40 Buick fuel gauge

[Chief-mark]

I have a 40 Buick Special businessman coupe. I had the fuel gauge dash unit sent in and repaired and worked for fine for a while. Now when the car is sitting still the fuel gauge will read correct and steady. When moving or even rocking the car the needle for fuel gauge will bounce around and once the fuel stops sloshing in the tank it will read correctly. when I put an ohm meter on the fuel level sensor wire near the  tank it reads steady until the fuel sloshes around (wiring between sender and dash unit is ok) .  My question is about 'damping or buffering' the slosh. I know on later models the dash unit had a resister inside to slow the needle movement when the fuel moved around, Does this car 'dampen' in the fuel sender or in the dash unit?

[37_Roadmaster_C]

Assuming (no flames please) the 40 is like the 37 the dampening is in the sender. There is a cork friction washer in the mechanical float assembly that dampens the float movement. It has most likely failed and crumbled from age. It can be repaired, but it takes work. @Bloohas done it on my 37 Buick and his 36 Pontiac. Hopefully he will jump in here and add his advise.

[Bloo]

I have to plead ignorance here. At some point around 40 or 41, they went to a different sending unit with no gears, and it *appears* no brake. Is there a brake on the later ones? Maybe someone here will know. The universal reproduction replacements are also a similar later design. I don't see a brake on them. I would expect a bunch of waving. They probably tried to control it with baffles as much as they could. These Buicks all have "balanced coil" gauges. They react instantly to electrical input, unlike the thermal gauges used on some other makes.

[EmTee]

Does it have the original gas tank?  Maybe baffle(s) has (have) failed?

[Chief-mark]

I will remove the sender to inspect the tank baffles.

 

Thanks for everyone's  input