Need help with bouncy speedometer and fuel gauge needles

[81Burb]

Anyone know how to fix the stock fuel/speedometer anolog gauges so they stop bouncing? Someone told me it's the spring getting weak but I've never seen anyone rebuild them

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[87slammer]

I have never seen a speedo that was connected with any kind of spring. Normally they work with a magnet spinning inside a cup. The cable drives the magnet and as the magnet spins inside the cup( which is connected to the speedo needle) it draws the cup along and based on how fast the magnet is spinning the needle indicates your speed. My experience with a bouncing needle is the cable has an issue.

[Rapid Roy]

Welcome

[bd]

Please include Year, Make, Model etc.. when posting

Regarding the speedometer, read through Common causes of "bouncy" speedometer needles in the Technical Forum.

An "erratic" fuel gauge can be due to intermittent electrical continuity in one or more branches of the fuel gauge circuit, including the sender and its ground.  Rapid needle movement that is most pronounced during acceleration, cornering and braking can result from the combined effects of slosh within the fuel tank and a loss of gauge mechanical dampening due to a loss of dampening fluid.

[Tommyd11730]

Dampening fluid on the factory fuel gauge?  Do tell.

[bd]

From research (I haven't had the opportunity to verify this yet), the fuel gauge axle is suspended by a bearing.  From the factory, the bearing is charged with a viscose silicone or fluorocarbon gel fluid (picture a super tacky, clear, greaselike substance) exhibiting ultra-high shear strength.  Dampening (aka, damping) fluid is used to create rotational drag on gauge axles in order to retard needle deflection rate.  Eventually, the fluid dissipates and loses effectiveness at which point the gauge needle dances in sync with fuel slosh in the tank.  Watch the linked YouTube video comparison of a used vs new fuel gauge.

[Rapid Roy]

From research (I haven't had the opportunity to verify this yet), the fuel gauge axle is suspended by a bearing.  From the factory, the bearing is charged with a viscose silicone or fluorocarbon gel fluid (picture a super tacky, clear, greaselike substance) exhibiting ultra-high shear strength.  Dampening (aka, damping) fluid is used to create rotational drag on gauge axles in order to retard needle deflection rate.  Eventually, the fluid dissipates and loses effectiveness at which point the gauge needle dances in sync with fuel slosh in the tank.  Watch the linked YouTube video comparison of a used vs new fuel gauge.

WOW!!!....Would have never thought about that for fuel gauges. That works somewhat similar to Glycerin in pressure gauges to insure steady (rather that sudden) needle movement and for reliable accuracy. Did more research on this and the fuel gauges can be restored by professional restoration shops. Mine has been jumping since purchase. I guess now it is time to get a new one. Thanks for sharing that info. 

[Oliver 1850]

I have never seen a speedo that was connected with any kind of spring. Normally they work with a magnet spinning inside a cup. The cable drives the magnet and as the magnet spins inside the cup( which is connected to the speedo needle) it draws the cup along and based on how fast the magnet is spinning the needle indicates your speed. My experience with a bouncing needle is the cable has an issue.

There is a spring that holds the needle at 0.  If it comes off the needle might register anywhere on the dial, even with drive cable disconnected. 

[philo_beddoe]

My fuel guage did the same thing, thought it was the sending unit. No  dice. Replaced guage, now perfect.

[Rapid Roy]

From research (I haven't had the opportunity to verify this yet), the fuel gauge axle is suspended by a bearing.  From the factory, the bearing is charged with a viscose silicone or fluorocarbon gel fluid (picture a super tacky, clear, greaselike substance) exhibiting ultra-high shear strength.  Dampening (aka, damping) fluid is used to create rotational drag on gauge axles in order to retard needle deflection rate.  Eventually, the fluid dissipates and loses effectiveness at which point the gauge needle dances in sync with fuel slosh in the tank.  Watch the linked YouTube video comparison of a used vs new fuel gauge.

A big Thank You bd for having and posting this info on bouncing fuel gauge needle. I am a believer in this now. After procrastinating for 2 months, I finally ordered a new gauge and now works great. I bought truck in July 2015 and needle has bounced since then, even after tank and sender replaced in December 2017. What a HUGE difference. A new gauge was all it took!!!

[bd]

Oops!  Wrong word.  Viscous, not viscose. 

Glad it was beneficial.