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1959 Coupe DeVille Exhaust System

Started by Gabe Davis, September 18, 2022, 02:36:49 PM

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Gabe Davis

Hi all,

I'm beginning to research the exhaust system for my '59 Coupe DeVille. The set that is on there now is from the mid 1990's and I can hear the leaks in the rusted pipes. It also has a Dynaflow muffler which, while not annoying, is louder than I'd like for it to be. There are also no resonators installed.

I have never done any work on exhaust systems and am curious as to how the original was setup on these cars. Was everything just bolted together? Was any part of the system welded? Is this something that I can DIY?

I haven't crawled under the car yet to grab pictures of what is there currently. I have a suspicion though that the original exhaust mounts are no longer there. I'd like to try and put things back as stock as possible. There seemed to be a couple of sources for the stock hangers.

There is one in Finland. Seems like a lot of money.

User Grant Owen out of New Zealand appears to have made reproductions in the past but does not appear to be active here on the forum, at lease recently. I did find his email address on the forum and have reached out. We'll see if he still makes them. He even used pieces of wide white wall tires.


Is there any other place to look for a set of hangers?

One of the other aspects is the flex insulating tubing over the pipes near the engine compartment.

Does anyone have any pictures of what it actually looks like on a '59? I haven't been able to find any pictures of what the original looks like. Did it go up the small section of pipe that comes off of the exhaust manifold or is to only the section between the first small pipe and the muffler? The section is circled in red in the drawing from the service manual.


Is it as simple as sliding a flexible exhaust pipe with the correct ID to fit over the hard pipe like this one? Is this the right type?

Is it common to put the additional flexible pipe over the hard pipe? The lack of photos of it makes me think it is very common for it to be omitted. I ran across a couple of posts about doing earlier cars and a custom 2x4 to aid in hammering on the pipe.

And then there are the pipes themselves. After reading a lot about the pros and cons of stainless vs. aluminized steel, I am pretty sure that I want to go with an aluminized steel system. They are cheaper too. I'd be curious to hear peoples thoughts. This car is a driver and is pretty much original so I'd like to try and keep it as original as possible, within the bounds of a realistic budget.

For suppliers, Waldron's Exhaust seems to have high praise, with a higher cost.

Any other exhaust suppliers I should be looking at?

I appreciate your thoughts! Thanks!

1959 Coupe DeVille
Rosewood with Dover White Top


I don't think you'll find a OEM steel exhaust these days, they're mostly all aluminized or stainless repro for vintage.  So it's a matter of what you're willing to go with more than getting OEM. 
Any local shop could bend up something, and the custom exhaust people have the OEM bend specs.  I had one made for the P and it fit nice, and was a very tight space in the Xframe.  When I need one for the '58, I'll probably buy a custom and go stainless.  It's got a muffler shop type modified steel system on it since I bought it that way.
If I read this right, you're in Finland, so no idea what's available there.
The potential problem is getting something export and DIY, it doesn't fit, and then your stuck w/o an exhaust, if you don't have the tools of the trade.  Something to ponder before you pull the trigger for big bucks.
I used some universal hangers when I fixed the '58.   I don't know of any that are OEM fit in kits.   You'd have to search around, and probably low chance of any and less Ex-USA.
The shop manual should have the instructions.   The parts list should show what parts came from factory.   I'd guess from memory, so I'm not 100%.  As far as I know the '59 authenticity manual is still nebulous but on the horizon based on posts this summer.  Just a thing with that year.  Plus you're complicated being by off the continent.
ps: back in the day, one used to be able to buy part or a complete steel OEM exhaust off the shelf at the parts store, but those days are kaput with the catalytic exhaust, etc of today.  I might have the Walker catalog listings for that year.  Some have pictures, some don't.  There's been posts here about the double wall, so you can search the posts, but just don't include '59, include years around there.'57-'62

Gabe Davis

Jim, thanks for your insights. No, I'm not in Europe. It's a lot warmer where I am in Atlanta, Georgia.  :)
The one vendor I found with the hangers is in Finland. That is what I was referring to.

As far as material, I'd be fine with the more modern aluminized steel. It does not have to be totally period correct. I would like to have the original hangers though so that part could be correct.

The hangers are briefly mentioned in the shop manual and in the disassembly/assembly procedures but their are no photos of the system other than the diagram I posted earlier. I used a lot of googling to even see what the originals looked like.

