Exhaust Systems -- The Ins and Outs of Muffler Repair

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There are more components to the exhaust system than just the muffler, a fact many people don’t realize. When confronted with a simple muffler exchange, the muffler mechanic might start talking about CATs, air injection systems, hydrocarbons and the like until your head spins.

Most exhaust systems are durable and can last up to 70,000 miles, or in some cases up to 100,000 miles, depending on the climate of the area you live in. Rain, snow, road salt and sea air salt can be determining factors as to how long the system will last.

EXHAUST COMPONENTS

THE EXHAUST MANIFOLD

The exhaust manifold bolts directly to the cylinder head. If your car has two cylinder heads (as in the case of a V8 or V6 engine) it will have two exhaust manifolds. A manifold is sealed to the cylinder head with a gasket, studs and nuts. -Its function is to draw hot exhaust gas from the head (s) and into the front exhaust pipe where it's routed through the catalytic converter, the muffler, then out the rear tailpipe where it makes a contribution to smog and the impending “Greenhouse” effect.

Common Problems—Some manifolds work in conjunction with a thermostatically controlled air cleaner. You can tell this by the appearance of a cowl or metal housing that wraps around the exhaust manifold. From this a flexible, aluminum coated hose is directed up from the manifold and secured into the bottom of the air cleaner snorkel. The prime function of this system is to increase the temperature of the intake air to the carburetor during warm-up. The hotter air helps vaporize the raw unburned fuel and provides a better air/fuel mixture for total combustion. This hot air is drawn up when the engine is first started—this helps the engine warm up faster and burn away any unburned fuel. Quite often, this flexible hose will tear, affecting the cold-starting capability of your car. Due to a choke system automobiles always burn a richer mixture of fuel during cold start. And this is when toxic emissions are most prevalent. This is an important point to remember during a smog check. For more on that turn to section 10.

There is not too much that can go wrong with an exhaust manifold. Between the cylinder head and the manifold is a gasket. This gasket can leak, which would result in a loss of exhaust efficiency, decreased power and an increase in fuel mileage. Sometimes exhaust manifolds crack which causes loud under-the-hood exhaust noise and often exhaust fumes. Replacing a cracked exhaust manifold might be a warranty item. If not, it’s expensive. In fact, replacing the manifold gasket is also very expensive. Not because the gasket costs much. It doesn’t. But the amount of time required to get at the gasket is quite high, and when it comes to auto repair, time is money.

THE EXHAUST PIPE

The exhaust pipe is generally maintenance-free. It is constructed of heavy gauge steel and is designed with the least amount of bends and constrictions to aid in the free flow of escaping exhaust gas. The pipe is typically supported by several shock-type mounting brackets. On many new vehicles the pipe is one continuous piece, with the muffler welded between the front and tail section. On vehicles equipped with emission control the catalytic converter is clamped into place to facilitate its ease of removal and replacement.

Exhaust pipes will suffer rot, rust and deterioration in conditions of snow, ice and heavy rainfall. Salt, when used to deter icy conditions on roads, has adverse effects on the complete exhaust system metal. Exhaust pipes and systems are equally subject to impact damage when vehicles hit low spots or obstructions. Furthermore, the hangers that hold them in place can become loose, especially rubber hangers, which causes the exhaust pipe to vibrate. Excessive and constant vibration can cause the pipe to crack at the weld seams.

Complete exhaust pipes, from the manifold on back, can be quite expensive when purchased from a dealer. As stated before, the exhaust pipe and muffler are often welded together as one unit, but quite often a muffler chain won’t have that single piece. What they do have is a multi-piece system and if that’s the way you go, expect to pay much more than the advertised special.

CAUTION

Many muffler shops don't carry muffler systems for many imports. Often, they will make a custom system to fit, for a much higher charge than a simple remove and replace muffler. If your muffler and tailpipe is one piece, for example, chances are the muffler shop can only replace it with a multi-piece system, and the labor and parts charges will be much higher. Unfortunately, your only other alternative, the dealership, may not be any less expensive. The best alternative? Buy the muffler system from the dealer or an import parts store and install it yourself.

THE CAT

The CAT, or catalytic converter, is the central component to an emission control system. The catalytic converter is an insulated stainless-steel container within the exhaust system resembling a conventional exhaust muffler. Exhaust gases passing through the converter are chemically neutralized by one or more activating catalysts. These catalysts, consisting of platinum and palladium, are used to speed up the burning of excess hydrocarbons and carbon monoxide, producing harmless carbon dioxide and water.

So, in essence, a catalytic converter is a chemical tank that serves as an afterburner to reduce harmful emissions. The extremely high temperatures that occur in the converter also help to burn off unburned fuel, HC and CO.

