After you’ve been building and modifying cars for a while there’s some things that you become pretty particular about. It could be just how you like something to look or function, or just an extra step you take to save yourself headaches in the future. One of mine is an exhaust system that’s leak-free and sounds good. I’ve had bad luck over the years of header unions leaking over time. It seems either they crack at the welds or they just fit poorly and leave much to be desired when fitting the rest of the exhaust.
There seems to be two common header unions out there, the “ball and socket” and a triangle shaped flange with a gasket that goes between. The ball and socket style has a rounded “ball shaped” end on the header and a small piece of pipe with a female portion that fits over the socket and a bolts on flanges on either pull them together. Some of the lower end headers tend to come with the ball portion in bare metal and some come with a fiber gasket/coating. Both of these tend to either leak right out of the gate or after a short period of time. Forget even trying to run an old used header! The triangle flange style works ok with a gasket bolted between the parts, but it has NO flex and I’ve had them crack at the welds for the flange over and over again. I decided to show my solution that has solved my header leak issues over the years.
On Project Pilehouse I have a set of shorty S10 V8 conversion headers (the truck sits on an S10 chassis) and since I don’t have an exhaust bender or a lift easily at my disposal I’m going to have some friends at a local exhaust shop fit up an exhaust to the truck. My drivers side header has the steering column running through it and requires disassembling the column and I didn’t want them to have to deal with all of that. I decided to build the exhaust from the headers and get it down under the truck where they could easily build the rest of the system back on the lift.
These headers had a 3 bolt flange and I started by using a reciprocating saw to cut the flange off. I had to make the cut extremely close to the flange itself as the collectors for the headers were only a few inches from the flange and I needed space to slip the end of the flex joint into the header.
Above are the flex joints that I like to use. They have a stainless mesh flex section that gives you a lot of flex for engine movement. They are also extremely strong and won’t crack or fail like a fixed joint would. These can be found online through many parts vendors by searching “mesh exhaust flex joint” or a well stocked parts store or exhaust shop should stock these. They are commonly used to repair OEM flex joints as they’ve become the standard flex joints on many modern cars.
For strength I decided to slip the flex joint inside the header. If you have an exhaust spreader handy you can flare the end of the header, but in my case I was working late at night and mine seems to have walked off! I decided to keep working and did an ultra basic method of flaring the metal with a crescent or adjustable wrench. I slowly worked my way around the edge until I had a large enough flare I could slip the flex joint into. Now this method will leave small dents in the metal, but if you’re careful they’re pretty light and can be sanded out.
Once I had the ends flared out I slipped the flex joint (I had to use a rubber mallet as the slip joint should be a tight fit) into the header and used a hammer to tap the metal tight all the way around the new flex joint. I then made sure the joint was sitting even and wasn’t cocked up, down, or side to side. With everything sitting how I wanted I put a single tack weld to join the two pieces. I then trued the joint up again (it will tend to move a little from the heat of the first weld) and put a second tack weld 180 degrees from the first.
With the flex joints secured I could work my around the union and weld it up fully. I chose to TIG weld the pieces together with the TIG 200 AC/DC, but a MIG welder will work ok as well. Just make sure that you COMPLETELY grind the aluminized coating off of the parts you’re welding if using a TIG as it will tend to pop and weld dirty. With a MIG you can burn right through the coating no problem.
With the flex joints welded I bolted the headers back on and used TIG wire to make templates of how I needed the short pieces of pipe to come out of each flex joint to get the exhaust down next to the frame and under the cab. I had the local shop bend me up two pipes to match and I fit and positioned them at the correct angle. I pulled them back off and fully welded those to the flex joints. The result is a set of headers and down pipe custom made for Pilehouse that will allow for a full exhaust to be fabricated.
The last step was to spray the header and dow pipe with Eastwood Hi-Temp black exhaust coating. I reinstalled everything and ran the truck for 5-10 minutes to cure the high-temp paint (it needs to be heat cured and puts off some smoke/fumes until cured). I really dig the subdued satin black look and it almost sounds too good to put mufflers on!
I like this idea and procedure dealing with header leak.
I had constant leaks in my flanges. In desperation I would replace the gasket, flatten the flange and add some muffler paste hoping it lasted long enough to pass the inspection. But I had to get it to the inspection station before the fix failed. Frustrated to this repeat problem I cut, hammered, welded a fix. I called it a C Flange Bracket. This is not spam. I made this in my USA basement. Please comment. If you know headers you know they leak.
https://www.youtube.com/watch?v=zBdFKlVRh48&t=28s
The video is a little generic but the problem and the fix is clearly demonstrated.
Other than losing the ability to remove a “sectioned” exhaust, this seems like a good fix.
Flex joints are used by some manufacturers close to the head and before catalytic converters. Have a look at a stock Mini Cooper headers for instance. The flex joint is used at the point where the primary tubes joint each other (within a 12 inches of the head) and before the front O2 sensor bung. I don’t know how commonly this is done, but it is done by at least BMW in this case.
