Piston Slap: When a Riviera’s sending unit fails to resist

1966 Buick Riviera dashboard

Paul writes:

I have a 1966 Buick Riviera. Is there a way you can keep the gas gauge from fluctuating back and forth when you have 1/2 a tank of gas, when you go around corners or stop and start.

Sajeev answers:

Yes, that’s usually a sign of the fuel-sending unit that needs attention. If the gauge reads accurately when full or empty, odds are everything else (i.e. the gauge, wiring, fuel tank, etc) are probably fine. What likely failed is the variable resistor inside the sending unit. It’s the part that adjusts the resistance relative to how much fuel is inside the tank. Think of this part like a vinyl record being rubbed down by a needle on record player’s stylus: At some point it wears off too much material and quality degrades.

1966-68 Buick Riviera sending unit
eBay | oldbuickparts

Judging by this eBay auction, a new sending unit is pretty easy to acquire and fairly affordable. Installation will be pretty straightforward, but I would ask the vendor about the accuracy of their reproductions. (And by accuracy I don’t mean the cosmetic appearance, only the part’s ability to operate the fuel gauge needle in an accurate manner.)

Quality isn’t guaranteed in the automotive aftermarket, but if you get good vibes from their reply, you should absolutely replace your Riviera’s sending unit with one of these.

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