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Old 09-13-2016, 11:58 AM   #1
moefuzz
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Default Speedo problems

Hi guys,
I'm wondering what would cause the speedo in my 49 M1 to chatter and bounce up to the end of the dial?

Is this cable/Lubricant or the actual speedo itself?
Thanks for the help,

moe




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Old 09-13-2016, 01:09 PM   #2
rotorwrench
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Default Re: Speedo problems

There is generally a small hole in the shaft bore of the speedo input housing near where the cable guide screws on. It has a small cotton wick for oil service and may have a small metal soft plug in it that can be removed. If the bearing gets sloppy on the shaft or if the speedo drag cup bearings are worn then the drag cup can try to stick to the rotating magnet inside there. This will make an awful noise and can peg the speedo needle out. It likely just needs to be lubricated. Some of these old instruments can go for 50 years or more without lubricant but they won't go forever.

Last edited by rotorwrench; 09-13-2016 at 01:18 PM.
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Old 09-13-2016, 01:16 PM   #3
VeryTangled
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Default Re: Speedo problems

Hi Everyone. Bouncing needle? Lube the cable. I think I used Syl-Glide but not sure if that was a good idea. What do others use?

https://www.amazon.com/Napa-7651346-.../dp/B0054DWS1W
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Old 09-13-2016, 01:21 PM   #4
rotorwrench
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Default Re: Speedo problems

Cables needing attention can make the needle jumpy but it won't try to peg out. It certainly wouldn't hurt to clean & lube the inner cable with some Lubriplate though.
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Old 09-13-2016, 01:49 PM   #5
deuce_roadster
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Default Re: Speedo problems

If the speedo has lots of miles without proper lube (probably most of them!) another culprit can be the bushing inside that the inner part spins on. There is not much clearance between that part and the can that has the needle so if it contacts the outer part the needle pegs. I think there are or there is a magnet that is spinning that pulls the outer part up as the rpm of the unit increases. IF this is the case, you probably should contact a rebuilder.
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Old 09-13-2016, 02:10 PM   #6
Kurt in NJ
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Default Re: Speedo problems

A kink in the cable will do it too. Take the center core out and roll it on a table
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Old 09-14-2016, 12:09 AM   #7
Alaska Jim
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Default Re: Speedo problems

I usually pull the cable out of the housing and coil it up and soak it in a coffee can of atf over night. It can be a bit messy putting it back in, but has worked many times for me over the years, may not be correct but it worked for me.
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Old 09-14-2016, 06:40 PM   #8
19Fordy
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Default Re: Speedo problems

Make sure the cable is coming straight out of the back of the speedo. No bends.
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Old 09-15-2016, 06:35 AM   #9
Mart
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Default Re: Speedo problems

I found once that if I oiled the cable it caused the speedo to bounce. I then greased the cable and it was ok. The grease acted as a damper.

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Old 09-15-2016, 01:14 PM   #10
moefuzz
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Default Re: Speedo problems

Hi guys,
Many good answers and lots of insight here...

I just supplanted a new Flathead in the low mile truck and am now getting 'round to tying up loose ends - hence it's time to get to the pegged speedo problem.

Thanks guys for the diverse answers....
Yes my needle pegs and makes noise so I suspect it is the actual speedo/magnates etc that need attention...
But I will also be pulling, checking and cleaning the speedo cable.

While the speedo/truck is not high mileage (in fact it is the opposite), and with just the fact that it is 67 years young - I could probably assume that the speedo has never been serviced...

...One things for sure, contorting to get under the dash of the old girl is not going to be easy as age and a spinal injury slow me down... But it doesn't stop me from moving forward and the Mercury needs her regular maintenance and tender loving care...

At 67 years and with only ~45,000 miles, i would speculate that she is about half way thru her life cycle and I'm doing what I can to Preserve this untouched original in hopes that she will make the magical 100,000 mile mark...
At the current pace that would be sometime in 2091!




God Bless and thanks again for the guidance..

moe in Canada.

Last edited by moefuzz; 09-15-2016 at 01:19 PM.
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Old 09-15-2016, 02:35 PM   #11
WestCoast
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Default Re: Speedo problems

ive found when working under dash it sure helps to pull the front seat so you can lay flat on the floor board to service the speedo or remove it or the dash
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Old 09-15-2016, 11:54 PM   #12
deucemac
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Smile Re: Speedo problems

I ran a chassis dyno for many years and along with the fun things to do on a dyno, I got to do speedometer call and repairs. I worked on Ford products in a dealership but talking to other dyno operators, we all had similar jumping/noisy speedos. I would pull the cable core out, inspect it for burrs or wear. If there was none I then dipped the cable in a can of STP, alll the way to the bottom. The STP would cling to the cable core for some distance. I would reinsert the core in the cable sheath and the extra STP would gather on the lip of THE sheath and deposit itself on the rest of the core as it slid in. In almost every situation it cured noise and the wild needle deflection. In the rare case when that didn't work, I would install a new cable assy. That almost never happened after the STP dunk. So I see 2 good uses for STP. It keeps Japanese Sumo wrestlers from stealing your screwdrivers and 2. It quiets noisy/jumping speedometers. I can't REALLY vouch for the screwdriver protection, I only saw it on the STP commercials .
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