Scraping sound under dash--'83 500SL Euro

[Froggy]

I've got a strange noise coming from i guess inside the dash. Only happens when I'm starting off, and usually when it's a little bit uphill, where there's a little more tug on the engine. It sounds just like someone is pulling a screwdriver across the inside of a metal garbage can and lasts about a second. I can make it last a couple of seconds longer if I give it a little more pedal. It's not super loud, but plenty loud so anyone would notice.

I thought it might be a heater vent door scraping against the duct inside there, or maybe one of those slave vacuum doohickies that opens the vents. I removed the inst cluster and trove it for a few days to see if I could isolate the sound, but that didn't help. Maybe its coming from just inside the engine compartment? Happens whether hot or cold, and whether heater of A/C is on or off.

Ever hear of anything like that?

[ScottinSoCal]

Originally Posted by Froggy

I've got a strange noise coming from i guess inside the dash. Only happens when I'm starting off, and usually when it's a little bit uphill, where there's a little more tug on the engine.

Not on a Mercedes, but I had a car that did that. It was bad motor mounts and a resulting geometry problem with the linkage between the engine and transmission. Replacing the bad motor mounts fixed it.

[nobby]

Good call, Scott.

[ReadySetSlow]

possibly speedo cable - common & easy/cheap fix

[nobby]

Originally Posted by ReadySetSlow

possibly speedo cable - common & easy/cheap fix

If it had one.

[Froggy]

Thanks Scott. That sounds pretty logical. How do you tell (visually) if the motor mount is no good?

[Froggy]

(PS I don't have a speedo cable.)

[donbryce]

Noises like this usually send me looking at suspension parts. I'd try to narrow down the location/source further, like inside or outside by having someone outside the car listen as you move off.
Noise will telegraph through the body and make it sound like it's coming from somewhere that is not even close to the source, like water leaking from the ceiling originating 10ft away on the roof..
Tough call on the motor mounts, as cracked rubber isn't very visible until the mount is actually in your hand.
BTW, are you in NB Canada?

Edit: Just for interest, this post is date/time stamped 'yesterday 12:56PM', post #8, and the next post, #9, is 'yesterday 11:36PM'.

[ScottinSoCal]

Originally Posted by Froggy

Thanks Scott. That sounds pretty logical. How do you tell (visually) if the motor mount is no good?

You really can't tell visually, but if they're older than about 5 years old they probably need to be replaced. MB used very soft motor mounts to damp engine vibration. While it made for a comfortable ride when they were new, it meant they have to be replaced more often.

[Froggy]

Thanks. I doubt my mounts have been changed in about 25 years. That's a good idea to have somebody on the outside listening. I'll do it with the hood up. (Look out! Look out!)

Nope, I'm not out of Canada, eh.

[Froggy]

Well, I figured I'd just spend an enjoyable afternoon replacing engine mounts, and looked through some threads on the subject this weekend. Apparently, that's not an eenjoyable afternoon at all. Sounds like itsright up there with a couple of days of waterboarding. I'm reading lots of recommendations to farm it out. But it sounds like about a $7 or $800 job to have the shop do it, so I guess I'm stuck.

It'd be nice to know the mounts are the problem before I rearrange my knuckles. Can you tell anything by putting it in gear and torquing the engine with the brakes on, forward then reverse? How much should the engine move?

[ScottinSoCal]

Originally Posted by Froggy

I'm reading lots of recommendations to farm it out. But it sounds like about a $7 or $800 job to have the shop do it, so I guess I'm stuck.

Yeah, it's not so enjoyable, and I did farm it out. But it wasn't $700-$800. It was more like $150. I had them replace the steering box, replace the coupler and replace the motor mounts all at the same time, and the total labor came to $300. Parts added a bit on top of that.

Come to think of it, it was probably less than that. To replace the steering box they had to dismantle to exhaust system, so that would have been the bulk of the labor. The only reason I didn't do the motor mounts myself is because I needed a tool I didn't have and didn't want to sacrifice a good quality tool to make. You have to whack a good chunk off a hex bit to make it small enough to fit in between the exhaust manifold and the bolt to be undone.

Originally Posted by Froggy

It'd be nice to know the mounts are the problem before I rearrange my knuckles. Can you tell anything by putting it in gear and torquing the engine with the brakes on, forward then reverse? How much should the engine move?

In my case it was very easy; one of them had broken completely. Every once in a while, if I didn't let off the gas immediately when the engine caught, the whole car would lurch with the torque of the engine. The difference in the feel of the car was night and day after they were replaced.

And if the idiot who did it had actually put the screws back into the heat shielding and tightened down the EGR valve when he was done, I'd have been very happy with the work he did.