Ha, that was what was wrong with one of the ones I returned

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Ok, I got the new vacuum pump installed. The old bolts didn't give me much trouble. New one went in, new gasket, cleaned the block area, tightened belts while I was there.

I need to use my hand gauge to ascertain the amount of vacuum I have. My dash mounted gauge is reading 13 in/hg, I may have it plumbed in too close to the vacuum control valve. I did notice my vacuum goes up much faster now, takes only a second or two to build up. Brakes work like they should on startup, no waiting a bit for it to be a useable petal anymore. Also, it retains vacuum a lot longer now, especially if I leave the AC set on defrost.

Took the old pump apart just to see if there was obvious damage. I saw traces of oil everywhere. Not a lot which would indicate it were sucking in massive quantities over the years, but small amounts, like from that cam plate spinning. Speculation at this point. The bearing on the cam arm though did rotate smoothly, no binding. Maybe a repairable pump? Oh, the cam plate had no play or slop in it, nice and firm.

Still idles rough, no change there. What is strange though, and making me shift my focus to something more rubber, is that when I park in my driveway (steep hill) the vibration is a lot less. At a red light, if the car is shaking pretty good, I can hit the throttle lightly with my foot on the brake, causing it to lurch a bit and raising the front up a little. When I do this, vibration is greatly reduced. Maybe my new mounts I replaced last summer are already bad?

Compression test and fuel pressure analysis are next steps.

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1985 Mercedes 300D turbo, w123, 722.3, 315K miles
1987 Mazda B2200, Dana 44, 283 v8, th350, np203

Ok, changed where I was getting a vacuum reading. Now I'm getting 23 in/hg from the pump to the fitting right in front of the booster. System is stable, needle barely moves when I turn on the AC and goes right back. Nice to have a strong vacuum again.

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1985 Mercedes 300D turbo, w123, 722.3, 315K miles
1987 Mazda B2200, Dana 44, 283 v8, th350, np203

Very good chance. Current mounts are known for collapsing quickly and a collapsed mount acts like a solid mount. A trick is to fill the mounts with urethane to prevent collapsing.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

I have been dealing with "too rough" in the cabin of my 1985 for the last year. The engine itself appears to run smooth and stable in the engine bay, with no noticeable motion, but vibrations get transmitted into the cabin. I tried fitting some hydraulic mounts (2000's Corvette) but ~1" too high plus made the shaking much worse (see post), but not sure they weren't really solid rubber.

I then re-installed the poly-urethane filled mounts as before, but w/ a backer plate to support the poly. It was better, but definitely worse than before I started "fixing" it. Now, I have 1 poly-filled and one factory (open) mount (driver's side) and it seems better, but varies day-day. Today, it seemed much smoother. Next, I'll try a regular mount on the R side too.

My suspicion is that these engines are very sensitive to the mounts and even small tweaks can change the natural frequency to make better or worse. You can also play w/ idle speed. Changing/adjusting the rack damper bolt didn't make a difference for me. The "throttle" linkage can also be in play. I felt like my engine was stumbling a bit coming off idle, but turned out to be the rubber coolant hose by the oil filter was rubbing the linkage. Also, insure the rotator rubber hasn't split. Of course, I may also be dealing with a fuel suction issue that started during my mount swapping.

I wonder if anyone owned one of these cars when new and remembers how smooth they were then.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

I own three W123 turbo diesels and all of them have a smooth idle for a diesel. Whenever I needed to change motor mounts I used genuine Mercedes mounts based on the recommendation of a long time Mercedes independent mechanic. I did purchase a new 240D in 1983 and a new 1985 300D and remember that both of these cars had a smooth idle.

Heck, mine was smooth a couple months ago.

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1985 Mercedes 300D turbo, w123, 722.3, 315K miles
1987 Mazda B2200, Dana 44, 283 v8, th350, np203

Ok, my motor mounts that I replaced last summer are completely toast. I hate Anchor brand now, they used to be good for previous projects.

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1985 Mercedes 300D turbo, w123, 722.3, 315K miles
1987 Mazda B2200, Dana 44, 283 v8, th350, np203

Got one mount (driver/IP side) replaced, vibrations went down quite significantly. The mount was in two pieces, heat shield smashed in, simple enough swap.

Head in the passenger/manifold side got rounded. I'm hoping this one is also completely broken, so I can jack it up and remove the two smaller bolts.

By he way, does anyone know the size/thread pitch of the main motor mount bolt?

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1985 Mercedes 300D turbo, w123, 722.3, 315K miles
1987 Mazda B2200, Dana 44, 283 v8, th350, np203