How To – Replacing Your Cars Exhaust System Cat To Muffler

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    In the shop today is a 1990 Honda CRX and we will be replacing its original 21 year old exhaust system.

    Why is this cars exhaust so old? Well you know the old saying if its not broke then don’t fix it. Although the car has seen a aftermarket weld in resonator and a patch pipe replaced during its life amazingly enough all of the other parts are original. This is true for most of the car and if you are following our howtos you may have seen a lot of work going on under it’s hood.

    Because the cost of a weldup system at a local shop would cost more then double the price of buying direct fit parts that mount with bolts and gaskets it was decided that doing the work ourselves would be the best option.

    Now if you own a new vehicle younger then 5 years old it may be in your best interest to look into any warranty or bringing the car to a muffler shop that will give you a warranty.

    However since most muffler shops  weld up generic parts and pipes the cost when  replacing a system the cost for an older car may be similar to a new car if parts are interchangeable.  Muffler shops normally only stock a dozen mufflers and catalytic converters for the hundreds of cars. Then they use parts of your old exhaust to make the repair.

    Unfortunately when new parts and pipes are welded together in a shop vs the manufacturing line the heat that changes the properties of the metal and burns off protective coatings will cause corrosion at the weld point.

    If you ask a muffler shop to use direct fit replacement parts with new flanges the price they will quote you will be hundreds of dollars more then a weld up system. Most likely you will pay at least double and have to wait a day or more for parts to come in.

    The Choice Muffler Shop or Do it Yourself

    So, now you know a little about the process and you have three choices.

    Bring the car in and have weld up generic parts installed. This option may save you some money up front but your system is likely to rust quicker. The turn around should be only a few hours and you don’t have to get dirty.

    Have the muffler shop use only direct fit parts that have been welded at the manufacturer. This will cost you twice the amount that a weld up job at your local muffler shop would cost and you may not have your car for a week.

    Both options above should come with a lifetime warranty on parts..

    The final option for most people is to buy direct fit parts that do not require welding and perform the work yourself. If you have ever attempted to repair your muffler system in the past then you know this is not an easy job but it can be done in a day if you have the proper tools.  Warranty for doing the work yourself should be the same Limited Lifetime on the parts but getting that warranty honored may be pretty difficult.

    Ordering Parts

    The first thing you need to do is inspect your system and understand which parts need to be replaced. If you have all direct fit parts now then it is possible to remove an individual part and keep the rest.

    Take a close look at the condition of the metal. If you see some light surface rust on your parts that is ok but if the pipe shows flaking of rust that you can chip off with your finger or a screw driver you should consider replacing the part if the cost is within your budget.  Flaking pipes will usually fail with a hole or break within 6 to 12 months.

    In addition to mufflers you are likely to need new gaskets on both sides of the part you are replacing.

    You may also need hangers that hold your muffler system to the bottom of your car.  Most hangers will last for years and on this 21 year old honda we won’t be replacing them unless we find a problem while making the repair.

    Once you know what parts you will need it is in your best interest to check with at least three suppliers before making the order. In our case we checked with two brick and mortar auto parts companies and then chose the YouRepair online store for making our purchase.

    NOTE! Ordering Online… make sure you verify all of your part numbers before you order large parts online. This means making sure that one supplier’s number is the same as the others. We are buying a Walker Muffler system because it is the cheapest reasonable solution. We do not endorse Walker as good or bad… but are using it for example. When checking locally we verified that the online part number matched the numbers that the local parts place was suggesting. If you order the wrong part online then you will have a huge return shipping cost.. When in doubt buy local or buy online and ship to local store.. but there is no reason to do this if the numbers match.

    This is our parts list

    Walker Exhaust 35129 Hardware-Spring Bolt Kit
    Walker Exhaust 31357 Hardware-Gasket
    Magnaflow 22635 Direct Fit Catalytic Converter
    Walker Exhaust 31354 Hardware-Gasket
    Walker Exhaust 46739 Resonator Assembly
    Walker Exhaust 31397 Hardware-Gasket
    Walker Exhaust 55001 Muffler Assembly-Quiet-FlowSS

    In addition we had to hit the local hardware store and pick up some 1-1/2″ bolts to replace the rusted ones that hold the parts together at the flanges. You can see the first item the Spring & Bolt Kit is a special bolt and spring kit used to mount the Catalytic converter.. you can not use generic hardware store bolts for this area.

    Total cost for this system was $278.00

    Cost for a weld up system installed was $540 estimate
    Cost for a Direct Fit system installed was $975 estimate

    Additionally we found a $30 manufacturers rebate bringing the price down to $248.

    As you can see you can save quite a bit of money and since shipping was free it was well worth the trouble of doing the work ourselves.

    Getting Started

    Remember to use eye protection at all times when performing the work Rust will fall off the system no matter how careful you are.

    You also want to jack the car up as high as you can get it while still being safe. We used two jack stands at the back of the car and car ramps on the front. DO NOT RELY ON JUST A JACK. However once the car is in the air you want to position your jack under a jacking point to protect yourself in case it slips off your jack stands.

    Once the car is in the air and you shake it a bit to make sure it is steady you can begin the work.

    Cut off the Muffler

    Since most of our system’s bolts were rusted beyond recognition the choice was made for us. The only way to get the system off easily was to make a cut on the back of the resonator pipe to remove the system in two pieces.

    We used an air cutoff wheel that took about 5 minutes to make the single cut but you could use a hack saw or reciprocating saw with a metal blade. Although a hack saw will be very difficult it will get the job done if you persist.

