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Old 07-08-2007, 01:42 AM
jenseng jenseng is offline
Diesel Fan
Join Date: Jun 2006
Location: Greater Seattle Metro
Posts: 6
Here there be Dragons

I have performed this modification of a M/T W115 240D to 3.0l (617) from a 1976 W115 300D parts car. I will try to highlight the high points of the modification and the overall relative difficulty involved in this changeover.

OMG this is a hell of a lot of work. I would have to say if you were to get this old dude to do this job and you got a bill for ~$3,000-$5,000 I would say you got a good deal.

First if you do not still have the 300D parts car at the disposal of the mechanic the flywheel is the least of your worries. Just about everything looks identical but they are slightly longer, shorter or entirely different. Nearly nothing from an interface stand-point can be directly used from the 240D without some sort of kludge resulting.

The starting and shut-off system will have to be dealt with. The starting system I had already modded to the fast-glow system with modern glow relay so all that was necessary was to add an extra "ice-cube" relay and an additional fuse. The 300's vacuum shut-off system requires either the use of the 300's ignition switch or to mod the "gorilla knob" to accept a vacuum valve to control vacuum shut-off to the IP.

The driveshaft will have to be ordered. I went through NW Driveline service out of Portland OR. I can provide you with the measurement and they will build one up for you. neither the 240D's or the 300D's driveshaft will work. The cost in 2006 was $375 + $75 core. No local driveshaft service shop would accept the job as the driveshaft is "friction welded" together.

The engine shock mounts will have to be sawed off of the 300D's frame and welded into the 240D's frame. Replace the engine and transmission mounts while you are at it. Without the heavy fluid filled torque converter this configuration has more vibrations, fresh rubber helps out significantly.

The exhaust manifold is a different geometry. and must be retained. I was able to attach the existing front and rear mufflers to the exhaust downpipe.

Misc. items in no particular order:
The idle control cable from the 240D is too short and has to be transplanted from the 300D. The speedo cable is now too short and has to be transplanted. The York air conditioner bracket looks the same, but is different. The high pressure a/c line from the pump to expansion valve is about 1" too short and must be transplanted. The air filter housing from the 300D will have to used. The radiator and fan shroud fromt he 300d must be used as the clearance and hose fittings are different. The shift linkage must shortened and re-threaded about 1.5" with a M10x1.5 die. The linkages must be tweaked a bit to get clearance around the transmission. Most of the throttle linkage from the 300D must be used as the clearance is much tighter with the extra cylinder. The heater hard lines must be transplanted.

Plus all of the stuff I have repressed, plus all of the opportunistic maintenance (omitted for brevity), and then, and then, and then.

I have over 12k miles on the beast and I love the car, but I would not do it again and I do not recommend it. Please feel free to comment on this. This took over 300 hours of labor between two very competent mechanics and still is not completely finished over 1 year later.
1975 240D 4-Spd
Converted to 3.0l (617)
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