The current exhaust was a custom job by a local Midas if I remember correctly. I would hazard to guess it was hastily fabbed up with the cheapest parts they had at the time. If I can save a little money or get closer to original, in this case, I think I would prefer to go with a prefabbed kit.
1959 Coupe DeVille
Rosewood with Dover White Top


With any luck, yours is held together with clamps. The joints on mine seem to have been all welded closed at some point in time. In a month or two, I will change mine out and my plasma cutter is waiting to make things easier. I am going with "Classic Car Exhaust Inc."
-----Dan Benedek
'57 Cadillac Sedan Deville 6239DX
'81 DMC DeLorean

Gabe Davis

I was under the car today working on the brake lines and got to take a close look at the exhaust system.

There are only the top most hangers above the axle that are original and they aren't connected to the current pipes.

I reached out to Grant Owen and he replied that he does indeed still make the hanger sets and that they would be $300 plus shipping to the US. I'll have to find the correct type of bolts to connect the mounts to the frame. I assume they are similar to the bolts used to hold the clips that mount the brake line. They appear to be a type of self tapping bolt with a wide head. The brake line bolts are 1/2" heads. Are the exhaust hanger bolts the same?


The current pipes are almost all welded so I'll have to cut them apart to get them out. They are for sure rusted through in places as I could hear an exhaust leak and was able to confirm it visually.

I'll try and snap some photos when I'm finishing the brake lines tomorrow.
1959 Coupe DeVille
Rosewood with Dover White Top

Daryl Chesterman

NAPA has (or can order) the flange headed self-tapping bolts like you pictured.  I am not sure what size you need, but you can go to NAPA's catalog page (link shown below) and in the sidebar on the left, scroll down to Fasteners, click on "Fasteners" and the catalog will appear in the pane on the right.   Click on the catalog icon and the complete catalog will come up.  On page 41 in this catalog it shows the bolt in the upper-left corner of the page, and you can pick the part number that corresponds to the size you need.

Daryl Chesterman

Gabe Davis

I was under the car again finishing the brake line project and snapped some photos of what is there currently.

It appears that the original downpipe from the exhaust manifold is still there as it looks like a regular steel pipe given the rust. The rest is aluminized.


The muffler is a Dynomax 17732 "Super Turbo"

While not super aggressive, it is way louder than what stock would be. Even being a "mild" sounding muffler that does sound good, to me, it is loud for the car. This is a Cadillac after all.


There is a decent hole blown out. I assume this was the low point where the water collected. You can really hear it especially when pulled up next to another car or wall.


No resonators are installed with the current system.


All of the original mounts had been removed and replaced with generic mounts welded to the frame. It seems pretty rigid with only a small amount of flex in the system.


I have a set of mounts on order with Grant. I'm excited to put the system together with the correct parts.

I'm still on the fence about either going with Waldron or Classic for the rest of the parts.
1959 Coupe DeVille
Rosewood with Dover White Top


I finally looked in my Walker catalog today, and it shows the '59 complete, but I think it was made in more pieces so they can do patch jobs.  It doesn't show the fluted pipe, but maybe just a rendering.   It looks similar to the one you shown.  They don't make these any more.  I can post if needed, but I think you have what you're going to find.
Fastenal is another supplier of those self tapping flange head screws.  I bought from them many times, then they closed my local store during covid.  Now I have to drive 30 minutes one way and if they don't have what I want they have to order, so I just order all my stuff on line.  I get better service out the warehouse.  Just shipping costs have gone wild so you have to buy more to justify.
I suspect the hanger rubber goes and they just lop off the hangers to make it easier to remove.  My '58s were all chopped off and some missing so I repaired the whole length. You probably could've saved a few dinars with a bunch of universals from NAPA, but to each his own.   I remember my friend worked at the local gas station garage and they had to use the air chisel to cut off exhaust pieces and it wasn't timely.
I think the '59 also has the pass through rubber isolators.  I was able to find some high temp belt material by the foot from BF Goodrich, for cheap, so I used that rather than try to find ready made.  Quieted things down no more rattle.

Seville Life

Gabe, that '59, that colour, just stunning, an example of grace, style and elegance. Beautiful motor car and something only Cadillac could make.

I hate this welding of exhausts. Using clamps allows you to fit and line-up the system without building up tension in it which ill produce noise. Likewise using stainless, noisy, I always go for regular steel and just look after it, ie, no short running filling it with condensation.

