Alternator Squeal

[Russm]

Driving me crazy.

My first Alaskan winter. When it started to get cold the alts started to squeal slightly, and Gen2 would stay lit when turning the truck on. A small throttle bump and both would go away. As it got colder the squeal and Gen2 stayed on longer until now only the squeal goes away when the truck warms up but Gen2 stays lit. The Alaska winter also broke a bunch of stuff I probably shouldn't have been putting off. When I was finally getting the truck back on the road. Both Alts were not putting out correct voltage (measured at the alt). Also they both squealed loud enough to make your ears bleed. Found rebuild kits online, followed the write up found here. Installed them back, voltage now does a yo-yo. Ok bad (new) regulator. Replaced regulator a couple times, no improvement. Lost confidence in my own work, got 2 new alts from hillbilly wizard. Bolt them on. Drivers side squeals a little initially, I watch the voltage bump up to 14.6v after some generous throttle, squeal stops. Passenger side: squeals with throttle applied until engine is fully warmed up. Output is around 12.9v measured at the Alt.
I've tried belt dressing, seemed to marginally help. All the belts are less than 6 months old.

The squeal returns when running the heater blower on high along with the headlights.

Have traced all the wires, following the Gen2 troubleshooting guide. Replaced the diode behind the dash just in case. Cleaned all the connections in the circuit

What else am I missing?

Wires corroded inside the insulation? enough for a continuity test with the multimeter, but not enough for the circuit to work?

This truck is an ex-police vehicle. Hacked up wires under the dash. Have I missed one that's cut or worse, are there some extra ones in there causing this problem?

Time to find an unmolested harness?

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[ezgn]

Driving me crazy.

My first Alaskan winter. When it started to get cold the alts started to squeal slightly, and Gen2 would stay lit when turning the truck on. A small throttle bump and both would go away. As it got colder the squeal and Gen2 stayed on longer until now only the squeal goes away when the truck warms up but Gen2 stays lit. The Alaska winter also broke a bunch of stuff I probably shouldn't have been putting off. When I was finally getting the truck back on the road. Both Alts were not putting out correct voltage (measured at the alt). Also they both squealed loud enough to make your ears bleed. Found rebuild kits online, followed the write up found here. Installed them back, voltage now does a yo-yo. Ok bad (new) regulator. Replaced regulator a couple times, no improvement. Lost confidence in my own work, got 2 new alts from hillbilly wizard. Bolt them on. Drivers side squeals a little initially, I watch the voltage bump up to 14.6v after some generous throttle, squeal stops. Passenger side: squeals with throttle applied until engine is fully warmed up. Output is around 12.9v measured at the Alt.
I've tried belt dressing, seemed to marginally help. All the belts are less than 6 months old.

The squeal returns when running the heater blower on high along with the headlights.

Have traced all the wires, following the Gen2 troubleshooting guide. Replaced the diode behind the dash just in case. Cleaned all the connections in the circuit

What else am I missing?

Wires corroded inside the insulation? enough for a continuity test with the multimeter, but not enough for the circuit to work?

This truck is an ex-police vehicle. Hacked up wires under the dash. Have I missed one that's cut or worse, are there some extra ones in there causing this problem?

Time to find an unmolested harness?

Sent from my LM-V600 using Tapatalk

Try placing a straight edge from the alternator pulley to the crank pulley and see if they are square with each other.

 

[Keith_J]

100 amps at 12 volts is a lot to ask from a single 2.75 inch diameter V belt. Actual specifications exceed 1400 Watts, that is almost 2 HP electrically. Well over that in mechanical power.

Get notched or Gatorback belts. These grip the smaller diameter sheaves on these alternators. Get a good tensioner as the difference between too tight and just right is a Goldilocks range.

Even with perfect tension, you have to accept a small bit of squeal at times. Too much tension is hard on the bearings. When the squeal is too much, the rubber is going bad.

 

[Russm]

Interesting observation from today:

Accidentally started the truck without the dash harness plugged in. No squeal at all.
As soon as I plugged it in... squeal away.

The semi new belts are the notched ones. Gates brand.


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[Keith_J]

Interesting observation from today:

Accidentally started the truck without the dash harness plugged in. No squeal at all.
As soon as I plugged it in... squeal away.

The semi new belts are the notched ones. Gates brand.


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Without the dash GEN light bulbs connected, the alternators will not function so there will be minimal belt load so no belt squeal.

If you have either GEN dash light illuminated with the engine running, there is a problem.

Read the sticky thread at the top in this forum.

 

[Russm]

Have been all over that sticky for several weekends now

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[antennaclimber]

Are you sure the glow plugs are not on all the time? Can you confirm that they are off when the squealing occurs?

 

[Tow4]

My belts will slip (squeal) if the engine is above idle when the glow plugs are activated for the afterglow after starting the engine. If I let the engine idle until the glow plugs stop cycling, I don't have the belt slip. To be fair, my belts are old, so I accept that.

The load on the alternators are highest after starting the engine because the glow plugs and the cranking draw pull the batteries down. The drive power that can be transferred via the single V-belt is not as much as the alternator needs so the pulley slips. A larger diameter pulley provides more belt contact area and works better. The new aftermarket alternators I have seen have a smaller diameter pulley than stock, and that may be part of the problem. If you have a new alternator, try putting the pulley from the original alternator on the new one. Try going to a wider V-belt, I've done that in the past and it helped.