Here’s a quote from an aftermarket flex joint ad:
“This range of flex connectors is ideal for use before the catalytic converter where temperatures are high, engine movement is high and there is considerable gas noise.
Can withstand up to 1100 degrees centigrade. Interlock liner creates an air gap between the liner and bellows improving the cooling of the exhaust gas. Flex connector prevents twisting of the exhaust pipework.The main flex unit is made from stainless steel.Each end is made of aluminized steel for extra corrosion resistance although as a result of high temperatures, corrosion is not an issue. Each flex-connector is designed to allow pipework to slip inside each end and to be welded in position.2 1/2 inch (63mm) inside diameter.9 3/4 inches (250mm) total length. Click on More Images for different views of this ILOC flexible exhaust joint”
1100 C is more than 2000 F….. If you’re out of that range, you have other problems.
The part is listed at $52
AutoZone has them.
i had to do the same exact thing when i put a 403 in a 84 hurst olds cutlass.as everyone knows the crossover pipe is no longer available for any car with a 403 and its abot 1 1/2 inches wider than the 307 ho motor..by doing this same thing with the flex tubing it worked flawlessly until i got the car tuned and had real dual exhoust run at my favorite exhoust shop here in madison heights michigan.nice tip but everything has its critics and supporters.
If you’ve ever had to install or replace one, you’ll see inside that the pipe inside the stainless braid looks like those universal radiator hoses. Accordion style. Nothing should leak unless it rusts out like the factory ones do. Should be okay for your Econoline.
Even better would be to add a V band then the flex joint.
Well I suppose it would make more to weld the flex section further down on a straight portion, but I guess that would be the difference between shorty’s and long tube headers now wouldn’t it? And as for not being able to disassemble the headers from the y-pipe/straight pipes I don’t believe it was Matt’s intention to disassemble the exhaust system in case you missed the part about where he said the steering column runs directly thru the header. I know this because I own a 99 s10 with a 383 but when I was still running the 4.3 v6 I had a set of eldebrock headers that used the triangle flange and I could never get the driver side flange to completely seal because it was right up against the frame and there wasn’t any room to pull it over because the y-pipe would be right up against my transmission pan, I did notch the frame because the was the only way to get it to fit. I was running 2.75″ pipes by the way. But this flex section idea would have helped my situation at the time and I wouldn’t have had to notch the frame. But just because this idea wouldn’t work best for whatever your situation is, doesn’t mean this isn’t a good idea for certain other situations.
The first time I saw a flex joint was in a S10 pickup as they come as original equipment on 4 cylinder engines . As a way to leave the ability to unhook the exhaust for transmission removal ,I weld up the entire exhaust and then use a cutoff saw to cut the exhaust pipe clear through and install stainless steel band style clamps . They don’t crimp the pipes and can be reused . I get them from Summit racing
If leaking is the issue, then what about the “V” Band flanges and clamps like on intercoolers but out of steel? The 3 bolt flanges have been flawed from the beginning and the Ball joint is interesting but having had a set they are not without their flaws also. The Flex unit is a GREAT concept but my concern is that (I have a Gen 1 Econoline Van) the potential exhaust gas seepage into the dog house could pose a problem inside the vehicle. Heat rises and there is only one place to go….Inside the dog house. Any Thoughts?
I used high quality stainless steel flex joints in an exhaust for a supercharged Bmw M3 and still had the the inside completely disintegrate and close the 2.5″ exhaust to 1″. Be careful to use this where it will see high heat for extended periods of time.
Great demo/advice, and really appreciated…I think it’s great to see the flex option so seamlessly put onto flanged setup…it reminds me to be more flexible in my thinking about what i can fit up. Thanks, this is great!
All the manufactures Highly recommend that the flex joint not be close to the header flange due to the amount of heat that they are subject to. another foot or more will give the flex needed and last a lot longer. They also recommend that the flex joint not be put in an angle but put straight line to aid in longevity. I know it is not always possible to do it this way but I don’t want to have to do the job over again. Hope this helps.
Yep, very good idea. I had the same thought about 5 years ago. One of my customers would need a new 3 bolt flange gasket at the end of the collector from a header on his Yota p/u . I noticed the se flex joints on mostly front wheel drive cars and normally when the exhaust side is in front and the pipe has to cross under the motor to reach the back of the car. After about the 4th gasket replacement on that header, I had the same thought. So I did the same thing. I welded the flex pipe section to the back side of the collector flange. I didnt want to alter the header itself. This has lasted going on 2 years now and rock solid no leak fix. One tip I may offer. Not all collector gaskets are the same. Use common sense and avoid the thin paper type. Use a thick metal sealed gasket. They last much longer and seal much better.
Nice write up and a great idea.
Wish people had reading comprehension skills so you wouldn’t have to answer the same question over and over. Not only are they in the write up but also in the comments.
…..i got all excited when i thought you would show top secret header flange fix…….i last made my own gaskets from aluminum street sign….lasts longer than most stuff but?????
