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Serpentine Belts


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As luck would have it, I have the perfect serpentine-belt story to demonstrate: 1) the strange side of automotive repair; 2) the crazy things you have to deal with as a counter professional; and 3) that professional technicians can make mistakes, even when we don’t realize it.

A few years back, a friend of mine had driven to Georgia for a month-long visit with family. While they were down there, one of the front brakes locked up. They took the car to a local shop, which quoted them a lot more money than they could afford to fix the car. Since they were a close friend, and since I always looked for an excuse for a road trip, I agreed to help.

I was confident in their description of the problem, and even though I had never worked on the vehicle – a 1991 Lincoln Town Car – I was sure the problem was either a caliper or a hose. I bought all the brake parts I could possibly need, rented the cheapest econo-box car I could find for one way, filled the trunk with parts and tools and set the cruise control for Georgia.

As soon as I arrived, I transferred my cargo to the Town Car, turned in the rental and went to work. All I needed to do was fix it just enough so the car would make it back to Ohio and the comfort of my shop. I slapped on the caliper, bled it out and it was ready to go. However, before hitting the road, I did a quick check-over of the rest of the car.

My only serious concern was the serpentine belt. It was severely cracked and worn – probably one of the worst I had seen. I envisioned it falling apart somewhere in the mountains, so I thought it was best to replace it. On the way to the freeway, I stopped at one of the large auto parts stores and bought a belt. Since I hadn’t planned on this, I also had to buy a serpentine-belt tool.

The belt took me longer than normal to replace because the accessories on the bottom of the engine were difficult to get to, but I could see them well enough to know the belt was on correctly, and all the pulleys and tensioners seemed OK. I started it up, the belt ran true, so I was good to go. The freeway was still a couple miles and a half-dozen traffic lights away. Sitting at the very last light before 600-plus miles of open road, the car suddenly started making a terrible noise under the hood.

The rhythmic nature of the noise told me something was wrong with what I had just done. I dodged the entrance ramp for the side of the road. The new serpentine belt had completely shredded and fallen apart. I removed the remains of it, and luckily still had the old one in the trunk. I double-checked all the pulleys and tensioners and could see no problem, so I reinstalled the old belt.

Clearly, it couldn’t have been my mistake, so I blamed the belt for being defective. But, I still wanted a new one for the trip, so I returned to the auto parts store. I explained the problem, but they didn’t have another one. They refunded my money with no questions asked – which was, from a standpoint of customer service, the correct thing to do, and from my standpoint, also correct since a defective part wasn’t my problem.

With no option for a new belt, I had no choice but to cross my fingers and make the trip. I made it back without a single problem. The next week I took the car into the shop to properly finish up the brake work and install another new belt. This time the car was on the lift, so I draped the belt in place from the top, and as I always do, raised the car up so I could loop the belt around the accessories on the bottom.

Then I saw the problem. It turned out the correct belt for the car was a seven-rib belt. Someone in the past had installed an earlier-model A/C compressor that had a six-rib pulley, and they had installed a six-rib belt so it would work. Oops. In my apparent haste, I didn’t notice that when changing the belt. Of course, a six-rib belt works fine on seven-rib pulleys. But when the seven-rib belt was forced to work on the six-rib pulley, it shredded like cheese going on a pizza.

The counter professional where I bought the belt didn’t question whether or not it was defective. He just refunded my money. But he could have questioned it and maybe he should have, and not necessarily with the intent to say I had made a mistake, but in the interest of figuring out what had happened. Admittedly, I was surprised by the “defective” belt, but my confidence got in the way of common sense. Had I been questioned, I may have thought a little harder and began to wonder if indeed I had missed something. Well, we all make mistakes.

Selling Serpentine Belts

So, what goes into selling serpentine belts? The application is normally the easy part unless you have a crazy story like mine, but you may often be asked how to tell if the belt is worn out. Small cracks in the top surface of the teeth are normal and common, even with low miles on a belt. When the cracks extend all the way down to base of the teeth, that’s a belt that should be replaced.

The more prevalent indicator, however, is the cross-section of the teeth. When they’re new, the belt teeth aren’t pointy. They are squared-off at the top, and the cross-section of the belt will mate perfectly in the pulley grooves, providing maximum contact area. When the belt wears, the teeth become pointy and the cross-section of the belt changes drastically, reducing the contact area.

These visual inspections almost always allow you to make an easy decision about the belt. However, if condition ever is in question, and the vehicle owner isn’t sure of age or mileage, then it’s time to replace it. But the belt isn’t the only factor. Idler pulleys and tensioner pulleys are ideal upsell recommendations. Any loss of proper tension and any misalignment – both of which can be caused by worn idler or tensioner pulleys – will cause premature belt wear and/or noise.

Noise is the big one, and usually the first thing that makes people think about replacing the belt. Serpentine belts normally run very quiet, which is one of the reasons we like them so much. Any squeaking or chirping usually gets blamed on the belt, and usually it’s the reason they’re replaced. Make no mistake: A worn belt certainly can make noise, but usually it’s in combination with other factors.

