'87 300D cat removal, trouble hanging exhaust? - PeachParts Mercedes-Benz Forum

AlexTheSeal · #1 10-21-2011, 03:07 AM

For those of you who have removed the catalyst on your '87 300D and replaced it with a "test pipe," did you have to do anything else to the exhaust to get it to hang like it did before?

On mine, the center muffler wants to twist to the left side, rotating around the single point of contact with the triangular rubber hanger, and bringing the rear muffler with it. Not only does this reduce ground clearance and twist the rear pipes sideways in a goofy way, but it also forces the new straight pipe upward and it ends up banging against the heat shield on bumps.

It seems like adding a hanger on the left side of the center muffler might help stabilize it, but there's no place on the underside of the car to attach one unless I start drilling holes.

The test pipe is not welded as one piece all the way back to the center muffler, there's a clamp in the middle... exhaust shop said that would make it less likely to crack. (Maybe that's part of the problem.)

Thanks for any input.

vstech · #2 10-21-2011, 10:09 AM

I'm not sure what I did... but mine does not rotate.
I likely welded in the test pipe.

AlexTheSeal · #3 10-21-2011, 11:04 AM

Quote:

Originally Posted by vstech

I'm not sure what I did... but mine does not rotate.
I likely welded in the test pipe.

What type of steel did you use and what gauge? I have seen different reports on whether the factory used stainless or not. It definitely is thick, 14 ga at least.

Zulfiqar · #4 10-21-2011, 11:57 AM

Any increase in noise after cat removal?

vstech · #5 10-21-2011, 12:24 PM

car sounded MUCH better than it did with a plugged cat!

I used an off the shelf exhaust pipe section from mcparts...
that cat is SERIOUS thick pipe, but the tail pipe itself is not.

Zulfiqar · #6 10-21-2011, 02:42 PM

I think because yours is a turbo the exhaust is a stream unlike an NA with split pipes like the 606 - which sounds like pants

sixto · #7 10-21-2011, 02:57 PM

As I see my car, the square flange has a flat surface to the ground. Is that how your forward flange was welded to the downpipe? Is the aft half of the flange free so spin or is it welded to the pipe?

Sixto
87 300D

AlexTheSeal · #8 10-21-2011, 04:56 PM

Quote:

Originally Posted by Zulfiqar

Any increase in noise after cat removal?

None whatsoever. Apparently the two mufflers (center and rear) do all the sound deadening on the 603 cars.

AlexTheSeal · #9 10-21-2011, 05:01 PM

Quote:

Originally Posted by sixto

As I see my car, the square flange has a flat surface to the ground. Is that how your forward flange was welded to the downpipe? Is the aft half of the flange free so spin or is it welded to the pipe?

If you're talking about what I think you're talking about (always a dangerous assumption

) then what you're seeing as a square flange is actually half of the locking mechanism for the connection between the back of the cat and the front of the center muffler. The two square "rings" are bolted together and hold the two pipes together tightly, but the actual contact surfaces of the pipes are round, so with enough torque they can rotate independently. Whether the potential for rotation is by design (to allow for engine torque twisting the pipe a bit on acceleration) or not, I don't know.

Alex

sixto · #10 10-22-2011, 02:16 PM

While assumptions are flying, I assumed your situation was that the aft section of the exhaust wasn't properly clocked relative to the forward section. If at least one flange isn't welded to its corresponding pipe, loosen the connection, set the pipes at the desired orientation then re-tighten the connection.

The flange sections shouldn't move or rotate relative to each other once installed. The rubber hangers and flex section accommodate movement between the engine and body.

Sixto
87 300D

AlexTheSeal · #11 10-23-2011, 11:12 PM

Quote:

Originally Posted by sixto

While assumptions are flying, I assumed your situation was that the aft section of the exhaust wasn't properly clocked relative to the forward section. If at least one flange isn't welded to its corresponding pipe, loosen the connection, set the pipes at the desired orientation then re-tighten the connection.

OK, now I get what you meant.

I got under the car again and took a closer look. The problem is that in addition to the square flange connector, or whatever you call it, the shop that put in the pipe gave me another slip-fit connection farther back before the center muffler. This connection has a clamp on it, but still has a tiny bit of play. I don't see any reason why I shouldn't just rotate the rear section of the exhaust until it's in the right place, mark the two pieces at the slip join, take things off, and weld the slip joint solid. (Well, except for the fact that I hear flux-core welding on exhaust pipe is a b****...)

Alex

sixto · #12 10-24-2011, 12:55 AM

You might drill a small hole through the slip joint and send a sheet screw to keep it aligned. Weld over the screw for good measure.

Sixto
87 300D

vstech · #13 10-24-2011, 07:22 AM

you have flux core welder? any chance you can add at least CO2 to it? lowes has small cans of co2...