Volkswagen Fan Belt




Volkswagen Fan Belt



The fan belt is responsible for spinning the alternator/generator pulley which charges the electrical system and turn the fan in the fan shroud which cools the engine.  If your belt breaks or it thrown, your generator light should come on, notifying you that something is wrong.  If you decide to continue driving, your engine can overheat and damage can ensue.



Belt Adjustment

Because the fan must be properly positioned within the fan shroud for optimal cooling, the VW design doesn't allow for alternator position adjustment for belt tensioning as you would with most cars without a self tensioning belt system.  VW instead developed a shim system that allows you to change the diameter of the alternator/generator pulley to allow for proper belt tension. 


There should be 8-10 shims with the two halves of the pulley on the alternator/generator.  The more shims you have between the pulley halves, the less the overall diameter will be on the alternator pulley.  Shims not used should be placed outside of the pulley for storage.


Tension should be great enough to allow you to turn over the engine by turning the alternator pulley.  Add or remove enough shims until you are just able to turn over the engine.  The play in the middle of the belt should be around 1/2 inch.



Belt Size

The fan belt used by VW has evolved over the years.  They used the 9.5 x 900mm V belt for their 6-volt engines.  The Continental 9.5 x 905mm V belt was later used on the newer 12v generator engines.  Continental later standardized their belts to a 10 x 900mm (111-905-137B) and 10 x 905mm (OEM 111-903-137D) belt and VW came out with new OEM numbers to reflect this change.


Earlier bugs had smaller belt which was sufficient for the demands of their low wattage generators and smaller fans of their time.  The 36hp engine had a fan with 24 blades and a 160 watt generator. The 40hp and 1300/1500/1600cc single-port engines had fans with 28 blades which increases the demand on the fan belt to a small degree.  Plus during that time, the generator output rose from 160 watts to 360 watts.  As a result, the 1500/1600cc single-port engines had a 5 hp load on the fan belt, whereas the earlier engines only had 4hp.  Later, in 1971, the introduction of the doghouse cooler also meant a 5mm wider (10% increase) fan which brought the load on the belt to around 5.5hp.  In 1973, the addition of the 220 watt alternator brought the belt load to a whopping 6hp.  And with signs of early failures from the thin VW belts, it was time to upgrade the belt size, so the 1973 alternator also got a much thicker heavier duty 11.3 x 912 mm v-belt.


In regards to what belt will work for an engine with an alternator or generator - thicker is better.  For the most part, you can run the older thinner belts in a newer engine with an alternator and likewise can run the thicker newer belt in an older engine with a generator.  You will just have to add or subtract shims as needed.  Properly fitted thicker quality belts should last longer than thinner belts in any VW.


Also note that belts from different manufactures also vary to some degree in true size and different combinations of pulleys and belts can have a surprising impact on belt tightness.  The stock pulleys for the generators and alternators are the same, but these pulleys are often replaced with aftermarket ones by previous owners, so you may have to go with a longer or shorter belt to get the perfect fit.  Because of this, you may need to experiment with several belts, remember which one works for your auto and remember to buy a spare.


Stock VW 1600 DP with Alternator Belt:

Brand Part Number Size US Conversion Metric Conversion
OEM 111-903-137-E 11.3 x 912mm 0.4448 x 35.9055" 11.3 x 912mm
Gates 7355 13/32" x 36 1/8" 0.4063 x 36.125" 10.3 x 917.6mm
Altrom (NAPA) ATM 11X912      
Gatorback (Good Year) 15361 0.438" x  35.500" 0.438" x  35.500" 11.1 x 901.7mm
Dayco 15358 0.44" x 35.75" (36.3" outside circumference 36) 0.44" x 35.75" 11.2 x  908.1mm
Goodyear 13355      
Metric 10X910      
Master Pro (O'Reilly) 7355      
Master Pro (O'Reilly) 15355      
Duralast (AutoZone) 15355  0.438 x  35.500"   0.438 x  35.500"  11.1 x 901.7mm
Bosch 1987947500      
Continental 11.3-912      
Continental 6578116      
DIN 11.3X912      
Gates Europe N.V. II: 6372      
Goodyear 11AV0913      
Motorcraft EJD91      


The US Gates 7355 v-belt is supposed to fit:

  Beetle 1960-1979
  Campmobile 1968-1970
  Karmann Ghia 1960-1974
  Super Beetle 1975-1979
  Thing 1973-1974


In case you need to convert inches to and from mm:




Loose Belt

If your belt is too loose with all the shims removed, you may have a one off pulley or worn alternator bearing.  A slightly smaller than stock belt is one potential fix.  The Gates 7350 (13/32" x 35 5/8") should do the trick.

