Hi, I'm new to this forum thing but I have a 1986 w150 318 with a np435, I'm looking to swap it out for an automatic just for the convenience and was wondering what trans I should use. Right now I'm running about 2300 rpm at 55mph and I was wondering what auto trans I could use to help lower the rpms to hopefully around 1500-1800 at 55-60mph.

Any suggestions would be helpful

 

it depends on your tire size and axle ratio.

 

the tires are 31x10.50r15 and I'm not sure on the axle ratio, there isnt any ID tags on the axle housing or anything. I'm just wondering what trans will get me the lowest rpm at cruising speed

 

Well w\o knowing the gear ratio I'll just say you should find an A518 4-speed auto from a 90-93 Dodge Truck or Ramcharger. You will need to swap to the NP241 transfer case to use the A518 (or an NP205) since the 208 will not work.

You will need the cross member for the auto trans, have drive shafts made, and run trans cooler lines, and figure out a shifter.

Your other choice is a 727 3-speed auto but w\o knowing your gear ratio I couldn't tell your final RPMs.

 

is there any way to tell the gear ratio without pulling the cover?

 

There are option tags on your truck but you can try this:

 

Ok I just checked and I have 3.20 gearing in the rear, will the 727 give me lower rpms at 55-60 then the np435?

 

The gears would then be 3.23's

With your set-up you would be at around 2k RPM's at 55 with the 727

Here: http://www.grimmjeeper.com/gears.html

You can go to that site and plug in and play with the numbers to see what would work for you.

 

yeah I was using that and if I put 3.23 gears and then 3.55 gears the 3.55 match up with what mine is with 55 at about 2250 rpm but if you do what that video says it is way closer to 3.23

 

If I go with a 727 and I get one from a 2wd can I just take off the tail shaft to make it work or would I need one specifically for a 4wd and will it bolt up to the np208?