I've got a '76 F250 with a 300 and NP435. I'm really wanting to get overdrive in my truck to help with highway driving, especially if I regear axles in the future like I'm thinking I will.My knee jerk reaction was to use a ZF5, but now I'm not sure that is the route I want to go given the floor/frame modifications needed. So I've pulled together a couple other options, and wanted to get some input from people who have maybe done the swaps, or if there's other options out there that I haven't found yet.

ZF5 Swap
Pros: Strong transmission, already comes in the 300 bolt pattern, relative abundance (but with 4x4 tailhousings and not 2wd, so...)
Cons: Junkyard/CL sellers charge a lot, have to figure out hydro clutch (either reinforce firewall, or use linkage somehow), physical size means floor modifications and custom crossmember

NV4500 Swap
Advanced adapters makes a kit to adapt dodge NV4500 to the NP435 bellhousing ($741)
Pros: More compact transmission than ZF5 (as far as I can tell) potentially requiring fewer modifications, strong, utilizes NP435 mechanical clutch linkage, very common
Cons: Popularity as a swap means prices are high, found more often with a 4x4 tailhousing

Gear Splitter
Advanced Adapters makes the Ranger Gear Splitter, which sits between a NP435 bellhousing and the main transmission body ($1651)
Pros: Probably the most simple install of the options, retains stock linkage, being a splitter also helps with the other gears too
Cons: More expensive, requires trans tunnel cover modifications (slides back 7"), shorten transfer case linkage, adds another lever to a crowded floor

One of the more overarching issues I run in to with either a ZF5 or NV4500 swap is that I either roll the dice on a junkyard unit, or I purchase a rebuilt transmission. But in the case of a rebuilt transmission, I wouldn't have a core to exchange so it tacks on another few hundred dollars and pushing each unit close to $2k.

Let me know what ya'll think. I'm also open to other suggestions than what's listed above, just happens to be what I'm researching currently.

 

I'm in the process of this on my '76 high boy myself. since I already have a Gearvendor I called them and they said I can put it between my NP435 and the transfer case. all I need to do is get the right adapter , shorten the drive shaft and put a switch in, which I will put on the shifter like a 2 speed rear end . done.

I don't think new Gearvendors are cheap is the only draw back. but it should be the cat's meow.

 

New GV units are wicked expensive these days. That was the first place I looked, and both the ones to bolt to the NP435 or to the NP205 are $3200. I know their products have a good reputation, just can't stomach that much.

 

If you're running oversize tires and a 300 are you sure how much overdrive you want ? GV told me with their overdrive , which I think is a pretty standard ratio , with my 4.10 gears and 35" tires I'd be at about a 3.09 gear ratio. with my 428 CJ that doesn't worry me but with a 300 it might be lugging a lot of the time . we're getting into car ratios here so I'm not sure but I'd think about it.

 

You did not say if you have a 4x2 or 4x4 truck?
I just did Advance Adaptor OD in my 81 F100 4x2 flare side.
Look in the 80 - 86 truck area for a post started by me on the T18 to NP435 & OD install.
On my phone so hard to link.
Dave ----

 

That's a good point, according to some math using the AA splitter (27% OD), my engine speed should drop from about 2450 to around 1800 at 60 MPH with my current 34" tire and 4.10s. If I gear down in the future to 4.88s or even 5.13s it'll bring me back up to around the 2100-2300 range. So it might be a little more gutless from 55 to 65 on the current gears, but once I hit 70 I think it should still work out okay.

I'll see if I can find the thread, curious to see how the install went. I have a 4x4 truck.


Thanks!

 

https://www.ford-trucks.com/forums/1...ver-drive.html
let's see if this works
Dave ----

edit: The link does work
I should let you know I did not want the OD stick to come thru the floor, not after putting floor pans in it, so I wanted it to come thru the trans pan.
I also did not want the pan to tall or the free carpet from and auto truck may not fit. The pan was from my parts truck and that shifter hole was back farther than the T18 hole but was not enough.
So I cut, trimmed and welded that pan to fit like I wanted it to. I heated the OD & NP435 sticks to feel right when driving. The trans stick is a little high but is not that bad.
I cannot tell you how the OD stick would play out with the transfer case stick as I have not seen where the 4x4 stick comes thru the floor.

Some people say the OD makes a lot of noise, like a bearing wine.
When I first got the truck on the road I did not have any floor covering, roll on bed liner top & bottom was it.
It was noisy but with the carpet installed I don't really hear it but it is a truck is it will make some noise.

 

That was a good read. thanks for sharing it!