Common Problems—I’ve seen stickers on new cars with warnings from the manufacturer stating that you must take care not to drive your car when the engine is malfunctioning in order to avoid damage to the CAT. I have only seen one case where a converter was noticeably damaged by an engine miss. And this vehicle was supposedly driven with a major engine malfunction for over a year in that condition. The outside appearance of the converter was noticeably burned, exuding a “rotten egg” smell. The metal skin of the converter, in particular the top and sides, gave the appearance of a bluish rainbow effect— evidence of extreme temperatures. It is safe to assume that this converter was damaged internally and would have to be replaced. But I think that the hype that has been printed about the precautions concerning the catalytic converter are, at best, extreme.

According to the MVPC (Motor Vehicle Pollution Control) Handbook for installation and inspection stations: “There is no universal field test method for inspecting converters at this time.” The California Bureau of Automotive Repair recommends that you follow the vehicle manufacturer’s procedure, which varies from car to car.

In an effort to learn more about the newest technology concerning the catalytic converter I contacted Mr. Duane Bilderback, an emission control engineer at the California Bureau Of Automotive Repair. It was his contention that there was really no surefire way to diagnose a faulty converter but they did have some new ideas lined up. “Most complaints with the catalytic converter have been symptomatic and imagined,” he went on to say.

So what does all this mean? It means that no one seems to be able to agree when the catalytic converter is bad. If you suspect it's bad, or are told as much, then go immediately to your dealership. For more on that, see Shams below.

MUFFLERS

Mufflers are a more simplified version of the converter. Like the catalytic converter they are constructed of heavy gauge steel, wrapped in a tank-like canister.

They are usually located behind the converter and attach inline with the exhaust pipe. They don't have any catalyst material inside. In stead they contain interior steel baffles and plates. These baffles are constructed and situated within the muffler to slow down and interrupt the exhaust flow, thus suppressing noise and arresting spark or hot particles.

That is a muffler’s chief purpose; to suppress excess noise and arrest spark. On many new factory cars, the stock muffler is often welded directly to the exhaust pipe. This probably cuts down on labor time and negates the use of clamps, which could be very costly when there are thousands of cars produced. When that stock muffler is replaced by one other than a stock unit from the vehicle manufacturer, it's torched, or cut off with a pipe cutter. Then a new muffler is usually installed with small adapter pipes and U-bolt clamps. From then on, if it requires another muffler it can be easily bolted into place.

Resonators—Resonators are made of the same material as converters and mufflers. They might be slightly smaller than mufflers and appear more cylindrical in shape. They are often located behind the muffler somewhere near the rear of the vehicle in proximity to the tail pipe.

Resonators are really secondary mufflers. Years ago they were used often on the large full-sized luxury cars such as Cadillacs and Lincolns. Still in existence today, resonators serve the purpose as an additional suppression device to further reduce exhaust noise to a minimum.

Resonators might cost more than mufflers because most repair shops, aside from the muffler chains, don't stock them. Often they are a special order part and are difficult to find. It is ironic that a resonator, a secondary or backup system to the muffler, can cost two or three times as much as a muffler. A vehicle with dual exhaust (two mufflers and two resonators), can get quite expensive when it comes to replacing the entire exhaust system.

Common Problems—It doesn’t take a test pilot to figure out when the muffler needs to be replaced, unless of course you’re hard of hearing, in which case passing motorists, the police, or angry neighbors will let you know that it’s time. Mufflers are subject to rust, rain, salt, humidity, sleet and snow, as well as vibration. These are all factors that can lead to deterioration.

HARDWARE

Hardware refers to all of the accessory items used to secure the exhaust system to the car. The stock system on your car may not have all of these components, but they are commonly used by large muffler chains to replace stock systems with their own generic kind. So if you go to a large muffler chain, for example, you might have to pay for some of these additional items so they can install their system on your car. More on this in a moment. First, let’s find out what the hardware is.

Hangers—Hangers are mounting hardware used to secure the exhaust pipe to the underneath of the car. They come in a variety of shapes and sizes for different make automobiles. Most of them have rubber or fabric shock-type bands that absorb vibration and are de signed to give when under stress and load. Many Toyotas, for example, have a rubber band connector that allows the exhaust system to move and shift when subject to heavy shock and vibration. Most hangers are stocked by the large muffler shops. Some foreign vehicle hangers can be ordered only via a dealership.

The important thing to remember about hangers is that they should be periodically checked to see that the mounting brackets are tight and that the fabric or rubber shock connectors are not worn, torn, or weathered. A $150.00 hanger that breaks at the connector can allow the exhaust system to sag in one spot, thus creating a condition where it might catch on speed bumps, curves or other obstacles. Even at a moderate speed a sagging muffler can catch on an obstruction and be torn away from the exhaust pipe.

Adapters—Muffler adapters are used to adapt a replacement muffler to the diameter of your exhaust pipe. They are about six inches long and come in various widths. Typically, two adapters are used on each muffler; one in the front and one in the rear.

