Exhaust in the cabin

[Geep]

Hey all… so I just got the muffler replaced on my 1976 2002. The original muffler was pretty rusted out the bottom and although a little loud, it wasnt too much if a problem save a little exhaust in the car from time to time. Once replaced however, when push WOT exhaust will BILLOW into the cab almost choking me out… its pretty straightforward and everything seems well fit as far as I can tell. Muffler shop says its coming in through the trunk (there are no seals) because of the vacuum created now that all the exhaust actually exits the rear of the vehicle as opposed to exiting under the muffler (and dissipating perhaps?) as it did before. I put some seal material around the trunk and though it has improved its still pretty bad. Any credence to the muffler shop’s claim, and any ideas on how to best prevent this? Just cut a hole in the bottom of the muffler and return it to its original state? Pic for reference 
 

Geep

['76mintgrün'02]

1 hour ago, Geep said:

Muffler shop says its coming in through the trunk (there are no seals) because of the vacuum created now that all the exhaust actually exits the rear of the vehicle as opposed to exiting under the muffler (and dissipating perhaps?) as it did before. I put some seal material around the trunk and though it has improved its still pretty bad.

 

I'm not sure what you mean by "seal material" but you need to install the real-deal rubber-seal for the trunk lid.  If you search the forum archives, you'll see a lot of photos of clothes pins holding the seal in place while the adhesive sets.

 

 

 You could also add a stainless steel exhaust tip, to get it out a little farther from the car.

[Mike Self]

Another thing to check:  did a previous owner cut holes in the package shelf to install flush-mounted speakers?  If so, that's a wonderful path for exhaust to wander from the trunk into the passenger compartment.  In addition in the corners where the package shelf sheet metal, rear window surround and the C pillar meet (and under the rear seat back) there are some openings that the factory stuffed with foam to seal.  That now 50 year old foam has disintegrated, and is another path from trunk to passenger compartment.

 

mike

[Geep]

5 minutes ago, Mike Self said:

Another thing to check:  did a previous owner cut holes in the package shelf to install flush-mounted speakers?  If so, that's a wonderful path for exhaust to wander from the trunk into the passenger compartment.  In addition in the corners where the package shelf sheet metal, rear window surround and the C pillar meet (and under the rear seat back) there are some openings that the factory stuffed with foam to seal.  That now 50 year old foam has disintegrated, and is another path from trunk to passenger compartment.

 

mike

there are ABSOLUTELY giant speaker holes cut in the shelf. My son noted the same. I’ll close those up! Also real seal ordered as opposed to the Lowe’s Thermoking quick fix I used. 

[0257]

Seal everything as Mike says. Extend the tailpipe as Tom suggests.  Then check the joint between the final muffler and the midsection for leaks.  They often leak badly; I’m still trying to decide how best to tighten up the seal on mine.  And most on this string already know, I now smoke-test my mufflers to ensure they don’t leak at every seam, quality control even of OEM mufflers for our cars not being what it once was.

[Geep]

On 2/6/2024 at 11:23 PM, '76mintgrün'02 said:

 

I'm not sure what you mean by "seal material" but you need to install the real-deal rubber-seal for the trunk lid.  If you search the forum archives, you'll see a lot of photos of clothes pins holding the seal in place while the adhesive sets.

 

 

 You could also add a stainless steel exhaust tip, to get it out a little farther from the car.

What sort of adhesive do I need to use?

['76mintgrün'02]

Here is a quote from the link I shared above.

 

"I used Wurth and it was fine. But as Bibm5 said, a good 3M type product from any discount store will save you money...also get a nice semi stuff paint brush, or actually a few of them, to get glue up inside the crack of the seal and to neatly place it on the metal . It can get messy if you try to move too fast and are not careful "

[Geep]

Thanks! I didn’t think to look within the shared post 🤦🏻‍♂️

[Mike Self]

On 2/6/2024 at 11:23 PM, '76mintgrün'02 said:

You could also add a stainless steel exhaust tip, to get it out a little farther from the car.

This is particularly important on squarelight cars with those big bumpers, and also US 73's with their extended bumpers.  If for no other reason than to keep the exhaust from staining/deteriorating the bumper finish, but also getting the exhaust well away from the car.

 

mike

 

PS--last time I checked, Autohaus Arizona had some very nice stainless steel exhaust tips for about half of what BMW was getting for their crack-prone chrome plated brass ones.

[0257]

There are many threads here on adhesives. Using the wrong one can result in some real frustration — and different rubber on different parts of the car want different adhesive, so I suggest you do plenty of homework before you start spreading goo.

[0257]

Often overlooked source of exhaust leaks is the gas tank: often the seal around the tank goes bad (or just doesnt’ exist any more).  3M black rope caulk is a good solution for completely sealing around the edges of the tank.

[Son of Marty]

I'd also add you need to scuff up the rubber in the glue area to clean out the mold release used these days. I use course steel wool and 3m adhesive cleaner.

[Charles in PA]

On 2/8/2024 at 10:57 AM, Mike Self said:

This is particularly important on squarelight cars with those big bumpers, and also US 73's with their extended bumpers.  If for no other reason than to keep the exhaust from staining/deteriorating the bumper finish, but also getting the exhaust well away from the car.

Is there an exhaust tip available that extends beyond the diving boards?  I have a 74tii.  The tips available at Rogers and Wallothnesch do not look like they'd extend beyond the diving boards.  Thanks

[71bmr02]

wait till it's dark out, or in a dark garage put a work light in the passenger compartment and you will immedialty see where the holes are located with the trunk open.  some large like where the rearseat bulkhead meets the wheel arch  and where the gas lines go thu into the pass compartment or small where previous owners have drilled holes to attach something.  I use elecrticians putty to plug most holes, it remains pliable thru a wide range of temps and is easy to push into large and small holes.  po had installed speakers in the package shelf, think they used a sawsall.  i put a bead of silicone around the perimeter of the package shelf and around the speaker holes then laid on a piece of heavy plastic .  AS mentioned earlier use a bmw trunk seal, some adjustment to the trunk lid can be made with the lock mechanism so you can get a better "squeeze" on the seal.  you dont want to stand on the seal but you can feel when the seal squishes and seats properly

['76mintgrün'02]

On 5/7/2024 at 8:52 AM, Charles in PA said:

Is there an exhaust tip available that extends beyond the diving boards?

 

I don't think you're apt to find a longer slip on tip; but I'll bet a muffler shop could do a nice job of extending the tailpipe so a standard stainless tip would work.

 

1 hour ago, 71bmr02 said:

You don't want to stand on the seal but you can feel when the seal squishes and seats properly

 

The metal ledge along the back of the trunk opening where the seal attaches is easily bent if it gets leaned on.  Luckily, it is easily bent back up.  You can check to see if the seal is being squished by closing the lid on a dollar bill and trying to slide it side to side and pulling it out.  If it is too loose, try bending that lip back up.

 

On my car, I could see soot on the underside of the lid where exhaust had been sucked past the seal.

 

My car is disguised as a '74 now, with a side exit exhaust.  I did have to extend the tail pipe before pressing the stainless (aftermarket) tip on, to get it out beyond the big bummper. 

 

I'll bet the original US '74 side exit mufflers had longer tail pipes when they came from the factory and now they all come cut short for tiny-bumpered earlier cars.