Warden , you are completely correct.... you caught me with my frugality showing... LOL... compared to putting out for a new cheap car someone could do an engine and put a five speed behind it and have a real long term keeper....
At least in the old days Car and Driver , when describing cars, would include some number which indicated the amount of piston travel per mile ... as a comparative wear index... all other things being equal, and people not lugging their engines by using 5th at the wrong times.... I expect that the 5 speed would increase engine longivity by decreasing the rpm's per mile....in addition to the possibility of increased fuel mileage...but certainly on the 240 should decrease that " wound tight as a jug " when going over 75.....

Actually, here's a question...what's the overdrive gear ratio?

I'm just wondering hat the RPM's would be at 70 with the 5 speed and my rear end (2.83, if memory serves)...hope it isn't so low as to be lugging the engine...

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2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999

Warden, You should check that by measureing it.. because if you have that low a rear end number ( high gearing ) I do not know that an overdrive would be good for you ....but many cars do not have under 3 for a ratio... and could benefit from overdrive...

I think it's 2.8x, but it's definitely numerically lower than 3...I can't remember if they used that gear ratio in '85 126's, but AFAIK, they used that ratio in all '85 123's...and apparently it was special for that year.

Actually, according to ring-pinion.com, at 70mph with a 2.83 gear ratio and a .78 overdrive gear (was an EWAG ), I'd be turning about 2000 RPM's...not sure if that's too low for the 617 or not. I know that my 6.9l Navistar diesel would be quite content there.

Warden, Since you have a used car the only real way is to measure it... someone could have swapped them in the past not even knowing they were changing the ratio... better to be safe ,, and it is just TOO EASY to measure it not to....
The max torque for these engines is listed at 2400 rpm... the max hp at over 4350....
But your wind resistance goes up geometrically with increase in speed... so at the speeds you are talking about I would not suggest being much below 2400....

Oops, thought I had said this...I pulled the differential cover when I replaced the axleshafts last December/January, and that number was stamped somewhere on the unit...I can't remember if it was on the ring gear itself or on the housing...also, FWIW, I turn 3000RPM's even, at 70mph...I think that, from what people have said, most 300D's turn slightly higher...

If and only if you are turning that many rpms I think you could use a 5 speed.... I see no problem with running the car at the max torque rpms.... I could be wrong.... and hope someone will correct me if I am.. but if you are at 2400 out on the road I do not think you will be lugging the engine....

My M103 turns 3000 rpm at 80 mph.

If he converted from auto to stick, could'nt he sell the extracted transmission?

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5 speed '91 190E 2.6 320,000 mi. (new car, fast, smooth as silk six, couldn't find any more Peugeots)
5 speed '85 Peugeot 505 2.5l Turbo Diesel 266,000 mi. (old car, fast for a diesel, had 2 others)
5 speed '01 Jetta V6 (new wifes car, pretty quick)
5 speed '85 Peugeot 505 2.2l Turbo Gas 197,000 mi. (wifes car, faster, sadly gone just short of 200k )
5 speed '83 Yamaha 750 Maxim 14,000 mi. (fastest)
0 speed 4' x 8' 1800 lb Harbor Freight utility trailer (only as fast as what's pulling it)

But I think you are speeding !

This is not a good tangent down which to tripping. I am sitting here imagining the 79SD with a 5 speed. I can almost hear the angels singing... WOW, what a package that would be!

It really does sound like an ideal package.... maybe that is why they are all over Europe.... LOL
Someone just decided that " luxury " cars were not going to sell with manual transmissions.....and perhaps they would not have here.... I don't know..

Unfortunately, that's pretty likely...with how many manual-transmission vehicles you (can't) find around here. When I was younger, me and a friend would go around auto dealers just looking around for the heck of it. Even at that point, finding a manual-transmission vehicle was a rarity...and most of those were special-orders. Seems like most dealers won't order more than a couple of vehicles with manual transmissions...

Really sad IMHO...

If anyone could design and execute one I think these guys could.. I know people who have used their vw trans to Sube 1800 engine adapter,,, very pretty...

http://www.kennedyeng.com/

If enough people would commit in advance to one engine/one transmission I expect they would be interested....

Greetings, I'm very intrigued by the adaption of an american manual trans to a turbo dsl. am currently working on an 83 300dt conversion to a mercedes 5 spd. just waiting fro the weather to warm up top finish.....but while searching for the mercedes trans I began collecting info on american transmissions... seems that the T5 trans out of the camaros and mustangs is a good candidate... all sorts of gear ratios available as well as custom adaptions. I have an extra backing plate and bellhousing from a donor 240d. Now to only locate a "world class" T5 to see how they match etc. I'm very curios to know how it would go together. For some futher info take a look at www.classicconversions.com or something like that. there's some good information around. any tips anyone?

I have been thinking about this for a while. A T5 behind an MB diesel. If you've ever driven a 5.0 you know how sweet a T5 can shift. What would be best is a 5.0 bellhousing with an adapter plate, use the MB flywheel machined to accept the T5 pressure plate/disk. That way you could use the standard T5 slave cylinder to actuate the clutch. Chances are the MB clutch master cylinder would work okay with the T5 slave. So the question is will the MB flywheel fit in a T5 bellhousing? If it does then a universal adaptor plate from Advance Adaptors with the T5 FoMoCo pattern on it could be indexed/drilled/machined to fit the MB block. Viola, your in biznez. RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K