speedcup to hit the magnet. The speedo needs repair. Disconnect the cable at the speedometer, if you run it like it is it will break the shaft on the speedcup or break the speedo needle.

 

Don't know where you're at but I would take it out and send to Speedometer Service (e1956v above). He's done 2 for me and I couldn't be happier, fast service (2 states away from me), phone call with price before doing the work, what I considered as very fair pricing and both work perfectly.

 

Some of the old speedometers have a screw that can be removed and you can see a wick, that a drop or 2 of oil can be put on. Yours may or may not have this, if it does it is by where the cable attaches on the back side. It may not help but after almost 80 years it is probably dry.

 

The best advise here so far is from e1956v.....

 

Mine did that and it broke the speedo needle. I had to repair the needle and lube the speedo itself. Works great now!


Sent from my iPad using The H.A.M.B. mobile app

 

Get it rebuilt. Had my 58 speedo do that and at one point it jumped around made the noise and then made a small popping sound and my speedo was junk.

 

An update to the speedo:

Per the advice here, I sent it to Rusty for a rebuild.



On the bench getting calibrated (*pic sent by Rusty).
It turns out that I caught it in time and avoided any serious damage.





Speedo back home! He was able to retain the original odometer numbers (*I guess the numbers are very prone to flaking off once dissembled) and get it working.

Cant say enough about Rusty and www.speedoservice.com
-I only wish I had more speedos that needed rebuilt!

~JH

 

thanks for the report, that's good to know!

 

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