79 300sd - PeachParts Mercedes-Benz Forum

#1 12-13-2001, 11:24 PM

I have just obtained a 79 300SD, with 75K miles. Very clean, but was setting to long. I just completed rebuilding the injection pump, (broken control sleeve for#2 injector) and cleaning, and pressure checking the injectors myself. The Fuel tank was flushed and cleaned, and I even dismantled the sending unit and cleaned it. I would like to obtain some information on the heater valve controller. I am currently rebuilding the existing one and would like to know how to align it. The motor in the unit was stuck, and the grease was solidified. I dismantled it, sonic cleaned it, and have the gear box back together,(I found the gear line up pin holes) but I think the feedback pot was set to approx 4K ohms. Where should the heater valve itself be positioned? I might add that the valve itself was not stuck, or leaked. Also,
How reliable are the 300 SD,S. What can I expect next.

psfred · #2 12-14-2001, 09:27 PM

Can't advise you on the heater servo, but have some thoughts on the W116s.

Rust, rust, rust! Start prevention early, keep good front and rear window seals in it, and inspect often. This is the worst chassis for rust since the 1960s models.

Engine is the same as all the other 5 cylinder 617s -- keep good oil in it, changed often, use good fuel, and it will run for 300,000 plus miles with no maintenance other than valve adjustments. Be obsessive about the valve adjustments, though -- they can go out pretty fast. Otherwise, you will need a valve job every 150,000 miles or so. You may, anyway.

Vaccuum pump may go south and cause great quantities of oil to get pumped down the intake -- about the only thing I know of that can make these trail blue smoke. You will know if it happens, easy fix.

Front subframe bushings are probably shot, ditto for rear. A pain in the butt, but not really difficult or expensive. Engine and transmission mounts are probably shot, too. Easy fix.

Transmission may be dicey after sitting for a long time. For sure it will be low of fluid -- the torque converter will drain down and overflow the housing, leaving you a quart or two short when you start it up. If it got much condensation in it the filter will plug, so I'd drain it and replace filter and fluid pretty soon.

You've fixed the IP and injectors, so the only other things I can think of that are a problem are battery and starter -- the starter can get weak and fail to start the car reliably -- diagnosis is excessive current draw. Get a Bosch rebuild, don't have the local place do it unless they will replace the armature after checking resistance -- these are very high load direct drive starters, and the windings aquire high resistance. Replacing brushes, bearings, and turning commutator won't fix this.

With only 75,000 miles, unless the engine filled up with water or something else horrible happened, you should be driving your 300SD for a long time!

Peter

'79 Super Turtle · #3 12-15-2001, 01:27 AM

Congratulations Peter G.! I love my W116, '79 300SD. It is rusty, but won't be after this summer. Mine has around 360,000 miles, and it has never had a valve job or any other major service. It seriously goes very, very fast, no smoke (after I put a new turbo on and replaced the valve stem seals), and burns very little oil, though it does have quite a few drips. I'm replacing the timing chain this spring (just on principle

), I also just put my second starter in two years on due to a non-Bosch rebuild that I installed. I had a problem with the starter draining my battery in the winter, so I'm excited about my fresh starter.

I have no real problems with this car, and have not had to do much of anything to it. I still have the same exhaust I've had for 6 years which was probably 6 years old before that. I bought new tires, and replaced nearly all of the vacuum components, but other than that, no problems. If your vacuum pump does give up, it's a cheap and easy fix. I'm jealous of your low miles. If you have black leather seats, I'll be even more jealous. Have fun!

I think the W116 is the classiest of the 300SD's.

mikemover · #4 12-18-2001, 02:02 AM

I love my 116 too!!! I'm a sucker for chrome, and the 79 300SD has a LOT of it! It's not exactly a sprinter, but it's fast enough with the turbo...leaves most other diesels in the dust, for sure!--and many other unsuspecting cars as well. Very little smoke, though I think when it's time for my next valve adjustment I'll have the seals replaced as well.

Luckily mine has no significant rust, that I can find, anyway, but I need to replace my dried and cracked rear window seal soon to make sure it stays rust-free...

Some photos...

www.mercedes300sd.freeservers.com/index.html

A couple of weeks ago, I took a chance on buying a used servo to fix my heat...it works great now, and was a very easy DIY job. Worth the risk of buying used, for sure! New servos are NOT cheap!

Hope you enjoy and take good care of your SD...they're great old cars!

Mike

Ether · #5 12-18-2001, 09:38 PM

Hey Mike,

Where did you find the servo. Mine has a few little quirks of it's own and I was thinking about maybe replacing it with a 'good' used one. If such a thing could be found.

mikemover · #6 12-20-2001, 05:07 AM

Hi Ether,

Check your e-mail, I just wrote to you about the servo.

Mike

dieselman · #7 11-30-2002, 03:53 AM

The 116 is in my opinion the best of all. I recently took my 80 SD on a 2500 mile trip to Florida. No problems and it will keep up with anything on the road. Mine had 129,000 miles when I got it. It now has 206,000 and runs great. How many cars can you pay 2300 dollars for and put 80,000 on it. I plan to drive it to 400,000

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