I'm on the French Riviera, pretty damn hot down here fella?
Paul Bedford

Gabe Davis

Quote from: Seville Life on October 05, 2022, 08:09:24 PMGabe, that '59, that colour, just stunning, an example of grace, style and elegance. Beautiful motor car and something only Cadillac could make.

Thanks! I think if you are going to have a 1959 Cadillac that Pink is a pretty suitable color! It's the iconic one! ;D
That particular picture was from my brother's wedding photographer who altered the images heavily. The car is a chameleon though. Depending on the light it can be tan, pink, purple or beige. Kinda neat.

Quote from: Seville Life on October 05, 2022, 08:09:24 PMI'm on the French Riviera, pretty damn hot down here fella?

Do you have extreme humidity there too? Gotta love how that makes it feel even hotter!
1959 Coupe DeVille
Rosewood with Dover White Top


try to call or email  0046-706678475 ELLAR MAILA

Gabe Davis

I pulled the trigger on a system from Waldron's. The website said 10-12 weeks lead time. I called to confirm this and the lady who picked up, Ruth, was very helpful in confirming the number of clamps and the quality of the system and that, yes, the lead time on the website was correct.

I'm excited to get the new system but the wait until some time in January is going to feel like a long one!

Grant in New Zealand shipped out the set of hangers so I should have them well before the rest of the system.
1959 Coupe DeVille
Rosewood with Dover White Top

Gabe Davis

I got a couple of boxes from Waldron's last week! Their estimated lead time was exactly right, coming in at 11 weeks. The parts look great and I'm excited about getting them installed. The hangers from Grant also look great. I have ordered the bolts and washers from McMaster-Carr and those will be here tomorrow.

What I did not realize is that the pipes are two different sizes. From the manifold to the muffler inlet is 2 inches and from the muffler outlet to the tail pipe is 1 3/4 inches.

The last piece I need is the flex pipe to go over the solid pipe from the manifold to the muffler. Does anyone have any size recommendations? If the OD of the solid pipe is 2", what would work best for the flex pipe? 2 1/4"?
1959 Coupe DeVille
Rosewood with Dover White Top

Gabe Davis

Time to play!

I got started installing things today. The last piece of the puzzle I needed before getting going though was the flex pipe. I found a chart from Walker exhaust that showed what was available by part number. Walker is carried by Advance and NAPA.

Screen Shot 2023-01-09 at 7.59.53 PM.png

I ordered 46974 (2 1/4") and 46975 (2 1/2") from NAPA. Total was 6' needed to cover both of the front pipes from the downpipes to the mufflers. Those sections of hard pipe are 2" and the rest of the system is 1 3/4".


The flex pipe was pretty evenly split between the left and right sides. The left side was 1" longer that the right.I cut it with a Dremel. I attempted to get the 2 1/4" flex over the 2" pipe but it was not possible to get it to bend around the tighter sections of the hard pipe. The 2 1/2" was doable but still put up a fight. I got it on there though.




1959 Coupe DeVille
Rosewood with Dover White Top

Gabe Davis

Once I had that sorted I started taking apart the old system. It was welded in place so I had to cut it with a sawzall.


The aftermarket mounts were welded to the frame and had to be ground off. I hit the bare metal with a bit of paint to stave off the rust.


The old system was full of holes and had an aftermarket muffler and no resonators.


The mounts from Grant Owen are extremely well made.


The only two originals on the car were up in the well above the axle. Comparing them with what he made shows that they are very accurate.



The holes all lined up except for one on the rubber anti rattle mount but that was easy to modify with a new hole in the rubber.

The bolts to hold them to the frame are 5/16-18 x 3/4. The originals were self tappers but I used regular bolts as the threads were already in the frame. I also added a lock washer to each new bolt.


Each of the anti rattle mounts requires 4 washers and the front most rubber mount before the muffler requires one each. These are 5/16" screw size, 0.344" ID, 1.25" OD, 0.120"-0.130" thickness.

The hardware all came from McMaster-Carr and is zinc yellow-chromate plated except for the large washers which are black oxide. They are Grade 8, massive overkill, but were what I could get with that plating. Military grade stuff, so it should last.

1959 Coupe DeVille
Rosewood with Dover White Top

Gabe Davis

I was very lucky that the nuts came off of the exhaust manifold studs without too much of a fight. The nuts were rusted and partially stripped so I replaced them and the lock washers behind them. I had forgotten to order new ones from McMaster-Carr. The nuts are 3/8-24 and the only ones I was able to get locally were stainless steel and not as tall as the originals so I doubled them up.





