1981 Mercedes 300td engine swap - PeachParts Mercedes-Benz Forum

mycodiesel · #1 03-28-2012, 03:55 PM

I am working on 1981 Mercedes 300td wagon with a blown 5 cylinder naturally aspirated engine. I am looking into replacing it with a OM617 turbo charged diesel, would there be any problem with that? the only thing i can think of is possible wiring issues and the exhaust down pipe. but everything else should be drop in? thank you for the advice and help in advance.

junqueyardjim · #2 03-28-2012, 07:12 PM

That should be an easy to do swap. Really can't see any wiring changes involved except perhaps in the tachometer hookup, (if any is used). I think perhaps that the whole exhaust system is a bit bigger also on the turbo and as you mentioned the down pipe is mandatory.

StaggerLee · #3 03-28-2012, 09:33 PM

I did the same thing to a 1980 wagon. If it's the same, you'll run into problems with the shock mounts (I had to cut the one off of the pass. side) and the transmission will need to be changed to one from a turbo version. The throttle linkage may also be different, mine was. It seems like there was an issue with the plug for the neutral safety switch too.

None are too har to overcome!

DeliveryValve · #4 03-28-2012, 10:01 PM

Unless the '81 is a Euro, the US version of the '81 300TD should be a turbo version.

With that said, it should be a fairly easy swap. If it is an '81, then you don't have to deal with the evil climate control servo that may be in the way of the turbocharger in the previous models.

.

mycodiesel · #5 03-28-2012, 11:06 PM

Okay, I have 4spd manual that is taking the slush box auto. I was wondering about the mounts and throttle, not sure if the rig is a euro model I will check this weekend. Thanks for the help fella's.

vstech · #6 03-29-2012, 03:23 PM

ah.
if it's a MANUAL tranny car, then it's certainly a EURO...
neato!
does it have manual heat controls or auto? if auto, are the pushbuttons vertical or horizontal?

mycodiesel · #7 03-29-2012, 04:59 PM

i am replacing the auto with a 4spd manual transmission, after i pull the blown engine. speaking of manual swaps, does anybody know which master cylinder reservoir in to use for the clutch master cylinder? and i guess there is no tach either? huh?

StaggerLee · #8 03-29-2012, 05:07 PM

On the brake reservoir, there is a nipple that comes out towards the fuse box. Connect that to the Master Cylinder through the gromet just below the fuse box.

mycodiesel · #9 03-29-2012, 07:35 PM

Okay that helps, I just assumed that I would have to replace it with a 240d master cylinder res. so, has any one put a tach on a 1981 wagon?

junqueyardjim · #10 03-29-2012, 08:04 PM

Well you are a long way away from hooking up or needing to hook up the tach. Get the engine and trans done first. Consider the speedo before the tach. Make sure the speedo and the differental are from the same car or car model. Then when your all done and bored, look for a tack. I think all but the 85 300 D are the two wire hook up. The 85 is a three wire hook up. The hook up of these two units are completely different, both difficult but can be done. That is all previously written in the Forum. You will also need to use the crossmember at the rear of the four speed from a 240D with an automatic. Also, along with the four speed I hope you have the shift rods. if they are from a 240D they need to be shortened 4" each. Also, you need to have the whole shifter assembly, gear shift thing,that mounts to the floor.

junqueyardjim · #11 03-29-2012, 08:07 PM

The master cylinder for the clutch is mounted under the steering column inside the car, way up against the firewall. It is long thin tubular and in the half dark kind of looks like an extra big cigar. Hope you got the one that was on the car you got the trans out of.

mycodiesel · #12 03-29-2012, 10:31 PM

Yes, I got all the components from the same 240d, including all shift rods, stick assembly, pedal assembly including MC and SC. I'm picking up the turbocharged engine on Sunday, and will getting started the swap on Monday. Need figure out the starting switch (park/neutral) and reverse wiring.

TchTchr · #13 03-30-2012, 10:25 AM

I don't know about the Euro's, but the US market '81 had an electronic speedo.

junqueyardjim · #14 03-30-2012, 10:37 AM

Well all that piddly stuff is easy done when the big job is complete. No doubt the hook up to the back up lights will have to be changed. Might be easiest to wire them in to a seperate switch on the center console unless you got backup switch with the transmission. I had trouble getting the starter circuit to work, same problem I had a couple of years ago when the starter circuit failed on my 85 300D. That was probably a problem in the ingnition switch, then I got this 240 D and the switch was really buggered and so I put in the switch from the 85. Probably why the starter didn't work. Anyway, I put a push button starter much like was in my 49 and 51 Ford and Mercury. Got it from NAPA for about $6.50, (Yes, box and all) used like a 3/4 inch, (but check your switch size) hole saw to drill through that plastic just to the left of the ignition switch. Use a good quality small wire, 2 of them, one from the battery to the push button, the other from the push button to the solenoid and it will fire up anytime. I turn the switch, see the glow plug light signal, hit the starter and that usually stops the glow plug light. If it doesn't I turn the key switch to start to eliminate the glow plug. After it is all hooked up and working use small cable ties to hide and protect your wiring. You are running quite a few feet and hide it, keep it safe and out of sight.

charmalu · #15 03-30-2012, 12:04 PM

Didn`t the 81 TD electric spedo get it`s signal off the tail of the auto trans?

When yuou get the manual trans installed, the spedo will have to be changed to one that is driven with a mechanical cable, as most W123 are run. 81 TD was a one year only with the electric spedo.
Get a spedo that is matched to the differential. the spedo`s are matched to the diff ratio. so if yuou have a 3:07 Diff, find a spedo from a car with that ratio. look on the back of the Diff. on the lower left corner of the case, scrape off the grease and grime, and the number is stamped there.

As far as the switch for the reverse lights, the 240D shifter has the switch mounted to it, and a wire with a plug on the end. drop down the under dash cover on the drivers side, and on the right side just above the carpet there is a plug connector. (this is where the NSS (nutral safety switch) connects to from the transmission.) two of the NSS wires are for the reverse lights, and two are for the starting of the engine.

In this plug above the carpet, are two purple wires, these are for the start. the other two are for the reverse lights.
this is where you plug in the wire from the shifter.

Before cutting 4 inches off the shift rods, be sure to measure twice, and cut once. as I remember when I did my 4-spd swap, two were cut 4" and one around 3 1/2".

After I figured out what rod hooked to what trans shift lever and the coresponding one from the shift assembly. push the rod into the trans grommet, then make a mental note as to how far the aluminum end is screwed on. remove it, and mount it to the shifter. then hold it horizontal, and lay the shift rod on top, then mark the rod where you want it cut. then cut your threads on the new end.

I didn`t see it mentioned yet, but the TD has the SLS Pump driven off the head. Only the TD`s have this head. Is this new turbo engine from a Wagon or a Sedan? you might have to secure a TD head, or get your`s rebuilt.

Charlie