Alternater belt keeps breaking

SOURCE: 2003 VW Jetta TDI what happens after timing belt breakes

you replace the engine or the head at the very least!!

SOURCE: How to change altenater belt on 87' cabi

INSPECTION

Inspect the belts for signs of glazing or cracking. A glazed belt will be perfectly smooth from slippage, while a good belt will have a slight texture of fabric visible. Cracks will usually start at the inner edge of the belt and run outward. All worn or damaged drive belts should be replaced immediately. It is always best to replace all drive belts at one time, as a preventive maintenance measure, during this service operation.

CHECKING TENSION AND ADJUSTMENT

See Figure 1
The belt tension on most driven components is adjusted by moving the component (alternator, power steering pump etc.) within the range of a slotted bracket. Some brackets (toothed) use a rack and pinion mechanism which moves the alternator side-to-side to adjust the belt tension. With this configuration, no prying tools are required. On Quantum (except 5 cylinder) and Fox models, the air conditioner compressor drive belts are adjusted by varying the number of discs (shims) between the halves of the crankshaft pulley. Before adjusting the belt tension on any engine, look at the mounting and determine what kind of bracket is used.
To check belt tension, push in on the drive belt about midway between the crankshaft pulley and the driven component. If the belt is less than 39.4 in. (1m) long, it should deflect between 0.80-0.120 in. (2-5mm). For longer belts, it should deflect between 0.40-0.060 in. (10-15mm). Belt size is usually printed on the back side of the belt. If it can't be read, it's probably time to replace it.

Fig. Fig. 1: To check belt tension, push in on the drive belt about midway between the crankshaft pulley and the driven component
Slotted Brackets
See Figures 2, 3 and 4

1. Loosen the adjustment nut/bolt in the slotted bracket. Slightly loosen the pivot bolt.
2. Pull (don't pry) the component outward to increase tension. Push inward to reduce tension. Tighten the adjusting nut/bolt and the pivot bolt.

Fig. Fig. 2: Alternator mounting with slotted brackets

1. Components, such as the power steering pump and some air conditioner compressors, may be mounted with a double slotted adjusting bracket using a threaded bolt and locknut to adjust and maintain tension. Loosen the locknut(s) and slightly loosen the bolt(s) in the slotted groove(s). Turn the threaded adjustment bolt(s) in or out to gain correct tension. Tighten locknut(s) and slotted bracket bolt(s).
2. Recheck the drive belt tension, readjust if necessary.

Fig. Fig. 3: Some components use a double slotted adjusting bracket with a threaded bolt and locknut to adjust and maintain tension. Loosen the locknut (shown) before adjusting the tension bolt

Fig. Fig. 4: An extension is helpful when adjusting the tension bolt. Be sure to loosen the nut/bolt on the rear slotted bracket first
Toothed Brackets
See Figures 5 and 6

1. Loosen the tension bolt and the alternator pivot bolt. These bolts should be loosened until the alternator swings freely under its own weight.

Fig. Fig. 5: Loosen the tension bolt (shown) and the alternator pivot bolt until the alternator swings freely under its own weight

1. Adjust the V-belt by turning the nut on the tension bolt while checking the belt deflection with your thumb.
2. Once the proper tension is achieved, tighten the tension bolt to 26 ft. lbs. (35 Nm). Tighten the pivot bolt to 15 ft. lbs. (20 Nm).
3. Recheck the drive belt tension, readjust if necessary.

Fig. Fig. 6: Adjust the V-belt by turning the nut on the tension bolt
Split Pulley
See Figure 7
On Quantum (except 5 cylinder) and Fox models, the air conditioner compressor drive belts are adjusted by varying the number of discs (shims) between the halves of the crankshaft pulley.

1. Remove the nuts/bolts securing the tensioner plate and crankshaft pulley halves.
2. Add or remove the amount of spacer discs between the pulley halves until the belt tension is correct.

Fig. Fig. 7: Belt adjusting shims on Quantum (except 5 cylinder) and Fox models. Extra shims are stored behind the tensioner plate on Fox and turbo diesel Quantums (shown)
If there are any shims left over, do not throw them away. On Fox and turbo diesel Quantum models, store the extra shims in front of the split pulley (behind the tensioner plate). On Quantums with 4 cylinder gas engines, store the extra shims behind the split pulley (in front of the crankshaft hub).

1. Secure the pulley halves. Torque the pulley nuts or bolts to 15 ft. lbs. (20 Nm).

REMOVAL & INSTALLATION

If a belt must be replaced, the driven unit must be loosened and moved to its extreme loosest position (usually by moving it toward the center of the motor). After removing the old belt, check the pulleys for dirt or built-up material which could affect belt contact. Carefully install the new belt, it may appear to be just a little too small to fit over the pulley flanges. Fit the belt over the largest pulley (usually the crankshaft pulley at the bottom center of the motor) first, then work on the smaller one(s). Gentle pressure in the direction of rotation is helpful. Some belts run around a third or idler pulley, which acts as an additional pivot in the belt's path. It may be possible to loosen the idler pulley as well as the main component, making your job much easier. Depending on which belt(s) you are changing, it may be necessary to loosen or remove other interfering belts to get at the one(s) you want. Some models have a front engine mount installed through the air conditioner compressor belt circle. Support the engine and remove the mount prior to belt removal and installation.
When buying replacement belts, remember that the fit is critical according to the length of the belt, the width of the belt, the depth of the belt and the angle or profile of the V shape (always match up old belt with new belt if possible). The belt shape should exactly match the shape of the pulley; belts that are not an exact match can cause noise, slippage and premature failure.
After the new belt is installed, adjust it for proper tension. This is sometimes a three or four-handed job; you may find an assistant helpful. Make sure that all the bolts you loosened are retightened and that any other loosened belts also have the correct tension. A new belt can be expected to stretch a bit after installation so be prepared to re-adjust your new belt.
After installing a new belt, run the engine for about 5 minutes and then recheck the belt tension.