Former VWDieselParts.com Forum

Odo now at 201111.

Tightened the belt today and once earlier, prolly around 199,500.

Does anyone know whether the constant retensionings are necessary because the belts are stretching, or because the engine vibration is loosening the tension from the alternator, compressor or tensioner?

I am in the middle of rebuilding my accessory/tensioner setup using the highest grade metric fasteners I could get, along with wedgelock washers to prevent loosening of the bolts from vibration. Previously I was either shearing off or having bolts fall out from the vibration on the alternator on a monthly basis. I eventually ditched the alternator and replaced it with a solar panel in my dash which I used for over a year. Now I am fixing the AC, replacing the alternator so I can drive for long periods of time and at night without having to stop to charge the battery. I will not put up with constant tensioning or replacement of the belts so figuring out whether the issue is due to bolt loosening or belt stretching would help to ultimately solve these problems.

I have NEVER had problems with vibration. Mine has always been a cheap ass tensioning device. I have never had a car with AC (79-92) that worked without constantly tensioning the belt. My 91 has no AC, just alt/waterpump/powersteering, but runs two belts and I tension them about twice a year.

This is what I did. I haven't retentioned in 30,000 miles. I removed the a/c but this could be done with the A/C you would just have to make more brakets than I did. Common aluminum turnbuckle that you can find almost anywhere.

Nice setup. Got any more pictures? I have power steering so I'm sure I'd have to do something different. It also looks like you are using a different alternator than mine uses.

On my rig it's belt stretch. It may be exacerbated by worn pulleys that aren't very smooth.

I can live with a tweek every 1200mi. It takes a couple minutes. I put a quart of motor oil in every 600mi, so I'm already under the hood at least every two weeks.

hows the belt fix working out tyler? break anymore? how many on your current belt?

bbob203 wrote:hows the belt fix working out tyler? break anymore? how many on your current belt?

Got about 3500 on the current belt. Did some travelling over this summer.

Still doing the finger-push test on the alternator fan for tension. Might be too light, but we'll see how it goes.

Some lugs came off the belt at 202,135.

Started at 199,176... so 2959mi.

The replacement is showing cracks between the lugs too. The colder weather may be reducing the belt's ability to flex back around the bearings.

More work is needed for a permanent solution.

If you to a belt manufacture or industrial supplier with the size of belt. They should be able to tell you the recommended smallest size pulley you can use to get good belt life. It should be in the manufactures catalog that lists all the belts. I think they call it minimum rap.

Looks like my belt is stretching too. I installed all the hardware with wedgelock washers and painted a stripe on the bolts as you can see in the pictures below. I have driven about 150 miles with the new bolts and belt and it has loosened up enough that I can turn the alternator fan/pulley. I suspect there will be some initial stretch in the belt since it is new, I will retension, remark and check again. I am thinking about adding a spring loaded idler pulley to keep a consistent tension on the system.

After further research I now understand that a new V belt will stretch a little after installation and should require retensioning after a run in period. In my case it was about 3 days of driving. I have retensioned it and now we will see if the diesel belt problem is due to hardware loosening or belt stretch. I bet it is a hardware issue not belt stretching.

I took a hardware class for work put on by the society of automotive engineers which I found to be very interesting. The thing I took away from the class is was that most traditional bolt retention methods like split washers and lock nuts DO NOT work, and loctite only works if the hardware is very clean. The lock nuts will keep the nut from falling off completely but it will not keep the clamp force on the bolted joint, and most lock washers (star and split washers) do not work. One interesting innovation lately is the wedgelock washer and according to the SAE teacher and everything I have read about them they actually do work. I bought a bunch of these washers and some loctite 243 which is oil resistant so its not quite as important to get the hardware completely clean before use, and replaced all the bolts on my accessory brackets with new 10.9 or 12.9 grade bolts. I suspect that the only reason the belt loses tension is because hardware loses its clamp force due to the vibrations of the diesel. If you look at how far away the alternator is in an AC car from the centerline of the engine it makes sense that this would amplify the affect of the vibrations from the engine. Picture a teeter totter. If you sit close to the pivot on the teeter totter you will move up and down less than if you sit all the way at the end. This is the difference between an alternator on an ac car and a non ac car as far as I can see. The alternator on a non ac car is very close to the centerline of the engine, its like sitting near the pivot point on the teeter totter. I believe this is why when one eliminates AC and relocates the alternator closer to the engine centerline the problems go away. One of the posters above showed a rod end tensioning bracket and stated that this worked well. I bet this is because it eliminated the problem of the hardware on the stock setup vibrating loose.

I had previously replaced all my bolts on the accessory brackets with what was available locally which happened to be metric grade 8.8 bolts. I installed them all with loctite but I found out after some time that they were not strong enough and several of them broke and others fell out. My alternator bolts were either breaking or loosening after about a month of driving so I am now determined to solve this issue once and for all. I would hate to have a daily driver that needs the belts retensioned every month.

I spent a good amount of time today researching belts.

9.5mm is about 3/8", but either way, not a lot of choices from Conti, Gates, Bando, Dayco.

Even a Bando marked 9.5 x 665 measured 10mm wide.

I can say for certain, the 10mm conti belts ride high on the compressor sheave.

I'll get a pic after lunch.

As you can see, the alternator belt rides high enough on the AC pulley to be pulling mainly on the soft portion.




A lug is missing directly under the idler.



I suspect the transition to 10mm belts has reduced the proper operation of a marginal setup.

I can't imagine belt life was so poor when these vehicles were sold new (w/ 9.5mm belts).

I got an AC compressor off the shelf and cut sections of belts for comparison.

As others have noted, the NAPA belts are more like 11mm-12mm.

The Continental belts are a true 10mm.

A DAYCO 3VX is 3/8" and rides fairly flush with the sheave.

I do not have a dead 3VX to section (yet). But, I can say it does ride deeper into the sheave, as it is a bit taller (as well as more narrow at the top).





So, I returned the path to stock, without the idler mod, to test the wear/stretch of a belt that seats better in the AC sheave.

ODO reading at change: 203,169. (So, about 1000mi on the Conti with cracked cogs, but not failing.)

I let it run-in for 200mi and tightened it.

I also have a 3VX 280 to try with the idler, when the 3VX265 belt goes astray.