They are made of the same material as the exhaust pipe and are usually supplied along with a muffler package.

Clamps—Muffler clamps are those U-bolts that you see that make the tight connection between the muffler and the adapter. They come in various sizes depending upon the diameter of the adapter and muffler connecting pipe.

Some familiar sizes are: 1-1/2-, 1-3/4-, 2-, 2-1/4- and 2-1/2-inch diameters. Clamps are normally part of a new muffler package unless you buy them separately. In most cases clamps and adapters are pro vided free with a new muffler—but not hangers and the brackets. You can expect to pay for them as an additional service part.

I would seriously question the policy of a muffler shop that charged extra for adapters and clamps with a new muffler installation. In any advertisement I would look for the words “complete muffler, $39.95, installed.” That means that they are required to furnish the parts to make their new muffler fit your car—adapters and clamps. I would not pay the additional and separate price for these parts with a “muffler special.”

SHAMs

Mufflers are one of the most common R and R items, and shops like this type of work because the profit margin is high. There are a couple of scenarios that you will have to be on the lookout for when approached by a mechanic or manager who informs you that you need a new muffler system.

Lifetime Warranty—Some of the larger chains will offer a “lifetime warranty” on the new muffler, or for as long as you own your car. This sounds like a deal too good to be true and it's . A few years later, you’ll come in to get the free muffler, and you could end up paying more than you did the first time. Sure, the replacement muffler will be free, but you’ll be charged premium prices for the pipes, labor, gaskets and the cost of torching. Second, if your first muffler lasted for 70,000 miles, will you still own the car for another 70,000 miles? The additional cost of a lifetime warranty may not be necessary.

The CAT Scam—I’ve heard too many stories of folks who have been told their car won’t pass a smog inspection because they needed a new, and very expensive, catalytic converter. Many of these same folks went ahead and paid the price, because in some states, a smog certification is mandatory (more on this in section 10).

Many owners will be shown a rusted catalytic converter and told “it’s rotted out, so you’ll need to replace it.” There are a couple of things wrong with this. More often than not, the rust will only be on the surface and the rest of the metal will be fine. But second, most parts related to emissions, such as the CAT, fuel injection, manifolds, etc., are covered under a 5-year, 50,000 mile manufacturer’s warranty. Why? Because the federal government makes it so. So if you’re told that the CAT needs to be replaced, don’t plunk down upwards of $500. Go to the dealer and have him check it out and if it needs to be replaced, it should be covered under warranty—provided the car is within the limit stated above.

The Rattle—Let’s say, for instance, that you pull into a service center for an oil change. You sign an invoice (for an L.O.F. only) then take a seat in the waiting room. Moments later you are summoned to the garage and a mechanic is waiting under your car, which has been placed on a hydraulic lift. He has the wheels off your vehicle and assures you that your brakes look just fine (funny, but you don’t remember asking about brakes) but he wants to bring something to your attention. He points to your muffler and, with the bottom of his fist, he gives your muffler a punch. You hear what seems to be pebbles rattling in the muffler.

The mechanic says, “You might want to replace that muffler before it gets any worse.” You ask him why and he says, “It’s burnt out. The insides are cooked. Hear the metal crashing around in there?”

You’re impressed, and want to fix the problem before it gets any worse. Furthermore, you’ll be pressured because it will be pointed out to you that the car is already on the lift, and they can get started right away if you’ll just sign for it. This is a common scam.

All mufflers on all cars are prone to interior moisture and unburned fuel (cold starts) which causes the insides to rust and corrode. Bits of baffle plate or rust will fall to the bottom of the muffler—not fist-sized chunks, mind you, but small pieces—particles.

The truth is that all mufflers are subject to this condition. It is only when they are internally broken and rotted with large chunks floating about that this diagnosis is correct. In such a state of decay the muffler would certainly be louder. Only you did not have a loud muffler. Just remember that small amounts of rust or decayed particles in your muffler are considered normal and you should not think that your muffler is “burnt out” because it rattles a little on the inside.

The Rag—This time the mechanic balls up a shop rag, and while your engine is running, he plugs up your tailpipe stopping the flow of exhaust. He brings your attention to a hissing leak at one of the muffler clamp connections. He tells you that your exhaust is leaking and you should replace the connection. He might even throw in a scare tactic and tell you that dangerous carbon monoxide could leak into the driver’s compartment and you wouldn’t know it until you passed out. So why don’t you spring for a muffler package with new adapters and clamps, a package they just happen to have on sale? Thinking that he is right you okay the repairs. Funny how that hissing noise stopped though when he removed the rag from the tailpipe.

