1985 300SD shop "truck" daily driver 5 speed project
 

I am tired of 12-18 mpg in my v8 mountaineer. It rides ****ty and handles bad. I need a wagon or pickup and wont deal with a w124 gas car though. So I picked up a prettty decent 300sd dirt cheap and have some plans. I have most of the info I need but I need some opinions and real world experience if possible.
The plan is to swap in an AX15 5 speed from a dodge Dakota. I have the adapter kit intended to put a om617 in a jeep. The gear ratios are almost identical in the transmissions plus a .79 OD in the ax15. I will be doing some towing with the car as much as a car in flat tow or a dolly, probably not a car on a trailer. It weighs almost as much as my mountaineer and has better brakes and suspension so I'm not concerned with that. It's not hard to build a class 3 hitch into the rear structure. I will also probably down the road a bit be chopping the back roof off and welding the rear doors shut to make it a pickup. A early s10 cap will fit pretty well.
So my questions are about power and gearing. Has anyone done any towing (or driving for that matter)with a turbo 617 with the 2.88 factory rear axle ratio changed? I have 3.07, 3.23, and 3.69 differentials available. 3.69 is dumb since it would actually end up as a 2.91 final with od. All the gear change threads I've found are NA cars and have power issues. I had s 85 300TDt which felt like it had plenty of power to pull more gear on the highway. So I could go with a 3.07 to get a little more off the line and considerable reduction in highway rpm or 3.23 which has a lsd(really makes me lean this way) and would really help with off the line towing my drift car or parts cars and would still reduce higway rpm with a 2.55 final drive in 5th. The only problem I'm worried about is if it can't pull od on the higway with a load in 5th I'll be increasing cruise rpm havling to run 4 th. So at that point should I just leave the stock gearing and get awesome everyday mileage and probably have to run 4th on the highway?
On top of that how about practical power increase in a om 617? I remember years ago hearing about larger elements being installed in a NA300d om617(which I have). Any input would be great. I miss driving a Mercedes everyday so it's time.

Double post. Please delete this one.

I purchased a 1982 300SD from someone on this forum. It had a lightweight trailer hitch that would only pull a very small 1-7/8" ball + trailer.
I removed that hitch when I had the car's rear quarter and rear bumper painted. I can tell you that with the vehicle's current stock AT the car is responsive, even when loaded with 4 x 200lb passengers. I don't know if that helps, but though you should know.

I'd love to put an MT into my 617.951 in a 126 body. Don't know if anyone has done that.

Thanks. Not really super helpful but i appreciate it. I had my old wagon with the same drive train loaded to the hilt plenty of times and it didn't really notice, when we're talking about towing another 3500 + pounds of car,dolly,tools,spares and all that is where I'm wondering. It's got a small receiver rated for 3500 so I'll probably load it up and take it for a drive late at night with less traffic to deal with and run it out on 495 up over a fairly steep bridge nearby to see. These autos are huge power sucking vampires though so it's not really a fair comparison. Anybody got power improvements for the 617? Bigger turbo? The horrible lag will be easier to deal with with a manual trans.

the stock auto wont take too much more power but if your swapping in an ax15 thats another thing altogether. i might worry about the torque limits of the ax15 if you start making more power. as for actually making more power you can get a little more from the stock pump but if you want any real improvements you need to get a bigger IP and turbo. this applies doubly when towing with a manual since the long injection time of a maxed out stock pump pushes your egt's up quite quickly.

Now were talking. I think the ax15 will handle a pretty good bit. They end up behind LS engines in jeeps which shock load is pretty rough and some mild hot rods. I would definitely not be bang shifting with a heavy load. So what are my pump options? Are stock injectors up to more flow? I have two na 617 to pirate parts from. Like I said, years back I was looking into more power for my 300TDt and found a guy doing larger elements in a na pump. I may have known what the pump designations were then (m pump etc.)but I've stuffed mass amounts of Mercedes knowledge into my head since then and none diesel really.

Dieselmenken pumps are top notch, and around $1200 (some of that is shipping cost) and are worth the money. You will play games for years trying to be cheap.
Think of it this way: $1200 for at least +60hp fueling. That's $20/hp, which isn't bad at all. http://www.dieselmeken.se/

Diesel Pump UK sells manifolds, as does F-Tune. None are cheap.

