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Old 10-30-2018, 11:07 PM
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rwd4evr rwd4evr is offline
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Join Date: Apr 2012
Location: delaware
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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.
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Last edited by rwd4evr; 10-31-2018 at 04:15 AM. Reason: Double thread
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