Well let me tell you, any exhaust system will leak somewhere if it’s force-plugged in this manner. Nine times out often it will be a muffler clamp connection that leaks in this fashion. Simply ask the mechanic to tighten the clamp in the vicinity of the leak. Chances are this will solve the problem. In fact, he may have loosened it beforehand.

With time and wear on the exhaust system, clamps and adapters expand and contract with heat. They lose their tensile strength. Exhaust pipe vibration will loosen the nuts on the U-bolt. A little tightening on these parts can remedy moderate exhaust leaks.

The Torch—Muffler installers have a habit of torching off your clamps then torch-cutting the adapters loose, because the nuts are usually welded tight with rust. This is fine when skillfully done. However, I have seen dozens of exhaust pipes slit and mutilated in this fashion.

What happens is they torch the adapter sleeve trying to peel it back and inadvertently create a slit in your exhaust pipe. The mistake is easy to cover up because a new adapter covers the slit or burn hole. This is annoying because it can weaken your exhaust pipe at that position, the position where the new clamp must be cinched down. If cinched down too tight, it could crush your weakened pipe. Personally, I would rather see them unbolt and slide these parts off, even if it means snapping the clamp bolt or nut.

Another sham involving torching: some larger chains will charge you for the amount of acetylene used! Now that's a cost I would ask up front about, and refuse to pay.

Unnecessary Parts—Muffler shops love to sell you an exhaust pipe along with your muffler. This happens a lot if your muffler is located near the rear of your car. Their explanation is that the muffler and exhaust pipe are welded together, and should be either replaced with a costly one-piece system, or with an even costlier custom, multi-piece system.

The truth is, large muffler chains generally carry the adapters in stock to fit their new muffler with your stock exhaust pipe. All they have to do is cut that weld between the stock exhaust pipe and muffler with a pipe cutter or torch, and install the proper adapter. At worst they might have to reposition your exhaust pipe at that position where it's secured to a hanger after they have done this. Why in heaven’s name would you want to buy another exhaust pipe when yours is in perfect working order?

As another example, you might be told that the one-piece stock system is only available at the dealer, but they can add a custom system that includes an exhaust pipe, muffler, hangers, adapters and clamps—a multi-piece system. Though only the muffler is damaged, you’ll have to purchase all the other pieces because “it’s the only way.” Nonsense.

That’s how muffler shops make up for their seemingly great “muffler deals.” Conceivably, you could drive into a shop for a $39.95 muffler special advertised in the paper, end up paying for four clamps at $6 apiece, two adapters at $10 apiece, and get conned into replacing the pipes on both ends of the muffler for $200. My arithmetic says that muffler special is now about $239.95 plus tax! Did the shop lose on the muffler special? No. Did you? Probably.

 

  • The typical exhaust system can last the life of a vehicle and can be considered almost maintenance-free. Mufflers, resonators and exhaust pipes suffer wear and deterioration more frequently than the other parts.
  • A slow engine warm-up might indicate that the hot air pipe on the TAS is not connected securely at the exhaust manifold and the air cleaner snorkel. You can make this visual inspection yourself.
  • Be extremely leery when a mechanic points to your catalytic converter and says that it’s “bad.” This rush judgment could cost you $500 or more. The likelihood that your CAT is bad, is very unlikely, and would rarely, if ever, cause you to flunk a smog check. Furthermore, if it's bad, it should be covered under warranty. Just tell the mechanic that you’ll have the CAT checked by the dealer.
  • Beware of the “rag in the pipe” and the “burned out” diagnosis scenario for mufflers. Exhaust pipe leaks (at the clamp positions) are sometimes mistaken for faulty mufflers. All mufflers accumulate a moderate amount of rust that falls to the bottom of the muffler canister. Severe breakage of the baffle plates, or excessive noise, would be legitimate reasons for replacing a muffler, but not a little rattle.
  • If your muffler is considered a “one-piece” assembly, and the mechanic says that it must accompany a new exhaust pipe, challenge him and ask him to use adapters to fit a new muffler to your old exhaust pipe.
  • Remember that clamps and adapters should come with a new muffler package. Question anyone who wants to charge you additionally for these parts. Hangers (mounting brackets) are an exception. They cost extra and many times have to come from a dealership.
  • If your old muffler is “torched” off your vehicle, make sure that they don't cut or mutilate your exhaust pipe in the process, nor that you are charged for acetylene waste.
  • It is very common for a muffler or resonator to carry a lifetime guarantee. Make sure that you receive your guarantee certificate and file it in a safe place. Slight leaks often occur after your exhaust system has been worked on. This comes from heat expansion and vibration and it could be a week or month after you have had the work done. Your guarantee and invoice is necessary in order to return to the shop and have the problem solved at “N/C” (no charge) to you. Any peculiar noise, rattles or thumps as a result of a misaligned exhaust pipe, hanger, or muffler fitting can also be taken care of at this time.

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