It’s not uncommon to install a new serpentine belt to remedy a squeaking noise, only to find the noise is still there. In most of these cases, the belt truly needed replaced, but think of the perception by the customer. If they’re not aware of the other factors involved, they’re going to blame it on the quality of the belt. It happens often. Go figure! Who would ever claim a new serpentine belt was defective?

As I previously mentioned, incorrect alignment or incorrect tension can and will cause noise. In addition to pulley and tensioner condition, when the belt is installed, it makes a great straight edge. If it’s not perfect, then something is misaligned.

The most common culprit for noise, however, is dirt, debris and particles lodged in the accessory pulleys. If you don’t see it at first, look closer. It often collects in the base of the pulley grooves. As innocent as it may look, it will cause you to pull your hair out chasing a noise.

There are plenty of ideas floating around about how to clean them, but the bottom line is that it simply doesn’t matter. Clean is clean. Here’s the catch. Often, the debris is embedded in the grooves to the point where you have to dig or scrape it out with a pick, then follow it up with a wire brush. It’s not always fun, but it’s the only way to ensure no noise from the belt. You can use any solvent or degreaser you want, but that’s just the finishing touch. The physical debris must be removed, all the way around each and every pulley.

When it comes to upsells, belt tools are nice to have in stock. These are generally just for releasing the tension on the belt, but there’s another tool that’s a long metal rod with two metal “fingers” on the end. They are designed to grab and maneuver the belt, so you can install it in cars with very limited space to work. These can be a real lifesaver.

If the car has more than one belt, it’s a good idea to recommend all of them at the same time. If one is worn out, the other most likely will be too. It’s almost always a dirty job too, and one that causes a lot of skinned knuckles because you’re working in such a tight space. Shop towels and mechanics gloves are a great recommendation. If they don’t want gloves, point them to the nearest drug store to pick up Band-Aids on the way home. They’ll probably need them!

Last but not least are stretch belts. All the same rules for wear and inspection still apply, but there’s no tensioner. They have an elastic core that allows them to keep tension on the pulleys. They work great. Period. But installation is different. You absolutely must use the correct tool. It’s not that the tools are earth-shattering wonders; they simply provide a smooth ramp to guide the belts in place. If you do it any other way, you risk damaging, and most likely will damage, the belt. 

Oh yeah, and for the record, I didn’t put another six-rib belt on the Town Car. I installed the correct A/C compressor pulley and put a seven-rib belt on the car. The way it should have been.

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    • By Counterman
      You might not be able to see it, but an accessory-drive belt is always both speeding up and slowing down. When a piston accelerates downward after the ignition of the fuel and air, the crankshaft speeds up and then slows down as it reaches the bottom of the stroke. These changes in speed are minimal, but big enough to cause problems over time.
      If the pulses aren’t minimized, they can hammer the belt and the attached rotating components. On a four-cylinder engine, the degrees of rotation between power pulses are greater than on a V-8 – so the amount of change in speed on the four-cylinder pulley is greater than on a V-6 or V-8. This has a direct effect on how the belt system is designed.
      The belt-drive system is working hardest when the engine is at idle. When the engine is below 1,000 rpm, the alternator, A/C compressor and power-steering pump are putting the greatest strain on the belt.
      Some of the forces can be taken up by the belt slipping on the pulleys. But, slipping causes friction and wear on the belt, as well as flutter. Over time, the slipping can get worse as removal of material from the ribs causes the belt to bottom out.
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      Some alternators have a decoupler pulley. This device serves two purposes. First, it helps to decouple the pulley from the alternator with a one-way clutch. The decoupler reduces parasitic losses by not having to fight against the momentum of the armature in the alternator while the engine is decelerating and accelerating.
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      One of the common signs of bad serpentine belt condition is cracking. With the engine turned off, pop the hood and grab a flashlight to inspect the serpentine belt. If you see more than three cracks in the belt along the same three inch section, it is time for replacement. Be aware though that some modern serpentine belts are made from materials like EPDM (ethylene propylene diene monomer). These materials are highly resistant to cracking, so a belt that is well past its prime may still look good with no cracking, so it is best to keep checking for other wear indicators if you suspect a worn belt.
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      link hidden, please login to view can also cause the serpentine belt to slip so be sure to check it or else your new serpentine belt may have a short service life. If the belt is chirping like a bird the problem might be one or more accessory pulleys are out of alignment. Not only is this annoying but it will also cause the serpentine belt to wear out faster or even cause the belt to come off.
      
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      Timing-chain replacement is often very expensive due to labor time, but, then again, so is engine repair when a timing belt breaks. They both require special tools at times, so there’s no winner on that argument. And, one more thing: Did we mention the latest technology of belt-in-oil drive systems? Here we go again. So, do you have a preference, or do you agree with my conclusion?
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      These step-by-step instructions and video detail a serpentine belt replacement on a 2012 Ford F-150 XLT, and will be similar for ...

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