05/11/2010
Understanding the Loss of Tension in the Accessory Belt Drive System (ABDS)
The belt is one of the most important parts under the hood of today automobile but it is often overlooked as a potential trouble maker when there is a problem associated with the Accessory Belt Drive System (ABDS). Today many of the components operate collectively as a system and the sum of all parts have to operate in harmony or the system can’t do its job correctly. In the case of the ABDSystem it’s all about the system as none of the accessories would operate at all if the belt was not in place. Can a failing belt turn the accessory pulleys? Yes it can. Can it do it effectively if it worn out or has the incorrect tension? No because if either the belt or the tensioner is not doing its job correctly then the belt begins to slip and accessories operate at a reduced output.
Suggest 100% inspection and cleaning of all pulleys before installing a new belt
· The Belts only job is to transfer the torque from the crank to all the accessories and it does so by the wedging force of the V’s into the pulley grooves created by the tension placed on the belt by the tensioner.
· Five of the most common belts failures seen today are glazing, pilling, side abrasion and cracks. However, cracks for the most part have been replaced with belt rib wear. In addition rib wear can also be a component of one of the other failures mentioned above. So a belt can have multiple forms of failure developing and is why it’s important to learn how to read and understand the failures.
· A belt can exhibit multiple forms of failures and can typically mimic in reverse what is happening to the system pulleys they are running on. This is why it’s important to learn how to read and understand belt failures, its underlying root cause which in most cases will lead to the corrective action.
· Belt compounding has changed over the years and the industry has moved from neoprene to EPDM. An EPDM belt can run well over a 1000,000 and not demonstrate any real signs of failure other than wear and just 5% of belt wear will facilitate loss of tension in the system.
Here lies the problem:
Customer comes in to have a failed component replaced. Tech looks at the belt, sees no cracks or real wear in their opinion and reinstalls the belt along with the new accessory. Customer is back a couple of days later because the component is considered failed again.
They reinstall a new component but again use the old belt and tensioner which was causing the problem to begin with.
This has created a real problem for the industry because of the wear characteristics of EPDM. We have to change the mindsets and inspection techniques. Use the belt wear tool to check for rib wear.
· If the belt has lost tension by either
(1) Belt rib wear from use or (2) a failing tensioner; the belt will slip. A glazed or shiny belt or complaint of belt noise is an example of loss of tension from these two areas. It is recommended replacing both belt and tensioner together.
When a customer complains about belt noise it’s not a belt problem. There is a problem in the system that is causing the belt to become noisy and normally that is due to loss of tension (replace both the belt and tensioner together).
· Belt slippage creates many problems for the system.
- As the belt slips it wears and just 5% loss of material can create loss of tension.
- Heat is generated by the slipping belt and moves right into the bearing creating premature failure for the components such as an alternator.
- ABDSystems today can only tolerate 1º misalignment. For each degree over that we start compounding 30º of heat for the system. A slipping belt adds to heat build up if the system is misaligned.
- ABDSystem can operate at a diminished output with loss of belt material (belt wear) or a decaying tensioner.
~ Belt glazing / wear resulting in loss of power transfer
~ Belt noise
~ Reduced cooling capacity from the fan
~ Reduction in performance from the A/C
~ Creates heat resulting in premature bearing / accessory failure
~ Pulley wear
~ Poor charging from the alternator
· False trouble codes may be generated within the OBD-II system due to a failing
belt or tensioner.
– P0300-P0312 ( Pertains to Engine Misfire)
– P0325 – P0334 ( Pertain to Knock Sensor Area )
– P0550 – P0554 ( Pertain to Power Steering Pressure )
– B1849 – B1862 ( Pertain to Climate Control Area ) NOTE: “B” codes are body control
– B1969 - A/C Clutch Magnetic Control Circuit Failure
– B2119 - A/C Compressor Failure
Tensioner -
The tensioner has two important jobs that it performs for the Accessory Belt Drive System. First it maintains the optimum amount of tension on the belt so it can transfer the torque from the crank to the accessories under all operating conditions. If the spring is failing in the tensioner it cannot place the correct amount of tension on the belt and the belt will slip (above failures apply under slippage).
Secondly, it dampens like a shock absorber the oscillations or impulses introduced into the ABDS as each cylinder fires or as accessories turn on and off. As the damper begins to lose its ability to dampen it allows the arm to oscillate or hammer the accessory next to it creating premature failure of this component as well.
A tensioner will also exhibit (3) failure modes that if the tech does not understand what to look for will create comebacks and loss of profits for them as well as very unhappy customers. Bottom line is, most techs overlook the tensioner as a failure area and simply miss replacing the tensioner in the repair process.
- Belt making noise (squealing) or is glazed and shiny normally indicates loss of tensioner either through a worn belt or failing spring tension in the tensioner. Replace both belt and tensioner together to eliminate future problems and comebacks
- Pivot bushing wear. A tensioner will cycle 1 billion times in a 100,000 miles period. This cycling wears out the little plastic part (pivot bushing) that separates the case from the arm. The separation allows the arm to move sideways which forces the belt to run uphill creating side abrasion for the belt. Replace belt and tensioner and use the alignment tool ( # 91006) to check for additional misalignment problems in the system.
- Tensioner bouncing (hammering) because of failed or failing damper. Inspect and clean all pulleys. Replace both belt and tensioner together along with any pulleys that are marginal in nature.
· Remember: Loss of tension in the ABDS can result from either a worn belt or a failing tensioner and that’s why it’s best to replace both at the same time if possible.
· A complaint by the customer that their belt is making noise (chirp or squeal) normally indicates loss of tension resulting in one of the above system problems.
or click on one of the links below
www.gatesprograms.com/beltwear Two Guys Garage (play video)
www.facebook.com/gatestraining Training Face Book page
For additional information please contact the Gates Training department at
or Bobby Bassett at
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