VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Speedometer screeching and needle jumping

1941 Chevy Master Deluxe, original trans.

Saturday took the 41 out for the longest drive we have done, about 50 miles. Shortly into the drive the speedometer started to make a screeching noise. Shortly after that the needle would jump from the 40 MPH we were doing to around 80 and then back down. (I am certain we did not do 80 at any point and that this car cannot accelerate that quickly ).

I had a similar thing happen in my 87 Monte Carlo. To fix that on I removed the speedometer cable and sprayed lube down the cable. Is it likely it is the same issue in the 41 or is there something else I should look at when I take it apart? Is the cable the most likely suspect or is there anything else to check?

I would start with the cable. Don't drive it while it's doing that or you risk damaging the cable and or speedometer. You can unscrew the housing from the back of the speedometer and pull the cable out. Lube it. I use white lithium grease. Go light the last few inches before the speedometer so that it doesn't flow into the speedometer housing. If that doesn't stop the problem you'll likely need a speedometer rebuild.

Just so I am clear. I can completely pull the inside of the speedometer cable out of the end that connects to the speedometer and then just feed it back in after lubing it. No need to disconnect it from the transmission to do this. Feeding it back in will connect it with the speedometer gear at the transmission without issue.

I was just going to shoot spray lube down it and hope for the best but if I can pull the complete cable out without worry then that is better.

Is there anything that should be lubed or cleaned if I take out the speedometer while I am at it?

If we find an issue with the cable that prevents it from being reinserted or something like that can I reconnect the housing to the car and still drive it?

There is no need to remove the cable housing. I guess I wasn't clear, I'm not recommending you do that. The cable I'm referring to is the inside part. To paraphrase the speedometer rebuilder that I've dealt with you don't want much lubrication the few inches of the cable closest to the speedometer because the lube can run into the speedometer itself. Cable lube and speedometer lube are not the same. The problem with using thin aerosol lubricants is you risk the lube running into the speedometer itself. Your first paragraph is correct about pulling the 'cable' out of the cable housing, lubricating it, then pushing it back in. Again I use white lithium. It stays thin enough to lube in the winter but thick enough to not flow where it doesn't belong in the summer.

Looks like this is the top priority now since it stops us from driving the car. Thanks for the advice.

Ruscar,

Gene's advice is, I think, right on here, just a few drops down the shoot should do it,

Best,

Charlie

BTW: I just now got a new temporary password. I hope this one lasted longer than a few hours. I wish I could get a new permanent one but I don't know how. The old one is lost and gone from memory and having been written down somewhere.

Make sure to protect your equipment from lightning strikes. This has been a mess.

Life got in the way of the car car for a bit but here is an update on the speedometer issue. We removed the cable and cleaned out any of the old greased we could and re-lubed it. Unfortunately this did not help at all. Next we disconnected the cable from the speedometer head only. This completely stopped the noise. As we drove the cable was spinning but not making a sound. Unfortunately the speedometer seems to be the issue.

When I got my '28 truck on the road 10 years ago, it had been sitting for at least 60 years.

Before I took it out, one of the items on my check list was to open the speedometer for an inspection. I found old crusty grease on the gears in there, so I carefully cleaned them with a Qtip dipped in WD40. Then I put a tiny bit of high temp grease on the gears and made them move manually. Then I put the guts of the speedo back into its housing and reinstalled it.

The speedo worked and was steady, but the speed it was showing was incorrect: about 30% slower than I was driving.

Luckily, I found a speedometer shop in Sacramento, CA (Commercial Speedometer) that employed a guy who could work on these old instruments. I mailed it to him and he re-magnetized it and calibrated the speedo so now it works like it should.

Cheers, Dean

Thanks for the advice on checking if it is lubed. At this point the car is down with a seized generator and the season is ending soon. We are gathering an ever growing to do list.

Pulled the speedometer yesterday while my son ran wires in the dash. Took it apart and I could feel it binding when I attempted to turn it by hand. Saw a YouTube video on fixing a later model. The visible gears were all fine. There was a brass plug on the side of the speedometer. Removed that (damaging it in the process) and added some oil there. The speedometer was perfectly smooth. Plugged the hole by pressing a lead pellet into the hole, that is how the brass plug was in there when we took it out. Using a drill it turns perfectly.

Now I did have to unassemble it a second time once I realized that somehow a large piece of dirt got on the lenses dead center of the speedometer. Cleaned that and it is sitting on the workbench ready to go back int.

Removing the brass plug usually isn't necessary, at least on the speedometers I've seen personally. All I've seen have a small hole to allow light weight oil to penetrate the packing. Glad you got it fixed.

I looked for the hole but could not find any. I tried down the shaft etc. but that did not work. Someone had covered everything in a thick grease at some point, had to clean that off too.

This is a different speedometer but indicative of the hole I'm referring to.
Maybe yours didn't have a hole in the plug but every one I've dealt with had an opening for putting light oil in so it could be soaked up by the wick.

That hole is what the brass plug was filling. Prior person just jammed a piece of brass in there. I took a small drill bit and made a hole, vary slowly, in the plug so that I could get a pick there to pull it out. My son had the idea to use a lead .177 pellet to plug the hole since lead is so soft and could be removed in the same way I removed the brass.