Any tips for getting a good exhaust seal with donut gasket

[bujbot]

Hi,

 

I've been struggling for over a month now to get the donut exhaust gasket to seal (gasket between the downpipe and the resonator pipe).  I've tried :

• Repositioning it a few times
• Getting a new gasket
• Under tightening
• Over tightening

More recently I noticed a hairline crack at the joint on the resonator side, thinking that was likely the culprit I replaced the entire exhaust system (the old aftermarket one also had a hole in the muffler) but that also didn't stop the leak.

 

My last resort is to install it with some high-temp RTV ... that is messy so I figured I'd ask here before I go that far.

 

Thanks!

[theNomad]

exhaust sealer

[bujbot]

2 hours ago, theNomad said:

exhaust sealer

 

Thanks, would I coat the donut with this just before installation?

 

Is this the standard way to install one of these gaskets?

[Mike Self]

My highly unorthodox solution--many years ago--was to saw off the two bell-mouths on each pipe end and install a sleeve to join the two pipes.  That's been working just fine for 30 or so years...

 

mike

[JohnS]

When I replaced the stock exhaust with a new OEM one, I was doing the job myself without a helper to hold things for me.  I ended up using contact cement on the donut and glued it into the bell-mouths on either side and it held the donut in place long enough for me to get the clamp tightened without the donut moving around.  It sealed really well.

Edited January 21, 2020 by JohnS

[tme]

Are you working with a stock down pipe or a header?  Do you have the exhaust transmission support?  My car has had a header since the 70’s and it has leaked for years.  Recently I noticed that the header flange has a flat surface while the resonator has a flared concave face.  The donut seals well on the resonator side but not the flat header face.  I found at some point I had acquired a hybrid gasket that was flat on one side and convex on the other.  So far it seems to have done the trick.  I also did not have the transmission exhaust support which I think was abandoned when the header was installed.  Installing it seems to have helped stop the flex at this joint.

[bujbot]

24 minutes ago, tme said:

Are you working with a stock down pipe or a header?  Do you have the exhaust transmission support?  My car has had a header since the 70’s and it has leaked for years.  Recently I noticed that the header flange has a flat surface while the resonator has a flared concave face.  The donut seals well on the resonator side but not the flat header face.  I found at some point I had acquired a hybrid gasket that was flat on one side and convex on the other.  So far it seems to have done the trick.  I also did not have the transmission exhaust support which I think was abandoned when the header was installed.  Installing it seems to have helped stop the flex at this joint.

 

I have the stock downpipe so it has the flared end on both side.  I also do have the correct support.

[bujbot]

1 hour ago, JohnS said:

When I replaced the stock exhaust with a new OEM one, I was doing the job myself without a helper to hold things for me.  I ended up using contact cement on the donut and glued it into the bell-mouths on either side and it held the donut in place long enough for me to get the clamp tightened without the donut moving around.  It sealed really well.

 

Will the cement hold so tightly that it can never be removed?  That's my biggest concern.

 

I was thinking the high-temp RTV because it can be removed with a sharp knife (and is flexible).

[albatcha]

The muffler cement stuff is very brittle when dry, and it doesn't hold that strongly, it can be chipped off with a flathead screwdriver by hand. And if there is any residue thats hard to chip off it can be ground, sanded, or filed off very easily.

[albatcha]

I use it once every couple years to fix a leak on a damaged flange on my old taurus that I don't want to fix the real way.

[Buckeye]

Get your downpipe fasten to support bracket first per service manual instruction then use hyd. jack to raise resonator inline with downpipe. At this time insert the donut and adjust resonator height as needed. Use a wet rag and wipe ends and donut. Apply sealer and proceed tightening bolts and nuts. Should be okay to go over the joint with your index finger.

You can break up the sealer if needed in the future.

[bujbot]

Ok great, thanks everyone

[JohnS]

1 hour ago, bujbot said:

 

Will the cement hold so tightly that it can never be removed?  That's my biggest concern.

 

I was thinking the high-temp RTV because it can be removed with a sharp knife (and is flexible).

The contact cement probably burned up after the first day of driving the car.  It was just to keep the donut oriented correctly while I tightened up the clamp.

[jgerock]

Closely inspect the mounting hardware at that joint.  If the bolt threads are too short, the nuts will not fully tighten up.  Cheap hardware can strip the threads while tightening.

 

As mentioned above, keep the back of resonator elevated and the muffler loosely attached while tightening the front flanged section. It usually takes me several tries to get it right.

[bujbot]

On 1/21/2020 at 12:10 PM, Buckeye said:

Get your downpipe fasten to support bracket first per service manual instruction then use hyd. jack to raise resonator inline with downpipe. At this time insert the donut and adjust resonator height as needed. Use a wet rag and wipe ends and donut. Apply sealer and proceed tightening bolts and nuts. Should be okay to go over the joint with your index finger.

You can break up the sealer if needed in the future.

 

Thanks Buckeye,

 

I ended up going this route today.  It made a big improvement but I can still feel a tiny bit of air with my hand (its barely there when the pipes are hot but I can still feel it). 

 

I'm not sure if I will run some more on the joint with my finger or consider the RTV.