Did the OP say the knocking was rhythmic? I didn't see that.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Okay, so.....

I checked the tie rods, etc. but they all looked fine, as far as I can tell, but then again I'm a novice so... I decided to take it to a local Mercedes mechanic that someone recommended to me a while back but had yet to visit. The goal is to try to do most of the repairs myself on this car and learn as much as possible but I'm a little short on time right now. I also figured it might be good to take the car in and have them diagnose a handful of other problems and then decide which repairs I would like to attempt myself and which ones I'll have done by a professional. Anyway, the issue turned out to be something I probably never would have figured out. Or at least, I wouldn't have figured it out until I tried ten other things first. Basically, the center bracket that holds the exhaust in place and keeps it from rattling around was missing a bolt and the other was stripped so that knocking sound was the exhaust moving around and knocking the bottom of my car. It sounded like it was coming from the front tire but apparently it was the exhaust. I am correct that it was only happening when I made right turns though. Not sure why that was the case but I'm assuming it has something to do with the way it's positioned underneath there. Anyway, he fixed it and also adjusted the enormous amount of loose play in the steering box and also topped off all my fluids and checked all the tire pressure in the tires for $60.00. Although these were all pretty simple things to fix, I am happy that I didn't have to spend days trying to troubleshoot it.

No he didn't, that's my point : I was trying to gather information .

It sounds like he's found an honest Mechanic so that's good .

I remember a Customer once came in and insisted I replace his transmission, I asked him why, what was the problem, he got snippy and said 'I know what I'm talking about !' ~

When I started the engine and revved the engine the broken off baffles inside the muffler rattled & buzzed, sounded nothing like any tranny problem ever, I $aved him a few hundred $ .

A DIY'er often misses something very basic due to lack of experience, nothing wrong with not knowing .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

So true. I may have figured it out eventually (or maybe not?), but I would have probably tried ten other things first and spent a considerable amount of time and/or money on it. The mechanic took it for a ride around the block, came back and put the car on a lift and figured it out in literally 5 minutes. That's what experience brings and I never take that for granted.

I would say you got a good value there. I mean shop rates are like $150 per hour out here.

As you found out where you think sound is coming from sitting in the Drivers Seat is not always a good indication where the sound is coming from.

Sounds like he did not do the other stuff that Mechanics do which is to look for more work to do while he was working on your Car.
One of my Shop teachers pretty much said that once you have a Car in the shop you start looking for other things to do to it beyond what the Customer brought the car in for and try to talk if not scare them into having more work done. So he did not do that and that is in his favor.

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84 300D, 82 Volvo 244Gl Diesel

Of topic story. I had the owner drive a used car I was thinking of buying and the test drive went with out a hitch.

After I paid for the Car and drove off everything was fine till I got it above 60 and had a similar banging as you were having above 60 mph. Then I realize that when the former owner drove the Car he kept the speed lower then 60 mph so it would not bang.

Fortunately it was just the Muffler hangers had rotted out and the noise was from the muffler and tail pipe banging on stuff.

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84 300D, 82 Volvo 244Gl Diesel

Whoa, whoa, whoa.... I never said he didn't find more work that needed to be done to the car. Ha ha!

In all fairness though, it was all stuff that I told him to check out for me, so it's all stuff that I knew I needed to get done. I just wanted to get his opinion on that stuff so I can figure out which repairs I was willing to do myself and which stuff I wanted handled by a professional. He really wasn't pushing for any extra repairs that I didn't initiate and he also talked me out of a few repairs that he thought were unnecessary, so that's a good sign, I hope.

What was meant was : he didn't try to force / scare you into more works right then, many do .

If you take the time to listen to all the advice and comments from the good people here then soft out the things / ideas that make sense to you, you'll soon be able to $ave $ome ca$h on initial diagnosis and thence learn how to do repairs....

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

For sure, I've already made a handful of repairs myself thanks to help from the fine folks here on the boards, but I still have a lot to learn that's for sure. This is such a great resource!

That's the spirit ! .

I'm a retired Journeyman Mechanic and I'm still learning things from the good folks here, as you do the simple and basic repairs you'll learn how to handle tools and what occurs when you use them, this is an important part of the entire D.I.Y. thing .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I am not sure where you live, but if you have the time you might consider enrolling in an evening adult education auto mechanics course. These courses are often taught by seasoned teachers with years of experience working on a variety of domestic and import vehicles. Other advantages include the use of quality equipment such as a lift, floor jacks and many other tools and equipment which most people do not have access to. It is also nice to get and offer help to and from your fellow students.