Another Alternator Belt Tensioner - 3VX belts?

[coke]

My old 90 Jetta came with AC. I can tell you from prior experience that the top bracket the alternator bolts to, that bolts to the cylinder head, is not an adjustment bracket. The "toothed" version was used on the top on gas models, and below on non-a/c models. The only factory tensioning adjustment on your vehicle should've been the idler pulley just ahead of the A/C compressor.

My AC compressor wasn't even bolted in and was flopping around like a turd in the toilet, so I tightened it up, tensioned the Alt belt as much as I could, and ordered a non-a/c alternator. I never looked back, either. It virtually eliminated my belt problems other than the occasional 6 month alt belt adjustment.

You're hypothesis about the sharp back bend in the belt is likely spot on, causing the cogs to tear off. Not sure what luck you will have with the top cog belt. I only use Contitech belts on my car. I have a sheet somewhere that lists the belt measurements per application, if you want them.

On your top cog belt, the 15- part # for Dayco tells me less than the 11A700. My guess is your top cog is 11mm wide, 700mm long. I believe the stock belt is 10mm by 690mm. However, you have added tension from the "idler bearings" you added to your setup. Hope your new belt works out for you.

In closing, it looks like someone modified the top alternator bracket to allow for some adjustment. I will bet you dollars to dimes they didn't get much out of that. That whole setup is a cheesy way to tension a belt. I hated it, and I've never had AC on any of my Jettas that lasted longer than a week before I ripped it off.

[coke]

I can also tell you from experience, do not buy our power steering belt from Napa. They sell only one size, and list only one size, for gas and diesel, 10x750 and its too long. The gasser version takes 10x730 and the diesel takes 10x740 up to 1991, depending on how late in 91 you go (I guess, they changed something in 91 or 92)

[TylerDurden]

(LoL, coke got in before me...)

Thanks for the updates.

You might want to check on the spec for your belt. My 1991 owner's manual indicates a 9.5mm x 695mm. A Dayco 15275 is 15/32" wide (11.9mm), 27.5" = 698.5mm. The length is not as critical as the width.

Also, the pulley and bracket on the alternator don't look like the ones on my rigs: I haven't ever seen a cast alternator pulley and the top bracket should not need any adjustment-slot , since the tension is adjusted by the idler. This makes me wonder if the parts are appropriate - you might check to see if the pulleys are in good alignment.

[coke]

Yeah, I know what the book says about it being 9.5x, but I've always used the 10x contitech belts and they have never failed me, ever. *knock on wood* All of the auto parts websites I go to seem to indicate 10x<insert random number here> for any of the VW belts with the exception of the AC compressor belt, which should be 13 something and is commonly listed as 11 or 12.

I dunno if maybe contitech recommended the 10x vs the 9.5x for some reason we'll never know, but my local VW guy stocks 10x belts for power steering and alt.

[MagicBus]

My old 90 Jetta came with AC. I can tell you from prior experience that the top bracket the alternator bolts to, that bolts to the cylinder head, is not an adjustment bracket. The "toothed" version was used on the top on gas models, and below on non-a/c models. The only factory tensioning adjustment on your vehicle should've been the idler pulley just ahead of the A/C compressor.

Good to know. Maybe it's been less messed-with than I suspect.

My AC compressor wasn't even bolted in and was flopping around like a turd in the toilet, so I tightened it up, tensioned the Alt belt as much as I could, and ordered a non-a/c alternator. I never looked back, either. It virtually eliminated my belt problems other than the occasional 6 month alt belt adjustment.

IF I keep the car, a non-AC setup or a serpentine setup may be in my future. Though, the more I think about it, this car (by design, not as much by condition) is a little too needy for the amount of miles I need to put on it weekly.

You're hypothesis about the sharp back bend in the belt is likely spot on, causing the cogs to tear off. Not sure what luck you will have with the top cog belt. I only use Contitech belts on my car. I have a sheet somewhere that lists the belt measurements per application, if you want them.

With yesterday's belt replacement, I was able to reduce the backbend, but I need to use a shorter belt to reduce it even more. The 28" belt on there now will stay, though, until it needs replacement. Then, in goes the 27.5" or the 27". Hopefully, reducing backbend will ameliorate or eliminate my shred problem.

On your top cog belt, the 15- part # for Dayco tells me less than the 11A700. My guess is your top cog is 11mm wide, 700mm long. I believe the stock belt is 10mm by 690mm. However, you have added tension from the "idler bearings" you added to your setup. Hope your new belt works out for you.

The length of the new top cog belt currently in there is 28". Not sure what that is in mm. I did the conversion yesterday but tossed my notes.

In closing, it looks like someone modified the top alternator bracket to allow for some adjustment. I will bet you dollars to dimes they didn't get much out of that. That whole setup is a cheesy way to tension a belt. I hated it, and I've never had AC on any of my Jettas that lasted longer than a week before I ripped it off.

I don't even think the AC works in my car anyway. I just don't know what I need to substitute a non-AC setup.

[MagicBus]

(LoL, coke got in before me...)

Thanks for the updates.

You might want to check on the spec for your belt. My 1991 owner's manual indicates a 9.5mm x 695mm. A Dayco 15275 is 15/32" wide (11.9mm), 27.5" = 698.5mm. The length is not as critical as the width.