    After the rear muffler was removed the resonator muffler and catalytic converter were removed as one piece.

    Since we wanted to try to save the spring and bolt kit from the old system the nuts were heated until cherry red with a propane torch. This allowed them to be removed with hand wrenches. I suggest that you use 6 point wrenches and or impact sockets if you can. They will be very tight and you risk burning yourself on a hot bolt or stripping the heads.

    After the spring kit was removed the resonator and cat were slipped off of the rubber hangers. It is best to take your time and hit the rubber hangers with some spray oil before trying to force them off.

    Inspecting New Parts

    Once all of the parts are removed lay them out as they were installed and match up your new parts to look for any problems.

    You want to make sure that the heat shield on your catalytic converter is facing the floor of your vehicle. Note the position of the hole pattern on the flange where it mounts to your manifold / header.

    Next you want to dry fit your parts without gaskets and make sure the flanges mount flush. Your gaskets will take up some of the play but if your flanges are miss positioned or bent you will need to replace the parts with new ones.

    Installing the New Parts

    The hardest part to install will be the catalytic converter. You will need to first remove the donut gasket that is probably friction (not actually) welded to the end of your exhaust manifold.

    Using a cutoff wheel is pretty much necessary and you may just need to mount one in a electric hand drill if you don’t have an air cutoff wheel  just for this specific job.

    Simply cut a relief cut through the side and you should be able to get it wedged open with a flathead screwdriver.

    When you remove the donut gasket make sure you do not cut into the inner pipe.  Look at your new gasket and you will see how it slips onto the pipe. Do not try to pry this donut gasket off without cutting it in half. You will only damage the pipes and this will require replacement of your intermediate pipe that sits between the header / manifold that comes off your engine and your cat.

    Now you can begin trying to mount the new cat in place. Don’t try attaching it to the resonator it is a spring loaded connection and will be hard enough to position all by its self.

    In our case the old spring and bolt kit will not even fit through the openings in the new cat. This is poor manufacturing by the catalytic converter manufacturer. In addition to the bolt kit not fitting the flange was pushed too far back on the pipe because they made too deep a flare on the end. The flare is the widened part where the donut gasket will rest on. The flange is the metal part the bolts go through.

    Even when using a new bolt kit which did fit through the flange on the cat the flare was so deep that it required cutting about 3/8ths to a half inch off of the spring so it would mount. This is not normal but was a last resort and again showed bad manufacturing to specifications by the cat manufacturer.  There is no excuse for this because these parts have been on the market for 2 decades.. if you can’t get it right in over 20 years then that is just poor craftsmanship. Remember these parts are DIRECT FIT original equipment replacement parts.. and we are paying extra for them to fit perfectly.

    When tightening the cat bolts you want to keep them about a half turn lose until you get the resonator connected and mounted on its hangers. This will allow you to line up the cat which is designed to flex a bit on the spring / bolt connection.

    Mounting the resonator muffler is easier if you attach the hangers to the muffler before connecting them to the car. Remember to use a little can spray oil to lubricate the holes and the hangers they slip over.

    Once the resonator is hanging in place you can slip the gasket between the cat and resonator then tighten the bolts. The gaskets that we are using are crush gaskets and they can only be crushed once. If you make a mistake and have to remove the connection you will more then likely need new gaskets that cost $10 so only tighten it fully once everything is aligned and the full system is in place.

    Now you can mount the rear muffler. This process should be the easiest of all. Simply mount the muffler on the rear hangers and you are ready to bolt it to the resonator. Remember to slip in your crush gasket and align the pipes for a correct fit.

    Tightening up your bolts is next.

    You should start at the catalytic converter and work your way back. If your car’s manual has a spec then tighten to the foot pounds suggested or just crank away with your impact hammer until you get the bolts as tight as possible. I would expect 80 to 100  foot pounds is where we set the wrench.

    Testing Your System

    With all of the gaskets and wrenching over it is time to see if there are any leaks. The easiest way to find a leak is to place a rolled up rag in your tailpipe and listen for hissing sounds.  Our new muffler had weep holes for moisture removal and they will leak exhaust but it is necessary to get down near your flanges and listen and also use your hand (NOT TOUCHING) to feel for any air blowing out the connections.

    If you do find a leak you can try tightening the flange bolts a little more. This should cure the problem unless the gasket is just not seating. If you need to replace a gasket this is the time to do it. You can probably wait a few weeks but after a few months the bolts will be difficult to remove and will probably need to be cut off especially if you pass through winter salt season.

    Adding a Exhaust Tip Extension

    The chrome exhaust tip on your system is not only for looks it is used to extend the system out from under your rear bumper. You need to extend the pipe at least 2 inches past any part of your cars body that way exhaust will not build up under the car when you are stopped at an intersection or parked but allowing the car to run.

    Final Note

    Quite honestly replacing your exhaust is exhausting. Not only will you be working in tight places with bolts that require a lot of muscle to break free but you will also need to make a cut though your pipe to get it off.

    If you do not have proper jack stands and tools then fork out the extra money and get someone else to do it.

    BUT if you are willing to take half a day on the weekend you can save yourself a lot of money.

    In our case there was more then money to consider but in the end it was worth getting the parts and assembling them while also saving more money then was expected.

    Almost every exhaust system manufacturer runs rebates or sales and it is important to research your options and get the best prices you can. If you can not find a discount then do the best you can and get prices from both local and online stores.


    The YouRepair Store carries a full line of Automotive Parts free shipping is available on most orders over $25.

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