Can a Mercedes 300SD be BOMBed?

[Blakers]

My mom has a 1981 300SD Benz 5-cylinder that's in great shape except for a transmission that seems to slip a little and the cruise and speedometer not working. I think the cruise and speedo problem is probably a sending unit. I've been to told the transmission is not worth fixing and to just drive it until it dies, which could be many miles away.



Anyway, I was wondering, if I put some work into the car and fix it up, can the engine be BOMBed?



I have an old 67 200D with no turbo and no power, but I start it up and run it every year to keep it going. The car is junk. Anyone want a good project engine for a tractor, etc? I rebuilt it several years ago.



Take care,



Blake

 

[LSMITH]

Wow, longer than I thought

Blakers, yes the car can be pumped up a little but not a whole lot.



First and foremost- the cruise control. There is a metal box about 4"x6"x1" up under the dash on the drivers side. It has one cable connected to it. This is the cruise control amplifier. Take it out, take the cover off and hit ALL of the solder joints on the back side of the board with a good hot iron (pencil point), make them shiny. You are looking to remelt the junctions WITH penetration, just don't melt out the solder totally. Hit it with a good shot of hairspray when it cools off, and reinstall it. Walla your cruise works again, I would bet it does anyway. If this scares you I will do it for you, just pay the shipping both ways.



The speedo is just as simple. Right on the drivers side fenderwell under the hood there is a round plastic doo-dad. It looks like a relay, about 1. 5" in diameter and about 2. 5" long. You will be able to unscrew the lock ring and pull it off. There are a couple pins in the bottom that plug into the socket you just took it off of. Pull the cover off of the part you took off. You may have to pull pretty darn hard but it will come off if you work at it. Inside you will see some potted electrical gear, don't worry about it. Take a styrofoam peanut and put it in the cover, and press the guts back in. I am totally serious here, just do it, worst case your speedo will not work still, but again I would give great odds that it does when you plug it back in and screw the collar down. Again if you don't want to take it apart just send it on out.



If you need more info about the above just let me know, it really is simple and a garage would charge you $400+++++ to fix it.





For the power it depends on how much more you want. A max gain of about 20% can be had which is back to european specs for the engine, but you need to install a boost gauge (temp one in is fine) to adjust the wastegate. You can get about a 10% gain just by adjusting the aneroid. Look at the injection pump, on the back end (firewall end) there is an aluminum box about 2" square and 1" deep. It will have a round metal knob with a black center coming out the top of the box. Take the plastic line off of this box and blow in it, it should be open and free, if it is not you need to make it so. Take a screwdriver and gently slip it under the metal at the top edge of the knob and pry out just a bit. This is a foil seal over the aneroid adjustment screw. The black plastic is a cover. Tear the foil off of the cover and then you can pull the cover off of the screw. Turn it 1 and 1/2 turn couterclockwise. Put the black plastic cap back on. Test drive it. You are looking for a grey haze out of the pipe at WOT as it goes through the gears. If it is seen as black back it off a quarter turn and drive it again. If it is clear give another quarter turn until you get the haze.



EDIT: let me know if you want to tackle the euro settings, I can walk you through it.



This adjustment helps tremendously with driveability. The TC in these cars is VERY tight, so letting the fuel come in a little harder on the bottom spools it quicker. The car tuned properly is a decent car to drive.



The valve adjustment on these things is a 15K mile routine. If it is not done economy, power and starting all suffer quite a bit. Also if the mileage is way up there, 300K or more, and the timing chain has not been replaced the valve timing is out of spec, you can either put in an offset key or new chain. Pump timing can be changed but I have seen very little gain, in power or economy. I have also never seen one that the pump timing slipped on unless someone had been trying to adjust it from factory.



Hope this gives you a little to chew on. Let me know if I can help any more.

 

[Blakers]

Thanks so much for the tons of advice!!



It will be a little while before I get time to do anything with it, but will certainly have your letter handy when I look at the car. One thing to note about the cruise and speedometer - they both quit at exactly the same time one day.



We had a 79 300SD, which I think was a much better built car and heavier, but the 81 seemed to have a little more power. Maybe this is because it is lighter? I don't think the 79 had a waste gate. Is the turbo different on the two? Are there any other changes in the engine?



I drive 100 miles round trip to work everyday, so I was thinking of fixing up mom's Benz or looking for another one. I like driving a diesel and a heavy safe vehicle, and it would save in fuel and where on my Ram. I grew up with Benz's - the oldest being 1962 190D and the newest being the 81 300SD - 14 of them over the years and every one diesel. The only one we bought new was a 73 220D bought by my gramps for $8,000 (wow! we thought back then). It did not come with power steering and he hated it because it steered hard. My 67 200D steered easy with no P. S.



All the early ones were gutless, but I think the 200D had more power than the 220D.



This got long. Take care,



Blake

 

[The patriot]

I had a 190D for a while. It wasnt too fast, but it would get 45 MPG all day long at 80 MPH. It had so many miles on it that it scared me. 1/4 million!!!!



As a side note, my parents witnessed a MB flip over several times on the median grass in PA a few years back. Both passengers were not hurt, and about 1/2 dozen guys from passing cars that had stopped rited the car (stopped resting on it's side) and they drove off with the vehicle with no major visable damage. This was one of the large bodies... . I'm thinking he told me an 450SEL. ????

Eric

 

[LSMITH]

OK, if they quit at the same time just do the speedo fix, both should come to life. Most times the cruise quits first and then the speedo. The 79 is the same engine as the 81 IIRC, but I am not sure on the turbo, I could look it up if you really want to know.



The 81 is a solid car, the small things that go wrong on a car that old are annoying but if you take care of them as they come up the car can be used for a LONG time. Glad I could help.

 

[Motorhead]

Blakers, Also check the boost line that goes to the top of the inj pump. MBZ uses a over boost switch that is located toward the back of the intake. It accuates a bleed off valve on the firewall. The line can plug especially if the EGR is hooked up and working. Take this line off at the intake manafold and ck for gunk on it. Also take it off at the pump,start the engine ,bring up the throttle enough to build boost and see if you get pressure out of the line. Ck the small rubber hoses at the vac bleed valve to make sure that they are not rotted. The vac valve can plug up too. Put a piece of vac hose on it and blow thru it with your mouth. It should flow freely. BEST thing to do is dis-able the EGR valve. Put a BB in the vac line at the EGR valve. This helps on low end and it also keeps the boost pressure up. CK THE VALVES! I work on alot of the five cyls and they tend to tighten up the intake valves.



LS, Thanks for the instruction on increasing the fuel at the pump. I have 2 of the 300's. MY wife has a '84 turbo wagon and my oldest daughter has a '85 turbo sedan. . Good Cars Chris