Also, the pulley and bracket on the alternator don't look like the ones on my rigs: I haven't ever seen a cast alternator pulley and the top bracket should not need any adjustment-slot , since the tension is adjusted by the idler. This makes me wonder if the parts are appropriate - you might check to see if the pulleys are in good alignment.

Unfortunately, that's the pulley that came with the car. I have no way to verify if it's correct or what SHOULD be correct.

As for the belt, the owner's manual does state a width of 9.5 mm, but I'm seeing a lot of vendors selling a 10 mm wide belt. I bought the Continental belts from GAP. I'm not an engineer, but .5 mm doesn't seem like enough to cause a problem.


As for the alignment, as best I can see, everything looks more or less OK. I lack a way to really measure it beyond lining it up by eye.


As of this morning, 50 miles on the new belt and counting. If I were a betting man, I'd figure this new belt will last for 1,000 miles or so (maybe more, maybe less, given the different style of belt), then I'll put on a shorter belt, which will allow me to adjust the alternator top anchor bolt out, reducing backbend as much as possible.

At least now I'm quick enough to be able to change the belt on the side of the road, or in a parking lot. The necessary tools now live in my trunk.

[tylernt]

With yesterday's belt replacement, I was able to reduce the backbend, ... Hopefully, reducing backbend will ameliorate or eliminate my shred problem.

Yup, that's why I used a 3" pulley for my tensioner, to be as gentle on the backbend as possible. I think another benefit of deleting the front V-pulley is to increase belt wrap on the alternator, which in turn reduces the amount of tension the belt needs and hopefully that reduced tension will increase belt life significantly. I really wish I could get the rest of my car finished and running so I could see if it works!

I don't even think the AC works in my car anyway. I just don't know what I need to substitute a non-AC setup.

It's pretty easy if you get a Mk1 1.6L (about '80 through '84) non-A/C alternator bracket and a non-A/C alternator and pulley. You can also use a Mk1 1.5L (up to about '80) non-A/C alternator bracket, but it tends to crack.

Anyway, if you can't obtain a Mk1 bracket, there are other ways of doing it with your existing bracket and some metal fab... there are several threads on this board discussing the various methods.

[82vdub]

I've read through several posts over the years about fixing belt tension problems. I don't believe that anyone has tried to install some type of tensioner/idler like the new serpentine systems have. To me, that seems like a pretty slick way to tension a belt, and I'd think it would work on a Vbelt setup if it's done right. Has anyone tried doing this method?

[TylerDurden]

I don't believe that anyone has tried to install some type of tensioner/idler like the new serpentine systems have... Has anyone tried doing this method?

The closest I have seen is this one:

It is not sprung, but it could be with some modification.


I'll PM and ask if it is still working. That looks like extreme back-flex... But, I have seen many v-belts with back-flexing idlers work for years, mostly on agricultural equipment (mower decks, blowers, etc.)

[coke]

I do believe that in order to delete the AC, you will need an MK2/A2 bracket, because the A2 bracket (I thought) used a different power steering bracket design that won't accommodate the MK2 one. However, there is good news. I deleted my AC and used the same bracket. The trick is using a few spacers and an adjusting bracket like the stock non-ac cars use. Worked like a charm, and I never had another belt problem... until one day when I tightened it and my wife blew it off and drove 5 miles with no water pump turning (PS pump disconnected) or alternator and when I got to the car, there was a puddle of coolant under it.

[tylernt]

I do believe that in order to delete the AC, you will need an MK2/A2 bracket, because the A2 bracket (I thought) used a different power steering bracket design that won't accommodate the MK2 one.

You're probably right. I didn't realize MagicBus has PS.

[MagicBus]

I'll PM and ask if it is still working. That looks like extreme back-flex... But, I have seen many v-belts with back-flexing idlers work for years, mostly on agricultural equipment (mower decks, blowers, etc.)

Good to know. Could be a fluke on my part in regard to the belt dying in 1 week. I'll keep an eye on it and keep you all posted. Made it into and out of work today without a problem.

[82vdub]

I'm sure the back bend on the belt and it's lifespan has to do with the radius of the roller that's bending the belt. Mower decks to bend the belt backwards, but they seem to have 4"+ size pullys on them. Hard to get another 4" diameter pully in the belt setup under the hood of a VW.

[coke]

If this is a vehicle you depend on going to work and back, I would most definitely remove the AC. Mine was one I used for just that. Everything. I was very happy when I got rid of mine. Even happier that all I had to do was source a non-a/c alternator. Got the toothed bracket from the local stealership and stole the harness from a junker I had. It was an 84, 3 prong plug in type with a wire bale that held the connector in.

My largest concern was if the AC compressor bearings froze up, then I'd be screwed, literally. I bit the bullet and adapted the correct non-a/c alternator and got rid of all that AC junk

[TylerDurden]

I'm sure the back bend on the belt and it's lifespan has to do with the radius of the roller that's bending the belt. Mower decks to bend the belt backwards, but they seem to have 4"+ size pullys on them. Hard to get another 4" diameter pully in the belt setup under the hood of a VW.

Agree... the radius and amount of wrap.

This does not appear too extreme and it's on the slack-side, but again, time will tell...


I got my modded rig out of winter storage, so I'll resume updates on its performance.