Brand Part Number Size US Conversion Metric Conversion
Gates 7350 13/32" x 35 5/8" 0.4063 x 35.6250" 10.3 x 904.9mm
Altrom (NAPA) 10X900      
Gatorback (Good Year) 15356 0.438" x  35.000"  0.438" x  35.000" 11.1 x 889.0mm
Dayco 15350 0.44" x 35" (35.6" outside circumference 36) 0.44" x 35" 11.2 x 889mm
Dayco 15355 0.44" x 35.5" (36.1" outside circumference 36) 0.44" x 35.5" 11.2 x 901.7mm
Goodyear 13351      
Metric 10X900      
Metric 10X890      
Master Pro (O'Reilly) 7350      
Master Pro (O'Reilly) 15350      
Duralast (AutoZone) 17350 (13AV0890) 1.3cm x 89cm 0.512 x 35.0" 13 x 890mm
Duralast (AutoZone) 17345 (13AV0875) 1.3cm x 87.5cm 0.512 x 34.4" 13 x 875mm


Tight Belt

If your stock sized belt is too tight, the the Gates 7360 at 36 inches (914.4mm) should work for you.

Brand Part Number Size US Conversion Metric Conversion
Gates 7360 13/32" x 36 5/8" 0.4063 x 36.6250" 10.3188 x 930.275mm
Altrom (NAPA) 10X913      
Altrom (NAPA) 10X918SET      
Altrom (NAPA) 10X920      
Gatorback (Good Year) 15366 0.438" x  36.000"  0.438" x  36.000" 11.1 x 914.4mm
Dayco 15360 0.44" x 36 (36.6" outside circumference 36)  0.44" x 36 11.176 x 914.4mm
Goodyear 13361      
Metric 10X915      
Master Pro (O'Reilly) 7360      
Master Pro (O'Reilly) 15360      
Duralast (AutoZone) 17360 (13AV0915) 1.3cm x 91.5cm 0.512 x 36.0" 13 x 915mm
Duralast (AutoZone) 17365 (13AV0925) 1.3cm x 92.5cm 0.512 x 36.4" 13 x 925mm


Continental 9.5 x 905mm for vintage VW diehards


12V Generator Belt

Stock VW 1600 with 12V Generator used a thinner belt (but can still use a thicker one too):

Brand Part Number Size
OEM 1966 to 1973 111-903-137-D 10 x 905 mm
Volvo 973547 9.5 x 905mm
Mercedes 006-997-02-92 10 x 910mm (37 3/4 inch)
Altrom (NAPA) ATM 10X905 10 x 905 mm
EMPI 00-9928-B 9.5 x 905mm


If this is too loose, you can try a 10 x 900mm belt used on the 6V VWs (OEM 111-905-137B)

Brand Part Number Size
OEM 1947-1966 111-905-137B 10 x 900 mm

Altrom  (NAPA)

ATM 10X900  

6 Inch Power Pulley


Power Pulley Belt

For those with a Power Pulley, you will need a smaller belt.

Brand Part Number Size Metric Conversion
EMPI 9120 9.5mm x 850mm  
CB Performance 2047 10 x 865mm  
Gene Berg GB 445    
Gates 7325 13/32" x 33 1/8" 10.3188 x 841.375mm
Gates 7330 13/32" x 33 5/8" 10.3188 x 854.075mm
Gates 7335 13/32" x 34 1/8" 10.3188 x 866.775mm



Air Flow Curves for the VW cooling fan



Smaller Generator Pulleys

The Porsche 356 generator pulley is smaller and allows you to move your fan faster at lower RPMs.  Some use it to compensate for a smaller crank pulley when installing dry sump pumps and others use it to increase cooling.  Care should be taken not to over tighten the belt as these can easily fail from over fatigue.  This should also make finding a properly sized belt for your application more exciting.


For VW pulleys, the 12 volt Generator/Alternator Pulley (stamped steel) was also used on the large diameter 6 Volt Generator (105mm OD). The very expensive cast-iron backed 6 Volt Pulley was used on the smaller diameter (90mm) 6 Volt Generators (GR11X) back to 1959 and aligns the belt differently than the newer pulleys and therefore is not interchangeable.  An even smaller pulley was used on the 36hp varieties because of their smaller Crank Pulley.



Other Part Numbers

Part OEM Number
Alternator/Generator Stand, Stock 113-101-211
Generator/Alternator Stand Baffle, All 1200cc-1600cc 113-101-221B
Generator or Alternator Stand Gasket 113-101-219
Generator or Alternator Pulley, 12 Volt 439-031-09
Alternator/Generator Strap 113-903-141B
New Generator GR15N
Nut, Alternator/Generator Pulley 111-903-181
Alternator/Generator Pulley Shim Set, 8 Pieces 111-903-131A8
Alternator/Generator Pulley Shim, Each 111-903-131A
Spacer, Alternator/Generator Pulley 211-903-183
Woodruff Key, Alternator/Generator Pulley N0127051



Serpentine Belt

There are a few aftermarket options available.  The CB Performance version can be problematic and the BMD seems like a quality unit that allows for easy belt tension adjustment and decreases or eliminates that possibility of the belt being thrown.


BMD Pulley System


The only potential problem with the serpentine system is that it is possible to over spin the fan.  With a stock setup, once you reach so many RPMs, the V-belt will slip.  With a serpentine system, you may have enough belt friction to turn the fan beyond the maximum RPMs that it is physically able to withstand.



BMD Pulleys

CB Performance



Cogged Pulleys and Belts


Bullys Pulleys



Spare Belt

After a spare tire (with lug wrench and jack), a fan belt is the most important spare item you should have in your VW.  And like a flat tire, you can't drive very far without a belt and shouldn't even try to.


Don't forget your screwdriver and 19mm wrench to change your belt.




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