Truck Topics

The Tool Box - Changing a V-Belt

Welcome to the Tool Box

This time we will look at changing V-belts.
These still do not hold your pants up, but are just as, if not more, important. V-Belts differ from micro V-belts in one main way:  micro V-belts have multiple V’s, whereas V-belts have one on the working side.  Although older design technology, they still do the same thing – run our engine accessories.   Accessories driven by the belts are the same, other than the fact that they may have their own belt or belts.

The wear characteristics are similar, but V-belts must be adjusted or replaced when worn whereas micro V-belts maintain adjustment with the tensioner, which extends life.  As V-belts wear they get cracks in the working side but also get narrower.  When they get narrow enough they will get to the bottom of the pulley groove and must be changed.  

Changing V-belts is different than changing micro V-belts, as each accessory has its own adjustment.  We will still need to get the right part numbers. These can be found at OEM’s or the part number may still be on the face of the belt.  You can get the belts at any auto parts store.  Normally the fan, crankshaft and alternator run on the same belt or a pair of belts and these must be changed in pairs.  The air conditioner compressor usually is run from a pulley on the back side of the fan pulley.

Ok let’s get started!!!  Alternators that use V-belts normally have a single bolt through a slotted adjustment arm on the top and two short or one long pivot bolt(s) on the bottom.  Loosen all of the bolts and the alternator belt will come loose with a simple tug on the belt.  Remove the belt in similar fashion as the micro V (threading over and around the fan blades).  

Install the new belt and pull on the alternator hand tightening the belt, then, using a pry bar (another tool for the tool box) pry on the alternator to tighten the belt.  The belt needs to be tight but not too tight, as over tightening can cause bearing failure in the alternator or fan hub.  The normal slack for a belt is about ½” of deflection when pushed upon (about 10 lbs. of pressure) in the longest section of the belt.  When you get the adjustment right, tighten the top (adjuster) bolt and recheck belt tension.  If ok, tighten the lower bolts and the alternator is ready to go to work.

Air conditioner compressors have two basic configurations: one is round with the adjuster arm and pivot bolt same as the alternator; the other is a large square compressor that has four bolts coming into the bottom of the case through a slotted bracket.  This kind usually has two threaded adjustment rods also through the bracket.  These are for adjusting belt tension.  Either way, loosen all the nuts and bolts, remove the old belts, reinstall new ones, pull the compressor tight by hand and use adjusting rods or a pry bar, whichever is the case for you.  Check belt tension and tighten all nuts and bolts.

Belt-drive water pumps will usually have another accessory as the tensioning device (alternator or air conditioner) or an idler pulley.  Either way, just loosen the idler or accessory and replace the belt.  Adjust the new belt to proper tension and tighten all loosened nuts and bolts. This should have you changing all of your own belts and saving you lots of money from shops.  

I change belts at least once a year, and change all of the belts at the same time. That way I know the condition of the belts.  As mentioned before, over tightening belts can be worse than having loose ones.  This job should take about two hours to change all the belts on the engine.

These methods are the same or similar for APU’s.  We have a Rig Master APU. To change the belts on it takes me about two hours because there is a lot of sheet metal that has to be removed to get to the belts.  

Until next time, keep the belts adjust properly.