I have 1980 f-250 with a np435 as my workin' truck. This is my travelin' truck, at most I would be pulling a small fishing boat. Will my Doug Nash overdrive/gear splitter be of any help to me meeting my goals?

 

I doubt the OD will be of much use with a stock 300/C6 combo with 3.55 gears. Maybe running empty on flat ground. But I doubt the OD will get much use while pulling much or having the camper on the back. Now add the 4.10/4.11 gears then that's a different story. The 3.55's just aren't enough gear when you are talking about a C6 equipped truck with camper pulling a boat over mountain passes. And the OD will be pretty much worthless on any incline with 3.55's.

Now if you had a highly modified 300 then it might be a different story. Or even a NP435 instead of the C6.

 

I love the np435. I have been looking a long time for an over drive unit for it. The overdrive that I found was on a c6. It will work with the np435 if I can find an adapter for it.

 

Me too! I like the NP435 so much I'm going to be using them in all my vehicles. Including my 89 E350 van.

The easiest OD unit for the NP435 would be the Advance Adapters Ranger torque splitter. It's a small gear box that goes between the bell housing and the transmission. This is the one unit I know of that can be used on a 2wd or 4x4 and be used while in 4wd. Most add on OD's can only be used while in 2wd. Not a big deal if you don't have a 4x4 truck.

The down side is it's a little over $1600. It moves your stock shifter back 7 1/2" and it adds another shifter coming up thru your floor( that wouldn't bother me but some people don't like it ) and will require driveshaft mods. It would work great with the NP435 because it would give you another gear between the 435's gears. Plus you get the OD. I want a couple of these bad. But they just aren't in my budget right now.

Here's a link to their website: Complete Units | Advance Adapters



The other choice is a aux. transmission like the Brownie box ( Spicer ). These are fairly large heavy 3 spd transmissions ( under, 1:1 and OD ) that remote mount between your transmission and rear diff. These were used in the old medium duty trucks I think from the 50's thru the 70's. These usually run $400-$1000 used.


I'm not all that familiar with the Doug Nash unit. But I don't think your OD unit could be used with the 435, without a bunch a fab work. Anything is possible with enough time or money thrown at it. It might be possible but is far from a bolt in deal.

 

Put a Holley 600 on there & you will notice a considerable improvement, gets better MPG too.. I know, can't explain, it but it is so...

 

I loved my last 89 f-150 with 4.9/c-6 and 2.73 rear. put over 60k miles on it and beat the dog **** out of it off road constant neutral drops, fot on floor betyween reverse and drive. Put it this was i went thru 4 sets of motor mounts a steering gear box sector shaft snapped and fan went thru radiator 3 times. Yet i still daily drove it(can you say early 20's haha)

10 years late ri just bought its clone for DD duty, 89 f-150 4.9/c-6 with 2.73's. I love this combo...cheap simple and reliable, works great for about anything you want to haul in the bed, towing over 2k or so it struggles. But it does great on the highway at 55 or 75.

 

Huh, that is interesting. I have a tricked out c6 and with 3:31 gears in the rear, and the off the line pep is my favorite aspect of the trans. I get a jump on everyone off the line, and can rev to over 5k before it bangs into 2nd and 3rd if I stay on it. I wonder if part of the sluggishness is t.converter?

 

Not sure but I'm certain that a new torque converter was installed. I can't find my receipt with the specs on it.
This setup does make running true duals with hedman headers difficult. I'm at my wit's end trying to get everything to sit without rattling off the crossmember.

 

Hey there. I routed one pipe around the front of the trans and around the driver's side. But my tubes coming down from the engine, still sits right on the back side of the cross member. It's driven me nuts for years. That's why I'm converting to Cliff shorties. I'm going to do a y right off the collectors and into a 3'' single for eight feet, and then into a flowmaster and out a 2.5" tailpipe.

I have photos of a guy who ran the hedman with true duals. I'll upload to google docs and post a link. He welded straps across the pipes to keep them from rattling. Me, I figure I'll get all the flow in the world with the 3" pipe, without the rattle or space constraint, and without having to install an X or H pipe. kevin. Good luck.

 

I have a pair of exhaust clamps welded 1" apart to a piece of bar stock, think old timey handcuffs. Have it wedged in there so that the tension from the one pipe holds up the other. It's a Chinese finger trap for sure. My next best option, as I suspected, is to make a 90° turn before the trans with one of the pipes.
On a side note for you , when I had my headers off a few months back I sanded down, painted and wrapped them things in Lava wrap. I know they will rot out faster but the engine bay is significantly cooler I don't instantly blister my hands when tinkering around hot pipes. The heat transfer to the cab is also greatly reduced. Plus I think k it looks cool. Practical,probably not.

 

Another member posted these photos, but I don't think he'll mind if I link to them because it might help you. https://drive.google.com/file/d/1lEj...ew?usp=sharing

https://drive.google.com/file/d/1Qr2...ew?usp=sharing

You can see it is very tight under there. That's why I elected to go with the one 3" pipe to the rear axle, and then drop down, once the gasses have cooled a bit, to a 2.5" tail pipe. The photos are of a truck with a ZF trans, which might be narrower than a c6? Good luck. Kevin