Thanks for this, I really appreciate the specific information. When I switched from the random mismatched set of 235/70's that came with my van to new Michelin LTX MS2 235/75 I immediately saw a 1mpg improvement. These are XL tires rated 50psi max and I am running mine 49psi front, 46psi rear. At 50psi the rear tires sometimes break loose around corners in the rain.

 

I am currently on the hunt for an OD trans with the idea of transplanting the fuel-robbing 3 speed trans currently mated to my 3.9L. Based on my research the hydraulically controlled (RH) OD trans (518) will bolt in as long as I have the driveshaft shortened, or source the proper size driveshaft. It seems that if the OD trans is controlled hydraulically it should go into top gear only when I'm cruising on a flat road over 50MPH, so I believe everything will work fine with the V6. I'm assuming the detent cable for passing gear uses the same clip mount at the throttle body.

The only things I'm concerned about now are (1) the transmission fluid line connections to the radiator, and whether or not I'll have to go to a bigger radiator (and possibly a separate cooler, too) to support the OD tranny (2) the speedo connector and (3) the backup light connector.

My thought for now is that if I source a circa '98 trans the chances of having everything connect together should be better. Guess I'll have to find a new instrument cluster also, or maybe the PCM will recalculate everything and provide proper MPH on my present speedo?

I don't really care all that much about the speedo if the OD trans can get me out of the 15MPG range into the 20MPG+ range. Based on what I have been reading the V6 with OD on the highway should easily achieve over 20MPG.

 

You should be able to use the transmission lines you have but you might have to adapt the ends to mate with the OD transmission. The radiators are the same for v6 or v8 and use the same AT cooler connectors so I doubt that will be an issue. However, mine has a large (maybe 10 x 15") factory AT cooler mounted in front of the radiator so I gather Dodge feels additional transmission cooling is needed. I believe the backup lights are controlled by the neutral safety switch/range sensor but not certain on a '98. The older vans used a switch on the gear selector.

The speedometer connector could be an issue though.

 

I don't see that happening for a number of reasons. First, the epa milage rating for that vehicle is 13 city / 16 hwy. If that vehicle only needed an OD gear to get it from 16 - 20mpg I have to believe Dodge would have offered it.

Second, the math just doesn't add up. You are pushing a 5000 lb billboard down the highway at 60mph on rubber tires. If the conditions are just right, you might hit 25 mpg briefly but your average gas milage will be much less. Gas milage, esp at highway speeds, is a function of matching an engine (capable of the needed horsepower/torque) with the correct gearing that matches the cam profile's most efficient point in the horspower/torque curve. There is a "sweet spot" in that profile where the engine is most efficient given a certain load. The gearing must match this so you hit that range at 55 - 60mph (or whatever your hwy crusing speed is, 70 - 75mph here in Texas).

When you randomly change gear ratios you don't know where you will end up in the engine's torque curve. The transmission that is mated to the 3.9L V6 is different than the V8 version. The V6 version has a lower first and second gear ratio because that engine does not make as much torque.

So based on the information available to us at the moment I predict your city mpg will drop by 1 mpg and your hwy mpg could be no higher than 18. Please do not take this the wrong way I am "guesstimating" but it is a guess that is based on 30 years automotive experience ( 10 of those working as a Ford mechanic ). I sincerely hope you achieve 24mpg and prove me wrong!

 

I think tuned headers and the right cam could help both gas milage and power. I decided to go with the 1.7 roller rockers and I posted this upgrade in a new thread. I plan to install Gibson headers this summer - assuming I can wedge them in there!

 

Dodge DOES offer it .... In the Dakota V6 3.9L. Just not in the Ram Van with the 3.9L V6. If he has the SWB Ram Van the OD should work for his needs. Look here and start at the A500 topic. http://en.wikipedia.org/wiki/TorqueFlite

My interest is to swap out the 3.92 rear gear ratio with a 3.55 one if it's doable. But, I'm at a cross roads since my van has the cancer.

 

I think its definitely doable and certainly worth 1mpg hwy. The 5.2L vans default gear seems to be 3.55 and the 5.9L is 3.92. So I think you can get the whole rear end from a salvage yard off of a 5.2L van. Or just buy the ring and pinion gears for $250 online if you are up to the challenge of setting the backlash and preload.

Hmm so my research says that the axle they put in 5.2L vans is narrower than the version they put in the 5.9L for some reason. You could still remove the gears and use them though.

 

Right, but the Dakota only weighs 3500 lbs and GVWR of 4750 lbs. Equipped with a 3.9L and the light-duty rear end, the '98 Ram 1500 van weighs just over 4,000 lbs and has a GVWR of 6600 lbs. The Dakota appears to have 65% of the front facing surface of a Ram van so the difference in wind resistance would be significant at 60mph.

It'll work, I just don't think it'll work well unless he is only driving unloaded/empty.

 

It should work. I had a 2000 Ram Van B1500 conversion with the 3.9L V6 and the 3.55:1 rear. It pulled a 4,500lbs travel trailer, the van packed and with seven passengers.

What would cause concern is the older /6 two barrel 225cid engine that was once in the Ram Vans with marginal Hp and not enough torque. The Magnum 3.9L does have plenty of pep to it.

 

Great thread Stev I will be starting on this list very soon.

Thanks for your help

SurfinSafari