As far as the pipes them selves, they are very well made. Not a burr on them and the bends are clean and accurate. The fitment was perfect and I did not have to force anything together. The included gaskets and clamps look to be high quality. I highly recommend Waldron's exhaust for these parts.

I did have to remove the rear shock to get the curves pipe up over the axle.





This car has two exhaust systems and I only got the left side installed today. I have time tomorrow to get the right hand side installed and then I can make comments on how it all sounds. But if it sounds as good as it looks it should be amazing!

More to come!
1959 Coupe DeVille
Rosewood with Dover White Top

Gabe Davis

I got the right side installed. It went the same as the left with great fitment and everything bolting right up.

Except for the exhaust manifold studs. Apparently in the past a repair had been done on this side and the studs were replaced. They were two different sizes and one of the studs came out when removing the down pipe. It had been tapped with a 3/8-16 thread and the stud was very rusty. I ran a 3/8-16 tap through it to clear the threads and installed a new stud but it was still loose and would not clamp down.

When trying to tighten the other stud it gave and is now loose too. So both holes in the manifold for the studs are toast.

What was the original stud size? If I helicoil the holes I'd like to install the correct studs if they will fit. I was reading it may make sense to go to the next closest side up in metric to keep as much material on the manifold holes as possible. I assume the originals have fine threads like the left side did. It looks like I may be able to drill and tap them in place. I really don't want to have to pull the exhaust manifold out to do this.

Has anyone ever done this job with it in place in the car? Any clues on the original stud size? Is helicoiling the holes the way to go or is there another repair process that would be more suitable?

I want to get this fixed so I can hear the new exhaust system without a massive exhaust leak!
1959 Coupe DeVille
Rosewood with Dover White Top

Gabe Davis


After reading a lot about helicoils I decided to re thread the holes to 3/8-18 instead of trying to directly tap m10 threads. I also already had the 3/8-18 studs from the earlier repair attempt.



I had to drive to a couple of different Ace Hardware stores but eventually found a Helicoil brand thread repair kit. It comes with the specific tap, install tool and coils. It did not include a drill bit which in this case called for a 25/32. I picked up one of those too.


There is plenty of room to get a straight shot to both holes in the exhaust manifold from under the car. I had to use about a foot of extensions but was able to get the bit to go in straight and bored out the old stripped out threads. The rear hole opened to the outside on the top. I don't know if it was this way when new as the old repair may have drilled it all of the way through. The front hole is blind but the bit went all of the way to the bottom without issue.

The next step was to tap the threads. Again, I used a long extension and attached a ratchet as there was no space for a tap handle. The process was slow but both holes tapped cleanly.


In the rear hole I stacked two coils so the thread was the full length of the hole. The front hole only had room for one coil.


Once the holes had the new threads I trimmed the stud length with a Dremel so they would catch as many threads as possible in the holes and have the unthreaded portions of the stud land flush with the manifold. They feel super strong and are tight and straight and true.


The down pipe bolted right up and the nuts with lock washers were torqued to the 20ft lbs the shop manual called for.


Needless to say, I was quite relieved that the repair process went well and everything came back together cleanly. No more exhaust leak!




So how does it sound? I was surprised that at idle from the outside of the car the exhaust note is pretty deep. Similar to what the Dynomax mufflers sounded like. It sounds like what a large displacement V8 should sound like. Yet, it is more refined sounding than the Dynomax. The most marked difference is while driving. It is much more quiet. Yet it sounds nice. Smooth and even. I think the correct exhaust mounting system made a huge improvement as well as the amount of vibration went way down. That makes sense as there was very little compliance in the aftermarket hangers that were there before.

Overall, I am very very pleased with how the project came out. I like the fact that the car is closer to how it came from the factory as the rest of it is a very original car. I very highly recommend Grant's reproduction mounts. They are accurate to the originals, high quality and bolted right up easily. The pipes, mufflers and resonators from Waldron's exhaust are also very highly recommended. The fitment, quality of materials and customer service are all top notch.

Anybody interested in some lightly used Dynomax mufflers?  ;D
1959 Coupe DeVille
Rosewood with Dover White Top

TMoore - NTCLC

Beautiful work and a great write-up - thanks for providing this.



Sorry for arriving late for this string - just missed it way back.

But, I couldn't agree more with TMoore - great job.
Love it when a guy does his own work and gets his hands dirty.

Here is a pic of an original cold rolled 59 wrap, to help document your journey.

Have fun,
Steve B.
S. Butcher