I am pondering the idea of possibly changing my transmission from the stock 4 speed to a comparable 5 speed that is assuming I can find one that will match up. I am only wanting to do this change out only to gain fuel economy, I have no other reason for wanting to do so. I drag a bass boat all Fishing season long, and I drag a camper all Hunting season - winter long. So I have found my self quiet fond of the granny gear that is equipped in my 84, it is great for getting my boat out of the local boat slip that stands at 65 degree pitch, and I enjoy the granny when dragging the camper deeper in the woods then most others would consider to drag theirs.

And now the but, every question has a but of course: I want and need better fuel economy. I am currently running 100% stock everything 1984 300 I-6 2X4, Immediate upgrade/change coming is a full exhaust change, dual manifolds, to "X" crossover to true dual cats, true dual flow 40 knock-offs, to true dual chrome tips, then next upgrade change out will be changing back to a 2 barrel carburetor, that someone previously had made this upgrade but it wasn't correctly done (installed to small of a carburetor)(plus old carburetor needs rebuilt or replaced blowing heavy-wet black smoke) so this will be done correctly! This is a 5,000 mile engine currently with a 100% full blown tune up after the engine build!
None of this will give me any true fuel economy changes! Nothing left but to change the transmission over to a 5 speed. this truck is running 2700 rpm's at 60 (accourding to the dial, but if clocked it is 5 mph off ) these are high rpms, if I could lower the rpm's then I could lower the fuel consumption hense saving fuel and gaining MPG's.

So next thought is to change the transmission, I have yet to climb under my truck ( find out what transmission but will do at first light in the morning and update this post with exact transmission I have) to find out exactly what I have but when I do I will be on the search of finding out what New transmission will be compatible fit to my truck, (I am thinking the 'newer' the transmission then maybe the 'newer' the components, and the 'newer' the technology went in to building and designing these transmissions so maybe I am getting a better transmission for the job?) I'm sure I am thinking incorrectly on this thought but that's OK since this is nothing more then a thought process at this time. I am looking for direction, right now I am going in several different directions hoping and searching for a light at the end of the tunnel!

I have spent countless hours using the search feature on this site and still not looking at definative answers to my thoughts and my thought process about making this transmission change! I have a junk yard at my disposal so if i can come up with a comparable upgrade/swap for my truck to make it a 5 speed then it is nothing but a phone to get what I need!
It has ben suggested that maybe changing the rear end gearing will assist with my fuel economy issues but I don't see the rear-end having anything to do with the rpm's that the engine is turning while matched up to the transmission! Again I'm sure I'm wrong on this thought as well.
Your welcome to ridicule me or even slaughter me for my ignorance, and I am willing to take it all, But this is a learning process! And I am willing to learn! So if your interested in giving light to this I do appreciate the help! Thanks way in advance, MrShadetree!

 

you'll want another 2 wheel drive donor truck...



and don't use the X-pipe with flowmasters, either H-pipe or use different mufflers

 

leave the 4 barrel carb in place

 

Keep the 4 speed and put something like 2.73 gears in the rear.

https://www.f150online.com/forums/ar...tion-page.html

Your tranny is either a NP-435, T18, or T19. Your only reasonable choice for an overdrive is a ZF5 out of a gas F-250 or bigger. The M5OD and SROD doesn't have a granny.

 

Well after several hours of additional research I was able to conclude that I do infact have the Borg-Warner T-18 transmission in my truck!

Wow who knew these trucks were equipped with a PTO, I didn't know!

Why would I need a complete donor truck just to get a transmission?
Why an "H" pipe ~vs~ an "x" crossover? I was looking to use knock-off Flowmasters not actual Flowmasters.

GLC, thank you for the correct transmission I am looking for to be considered for this project. Will this ZF5 out of a gas F-250 or bigger, help with reducing my fuel consumption? While leaving me a granny gear to climb, and drag with? You did notate that the The M5OD and SROD doesn't have a granny, so I won't even be considering them as candidates for this project!
Thank you very much for your help and assistance with this issue.. Just hope it all works out!! Might be delaying the carburetor , and exhaust to pursue the transmission project!!

 

Is the ZF5 going to be a direct bolt on transmission? Or will I be changing tailshafts, Driveshafts, or any things else?
Thank you very much for your help!

 

You will be changing quite a bit. Like I said, a regear would be a lot easier.

 

GLC, are you interested in spending a few moments to help me understand a re-gear? What takes place in a re-gear? Of course a gear change, but what happens and why does it change things? I was told I shouldn't re-gear since I use this truck for hauling, I drag a 3200#lb bass boat, and a 2900#lb camper regularly. I have heard of re-gearing for racing applications where drag weight doesn't become an issue. But this is by no means being considered a racing application. My truck works often enough to leave it a work truck. I don't want to be restricted from going to lumber store to grab a load of sheet-rock or going to gravel yard and getting a ton of gravel (1/2 mile away 1 ton half a mile really doesn't hurt anything)

 

A regear wouldn't impact on your pulling ability much at all when you have a granny to get it moving. The 300 has tons of low end torque. You will just be keeping it in the lower gears a bit longer.

You don't have to do any mods with a regear except a different speedo drive gear.

 

I have an efi 300 with a 5 speed and I honestly don't get very good gas mileage.
Granted it is running rich right now, but I only get 12-14 on hilly back country roads.
What do you get with your 84 if you don't mind sharing.

 

also what is your rear end gearing? would be easier to tell you what to go with.

 

To find out your gearing, look on the door jamb sticker for the axle code.

 

Check this out; http://www.gearvendors.com/agmanual.html
It replaces your extension housing.

 

That's a lot of bucks! You can regear for around $800 parts and labor.

 

Yup. Just wanted to present another alternative.