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How Much Do New Belts Stretch?

So I recently replaced both AUX belts on my 1983 VW Jetta (1.6 TD) a few days ago. Today, the alternator belt was flopping around and squealing, so I tightened it up. Now the belts are once again chirping at me (only at idle). I believe its probably the Compressor/water pump belt is loose.

Should I expect to readjust a standard V-belt a few times or should I be checking the pulley alignment?

V-belt should NOT stretch as much as you describe. V-belts can wear-in and loosen a bit over many miles but they don’t usually require re-tightening after a few days. I think you have a problem.

Fantastic. I’ll have to take a look at the pulleys then. Maybe it’s an alignment and/or pulley issue


I’ve had different experiences with v-belts

In every case, I did have to retighten new belts after a few days

@db4690 It’s been a long time since I had a car with v-belts but I also had to retighten them.

Different story here. I snug up new v-belts a touch more so I don’t have to go back and re-tighten them. You can go overboard and ruin bearings that way but I never had a problem.

I’ve never had to re-tighten a new v-belt within a few days of installation. Sometimes I need to retighten, but that’s only after 3-6 months of driving. It probably varies car to car, but you probably have some other issue. You know the proper procedure right? Assuming this isn’t the first time you’ve it. If you are new to this, let us know. Maybe you are just forgetting to do something.

So I just went out a retightened everything properly. However I still have the chirp/squeal. As soon as I give it some gas, it goes away. From poking around with a stethoscope I determined its originating from main pulley/water pump area.

Doesn’t sound like a bad water pump… So could a bad main pulley be the issue?

It was always a good idea to run an engine for a few minutes after installing a new belt and then retighten it. Dayco and Gates belts never had a problem with stretching after that but the cheap McParts belts were notorious for stretching years ago and may still be. One nightmare with a McParts belt was enough for me. And the largest McParts chain’s VP learned that his belts were junk when he visited my shop 20 years ago. He and his yes men left in a huff in a Jaguar. I was less than cordial.

I am not aware of the current quality of belts other than Dayco and Gates and OE but would advise sticking with the known quality belts.

The problem is rarely the pulley itself. If it is not the belt, and you are using the correct belt and didn’t do anything to change the belt alignment, it would usually be something wrong, like a bad bearing, on one of the accessories or tensioners used by that belt.

One thing I’ve learned over the years as a DIY, be sure to carefully compare the old belt to the new before replacing belts. They should be the same length, same width, same cross section shape, and, if grooved, have the same number of groves.

I have even had problems with Gates belts

Let me qualify that statement . . .

If the OEM was not Gates, I’ve had problems with aftermarket Gates belts making noise. And it was not the idler, tensioner, etc.

After replacing with a factory belt, the noise was instantly and permanently gone

However, if the OEM was Gates, I’ve not had problems using aftermarket Gates belts. As long as the length was exactly the same . . . 6PK2435, for example

I thought modern belts weren’t supposed to stretch at all. One mechanic told me they actually can’t.

Serpentine belts don’t stretch much. This car is an '83 Jetta so it has V-belts and those can loosen up a bit after some use.

My memory is very hazy on this but some VWs of this era used rubber mounted alternators and/or rubber mounted A/C compressor/alternator brackets. Those could be a problem; however, I can’t remember if this year diesel had that setup or not.

Another possibility could be a timing belt tensioner issue or chirping vacuum pump which is resonating through the engine.

I just had the vacuum pump out, but it seems localized and not something resonating. The timing belt tensioner is a maybe, I sure hope not though.

The alternator and compressor are not rubber mounted on the bracket

Try spraying the belt with a little bit of water and note if the chirp goes away. If it does then it’s the belt.

It’s also possible to get belts that for one reason or the other just won’t get a bite on the pulley. Hopefully the new belts are the exact same width as what is supposed to go on there. Even a 1/16 of an inch can cause chirping, squealing, or slipping. I’m assuming the belts are the correct width; just pointing out a what-if.

I’ve had v-belts and multi-groove belts stretch a bit after installing. Not every time, but maybe 1 in 5 will chirp a bit a couple of days later. A quick retightening and all’s good. Just did one like that this morning.

So here’s what I found. By spraying belt dressing onto the water pump pulley, the squeaking disappeared (until the dressing wore off). So maybe the pulley is polished?

@Woogies‌, recheck the tension. The belt should not deflect more than 1/2 an inch between the pulleys with proper tension.