Speedometer display bounces

[ThosD]

When driving on very smooth roads, my speedometer display is fairly stable. Other times, the readout jumps up and down across a 10 mph range; rough roads may be the reason. Is this normal? Or, is the drive gear/ shaft defective? Or, does the speedo need rebuilding? When stable, the speedo seems pretty accurate when compared to the displays on radar triggered roadside speed limit signs. I'm curious and it's not a priority repair.

[Oldgearz]

Doesn't sound normal to me. Mines very steady.

[mcgarrett]

I'll jump in here with a possible solution. First of all, it's not a normal condition. Sounds like the speedo cable is binding in the flexible housing and needs lubrication. Start by disconnecingt the speedo cable at both ends and remove it from the car. Hang it vertically and drip some lightweight household oil like 3 in 1 oil or similar down inside the flexible housing until it runs out the the other end of the cable. Spin the cable inside the flexible housing to fully bathe the cable in the oil. Reinstall and road test to see if that eliminated the problem. If not, you'll need to have a look inside the speedo itself to see if the shafts and gears need a little oil too.

[McMimmcs]

My speedometer did the same and required lubrication. I believe I used a graphite grease. Wayne

[AlphaBob]

100% dead spot on - cable needs lubrication. My personal preference is SAE30 Non-detergent motor oil - it is a little difficult to find (most SAE30 contains detergents), but the non-detergent SAE30 is a fantastic overall / universal oil. I even use it for bar oil on my chainsaw. Advance Auto Parts carries non-detergent SAE30.

Not to go on-and-on, but non-detergent SAE30 is used in pressure water pumps, the hydraulic lift mechanism on outboard motors, and a whole variety of other things - good to have in the shop.

[Kurt in NJ]

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Another cause is a kink in the inner cable, pull it out and roll on table, any kinks will be evident then.
for lubricant i usually use cv joint grease, wipe old lube off inner cable, add grease as i am reinstalling the inner cable

[ThosD]

Thanks everyone. Lubrication is an easy fix!

[Pamodelaroadster]

Pull out the cable in the middle and lube the whole length with lubriplate, they had the same problem with newer cars with speedocables

[David in San Antonio]

@PAModelARoadster - I’ve been hearing about “lubriplate” for years and never knew what it was. So just now I went to their website and they have dozens of products! Which one are you using on Speedo cables?

[Pamodelaroadster]

White lithium grease, it’s not to thick. I think a grease fills the space in the cable housing better and stops the bounce better.

[gary678*]

Another thing to check...worn cable ends that could cause the cable rotation to skip. I have used graphite speedometer lube with excellent results.