That early morning screach

big_white_dog84

big_white_dog84

big_white_dog84

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What causes that screeching / squealing sound that some cars / vans / buses etc make when they move off sometimes? Tends to be in the morning when I hear it, but maybe that's just cause the dude over the street wakes me up with it when he moves off in his van.
 
As echoed above, it's almost ALWAYS a slipping accessories belt.. not fan belt, most cars fans are now electric :P... its the belt for things like.. alternator, power steering pump, air con pump, sometimes water pump (if not electric).. etc..

you tend to hear it more in winter because the metal components (pulleys) have shrunk.. making the belt slack(er).. so they slip until they've warmed up.. :)
 
I always thought that the reason the belt stops squeeling is because the friction between the belt and the pulley as it slips creates heat.


This in turn makes the surface of the belt slightly tacky and it grips.
 
TaKeN said:
I always thought that the reason the belt stops squeeling is because the friction between the belt and the pulley as it slips creates heat.


This in turn makes the surface of the belt slightly tacky and it grips.
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thats also true, but if you actually go under the bonnet (i have to do this often - damn mini).. in winter the belt seems to be quite a lot slacker.. another factor is the type of belt.. if you look on older cars such as mine it'll be a single belt that fits in V shaped pulleys.. on newer cars they have teeth running down their length (more surface area).. thats why it happens more on old cars than new cars :p
 
big_white_dog84 said:
Thanks. I'm assuming it's not a serious problem if Mr Screechy over the road hasn't seen fit to get it fixed and let me sleep past 6am since about August?
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It could wear the belt quicker, or so I read the other day.

(Mr. Screechy might not be very screeching for much longer) :)
 
big_white_dog84 said:
Thanks. I'm assuming it's not a serious problem if Mr Screechy over the road hasn't seen fit to get it fixed and let me sleep past 6am since about August?
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Not really until it goes totally, but also a blast of WD40 while the belt is turning (ie engine running) will temporarily cure the problem in most cases. This is what a Ford mechanic told me recently and the belt stopped making any noise within a few seconds of starting spraying.
 
I was also told to put some WD40 on the belt to stop it squeeling.


Surely it just lubes between the belt and the pulley and takes away the squeek :confused:

But the belt must still be slipping slightly
 
WotDa said:
It could wear the belt quicker, or so I read the other day.

(Mr. Screechy might not be very screeching for much longer) :)
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After 4.5 months of it I hope so. Thing is I don't really know who it is - I think it's the van man over the road but on the few times I have been bothered to look I have been too slow to get up and he has disappeared away round the corner.

Another question: if it is this belt, why does it get much worse when the vehicle is moving off eg from traffic lights?
 
Because the belt spins off the engine crank which means it gains speed with the engine revs rising

Faster speed = more screaching noise until the alternator and other devices gain enough speed for it to grip.

Have a look at your own car and you'll see what we are talking about. The simple fix it to either adjust the tension so it doesn't slip, or to replace the belt as it's worn and then to tension it.
 
No never use WD40 on a drive belt....

If it is squealing, then you should make sure it is adjusted properly, and then use french chalk on it....

Usual cause of squeal is the extra load of all the lights, heating, rear demister etc causing extra load on the alternator..

:D
 
Stonedofmoo said:
Because it's far better to spend the 2 minutes it takes to simply adjust the belt correctly? :confused:
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I will get it replaced at its next service in a few months (the belt took a battering recently chewing something up - long story). But in the short term I was basically told that it happens most on cold winter mornings because its something to do with the moisture making it slip, the WD40 or similar repels the moisture stopping it from happening. I've never heard it happen on a warm engine so I assumed this to be correct.

EDIT: Just thought I would add I'm not arguing this as a long term fix, but is useful if you can't get around to sorting it for a while, and in this case stop the noise annoying other people :p
 
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Matthew.M said:
Why not? I was told it was fine by a Ford mechanic and its successfully worked on both the cars I've tried it.
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Wow a Ford mechanic that understands the effects of solvents on rubber and petrochemical based plastic products...

NOT!

We used WD40 to soften tyres for RC cars to give them more traction... After wiping off, but otherwise WD40 has a lubricant effect which can reduce the efficiency of the belt that usually drives the alternator and the water pump..

If you are using a kevlar multi-v belt, these are much more resistant to the solvent, but you are still adding a lubricant...

On these belts, and where the squeaking is caused by the belt back, rubbing on tensioners, you CAN apply wd-40 to the BACK/OUTSIDE of the belt, but not on the faces of the pulleys... or the area of the belt that touches the pulleys...

I have seen belts that have had this done suffer badly when the alternator goes under heavy load...

But its your call

;)
 
Matthew.M said:
I will get it replaced at its next service in a few months (the belt took a battering recently chewing something up - long story). But in the short term I was basically told that it happens most on cold winter mornings because its something to do with the moisture making it slip, the WD40 or similar repels the moisture stopping it from happening. I've never heard it happen on a warm engine so I assumed this to be correct.
:p
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It slips because the alternator is under its heaviest load on a cold morning...

Rear demister, heater fan up to full, lights on... this additional drag causes the belt to slip and squeal, as the drive cannot keep up with the load due to the belt being slack...

Enough moisture on the belt to cause it to slip is also sufficient to stop the squeal....

The other most popular time to hear the slipping fan belt is at night again when the alternator is under heavy load... during the day, with no lights etc its only heard where the belt is so loose its risking being thrown off, just like it did on a hire car I was given once...


:eek:
 
It was always going to happen....I have now got the same problem on my car. Assuming I don't even know where to find this belt am I better looking through Haynes to figure out how to fix it, or just taking it to my friendly (if overpriced) local garage?
 
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