HELP - Adjustable Serpentine Belt Tensioner

First off - 97 Jetta 1.9L TDI 5 Speed. It has a manually adjusted serpentine belt tensioner. It has a hex key insert sticking out of the black cap on the back [See Pic] VW dealership confirmed it IS an adjustable tensioner [btw]. Can anyone give me instructions on how to make adjustments?

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It's not.
What are your symptoms?
The hex screw simply secures the tensioner hub to the shaft which has one logical position that it can be mounted. No adjustment.

If it is not providing adequate belt tension then it needs to have the shaft and bushings cleaned and lubed, replaced or the tensioner on the end replaced.
If you are trying to solve a 'chirp' due to slippage it is more of an issue with the harmonic balancer rubber ring being deteriorated.
Another possibility is that the alternator overrun pulley has seized up. That will cause the serpentine belt to bounce especially during cold idle.

https://youtu.be/r22GrCiZhl8

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JETaah said:

It's not.
What are your symptoms?
The hex screw simply secures the tensioner hub to the shaft which has one logical position that it can be mounted. No adjustment.

If it is not providing adequate belt tension then it needs to have the shaft and bushings cleaned and lubed, replaced or the tensioner on the end replaced.
If you are trying to solve a 'chirp' due to slippage it is more of an issue with the harmonic balancer rubber ring being deteriorated.
Another possibility is that the alternator overrun pulley has seized up. That will cause the serpentine belt to bounce especially during cold idle.

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This ^^^^^

And I'd wager your alternator pulley is shot due to the missing lower shield, missing cap, and rust inside of it.

Do I need the clutch or freewheel alternator pulley?

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You need an INA brand pulley.

Like this:

https://www.idparts.com/clutched-alternator-pulley-a3b4-p-3302.html

But before you order one, I'd make sure you can even get the old one off. You may end up just needing a new alternator, too.

B0B C. said:

Do I need the clutch or freewheel alternator
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Click to expand...

They are referring to the same function. apples and apples

Either will drive in only one direction and freewheel in the opposite direction.
'Overrun pulley' is yet another term for it.


It takes a tool to get it off and on like this
http://www.metalnerd.com/catalog/product/2644937fbe324184a25e586d88a2e97d






The larger spline holds the pulley inner hub and the smaller holds the alternator shaft. Choice is for two different styles of alternator shaft.

Given the rust that's showing in the picture... yup... if possible, worth seeing if you can get the old one off before you invest in a new pulley.

A good soak with a proper penetrating oil (ie NOT WD40 etc) may help.

Vince Waldon said:

Given the rust that's showing in the picture... yup... if possible, worth seeing if you can get the old one off before you invest in a new pulley.

A good soak with a proper penetrating oil (ie NOT WD40 etc) may help.

Click to expand...

I'm partial to PB Blaster but open to suggestions

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B0B C. said:

I'm partial to PB Blaster but open to suggestions

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Click to expand...

Yup, that's a good one. Just see lots of people fighting rusted bolts "but I sprayed it with WD40 why won't it loosen".

Vince Waldon said:

Yup, that's a good one. Just see lots of people fighting rusted bolts "but I sprayed it with WD40 why won't it loosen".

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To be honest I haven't touched a can of WD-40 in at least a decade

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It's just light oil, metal likes it, but won't really penetrate. Repeated PB, tap it with a hammer can help. They make stronger products like Kroll, available at your local gun shop.

The two types of inner splines are for Bosch or Valeo alternators usually.

I usually just take the alternator OFF the car if I suspect it is going to fight me, lay it pulley side up, fill the end of the pulley up with PB Blaster (seriously, that stuff works VERY well), and let it soak for a while.

Then I tap the center bit into the end of the alternator shaft, to get it good and seated, and try the normal method to remove it. If that does not work, and the inner splines start to want to round out and push the bit back out, I just put a 17mm socket on my 1/2" impact, place it over the pulley socket, and give it a zip and it 99% of the time comes right off.

You may be able to get in there and do this with the alternator on the engine if you remove the air cleaner and maybe loosen the fore and aft mounts and lift the engine up a couple inches. I honestly cannot remember on the older cars, been a while since I have even seen one in here.

BobnOH said:

It's just light oil, metal likes it, but won't really penetrate. Repeated PB, tap it with a hammer can help. They make stronger products like Kroll, available at your local gun shop.

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Actually its Kroil. In most cases its the go to product in power generating plants. It gets the job done.

Thank you. I was wondering if I should leave it on and let the bracket hold it or if I should remove it. I've only ever replaced entire assemblies this will be the first time I've done just a pulley

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Poor man's rusty-nut-buster: 50-50 mix of acetone and ATF (automatic transmission fluid). Actually tested to work better than most commercial stuff.
I finally put some of that together after years of SeaFoam (which certainly helped)...and the acetone / ATF stuff does indeed seem to do a better job.

And to the point of this thread...it (and some heat) is what helped get the pulley off my alternator in my 2003 last week.

Yup, if I was going to pull an alternator pulley for the first time I'd probably pull the alternator first so that I could do the job on the bench, see what I'm doing, let gravity help with the penetrating oil, and add heat without risking an engine fire, get longer wrenches, etc. j

They can fight at the best of times, and given that it had no endcap and is showing rust... it's likely that it will not come off easily.

Vince Waldon said:

Yup, if I was going to pull an alternator pulley for the first time I'd probably pull the alternator first so that I could do the job on the bench, see what I'm doing, let gravity help with the penetrating oil, and add heat without risking an engine fire, get longer wrenches, etc. j



They can fight at the best of times, and given that it had no endcap and is showing rust... it's likely that it will not come off easily.

Click to expand...

If I wanted easy I'd have a desk job

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So turns out it's NOT adjustable. Guy at dealership had no idea so he just agreed with me. What it does have is a replaceable spring on the back [the black cap with the allen wrench hole]

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Best penetrating oil? This guy tests them all.

https://www.youtube.com/watch?v=xUEob2oAKVs