The electrical load on these trucks are small compared to the full size GM cars the 27SI was originally used on. The head lights and heater blower should not make the belts squeal. The regulator set point is 14.8, if you are only seeing 12.9 at the alternator, it's not working or you have a heavy electrical load. Are the output wires hot? Are the glow plugs staying on?

Have you done the test sticky at the top of this forum? Click Here

Since the vehicle wiring has been modified, I would do the test running wires directly to the battery that the alternator charges. Don't use the vehicle wires at all. Once you determine that the alternators work, or not, you will be able to narrow where to look for your problem.

 

[Keith_J]

Tow4, absolutely correct. I have a dash mount multimeter measuring voltage, current and power. Current shunt is on the negative to ground wire of driver side alternator as this is the harder working alternator.

I see 100+ amperes after startup, while glow plugs are cycling. It also shows draw of various circuits like heater blower at 15 A etc. The required torque to generate requested power is highest at idle speed, even though the alternator only produces 65 A maximum at that speed, WHEN VOLTAGE IS LOW.

Once batteries are happy and registering 14.2 to 14.5 volts, the regulator in each alternator is matching and torque load minimum. When the #1 wire to the regulator is only 12 volts, the regulator calls for higher output voltage by increasing the current in the rotor, the spinning magnet in the alternator. The magnet strength is directly proportional to the rotor current. And the spinning magnet induces current in the field windings based on both magnetic field strength and rotor speed. This is alternating current (AC) with frequency proportional to rotor speed. The AC is then converted to direct current (DC) by the bridge rectifier mounted on the back wall of the alternator case.

The typical function of the alternator from pre glow to full charge is as follows:

Pre glow is that wait time, 5 to 40 seconds, when the glow plugs draw battery power. About 100 amps initially, dropping to 50 amps steady state. Then the starter places a 300 to 600 amp load on the batteries. During this time, there is voltage to both regulator connections but output voltage is less than battery so no current flow. This causes the GEN lights to illuminate.

Once the engine starts, the alternator is now spinning with voltage at regulator terminals (switched power at 2, light continuity at 1). This let's the alternator bootstrap itself, power now flows from the diode trio to the regulator which controls current to the rotor in proportion to make the output voltage at least 14.2.

Note, the measured voltage set point is from regulator terminal 2, very little current flows in this circuit. The main output lug voltage can be much higher than battery voltage because of output current and resistance in the wires.

When the battery voltage measured on regulator #2 connection reaches 14.2 to 14.6 volts (temperature dependent), the regulator reduces rotor current which then reduces output voltage. This also reduces output current.

What does this all mean? Alternator draw varies with battery charge and engine speed and is highest immediately after starting. Blipping the throttle can get the belt out of the slipping condition because higher speed requires less torque. Letting the belt slip only increases wear. As long as the engine has oil pressure, there is no harm to blip to 2000 RPM.

The water pump and fan are also belt driven, the fan is clutched. Most clutches are engaged at starting due to internal fluid leaks and need a blip on the throttle to shift the fluid outward in the disengaged storage area to decouple the clutch, reducing belt load.

 

[Russm]

Very educational. Thank you for the write ups.

I started unwrapping the wrapped harnesses, looked like really old electrical tape, not sure if that's from the factory. Found another loose cheapo wire union. Pulled it off and fixed it properly with heat shrink tubing and some soldering.

Remembered I had a spare cluster + circuit board. Figured why the hell not, won't hurt to see if a different one works.
Go figure.
After the cluster swap, everything works suddenly. No Gen 2 light, front battery reads ~14.6v, rear reads ~14.9, after 30 sec of belt squeal. Good enough for me.

Left turn signal indicator doesn't work on this board, idk why, but the external lights still flash and the turn signal flasher still clicks. I'll happily have this problem instead of the other one.

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[Russm]

You fix one issue, you find another one.

I think my starter just grenaded itself.

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[ezgn]

Very educational. Thank you for the write ups.

I started unwrapping the wrapped harnesses, looked like really old electrical tape, not sure if that's from the factory. Found another loose cheapo wire union. Pulled it off and fixed it properly with heat shrink tubing and some soldering.

Remembered I had a spare cluster + circuit board. Figured why the hell not, won't hurt to see if a different one works.
Go figure.
After the cluster swap, everything works suddenly. No Gen 2 light, front battery reads ~14.6v, rear reads ~14.9, after 30 sec of belt squeal. Good enough for me.

Left turn signal indicator doesn't work on this board, idk why, but the external lights still flash and the turn signal flasher still clicks. I'll happily have this problem instead of the other one.

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It might be your left turn signal bulb or a bad ground to your left turn signal. The ribbon circuit is probably fine. Check your left turn sidelight and see if it lights up with the lights on.

 

[Keith_J]

This is why I have spare starter and alternator on hand.

Should bolt it back together and try.

 

[Russm]

This is why I have spare starter and alternator on hand.

Should bolt it back together and try.

I have my old (bad) one. Turns out one of the long bolts that holds the starter together is about 1/4" shorter than what my dead starter had. It was probably always holding on by a few threads and just came apart on its own. Swapped the bolts around .... It started right up

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[Russm]

It might be your left turn signal bulb or a bad ground to your left turn signal. The ribbon circuit is probably fine. Check your left turn sidelight and see if it lights up with the lights on.

All the external lights work.
It's ok. 35 year old truck always has to have a problem. Let it be this for now

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