Hello experts!
I am in my first week with my new old MB, 79 300SD and so far these are the things I need help with:
1. When I bought the car I had the mechanic do a compression test, passed with great compression. Had him replace the timing chain and adjust valves. Car starts on a dime and gives back change, but is REALLY slow off the line,expecially when cold..When warm it is boggy till the turbo kicks in then it goes pretty good..Little to no smoke out the back. Should I have had him check the pump timing too? Could it be retarded now? Also the vacuum thing on the injector pump buzzes when you turn the car off, like it is bleeding off.
2. The electric cooling fan in the front, should it run with the ac compressor on? It never comes on. What should I look for there?? Where are the relays, in my 240 they were in the fuse box but not in this one.
3. The cruise control works when it wants to. When it works it works perfectly, but sometimes won't engage at all..Whats the first thing other than fuse I should look at?
4. Lastly (for now) the car has a strange vibration above 45mph. It is more of a hum that you can hear than a vibration. Pitch increases with speed. I thought it was tires but had them replaced..It is not affected by throttle pressure, and doesn't go away when I shift into neutral...Any ideas??? Any help would be great, I haven't owned a MB in a long time so haven't gotten familiar yet. It is going to the local shop (Ben's workshop Austin TX) Wednesday to have an oil leak looked at..Thanks for any help everyone! John
PS, it has 285,000 miles on it.

John,

Glad ot hear you've joined the W-116 300SD rank! I have an '80 SD which I absolutely love. As far as your questions, I'll do my best to clear them up for you..

They are naturally a little sluggish off the line until the boost comes in (around 2,200rpm). You might want them to check pump timing which would help in acceleration, and they can richen the fuel injection, but that will of course lead to more noticeable tailpipe emissions. About the buzzing, that is normal. Don't worry about it. The electric cooling fan forward of the radiator will come on when the engine reaches a certain temperature. If you're sitting in traffic for a while in hot weather, you'll probably notice it coming on. Check that the fan operates freely. If not, then the fan is locked up and you'll have to get a new one. Also, if the fan is indeed locked up, then don't run the A/C until you correct the problem. As with the driveline vibration, they all seem to have a slight vibration, but it can't hurt to have the driveshaft checked. Cruise control: If it works intermittently, you'll have to determine whether the switch, amplifier or actuator is going bad. There is a tester made to check the switch, and any good MB shop should have one in their special tool arsenal. If the cruise picks up when you lift the switch but won't hold, then the amp is bad. They run around $180 or so rebuilt with an $80 core charge. What kind of tires did you have put on the car? I have Michelin Energy MXV4s on mine and they're terriffic. The next best tire in my opinion would be the Pirelli P4000 Super Touring. A little noisier than the MVX4, but a heck of alot cheaper! I think they're about $54 each for the Pirelli versus $94 each for the Michelin. Ok, hope this helps!


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Rgds,
Aaron Greenberg
MB technician
Precision Motorcars, Cincinnati, Ohio
'67 250SE Cabriolet
'77 450SL
'79 6.9 (SOLD)
'80 300SD
'85 380SE
'89 420SEL
'93 300E 2.8

Thanks for all the information Aaron, makes me feel better! It is going to the benz shop Wendesday to see about an oil leak, I will ask them about the driveshaft and the cruise..Funny thing when the cruise works, it works perfect! You just never know when you get in whether it will work or not! Tires, hmmm, I didn't go Michelin or Pirelli, the Previous owner had a pair of brand new tires put on and I think they were house brand cooper..I had a pair of Pep Boys Euro sport metric put on..I believe they are cooper or Kelly springfield..I worked for Pep Boys for 10 years and always used their brand and never had a problem..But I think once the car proves itself I will treat it to some nice tires!!! Ugh..Hope that oil leak isn't serious! I called the shop and told the guy I thought it was the oil pan, the big one that goes all around the bottom of the engine..He said it was very unlikely it was that, that probably something wrong with the filter housing or where it is mounted, being that was about where the leak is...So I guess I better take the big bag of cash :-)
Thanks again for the help! John

John,

The oil leak is probably coming from the oil filter housing-to-block gasket. It will blow oil all over hell when you're on the road. It is definitely a wise move to repair it soon if that is the culprit. It's not difficult to repair, maybe 2-3 hour job as the filter housing and related lines need to come off, and the gasket's about $5. Hope this helps!


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Rgds,
Aaron Greenberg
MB technician
Precision Motorcars, Cincinnati, Ohio
'67 250SE Cabriolet
'77 450SL
'79 6.9 (SOLD)
'80 300SD
'85 380SE
'89 420SEL
'93 300E 2.8

You want to check the wheel bearings when tracing your mystery noise.

Ab