Thread: 302 Stroker??

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Ferrite beads are what we call "Gremlin Catchers", they're used on most electronics now days, you'll often see one on the power cord and other cables on your computer (the bulge in the cord). Basically they trap and store unwanted frequencies (A/C).

Most likely at the higher speeds the fans are forced to turn faster than their motor will allow (sometimes referred to as the generator effect), this can cause the brushes to arc on the commutator producing A/C frequencies that can interfere with sensitive equipment.

The ferrite bead, either applied to the sensitive equipment (speedo) or the the source equipment (fans) will absorb the phantom frequencies and store them until the equipment is turn off. Ferrite beads are usually applied to one (sometimes both) wire of the equipment, usually the wire goes through a hole in the bead (bead slips over the wire’s insulation), the bead does not physically contact the wire electrically (leave the insulation on the wire), rather it works by inductance.

Ferrite beads come in all sizes, you’ll find them online. Check with your speedo manufacture for a size (frequency range) they recommend. Slip the bead over the wire tape it in place and it’s done.

overpost sorry

overpost sorry

What I don't understand is how this "frequency feedback" travels without a complete loop. At 75mph your fan is not needed, and the thermostat/controller would be open, eliminating the path for 12v power to the fan motor. The fan is freewheeling, but the path back to the electrical system is blocked by an open switch, either a physical contact or an electronic switch in a controller. How does this feedback get to the other components if the fan is OFF?

Originally Posted by Dave Severson

Sounds to me like the flux capacitor is whacko again, hate it when that happens!!!!!!!

Nah.. the flux capacitor only reacts at 88 mph! ROFL!....

Roger I agree with you, if the fan relay is open there is no feedback/generator effect, only if the relay is still closed could the effect be present.

Usually, analog circuits are less sensitive to the gremlins that effect digital circuits, and I agree with you again that his gauges being analog (not digital) chances of this effect causing his problem are slim.

Originally Posted by rspears

What I don't understand is how this "frequency feedback" travels without a complete loop. At 75mph your fan is not needed, and the thermostat/controller would be open, eliminating the path for 12v power to the fan motor. The fan is freewheeling, but the path back to the electrical system is blocked by an open switch, either a physical contact or an electronic switch in a controller. How does this feedback get to the other components if the fan is OFF?

I only control the ground side with the relay! The positive side goes right back to the main power connection, aka battery.

Originally Posted by 36 sedan

Ferrite beads are what we call "Gremlin Catchers", they're used on most electronics now days, you'll often see one on the power cord and other cables on your computer (the bulge in the cord). Basically they trap and store unwanted frequencies (A/C).

Most likely at the higher speeds the fans are forced to turn faster than their motor will allow (sometimes referred to as the generator effect), this can cause the brushes to arc on the commutator producing A/C frequencies that can interfere with sensitive equipment.

The ferrite bead, either applied to the sensitive equipment (speedo) or the the source equipment (fans) will absorb the phantom frequencies and store them until the equipment is turn off. Ferrite beads are usually applied to one (sometimes both) wire of the equipment, usually the wire goes through a hole in the bead (bead slips over the wire’s insulation), the bead does not physically contact the wire electrically (leave the insulation on the wire), rather it works by inductance.

Ferrite beads come in all sizes, you’ll find them online. Check with your speedo manufacture for a size (frequency range) they recommend. Slip the bead over the wire tape it in place and it’s done.

One of my "tasks" over this coming winter is to replace existing gauges with a new set from Classic.. Thanks for the info on the beads!

Originally Posted by rspears

I'm thinking an intermittent ground problem, a battery going to ground or an alternator getting crazy.

I'd be looking/checking ground, it is the common link, and would be easy to check. Two alligator clips and a some wire, not knowing how the instrument cluster sits. Just throwing out the idea you figure out the attachment point. Jumping all over says to me intermittent connection.

You could clip on the mounting bracket of any one of the gauges, again the common link to all, go to a different body bolt beyond the dash. Or to make sure you eliminate all the ground paths from the body go straight to the bat -, then go for a test run, I think you said the threshold was 70, see if it repeats, or is stable. Then remove the giant ground jumper you have and have another run at it. If this is a glass body then I would think you have a ground buss that all the gages tie to, it that is the case attach your jumper there.

General rule of electronics is to control the hot wire not the ground.

It works either way, but sometimes it can preclude problems.

If the fan is really injecting AC into the system, then I'd want to totally isolate it: use a double pole relay and cut ground AND hot. AND if the thermostat switch is too low, then the fan will be on at speed, whether It's helping or not.

Originally Posted by pepi

I'd be looking/checking ground, it is the common link, and would be easy to check. Two alligator clips and a some wire, not knowing how the instrument cluster sits. Just throwing out the idea you figure out the attachment point. Jumping all over says to me intermittent connection..

Good thought and relatively easy to do! TIA!

Originally Posted by firebird77clone

If the fan is really injecting AC into the system, then I'd want to totally isolate it: use a double pole relay and cut ground AND hot. AND if the thermostat switch is too low, then the fan will be on at speed, whether It's helping or not.

One of my thoughts for testing if it was even related to the fans, was to ground the fans and let them run, take a spin down the highway and see what happens with them running. This should easily prove if they are even a culprit!

I'm slow, but I do get to the finish line eventually..

Just thought of this: if you run it to high rpm in first, and it doesn't occur, then you can rule out the alternator

Originally Posted by firebird77clone

I Just thought of this: if you run it to high rpm in first, and it doesn't occur, then you can rule out the alternator

I guess that would hold true.. But the aggravating part is it's intermittant. I took it out between rainfalls last night and ran down the same stretch of highway and it wouldn't react to any speed even to 80.

So perhaps something is / was loose and shaking?? or?? idk..

So I think I'll just go through and verify connections and make sure they are secure & clean..

Could be temperature related. If the temp switch cuts out, the relay opens, and the fan looses ground, free wheels , generating a floating voltage

Or perhaps (speed) something was shaking a connector loose enough to cause the headache!?!?! Or perhaps I'll never know!?!?! Sigh.. LOL..