1975 280C - Catalytic Converter

[alfredgee]

Hi Gang,

I have been having performance problems with my 1975 280C and the shop has finally traced it down to the Catalytic Converter. It appears that it’s breaking apart, causing periodic blockage of exhaust flow. You can literally hear the pieces shooting through the exhaust system sometimes on acceleration.

For those unfamiliar with the car, the Cat in the 280C is in the engine bay, under the air intake, right at the exhaust manifold.

I have three options, one is to cut it out and fashion a new pipe system, two is to cut it open and hollow it out so that the car appears stock or three, buy a new one.

I am curious what other owners have done, or if anyone has a suggestion on what some other alternatives are that would be great.

[ctaylor738]

Are you sure this is a cat and not a thermal reactor?

If it is the latter, then the last quoted price I heard was $3400 for a new one. If you are not worried about emissions, I would find the standard M110 exhaust manifolds and downpipes and hook them up to the exhaust.

[Tristar1959]

There's a guy locally selling his whole 75 280C for about U$2K, which has an intact reactor. For that plus expenses, I'll bring you that coupe, if you don't mind my stopping by a friend's in Edmonton on the way...course, I'll doubtless need to take the southern route to you, since Banff-Kamloops route is likely snowed under and closed, at the moment...
Still cheaper than $3400....

If you go the other route, but need a Cat to help pass emissions tailpipe tests (they're pretty Green, out there, aren't they?) -
note that the US "California" version of the M110's in the later 123 bodies had THREE Cats and air injection into the front two plus port injection, whereas the "Federal" version of same cars only had one Cat and the port air injection...
Both had vacuum controls and air pumps - the significant difference being, in the Left Coast version, one more temp-vacuum switch in the chain to the air valve, plus the stainless steel flex tailpipe injection tubes from the air valve, rather than its dumping to a "muffler" when not in range to port inject.

Sincerely hope you can make do with the "lightened" higher-bypass modification or a straight manifold.

One factor which can seriously deteriorate any of those reactive scrubbers is running too rich a mixture - set mixture as lean as properly in correct range...

[Tristar1959]

Alfred,

Checked out my '73 114 sedan with the M110 carb'd engine -
Looks like a good candidate for non-cat manifold/pipes - very fluid layout of manifolds, which should give great flow; plus has a conventional heater box on the rear manifold for a stack to give you warmed intake air for your carb.
I understand the first cats, by whatever name, were '74 - '75.

My point being that the '73 M110-engined W114 sedan, at least, should be a good donor for yours, if you're junkyard-prowling...

[ctaylor738]

Remember that this is the carbed engine, which runs 4.5% CO at idle and can only be adjusted at idle. A cat is not going to get along with a mix like that very well.

[alfredgee]

Hi Everyone,

Thanks for all the responses.
Yes, we are very, very Green up here with annual emissions testing, but the MB is a Collector Car, so it is exempt unless I sell it.

I found the description in the shop manual on-line, they call it a catalyst and you can replace just the innards. I called my local dealer and it is still available, but it has to come from Germany and the cost is $1,773 CDN, much better than the $3,000, but still not great. I am going to take it apart to see how bad it is, and with it removed, I should be able to verify if my performance issue is truly due to the catalyst.

I like the idea of switching to a pre-catalyst set-up; I’ll have to scour the local yards to see if I have some luck finding a suitable donor.

Thanks again for all the responses!

Cheers!

[Tristar1959]

Good luck with the parts search - hey, for a LOT less than that refill, you should be able to find not only the manifolds and pipes, but a whole 69-73 CAR of spare pieces-parts...although, with that Detroit/Windsor iron contaminating your driveway, you may not have room...

Regardless of your ultimate solution, you might want to consider dropping the whole system and "shaking it out" (back-to-front) to dislodge any bits still possibly partially blocking the system...

Believe me, if and when my daughter's (3 cats/inj pipes) California version W123 280CE eats its cats, I'm going to convert it to at least the "Federal" (1 cat) version from one of my parts cars. Already had to replace the vacuum valve and all of the crispy hoses and piping all the way back to the bypass/dump valve, when the flapper in the "anti-regurgitation valve" in the air injection failed, and allowed exhaust to melt the vacuum valve and spit molten aluminum almost all the way back to the pump...

Tailpipe tests haven't yet worked their way south from Northern Virginia, but I anticipate it soon...so far, down here in the country, away from the Beltway, the dictum seems to simply be "if it's there, it has to work..."

Happy hunting