The main point to remember with this fix is: Will it work for my application? It is not a fixall for every situation,merely a very good suggestion. Thank you
Stock exhaust systems used to use steel doughnut gaskets. These worked fantastic in place of the gaskets in 3-bolt flanges. That is all I ever used. Never ever leaked, are reusable and last for ever. The only modification was longer bolts.
wouldn’t it make more sense to weld the flex joints in the straight portion of the connector pipe. Just cut out the size of the flex section and weld in. that would take the stress off the header connection, and likely wouldnt work loose or crack at that joints. That is the reason for the flex in the line any ways as the engine vibrates and moves in the mounts and the rest of the exhaust is more rigid.
That’s very attractive looking and actually is a lot cleaner than the flange connection. If every thing else is done right there really is no need to break the exhaust system for quite some time any way.
I think it’s a good idea to always leave a way to unbolt the exhaust. In the 70s, when Kustom vans were all the rage, I had a ’67 GMC Handivan with the engine between the seats. It had a 250 ci six and I had headers with dual exhausts that exited thru the sides in custom molded body vents. Shortly after I had the exhaust shop make my dual exhaust, my clutch went and the only way to get the tranny out was to cut the exhaust system. It never lined up right after that, and looked wonky!
Most all auto parts store’s that carry exhaust parts will have them or can get them.
The flex joint isn’t a removable joint. Sometimes the exhaust needs to be removed to service the transmission, starter motor, etc. These flex joints are the weak link in the system and are designed to allow the exhaust to move when the engine torques. They are designed so that they fail rather than brackets, manifolds, and more expensive parts. They are a good idea to have in every exhaust system, but they don’t replace a flange joint.
We have had vehicles in our workshop that had been to a transmission workshop, and because there was no joint that was unboltable, they cut the exhaust pipe with an angle grinder. Then we had to fix the mess for the customer.
A flex is good, but make sure you have joints that can be unbolted. We usually flange the header and have another join in front of the diff so the whole centre section can be removed easily. This also means the tailpipes can be removed and replaced easily.
Gaskets are cheap and easy to replace. Flanges are much better than slip joints with clamps.
If you are after a neater type joint, there is a “V” band kit that comes with 2 stainless rings which get welded to the exhaust pipes, but they are far more expensive.
Most good exhaust or auto parts shops will stock these or you can google for online retailers by searching “mesh exhaust flex joints”.
You could alternatively add a flex joint after a bolt-together union, or you could add a union if you want a place to take your exhaust apart at in the future. In my case the exhaust will be welded completely.
If the joint is welded completely these will have no issues with leaks.
For optimal performance (like a race car) I can agree about the joint being “in the exhaust flow”, but in my case the .05 horsepower loss won’t bother me much. I agree though if performance is your #1 concern!
Most good exhaust or auto parts shops will stock these or you can google for online retailers by searching “mesh exhaust flex joints”.
Thanks for reading!
Hi Rich,
Great question. Normally the mesh portion of the flex joint is stainless steel and doesn’t need to be painted, but you could if you’d like. Just realize that the flexing of the joint may cause paint to flake over time. We offer high temp paints ad coatings, but no equivalent to Jet-Hot. They could probably speak on compatibility on a mesh flex joint.
I’ve had both ball and socket and triangle joint type headers. The ball and socket on my Hedman Elite headers worked quite well, but the “flex joint” is the way to go. I’m running exhaust manifolds on my ’69 Buick GS 400 right now, but if I switch to headers, I will definately use the flex joint method.
Great tip!
Good information. Would be helpful to include the correct type of wire to use for welding different metals. Exhaust systems use carbon steel, 409 and 304 stainless. If you don’t know what metal your pipes are made of or what wire to use, better do the research and find out. The guys at Eastwood and experienced welders know, but the average person could use advice before starting such a project. Keep those Tech Tuesdays coming!
Do you paint the flex joints too? Can they be coated with something like jet-hot? Does Eastwood have that type of product?
Very interesting, I have Sanderson headers on a 56 chev,the stupid collectors point down and the car is l I were 2 inches,this might be very good for me.thanks for the tip
Excellent idea!
(2) comments:
1) Suggest that your joints should be created so there is no pipe edge pointing into the exhaust flow (reference attachment of the flex to the collector).
2) where do you get those real cool flex joints?
Thanks,
Brian
Is the flex joint leak proof enough not to effect an O2 sensor installed down wind of the flex joint?
good job
where do you get the flex pipes?
Without a place to unbolt your headers from the rest of the exhaust, will this now be a permanent install with no way to ever remove? Or did I miss something?
I got the flex joints from a local exhaust shop but they can be found at most any exhaust shop or online. Thanks for reading!
I got the flex joints from a local exhaust shop but they can be found at most any exhaust shop or online. Thanks for reading!
Where did you purchase the flex?
thanks for the great ideas. gives me a few ideas of my own.
by the way
great welds.
Looks like a good solution, but where do the flex joints come from?
Very useful information. and nice work.
Good advice as usual from this site