This morning with warmer weather, I decided to exercise my W108. It started right up and all looked normal. When I got out on the road and hit 40 mph a horrible squeal developed behind the instrument panel. The frequency and volume changed with the speed. When I pulled over (which I did immediately), it stopped.

When I started again it was gone, but when I hit 40 mph it started. This time I felt the instrument cluster and it was vibrating. I am assuming it is the speedometer cable, so will disconnect it and take a drive.

I thought I would ask if I am missing anything? Is there something else to check before driving it while I have the instrument cluster removed? I would hate to do any damage to other components as they are getting harder to find.

Ron
1972 280SE

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Ron
1972 280 SE 4.5
2017 Lexus ES 350
2011 Ford Escape
2006 Chevy Silvarado

I’ve heard the same before not sure if It was speedo cable or a grinding gear in my 73 450sl. It went away and never came back. I bet you could drop some oil in the end of the Speedo cable and even try a different cluster to determine if it’s the cable or cluster


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Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl,

Be careful with the oil. I got oil into the speedo once and had to clean it to restore full function.

The cable does squeal on these when it has just the right (or wrong) conditions. Most lubes make the cable worse as they push gunk further down the cable where it collects in one spot (such as a bend). Usually once they get noisy they need replacing, unless you can pull it and clean the whole cable, and you'd probably need a dry lube like graphite I'd imagine.

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Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

Sounds like the infamous squealing speedometer. Did the noise go away after the car warmed up inside?

It was the speedo cable on my 300CD. Pulled the dash, used a small amount of Marvel Mystery Oil down the cable and a small dab of grease on the bronze bearing at the end of the cable where it enters the speedo head.

Lasted for about two years then started again so I replaced the cable (easy). I used teflon spray lube on the new cable instead of graphite. Three years now.

I'd send the speedo and cable out to a shop for a refurb. I've seen various makes of cars seize the bearing between the needle and magnet that is driven by the speedo cable, this makes the needle spin round and round destroying the clock spring.

A speedo works by a magnet spinning and dragging a cup attached to the needle.

This also brings up the point that old cars need a comprehensive relube of systems not normally considered a maintenance point. ( Like wiper motor gear boxes , window motors, window regulators , and such. )

Thank you all for responding. I did get the cable disconnected and the noise and vibration are gone. Now to determine if it is the cable or Speedo head. I had the speedo serviced a couple of years ago, so I am hoping it is the cable. I have a new one and will replace the old when the weather gets better here. I do hope it is an easy replacement. For now I will use my GPS for speed...and bonus, I now know what direction I am going.
Thanks,

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Ron
1972 280 SE 4.5
2017 Lexus ES 350
2011 Ford Escape
2006 Chevy Silvarado

What was the temperature? It is very common for 110, 111, 112 and 108 speedo cables to be noisy in cold weather. It will go away with warmer temps or when the car has warmed up inside.

If you want to eliminate your speedo cable and correct for ratio changes you can use a product like this:
http://www.atrol.com/cablex.htm
They also have the electronic signal generator that connects to the transmission.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

IF and when you remove the speedometer you will find a metal cover on the back of it that can be removed by taking out a few screws. You will then be able to see the internals of your speedometer.

Where the cable goes in there is a bearing which holds the spinning magnet in place. This is not complicated and when you can see it you will see how simple this is.

That bearing will seize if not lubed every ten or fifteen years. You say you had the speedo serviced about two years ago. I doubt the shop replaced this bearing as that is a massive job for such a small bearing.

Lubing the cable is always a good thing, but if the noise persist then you might consider removing the speedo, pulling the cover and lubing the bearing. I usually use "3 in 1 oil" with the blue cap.

There are also a number of other pivot points in there that could do with a bit of lube. A tiny bit is all that is necessary for many years of service.

To troubleshoot the noise location, Can you remove the speedo, connect something other then the suspect cable as a drive line to the speedo, connect a drill motor and Spin the speedo. If it makes noise, your speedo is guilty.

Again, thank you all for the suggestions.

Dobroman, it was VERY cold out the day this happened, which makes me understand the noise, but not the vibration. The vibration was significant which makes me suspect the speedo itself. Or maybe the bearing referred to by Idle.

FreddMerced’s suggestion of pulling the speedo is my next step....when it warms up. Maybe June the way this winter has been.

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Ron
1972 280 SE 4.5
2017 Lexus ES 350
2011 Ford Escape
2006 Chevy Silvarado

That bearing is small and well built but when it starts to go it allows the speedo spinning magnet (you will see what I mean if you take your speedo apart. It looks like a little flywheel) is a lot of metal to get unbalanced in a small space.

So it would cause your speedo to vibrate which would of course shake your instrument cluster.

I can't remember if the speedo cable can be pulled from the cable housing. I seem to remember doing this and rubbing the entire cable down with graphite, which you can get at any locksmith shop and most auto parts stores, and that helped a lot.

But I have had a lot of old cars so this may have been another make.

This was a messy job. That stuff will not come out of your clothes easily if at all.