Squealing Alternator

[puffernutter]

This is about a transit 2.5DI (in an LDV LWB if it makes any difference). The vehicle is an ex utility vehicle and had twin batteries (just simply paralleled, nothing clever). Also as far as I am aware, the belt is tightened to the correct tension and the alternator is brand new.

When you first start the van there is a squealing noise that comes from the alternator, the volume varies with speed and the tacho needle will only read around 500rpm and doesn't move. The noise seems to come from the alternator, although everything is spinning (as far as I can see). After a while (depends on the load on the alternator I assume) it will quieten down. Worse after it has been left for a while and much worse when the headlights are on. The alternator was replaced as the previous one was making this noise and I assumed it was an alternator on the way out!

I've just fitted a voltmeter and off load (ignition on but nothing else) it reads just over 12v (about what I would expect). After starting it reads just over 13v and gradually creeps up to just over 14v (again what I might expect). The noise seems to stop (on just one observation tonight) when the volts have been over 14 for a while. Certainly experience shows that after starting it makes the noise and it will appear to stop, however if the revs drop for a period (e.g.waiting at traffic lights or a junction) when you start off again the noise will re-appear, but then go after a a shorter time.

As the alternator is new (and it does the same as the one it replaced) I wonder if the problem is the batteries getting old and taking too much charge after starting? As they re-charge the noise goes away. After a period of driving, you can stop and restart without teh noise, leave if for 4 or 5 hours and it reverts to the noise at start up.

The only difference between this alternator and the older one is that the older on would squeal for longer!

Any thoughts or suggestions. I don't really want to shell out on a pair of batteries unless I have to as it wont be cheap and they do start the van OK at the moment! (It is only an occasional use as it what we use to take our Clumber Spaniels and Italian Spinone to dog shows!)

Cheers

Peter

[pedracer]

Is the belt and alternator aligned correctly? Unless the bearings are goosed, I doubt a duff battery could impart a load that would make a belt slip.

[puffernutter]

As far as I am aware. I'll check tomorrow when I get a chance. But why would the squealing stop after a while? It's interesting that something isn't right as the tacho isn't working when it's squealing, but it is charging (based on what I've seen tonight). I would have though that as long as there was output, then the tacho pulses should be present.

Cheers

Peter

[stalwart]

Some of this spells out worn alt bearings ,you sure the belts at the right tension,is it slipping,have you changed it?
Is it inline with the rest of the pulleys as this wears the bearings out rather quick, eye it all up and see.
On the volts side if the batteries are good you should read 12.3v before start,then when running even at idle you should get 14.2v(well i do on mine)
You sure the alts new?

[stalwart]

I dont think you Tacho will have anything to do with a duff alt,but dont quote me on this,i do have a complete workshop manual on ldv's with 2.5di fitted,will need to source it out though

[puffernutter]

Brand new alternator. Probably done less than 1000 miles so far.

I decided this time to pay more for a new one, not to risk a secondhand one from ebay!

Cheers

Peter

[vanfox]

Welcome to the piggy squeal club. Mine squeals at cold start up, goes away in a couple of hundred yards. I would put money on your belt slipping. (That's why your rev counter isn't rising)

It's a poly vee belt, what happens ( I believe) is the vees wear out leaving less belt to grip the vees in the pulley so the belt starts running on the top of the vees and slips/squeals. Check the vee side of your belt for cracks and bits missing. A new belt properly tensioned should ....cure it.

The voltages look OK. I have a spare belt in case mine snaps before I get to change it, The steering belt has to come off first, damn it!

[F111ORY]

Hi, My van does this when it is due for a new battery. Old batteries that will not start you when the frosty mornings come take a huge amount of power from the alternator following startup, this is usually when they get to their third winter.

[Aardvark]

Definitely a belt tension issue. After a cold start, the alternator is trying to put out max power back into the battery so it is creating a higher load for the belt to pull. Also a cold belt is harder and more likely to slip than a warm belt that has been running a few minutes. Some tachos run off the alternator so the lack of grip is indicated by the low reading on the tacho. When everything warms up, the belt softens and grips better and the squealing stops and the tacho reads normally, yes??
Apart from the belt tension you need to have a look "across" the front of the engine and try to visualise the path of the belt as it goes around all the pulleys. A common problem is the long bottom bolt that the alternator swings on wears away the holes it passes through, moving the alternator out of line with the other pulleys. This misalignment adds to the loose belt issue.

[Altransit]

I would totally agree with the worn belt theory
You do need to make sure it's all running in line, because these have a habit of wearing the lower alt mounting hole, causing it to sit at an angle to the rest of the pulleys

[weseeyou]

its more likely to be a dry Alternator or water pump Bearing, causing the belt to slip and squeal.

I have exactly the same on my 95 LWB Diesel at the moment.

Try squirting WD directly into either the the alternator bearing or the water pump bearing whilst its squealing. Don't spray both at the same time or you if the squealing suddenly stops you won't know which was squealing.

You will probably need to spray for up to 10 seconds or more and leave it for a few seconds more before sufficient WD gets to the bearing.

take care you don't get WD on any of the belts so use a new WD can with the attached spray pipe.

If that doesn't work try putting some talcum powder or resin onto the pulley wheels and inside surface of the belt .

I wouldn't recommend tightening the belt or the increased stress on the bearings could cause one of them to fail

[puffernutter]

Yes indeed, an embarrassed smiley!

Belt alignment was fine, just the tightness was the problem! A bit of tightening and all was quiet (both the alternator and belt were both new about 4 months ago). I guess it just wore a bit and stretched.

What is the rule of thumb for tightening flat belts? How do you know when it is tight enough and not too tight?

Cheers

Peter

[vanmann]

Hi, When you fit a new belt it needs to be readjusted after a short time.
Glad to see you have it sorted.
Regards

[Hugh Venables]

What a great website. Just borrowed a Mk 5 for a trip. It had a squeal and low tacho reading on start up, more often from cold. The owner tells me that it has been doing it for quite a while since the belt was replaced. When I dropped the belt off I noticed that the tops of all the multi vees were shiny on the alternator pulley. This indicated that the belt or the pulley has worn the sides off the vees so that the flat surfaces are holding the belt off the vees which won't drive as well. I put the pulley in the lathe and turned about 0.4 m.m. off the top of each vee and put it back together with the belt quite tight and the squealing has stopped. The belt should probably be replaced as the slipping has probably worn the sides of the vees away.