NA intake manifolds flow better than turbo manifolds. If they're the straight NA manifold, you will have to space the turbo off the flange to clear the runners.

Is it an ASD or LSD rear? LSD rears are rare for w123s. If it's really an LSD rear, use that and adjust tire size for gearing compensation.

I built my own hitch on my old 300D. Pulled heavy loads at highway speeds with the auto and she never let me down.

Mine had a 2056V (variable vane turbo) swapped on, so boost was always instant. It was nice.

So 60 plus hp I'm assuming with a bigger turbo? How much are you making with Ported head and all? Is there really a 200hp limit on rods I've read about? Im not tryng to be cheap but I spent 3x less on the car! I don't want too murder mileage completely either.

The 3.23(or 3.27 I forget at the moment) lsd is in my 380SLC that has another desitiny. I actually have a 3.46 in the 300TD I forgot about too(gotta love a Mercedes junk yard in your yard). But I really like to spin both tires and welded diff and towing are not a fantastic idea( not saying I wouldn't do it though)I have two na 617. On is a from a w116 I believe but now in a w108 mess and a 300TD euro car. I'll have to look at them to determine which mani it is. How much weight would you say you were pulling? This is a w126 300SD Bynthe way too.

Not sure either but my friend fonzi has a 280se 4 speed I was using for a while and it had sls delete with some stiffer springs and it feels like a completely different car. You can throw it around like a little sports car. 200 hp diesel w 5spped and killer mileage would get me past the fact the styling doesn't do that much for me. The auto and pillow ride kill these cars. A v8 manual would rock too. This diesel could make way for a m119 and manual if it can't do what I want it to eventually.

200hp is not the limit of the rods at all. i am somewhere north of that now and the only thing stopping me from turning it up more is my transmission and the need for a bigger turbo. the issue is getting air into the engine. a holset hx35 should safely support 250-300 on a 617 with not horrible lag at least with a manual. i would of course fit the biggest intercooler you can and maybe consider water injection (not methanol since with the larger pump you wont need the extra fuel) for cooling if you will be towing. head work is good if you want the most out of it but i might not recommend it if your just aiming for a decently powerful tow rig.

I never dyno'd the car, I was broke as hell back then. Didn't get any more fuel than normal, I just pulled the ALDA to get more off-boost fuel.

I played with methanol sprayers, and they definitely made power, but really the right way to do it is take a deep breath and just buy a real injection pump. Sell off some of your extra wagon parts on eb*y.

Big tow #1-7ft x 10ft flat deck trailer (est 1500lbs empty, it was a redneck special) with a k440(360lbs) a zx600(450lbs), two beds, two dressers, all my tools (500lbs?), and the rest of the random crap when moving. So at least 3,000lbs.

Big tow#2-Uhaul box trailer that was bigger than the car (I don't know how they let me drive off with that one). Full of furniture but it was a giant sail slowing me down.

Cool, good to know. So how was performance towing? How about fuel economy? Are there different cam profiles between NA and turbo? What about the heads too? My car has about 300,000. If I'm
Gonna start trying to make decent power I'm going to be freshening a head for sure at least.

porting the head can help a lot especially if you are going further than just a bit more than stock power. the key to towing or any high load for a long time situation is a good intercooler, radiator, and oil cooler. as long as you can keep all your temps stable and your brakes are ok it shouldn't care what your towing. if you are interested in a ported head pm me i have rebuilt and ported a few now.

Yeah that's possible. It is something I'd like to do myself but I have a lot of projects planned for this winter in my new shop, so I'm not sure what I'll get to. I'd like to do what I can with what I have for now and save up for a pump. First thing on the agenda is the manual swap l, that was the one thing I couldn't stand about my wagon. I actually bought a parts car to convert it to a four-speed with the 300 D parts but it needed everything besides the engine basically so I ended up selling it. Kinda regret that now. It wasn't as rusty as I thought and then prices went nuts on wagons. So maybe a bigger turbo on stock pump for now? I never "turned it up" on my last turbo since the trans was questionable and honestly I dont even remember what to do. I knew then like 5-6 years ago. At 300,000 oh miles would you be looking for a lower mile foundation to build for the future? Is the na head I have the same to rebuild?