Building custom hot rods is not an exact science and many times builders are left making a custom part for their hopped up street rod. Lets take fuel tanks for example. Often times space is very limited and a fuel tank must be constructed or reworked to fit in the available space. This is not an issue with plumbing but can be a show-stopper when it comes to fuel level measurement. Classic Instruments has recently released their new tube style fuel sending unit to the performance parts aftermarket to help solve these concerns.

Typical OE-style fuel sending units have been a lever style sending unit that employs a swing arm that contacts a resistance spring or card. At the end of the swing arm is a float that rides along the top of the fuel. As the float moves up or down with the fuel level, the other end of the arm contacts the resistance card, which increases or decreases the resistance in the signal to the gauge. It’s a pretty simple system and works well unless the float gets a hole and fuel fills up the float, or the arm does not have the room to move properly. There are adjustable swing arm sending units, but they have their drawbacks as well – calibration being one of those issues.

A second type of fuel sending unit has become popular with high performance and custom builders, the tube style fuel sending unit. When space does not allow for a swing arm style sending unit, these compact tube sending units are often the best and only choice left. A wooden yardstick being the final measuring solution for those that don’t need to know the fuel level at a glance.

How It Works

We talked to Classic Instruments’ Samantha Martin, about the sending unit. “Our tube style fuel sending unit is the latest innovative product to give your hot rod or classic car the finishing touch,” she began. “This tube style sendin unit is ideal for applications where conventional swing arm senders will not fit due to clearance issues,” she added. “They are also less susceptible to cause erratic readings due to fuel slosh in a tank where baffles are not present.”

Fuel enters tube from a small hole at the bottom. There is a vent hole in top of the tube that allows tube to fill. This design makes the tube fill and empty slowly, minimizing the effects of fuel sloshing in the tank which normally would cause a fuel gauge needle to sweep back and forth.

According to Classic Instrument’s engineer Jake Bernthal, “The tube style fuel sender has a float inside it that triggers the fuel level resistance of the sender.” Which means the sending unit measures accurately without having to worry about fuel slosh under hard driving or traveling on a winding road or other fun types of driving.

About The Unit

The sending unit comes in one-inch increments from six-inches to 36-inches in length. The Classic Instruments’ engineering team recommends buying a length that is within one-inch of the fuel tank’s total depth. For example, a tank that is 10.5-inches deep would use a 10-inch tube style sending unit. The extra half-inch allows for a little reserve fuel as an added benefit.

The unit requires no setup and has the standard aftermarket five-hole pattern mounting bracket. The unit requires no adjustments or calibrations but must be mounted perpendicular, with the ground at the top of the tank.

The sending unit has studs for signal wire and ground wire, which means that it doesn’t rely on tank contact for ground connection and will work on non-metal tanks.

This sender is available in five different ohm ranges: 0-30, 0-90, 73-10, 240-33 and 10-180. The sending unit is designed to give resistance readings every 1/8 tank for a total of 9 different resistance values (Full, 7/8, 3/4, 5/8, 1/2, 3/8, 1/4, 1/8, and empty). Pricing for the tube style sending units are reportedly $89 for lengths from 6 to 10-inches, and $99 for lengths from 11 to 36-inches.

For more information about this or the other fine products from Classic Instruments, visit them online at www.classicinstruments.com.